Now we start to get into the really disturbed stuff. This is where Ginenthal throws out the evidence or glibly explains it away, while accusing Ellenberger and Mewhinney of doing exactly the same thing, where he rewrites Velikovsky's scenario while accusing Ellenberger and Mewhinney of ignoring what Velikovsky said. Ginenthal claims to show that "the deeper icecaps were built up extremely fast, as Velikovsky claimed." Therefore, "Nothing in the top layers of the icecaps has anything to do with Velikovsky's hypothesis." 1 So long, evidence.
In Velikovsky's own scenario, the ice age was terminated by a pole shift: "...oceans and seas evaporated and the vapors precipitated as snow on new polar regions and in the higher latitudes in a long Fimbul-winter and formed new ice sheets." (WiC, p. 120) To generate instant ice sheets, Velikovsky's scenario had the oceans boiling in many places, followed by rapid cooling. He considered a number of possible (and some impossible) sources of heat for this boiling: volcanic activity, conversion of the kinetic energy in earth's orbital or rotational motion to heat, heating from electrical exchanges with another planet or from interaction with its magnetic field, even chemical or nuclear energy! (EiU, pp.117-118) Ginenthal introduces a new, post-Velikovskian wrinkle, borrowed from impact catastrophism: bombardment by meteorites in vast numbers.
"The ocean would indeed have boiled above the target site! The amount of water vapor thrown out into the air would supersaturate the stratosphere above an area several thousand kilometers across. The vapor would rapidly recondense ... out of the atmosphere. Croft estimated that most of the vapor would return to Earth's surface in a few months. Total precipitation would amount to a thousand meters or so, coming down at an average rate of 5 to 10 meters, or 200 to 400 inches, per day." 2
Which should leave signs of severe flooding and erosion. Ginenthal here is quoting Kenneth Hsü's The Great Dying, a popular account of the discovery of the Cretaceous-Tertiary impact, and developments in the scientific understanding of its role in mass extinctions. The attitude of most Velikovskians toward these developments has been one of resentment -- on the one hand it isn't recent enough to suit them, and on the other, they claim that somehow Velikovsky deserves credit for the discovery. In trying to graft elements of this research onto Velikovsky's scenario, Ginenthal's response is unusual.
Major impactors are certainly efficient at converting kinetic energy into heat. They also leave rather conspicuous traces, which we probably wouldn't be around to see, if one had fallen a few thousands of years ago. The K/T impact left behind a layer of tektites that tapers from a couple of feet thick in Florida to two inches in New Jersey, for example.
The impacting body Hsü was discussing was "a stony object 10 kilometers across hitting an ocean at 15 to 30 kilometers per second." That's a major impact. But it doesn't come anywhere close to producing enough vapor to create an instant ice cover. A thousand meters of precipitation sounds like a lot. But such an impact, Hsü says, "would vaporize a volume of ocean water..." of only "1,000 to 5,000 cubic kilometers." According to the Encyclopaedia Britannica, the Antarctic ice sheet contains about 29,000,000 cubic kilometers of ice, and the Greenland ice sheet, about another 1,800,000. Together they comprise 99% of the earth's land ice. Five thousand cubic kilometers is only 0.0156% of this, or a mere 0.2% of the volume of the Greenland ice sheet alone, so even if every single drop (or flake) of precipitation fell on Greenland and Antarctica, and there was no runoff, it would be utterly inadequate to create a thick ice cover.
Hsü didn't cite his sources, but they're not hard to find. This information comes from Croft's paper in a 1982 Geological Society of America Special Paper on asteroid and comet impacts. 3 Croft writes, "the vapor will locally supersaturate the stratosphere in a zone on the order of a few thousand kilometers in diameter..... most of the vapor will return to the earth's surface on a time scale of weeks to months." 4 During this time the affected parcel of air will move a great distance around the earth, breaking up into eddies and mixing, and the precipitation will be scattered about one or both hemispheres. The figure of 1,000 meters' total precipitation comes from Hsü himself 5, but it is not consistent with Croft's assumption that "The pillar of vaporized water," initially only "20 or 30 kilometers across" would spread out to saturate an air mass as much as several thousand kilometers across: 5,000 cubic kilometers of water could leave a thousand meters of rain (equivalent to 1100 meters of ice) on an area no greater than 80 kilometers in diameter. And no single part of the earth would receive that much precipitation, because the air would be moving. The figure of 1,000 meters could obviously not be a global average: To produce that much precipitation, more than one third of the volume of the oceans would have to evaporate! Spread out evenly over the face of the earth, 5,000 cubic kilometers of water is less than one centimeter deep -- not much of a starter kit for someone who wants to build an ice sheet.
But it's worse than that. As Hsü notes, "Small meteors burn up or disintegrate in the air because their trip through the atmosphere is a distance many times greater than their own diameter. The atmosphere is about 7.1 kilometers deep; the ocean's mean depth is about 3.6 kilometers. A trillion-ton meteorite with a diameter of about 10 kilometers is as thick in the middle as atmosphere and ocean put together." 6 Such a body would lose only about 5 percent of its energy on passing through the atmosphere. This is the case on which all of Croft's calculations are based. Ginenthal wants to use the results of those calculations, but the impact of a single large body is not what he envisions at all. Rather, he has in mind the fall of millions of small meteorites in the sea. As evidence of such a thing having actually happened, he presents this passage from a 1979 article in New Scientist:
"The topography of the seafloor around Britain, like that of its land area, has formed over many thousands of years and results from many well understood geological processes. So it is surprising that recent studies have discovered a wide expanse of seabed in the middle of the North Sea -- between 15 000 and 20 000 square kilometers in area -- which appears on sonar pictures to have a topography much like a miniature lunar landscape." [word in italics restored] 7
The scientists refer to these features as "pockmarks." Ginenthal calls them simply "craters," meaning impact craters. The article states that 2500 such depressions have been identified in a detailed survey of 80 square kilometers. At that rate there would be half a million in the North Sea alone. As another of Ginenthal's sources notes, "They have been reported from the Adriatic, from an area near New Zealand, from the Gulf of Mexico, the Bering Sea, the Great Lakes, the South China Sea, the Baltic, the Aegean, the Gulf of Corinth, the Delta of the Orinoco and the Scotian Shelf off Nova Scotia." 8 But never on land: "they have neither been found on the land surface nor in the lithified geological record." 9 There are millions of them, and they are found only in water.
Pockmarks are anywhere from one to 350 meters in diameter, and up to 30 meters deep. Some of the larger ones consist of a number of smaller internal pockmarks. 10 Unlike impact craters, they lack raised rims. The pockmarks in the North Sea and some other places are elongated in the direction of current flow. They have been found at depths ranging from a few meters to 4800 meters. Such small impact craters could never be formed in deep water. Recent calculations show that even a one-kilometer-diameter asteroid would not penetrate the deep seafloor. 11 Pockmarks are associated with the presence of hydrocarbons, especially methane, and as Ginenthal's source notes, it has long been believed that they are erosional features caused by escaping gas. Where pore pressure is high enough, buoyant gas finds a path to the surface and escapes with enough force to dislodge sediment, which is then removed by bottom currents. Pockmarks have been observed actively venting gas in the Ionian Sea, the Persian Gulf and the North Sea. 12 Recent discoveries, according to Fader, include "active pockmarks resulting from earthquakes... pockmarks induced by the grounding of icebergs... [and] pockmarks induced by... trawling and ship anchoring." 13 Ellis and McGuiness note, "There is evidence that any activity, anchoring, rigs jacking up, or fish feeding which disrupts bottom equilibrium can initiate pockmark activity. At one location a pre-construction survey showed no pockmarks. A post-construction survey only a year later found seven pockmarks, five of which were active." 14 For several days after an earthquake, most of the pockmarks in a field in the Patras Gulf vented bubbles of gas. 15
As though this were not already absurd enough, Ginenthal adds a final touch: "It is proposed that these craters were produced, as were those of the Carolina Bays, by atmospheric explosions of soft meteoric material which threw immense amounts of water and water vapor into the atmosphere." Maybe he thought explosions would sound more dramatic, but if you want to get a lot of water vapor into the air, that just makes it more difficult.
Unlike pockmarks, the Carolina "bays," with a distinctively different size range and morphology, may actually be impact features. But with radiocarbon dates as high as 18,000 years, they are much too old for Velikovsky's second-millennium scenario. 16 In his later writings, it seems, Ginenthal stirred more into the pot, adding oriented lakes of various kinds from around the world. Some are oriented by the prevailing winds, some, usually almost perfectly rectangular, sometimes L-shaped or T-shaped (!), follow the outlines of fractures in the basement rocks, and some are apparently caused by freeze-thaw cycles in permafrost. (See Fig. 1.) For Ginenthal, apparently, any hole in the ground will do. See Gunnar Ries' web page on junk science and pseudoscience at:
Most Velikovskian literature follows a standard formula: The writer identifies some phenomenon which he claims constitutes a difficulty for "conventional" science, exaggerates the surprise and puzzlement of scientists, derides their efforts to explain it as ad hoc and hopelessly inadequate, then offers some vague "explanation," usually a crude analogy or bald assertion, which he claims is superior to those of the scientists, because, of course, they have the wrong paradigm. There is a ritual flavor to it. In these rhetorical exercises, the most critical distortion takes place not in the "explanation" itself, but in the description of what is to be explained -- especially in what is left out.
According to Ginenthal, it is a "fundamental problem" for ice-core researchers that they have found repeated, rapid climatic fluctuations in the ice of Greenland. "Based on" what he calls "the uniformitarian concept," he asserts, "any temperature swings based on Milankovich should be long-term and gradual." I will come back to this sentence later. He then refers to an article in the "News and Views" section of September 9, 1993 Nature by Scott Lehman, "Ice Sheets, Wayward Winds and Sea Change." The whole passage, with a couple of words restored, runs as follows:
Last September came the first report from one of two teams drilling on Greenland confirming that much of the period 8,000-40,000 years ago was marked by sudden 5-10-degree C switches in temperature over the ice sheet. In February came news from the other team that the switches were in fact jittery, embracing large oscillations in climate lasting in some cases less than 5 years. And then in July came the further discovery that the past 8,000 years of relatively stable climate have been a geological oddity -- the last time that there was as little ice on Earth as today (the Last Interglacial period), temperatures over Greenland varied even more wildly than during the glacial period, shifting by as much as 10-12 degrees C in just decades and remaining in place for as little as 70 years. Although climate modellers and geologists are racing to understand and test the implications of the new ice-core data, one thing already seems certain -- the heat-carrying capacity of the Atlantic Ocean must somehow be involved in producing the sudden climate changes around Greenland. 17
Ginenthal asserts that because of various "fundamental contradictions," these rapid temperature swings in the ice cannot be interpreted as indicators of global climate, and he dismisses all scientific attempts to explain them as ad hoc. But before we look at scientific explanations, and Ginenthal's criticisms of them, what is the kerplopist explanation, with its armada of hydrophilic meteorites boiling off perhaps a third of the water in the oceans? "Snow," Ginenthal says,
would have been derived from both cold and warm water sources. Not only would the oceans boil in some places, but meteors would have fallen into the oceans in cool regions, lifting immense amounts of water and water vapor into the atmosphere......
Hurricanes sweeping over the entire Earth would have carried the water vapor thrown into the atmosphere from vastly different oceanic temperature regimes to the polar regions, to fall as snow. Present-day amounts of snow which would have taken decades to fall would have done so in a few days. This snow, derived from warm, cool or cold oceanic regions, would contain totally different amounts of oxygen-18 or oxygen-16 mixtures. Two hundred or more feet of snow may have fallen from either a warm, a cold or a cool region. This snow would be quickly compressed to form firn and would create many layers via the rapid diffusion of oxygen-16 and oxygen-18 into layers. [I will let this piece of idiocy pass for now, but I will return to it in a later section.] But the overall property of the layers would be to create the appearance of decades of ice with either a warm, cool or cold climatic temperature. 18
This is what passes for "explanation" in Velikovskian science. What force would generate these hurricanes? What would keep them from dropping most of their moisture before reaching the polar regions, as the air does now? What would keep the air masses from cooling en route? Westerlies drift slowly toward the poles today, but most of the water vapor they pick up from warm regions drops out along the way, so by the time it arrives over the polar regions, regardless of where it arose, the air is greatly depleted in heavy isotopes. The isotopic composition of precipitation is much more strongly correlated with the temperature of the precipitation, and with distance from the source, than with temperature of the source region. But at most, all this furious hand waving just amounts to saying that the isotopes would fluctuate wildly at random. Why would the fluctuations be more intense in Greenland than in Antarctica? Why would the overall shape of the isotope curves in Greenland and Antarctica, plotted against independently derived time scales, match each other so closely? Why would they match the isotope record of calcite in ocean sediments, which, according to Ginenthal, were churned up and settled out by specific gravity, and the calcite in cave deposits such as Devil's Hole as well? Within Ginenthal's demented phantasmagoria, there is no way to account for these correlations, which we have noted before. Each one requires a separate divine miracle, and we have just begun. Why does the dust content of the ice go up whenever the oxygen isotopes of the ice indicate a return to colder conditions, opposite to what Ginenthal expects? (See Fig. 2.) Consider the composition of the air enclosed in the ice. Why do levels of methane go up and down together with oxygen-18 of the ice, and oxygen-18 of the enclosed air? (See Figs. 3A, 3B, 3C, and 3D.) (The mean atmospheric residence time of an oxygen molecule is 1200 years! 19) How could these quantities change dramatically over a period of 3 or 4 months? One shudders to think that there are actually people living in the world today who could read this tripe and take it seriously.
Ginenthal's indictment of science's performance begins with the sentence, "Based on the uniformitarian concept, any temperature swings based on Milankovich should be long-term and gradual." So what is "the uniformitarian concept," and how does it concern us? Geology today recognizes catastrophes when supported by evidence, not imagination. Ginenthal is attacking an irrelevant 19th-century caricature. But "uniformitarian" is a label Velikovskians apply reflexively to anyone who doesn't believe the solar system turns itself inside out every few thousand years. Who is Charles Ginenthal to tell scientists collectively, first, that they are all uniformitarians, and secondly, that they can only posit long-term, gradual climatic changes if the ultimate agent of those changes is insolation? This is to ignore the role of the ocean in transporting heat from the tropics to higher latitudes, in driving the hydrological cycle, and as a source and sink of atmospheric carbon dioxide, and this ignorance is quite deliberate.
Ginenthal speaks of these rapid climatic oscillations as though they are found only in Greenland ice cores. But the very sources he cites make it clear that they have their counterparts in deep-sea cores and continental records, so they cannot be mere artifacts. The "News and Views" piece by Lehman quoted earlier is principally concerned with the implications of an article by Gerard Bond et al. In the same issue of Nature, "Correlations Between Climate Records from North Atlantic Sediments and Greenland Ice." 20
From that paper, we learn that "records of sea surface temperature from North Atlantic sediments spanning the last 90 kyr... contain a series of rapid temperature oscillations closely matching those in the ice-core record," 21 with sharp boundaries and estimated amplitudes of up to five degrees Celsius. "...Rates of change in ocean temperatures must have been nearly the same as in the ice core; that is, several degrees within decades." 22 As noted elsewhere by one of Bond's co-authors, Wallace Broecker, "The abrupt termination of the Younger Dryas [cooling episode] raised temperatures in the northern Atlantic basin about 6° C in less than three decades." 23
These are not random oscillations; they fall into a repeating, quasi-regular pattern, each series of events lasting about 10,000 to 15,000 years. Within each cycle, there are several abrupt warming events ("interstadials"), followed by slower cooling, giving the isotope record its characteristic asymmetrical sawtooth shape. Each warming event in a series is slightly cooler than the last, and at the end of each cycle, there is a surge in ice-rafted debris in North Atlantic sediment cores, reflecting a greatly increased discharge of icebergs from northern-hemisphere ice sheets. These are called "Heinrich events," after the researcher who first called attention to them. (See Figs. 4A and 4B.) Every third or fourth cool stadial period is a Heinrich event. (The ice-core people call them Dansgaard-Oeschger events, but "stadial" is easier to remember.) The stadials in between Heinrich events also show increases in ice-rafted debris, but they are much less pronounced.
Heinrich events are also mirrored in pollen buried in a Florida lakebed. A 50,000-year pollen sequence from Lake Tulane, Florida shows that each of the last five Heinrich events was associated with a marked increase in pines and a decline in oaks, indicating wetter conditions. 24 (See Fig. 5.) And the last three Heinrich events were matched by glacier advances in the mountains of Chile and New Zealand. 25
What surprised ice-core researchers is the extreme abruptness of the transitions between cold and warm conditions. But then, no other long, continuous climatic record has been studied with such fine resolution as the new Greenland ice cores, and with most kinds of records, it is not possible. Analyses of dust and electrical conductivity in the cores show this most clearly. Enhanced dustiness is closely associated with colder temperatures. Unlike isotopes, dust does not diffuse through the ice. Above a certain threshold, dust curtails electrical conductivity, so measuring the conductivity is one simple way to see how dusty it was. In the GISP2 ice core, Taylor et al. found that the transitions "between glacial and near-glacial conditions" frequently occurred "in periods of less than a decade, and on occasion as quickly as three years." 26 They compare the atmospheric circulation over central Greenland to "a flickering switch that fluctuates between two states before stabilizing" for centuries or thousands of years at a time.
The oscillations also show up in ocean sediment cores far away from the North Atlantic. Sedimentation in the shallow Santa Barbara basin, off southern California, is sensitive to changes in the oxygen content of bottom waters. In periods of cold climate, sediments are extensively reworked by bottom-dwelling organisms. In times of warm climate, such as the present, bottom waters are deficient in oxygen, and the finely laminated sediments are undisturbed in this sterile environment. Nineteen of the 20 glacial warming events seen in Greenland ice cores during the past 60,000 years can be recognized in the Santa Barbara basin. 27 (See Fig. 6.) A similar sequence is recognized in sediments of the Gulf of California.
Sediments in the Arabian Sea off the coast of Pakistan show another such sequence of dark, partly laminated, sterile layers laid down during warm periods, alternating with light-colored, organically rich layers. All 24 interstadials within the past 110,000 years can be distinguished in the sedimentary record. 28 Corresponding changes in the pattern of monsoon winds are marked by increased atmospheric transport of dust from the land during cold periods. 29
Cores from the Cariaco basin, in the southern Caribbean off Venezuela, show a similar high-frequency variability. Sedimentation in the basin alternates between a dark terrigenous layer deposited in the summer rainy season, and a light, plankton-rich layer in the winter, when strong trade winds cause upwelling of nutrient-rich waters. A record of layer thickness and coloration in shallow sediment cores covering approximately the last 13,000 years shows an excellent correlation with the ice-core record: when oxygen isotopes show cooling in Greenland, the basin sediments are thicker and lighter-colored. 30 (See Fig. 7.) Clearly, the circulation of the world oceans was affected by these events. Incidentally, the dating of the onset of the Younger Dryas cold period (which ended the last glaciation) in the Cariaco basin agrees with the GISP2 ice-core date "within a couple of decades" 31 --another miracle for the kerplopists to explain.
As noted by Bender et al., "There are 22 distinct interstadial events recorded" in the ice cores from central Greenland between 20,000 and 105,000 years ago. Nine of these lasted more than 2,000 years. Of these nine, eight "can be clearly recognized" in the Vostok isotope record, although the amplitude of the oscillations is not as pronounced in Antarctica as in Greenland (as seen in Fig. 3A.). 32 Nature is trying to tell us something. But Ginenthal is deaf.
Ginenthal claims that temperature swings found in Greenland ice are not reflected in climate records on land, but the very source he cites to illustrate this belies the claim. Speaking of the Dye 3 ice core, Hans Oeschger writes, "The shifts of 18O at the transition to the Holocene 15,000 and 10,000 years B.P. are also recorded in carbonate deposits of Central European lakes. Figure 3-10 demonstrates the excellent correlation." 33 (Oeschger's figure, glaring at Ginenthal from the same page, is reproduced here as Fig. 8.) Then, on the same page, in the sentence quoted by Ginenthal: "Such pronounced correlations are not found in climatic records from the North American continent." Ginenthal's comment:
"He had found these temperature swings in the Dye 3 ice core and admitted that they are not found in the varve record for North America. This poses another fundamental contradiction. One cannot change the temperature of the North Atlantic Ocean so as to affect the Greenland icecap, for both long and short time periods, and then not leave the same climate record in North America.
"This indicates that the temperature swings had nothing to do with any other theory proposed except that of Velikovsky. If the icecaps were formed in one year, there never would have been innumerable temperature swings on the land, as Oeschger reported. Why should temperature swings exist only in the icecap, showing no corresponding swings in the land varves, if the ice core record is accurate? These swings should be found in both North American and European varves, but they do not exist. This means that the ice core record is wrong and cannot be relied upon to explain ancient weather patterns." 34
But Oeschger does not say there are no correlations with North America. He says they are not as pronounced as "the excellent correlation" with Europe, which is downwind and warmed by the Gulf Stream. Ginenthal has the audacity to attribute his falsehoods to a source which says the very opposite. Why such a compulsion to confabulate? Why commit decades of one's life to such a dreary enterprise?
As for the "pronounced correlations" which Oeschger said were lacking in North America, they have been found. In Twiss Marl Pond and Crawford Lake -- two small lakes just west of Lake Ontario, the Younger Dryas and a number of finer climatic oscillations preceding and following it are faithfully reflected in the oxygen isotopes of lakebed carbonate, as well as distinct vegetation changes revealed by the pollen. (See Figs. 9A and 9B.) 35 In both Europe and North America, what Ginenthal sloppily refers to as "the varve record" varies in step with Greenland ice cores.
Clearly, the sharp climatic swings preserved in Greenland ice of glacial time are very real, and their impact was global. They have their counterparts on land and in the seas -- Atlantic and Pacific. They have left their imprint in the ice of both hemispheres. But in the lowest ten percent of both Summit cores, in ice more than 115,000 years old, it is a different story. There, all the nice correlations between cores and with other global climate records break down. The findings in this part of the GRIP core (the first to be drilled), incorporating ice from the Eemian interglacial period, were already suspect, because while climate in the Holocene, in which we live, has been more stable than in the ice age, the oscillations during the Eemian seemed to be even more extreme. Then, when the GISP2 core was brought in from 28 kilometers away with the corresponding section also showing steep climate shifts, but in different places, it was obvious that the stratigraphy of at least one, and possibly both cores had been disturbed in the lowest 300 meters. Since the GRIP drill site lies over the current ice divide, it was considered less likely to have been disturbed. If the divide has always been in the same spot, the ice there should have moved only vertically. But over tens of thousands of years of climate changes, it could easily have moved a few kilometers.
Close examination of visible layers with transmitted light shows increasing signs of disturbance with depth: "... the cores the U.S. team obtained in Greenland contained layers that, from top to bottom, went from being horizontal, to having small wiggles, to showing Z-shaped folds, to becoming slanted at angles up to 20 degrees in ice older than about 110,000 years." 36 The ice in the European GRIP core shows similar changes at only slightly greater depths. (See Fig. 10.) This suggests that in the lower levels, younger ice may have been folded over into older ice, mimicking the appearance of abrupt climatic shifts. Sophisticated analysis of the enclosed gases and their phase relationships points in the same direction. 37 Likewise, a new North Atlantic sediment core drilled in an area of very rapid accumulation, covering the time span 340,000 to 500,000 years ago shows greater climatic variability in glacial than interglacial stages, casting further doubt on the reality of the extreme fluctuations in the Eemian sections of the Summit ice cores. 38 ) A new ice core drilled 340 kilometers to the northwest of Summit at "North GRIP" should resolve the question.
Predictably, while ignoring all the detailed correspondences between the Greenland ice cores and other climate records around the world over the last 115,000 years, Ginenthal makes much of the discrepancies in the bottom ten percent of the cores. Imposing his paranoid fantasy on fact, he tells us: "In order to explain away these temperature swings, a three-day conference was held by the European and American ice core teams to present papers stating that these swings may not have existed during the last Interglacial." 39 In fact, there have been several joint workshops to compare the dating of the two ice cores, at which various issues were debated, including climate variability during the last interglacial, but none that was devoted specifically to the Eemian. 40 It is Ginenthal who tries to explain away the abrupt temperature changes in the ice cores, Ginenthal who ignores the corroborating evidence from land and sea, Ginenthal who misrepresents the words of his sources. And it is the scientists who put their ideas to the test. They compared and analyzed the evidence available to them, and when this did not definitively resolve the issue, they went out to collect more evidence. One of the principal motives for drilling a new core at North GRIP was to settle this question.
Ginenthal also claims that "Climate swings of about 20° F" would cause extinctions of plants and animals, including insects and cold-blooded animals, and demands, "How can Ellenberger or Mewhinney explain these contradictions?" 41 I can only ask, what "contradictions"? In fact, there have been extinctions of many species of large mammals during the time period covered, and climate certainly may have played a role. But one must remember that to cause extinction of a species, mass mortality is not enough; you have to eliminate all the individuals across the entire range of that species. Of course, the amplitude of these temperature shifts was greatest in Greenland and the waters around it. After all, there is a flickering switch right next door, in the North Atlantic.
Scientists have long looked to the north for the cause of the ice ages. Owing to the asymmetry between hemispheres in the distribution of land and sea, that is where the great changes have taken place between glacial and recent times in the growth of continental ice sheets. So it is that the amount of solar energy falling on high northern, not southern latitudes, is thought to be the ultimate force driving great climate changes. Why is climate more variable in the north than in the south, and why is the Antarctic colder than the Arctic?
The answer to both questions seems to lie in the deep circulation of the oceans. Ocean currents carry great quantities of heat from the tropics to the high latitudes. They can deliver this heat closer to the north pole than to the south pole. The earth's rotation pushes ocean waters up against the eastern edges of the continents, where they are forced to turn north or south. In the southern hemisphere, there is no land beyond the southern tip of Tierra del Fuego to drive those waters southward, and little of their heat penetrates the interior of Antarctica. But every winter in the north Atlantic off Greenland, an enormous amount of heat is transferred from the ocean to the atmosphere when salty northward-flowing waters, arriving at a temperature of 10 or 12 degrees Celsius, are cooled by the winds to between 2 and 4 degrees, making them dense enough to sink to great depths. There they reverse direction and flow very slowly south again. The heat released to the air is equivalent to 35% of the energy received from the sun by the surface of the Atlantic north of 40 degrees latitude. 42 It maintains northwest Europe at a temperature between 5 and 10 degrees warmer than it would otherwise have. 43 Water is chilled and sinks to the depths around Antarctica too, but much of this activity takes place beneath the ice shelves of the Ross and Weddell Seas, where transfer of heat to the atmosphere is restricted.
There are very few places where this sinking of surface waters to great depths can take place. It doesn't happen in the Pacific. It gets quite cold in the North Pacific, but the surface waters aren't salty enough, and they never become dense enough to sink more than a few hundred meters, even if cooled to their freezing point. There is plenty of evaporation in the equatorial Pacific, but the trade winds blow fresh water across the neck of the Americas from the Atlantic to the Pacific, maintaining the greater buoyancy of the surface waters there.
As long as the sinking of surface waters continues in the North Atlantic, it draws more warm waters up from the south to replace them, perpetuating the transfer of heat from south to north. Wallace Broecker has likened this recirculation to a conveyor belt, with a lower loop removing salty waters from the Atlantic and an upper return loop feeding it. But if something should interrupt the process, such as an influx of fresh water, the conveyor could be difficult to restart. Without a strong current from the south to sweep fresh water out of the way, it could build up enough to prevent or greatly reduce downwelling. That is just what appears to have happened during the Heinrich events, when great fleets of icebergs were depositing glacial debris across the North Atlantic, and adding their meltwater to the ocean surface.
The salinity of surface waters reaching the North Atlantic is currently maintained by a balance between evaporation, precipitation, and runoff from the continents. In the south, the balance strongly favors evaporation over precipitation and runoff. But in the north, the balance is reversed, and water transported from the south is progressively freshened as it travels further northward. If the salinity of the North Atlantic were to fall below some critical threshold, deep convection would be curtailed, triggering an abrupt cooling. Today there are about two and a half million cubic kilometers of land ice in the northern hemisphere, nearly all of it in Greenland. In peak glacial times, there were another 40 million cubic kilometers in Europe and North America. The presence of so much fresh water locked up in northern ice sheets made the climate potentially unstable. Whenever a substantial fraction of the ice started to melt, it would flood the North Atlantic with a lid of fresh water, shutting down deep convection and the transfer of heat to the north. The sudden cooling would in turn shut off the sudden increase in meltwater, allowing salinity to slowly build up in the North Atlantic again to the point where it deep convection could resume. Thus in Broecker's conception, in glacial times the Atlantic Ocean functioned as a gigantic "salt oscillator" in the climate system.
Downwelling need not come to a halt to cool off the North Atlantic. A change in the site of convection can make a significant difference, as Lehman and Keigwin point out. Most deep convection in the North Atlantic takes place north of Iceland, but there is also convection southwest of Greenland, in the Labrador Sea. The waters sinking there do not lose as much heat to the atmosphere as the waters north of Iceland, and they do not sink quite as deep, so in effect the ocean conveyor has two belts beneath the surface: an upper one in the south and a lower one in the north. Water feeding the "lower" belt north of Iceland "releases twice as much heat to the atmosphere per unit mass." 44
The waters of the North Atlantic are quite distinct from those of the Antarctic in their temperature, salinity, nutrients, and carbon isotopes. After sinking into the abyss, they trace serpentine and poorly charted paths, gradually mixing, warming, and becoming more buoyant, until they emerge centuries later and tens of thousands of miles away. Because of their very low rates of diffusion and mixing, these deep water masses can still be distinguished thousands of miles from their origins by chemical and isotopic tracers. These tracers are metabolized and incorporated into the skeletons of microscopic organisms that live at different depths in the water column, making it possible to reconstruct the properties of the water masses at different depths in the distant past, to a certain extent. And what scientists have found is that the circulation of the oceans was very different in glacial times from that of the present.
At present, waters sinking in the basins north of Iceland spill out in three places over a sill running from Greenland, to Iceland, to Scotland. Making a hard right turn, these three streams join together and flow into the Labrador Sea. Together, they form the lowermost component of what is called North Atlantic Deep Water. The uppermost component joins the stream there. (See Fig. 11.) Pressing up against the land, it flows southward along the continental shelf as the Deep Western Boundary Current. This water mass occupies a depth range between approximately 2,000 and 4,000 meters, spreading out to fill most of the North Atlantic at this level, and much of the South Atlantic. Crossing the equator off Brazil, it overrides a tongue of Antarctic Bottom Water pressing up from the south. Reaching as far as 60 degrees south, North Atlantic Deep Water wells up and mixes with the waters of the Antarctic circumpolar current.
Aside from their temperature and salinity, deep water masses differ in several other properties which vary together as a consequence of the effective "age" or residence time of the waters beneath the surface. Nutrients are continually raining down from above. There is little life in the depths to use them, so they keep building up. The decomposition of organic matter does deplete oxygen, though, which can only be renewed at the surface. It also reduces the ratio of carbon 13 to carbon 12 in seawater, due to chemical fractionation. So the concentration of nutrients constantly increases, while 13C/12C (delta 13C) declines, as deep waters move away from their place of origin at the surface and "age". Deep waters from the Antarctic give every appearance of being much older than those from the North Atlantic, because they either form beneath a skin of ice, which restricts biological activity and gas exchange with the air, or they spend only a short time at the surface before plunging to the depths again.
Measured in seawater, these water-mass properties trace out gradients which have been mapped at different depths throughout the ocean basins. Even without direct measurements from current meters, such a map suggests the broad patterns of deep circulation in the modern ocean. By examining the sediments in deep-sea cores, paleoceanographers can piece together pictures of the ocean at different times in the past for comparison, although not so accurately, and with much coarser resolution.
In the modern ocean, North Atlantic Deep Water is about 5 parts per thousand (%o) richer in 13C than Antarctic Bottom Water. At about 30 degrees south latitude, the Deep Western Boundary Current is forced through the narrow Vema Passage off southern Brazil. There are really two different flows: a core of southward-flowing NADW overlies northward-flowing AABW. There is a steep gradient in carbon-isotope values in the mixing zone between these two water masses, with the sharpest change between 3.5 and 3.9 kilometers. By sampling the delta 13C values in benthic (bottom-dwelling) foraminifera in a series of cores ranged along the sloping channel walls at depths between 2300 and 3900 meters, Curry and Lohmann 45 found that in glacial times, the sharpest change in the depth profile of delta 13C was much higher in the water column, at 2.7 kilometers. There was no significant change in 13C values between glacial and recent times in the shallowest or the deepest cores -- only in cores of intermediate depth. This indicates that in glacial times, either the boundary between North Atlantic Deep Water and Antarctic Deep Water shallowed by as much as a kilometer, the flux of NADW relative to AABW was much lower than today, or both.
The deep Atlantic is separated into two basins by the Mid-Atlantic Ridge. Deep water spreads slowly from west to east across the Atlantic, crossing the Mid-Atlantic Ridge mostly through the Romanche fracture zone in the tropical North Atlantic. A sill depth of 3750 meters allows North Atlantic Deep Water to pass unhindered into the eastern basin, but restricts the flow of underlying Antarctic Bottom Water. In the modern ocean, the water entering the eastern basin is about 3 or 4 parts NADW to 1 part AABW. Studies of benthic foraminifera in cores at different depths on the Sierra Leone rise, near the eastern exit of this fracture zone, show that in glacial times, much more AABW was entering the eastern basin. Looking at changes in the carbon-isotope ratios, Oppo and Lehman estimated that the water in the eastern basin was equal parts NADW and AABW. 46 Beveridge et al., using the ratio of cadmium to calcium as well, which serves as a proxy for nutrient concentrations, estimated the proportion as only 1 part NADW to 3 parts AABW, the reverse of the modern situation. 47 Once again, the evidence points to a marked reduction in the flow of North Atlantic Deep Water, a shallowing of the boundary with Antarctic Bottom Water, or likely both. 48
In the modern North Atlantic Ocean, deep waters are more depleted in nutrients than intermediate waters, so they measure higher in delta 13C and lower in cadmium to calcium (Cd/Ca) ratios. The reason for this is the deep convection in the northern North Atlantic, which drives a stronger horizontal flow at the buoyancy level of NADW than is found at shallower depths. The waters at intermediate depths are older, because of the stagnant circulation. Boyle and Keigwin pointed out that during glacial times, the situation was reversed: waters at intermediate depths were more depleted in nutrients than deep waters, indicating that the intermediate depths of the ocean were better ventilated than the deeper levels. 49 They suggested that deep and intermediate circulation wax and wane alternately, one at the expense of the other. Cold conditions favor the formation of intermediate water, and warm conditions favor the formation of deep water, because of the greater evaporation and salinity. This is borne out nicely by a recent comparison of the benthic record over the last 17,000 years in two high-resolution cores at different depths by Marchitto et al. 50 One is located on the Bahama Banks at a depth of 965 meters; the other on the Bermuda rise at a depth of 4,450 meters. The benthic Cd/Ca curves are virtually mirror images of one another; when one curve rises, the other falls. (See Fig. 12.) This helps to explain why, as we noted, numerous shallow, oxygen-starved ocean basins around the world, where sterile, laminated sediments are being laid down today, were better ventilated during cold periods in the past.
When we turn from chemical and isotopic evidence to direct physical indicators of deep current flow, they tell much the same story. The overflow of deep water through the Iceland-Scotland rise was much weaker in glacial times. From measurements of the magnetic anisotropy of sediments downstream in the Gardar Drift, Kissel et al. estimate that as a "very rough approximation," the overflow was "reduced during glacial periods to about 30-35%" of its present strength. 51
In their multi-parameter study of a series of cores on the flanks of the Reykjanes Ridge, south of Iceland, Moros et al. identified a regular succession of climatic oscillations paralleling those in Greenland. The stadial periods are marked not only by cooling and heightened levels of coarse-grained, ice-rafted debris, but also by a reduction in mean grain size in the size fraction less than 20 micrometers, indicating a weakening in current strength. 52
In the Labrador Sea, Holocene sediments deposited by the Deep Western Boundary Current are much coarser than their glacial equivalents. The rate of sedimentation is also lower in the Holocene, perhaps due to greater erosion. Both are indications of weaker current speed in the past. 53
On the continental rise off the northeastern United States today, the core of the Deep western Boundary Current lies at a depth of 4900 meters. It is marked by a 300-kilometer-wide zone of coarse-grained sediments, with the particles preferentially aligned parallel to the direction of flow. A study by Ledbetter and Balsam of mean grain size in 7 sediment cores ranging from 3000 to 4900 meters in depth shows that the current has moved up and down the continental rise over the course of the past 25,000 radiocarbon years, while changing in speed. Within this time span, the current has never been deeper than it is today. The detailed record, with a sampling interval of about 1,000 years, shows many fluctuations in current speed. (See Fig. 13.) The authors summarize the principal changes as follows: "The axis of the zone of coarse sizes (greater bottom-current speed) remains at ~4400 m from 25 to 17 ka while fluctuating in speed. At about 16 ka the high-velocity axis splits into a shallow, major axis of intense flow [as little as 4,000 meters deep]. Both axes rejoin at about 5 ka when the major axis suddenly deepens to ~4500 m and continues to deepen to the modern position at ~4900 m." 54 Note that while the flow was shallow during the height of glaciation, it shallowed even more during the subsequent deglaciation, when freshwater from the melting of northern ice sheets was being returned to the ocean.
Further south, where the Deep Western Boundary Current curls sharply around the Blake Outer Ridge east of Georgia, its main axis today lies at 4200 meters. From an examination of the grain size in a series of cores at various depths on the ridge, Haskell et al. Found that "Prior to 12 kyr, circulation was focused on the upper part of the ridge above 2700 m." 55
The Broecker salt-oscillator model predicts that slowdowns in the flux of North Atlantic Deep Water are triggered by reductions in surface salinity. So it is of great interest to know the timing of variations in salinity of the Atlantic. Salinity can be estimated from the oxygen isotopes recorded in planktonic foraminifera, after subtracting out the effects of global ice volume and local temperatures. The process is complicated, messy, and subject to a number of uncertainties, but the exact values are not so important as the timing and direction of the changes. Maslin et al. have made a detailed reconstruction of salinity covering the last 45,000 carbon-14 years for a site in the northeast Atlantic, west of Ireland. Overall, salinity was low at this spot between 30,000 and 13,000 years ago. As expected, they find that local salinity plunged markedly during Heinrich events, when fleets of icebergs moving east along a track from 40 to 55 degrees north were melting and dropping loads of subglacial debris on the seafloor. (See Fig. 14.) Taking the process a step further, they use these results to calculate the hypothetical density of surface water if cooled alternatively either to 6 degrees or to one degree Celsius as it flowed further north. And they find that while prior to 30,000 14C years ago, there were periods between Heinrich events when deep water could form in the northeast Atlantic, no amount of cooling could cause deep water to form between 30,000 and 13,000 years ago, because the surface waters could not attain sufficient density. 56 (See Fig. 15.) This does not exclude the possibility that convection could have been taking place elsewhere in the Atlantic, perhaps further south and in a shallower mode. Their reconstruction of past salinity also shows numerous, less pronounced salinity minima in between Heinrich events, which apparently correspond to other stadials in the ice-core record. Sarnthein and Altenbach observe that the negative delta 18O excursions produced in numerous North Atlantic sediment cores by "various meltwater episodes.... are clearly coeval with Dansgaard-Oeschger events" (stadials). 57 And Duplessy et al. have shown that the last two clearly defined cold periods, the Oldest and Younger Dryas events, were accompanied by sharp reductions in salinity in the North Atlantic, although the origin of these fresh-water spikes is unclear. 58
If low salinity is the trigger that shuts down convection in the North Atlantic, is there a smoking gun? Cores lying just south of the main track followed by icebergs across the Atlantic show a marked drop in benthic delta 13C during Heinrich events. In a core from mid-ocean at 40 degrees North, Chapman and Shackleton found "a series of high-frequency events" with "high delta 13C broadly equivalent to those found in the Holocene... punctuated by rapid reductions... of up to 0.7%o." Some of these "Decreases in benthic delta 13C values closely parallel increases in IRD [ice-rafted debris] input and the reduction in SST [sea-surface temperature] during [Heinrich] events H1, H3, H4, and H5" and "appear to provide evidence for a shutdown or major reduction of NADW formation." 59 Other decreases fall between the Heinrich events. In another core from off southern Portugal, Zahn et al. Observe a "Marked depletion of benthic delta 13C by 0.7-1.1%o during the Heinrich events" with other, more frequent depletions in between. 60
Further north, Rasmussen et al. have identified all 15 stadials during the past 58,000 years in a core from just northwest of the Faeroe-Shetland channel, where deep water from the Norwegian Sea spills into the North Atlantic. During interstadials, benthic foraminifera outnumber planktonic foraminifera by an average of 2 to 1. During stadials, planktonics outnumber the benthics 10 to 1. To Rasmussen and her coworkers, "The difference between the surface and the deep-water productivity points to a decoupling of the surface and bottom environments and a stop in the deep convection north of the Faeroe Islands." 61 They suggest that during every cold episode, the location of convection shifted south of the Iceland-Scotland Rise, returning after the ocean surface warmed up again.
So there are three things that seem to be related here: cold temperatures, low salinity in the North Atlantic, and a slowdown or shallowing of NADW formation, probably with a change in the locus of convection, often accompanied by a fourth -- to a greater or lesser degree -- an increase in ice-rafted debris -- with oscillations on a time scale of a few thousand years. If this does not prove Broecker's salt-oscillator theory correct, at the very least it implicates the deep ocean circulation as a key agent in abrupt climate shifts. It's hard to pin down the exact causal links between these phenomena, partly because ocean sediment cores do not have fine enough time resolution to reveal changes that take place in as short a time as a couple of centuries or even a decade, and to establish precise cross-correlations between different marine cores, or with the ice-core archives, and thus establish the leads and lags between different elements of the climate system. Typically, ocean sediments are disturbed for a depth of up to 8 centimeters by worms and other burrowing organisms, and in most deep-sea cores, this represents a time interval of several thousand years.
But there are other kinds of evidence that can reveal abrupt changes in the deep circulation of the oceans, one of which is corals. These are not the familiar reef-building corals of the tropics, but those that live in cold, deep water, mostly as solitary individuals. A single coral records changes in the properties of the waters in which it grew over the course of its lifetime, changes which may sometimes be very abrupt, indeed. Corals can be dated by uranium series, and they have been used to calibrate the radiocarbon method beyond the reach of tree rings. Three of the coral specimens studied by Adkins et al., all from Kelvin Seamount in the North Atlantic, at depths between 1784 and 1954 meters, yielded 230Th dates between 15,400 and 15,410 years -- their true dates, within errors. These three corals were also radiocarbon dated, at top and bottom, and they showed radiocarbon age reversals of between 140 and 670 years, that is, the youngest part of each coral -- the top, dated older than the base, which is the oldest part. To this should be added the lifetime of the coral, estimated to be between 30 and 160 years. This is no fluke. The authors interpret this to mean that during the lifetime of the corals, North Atlantic Deep Water shoaled above the depth at which they were growing. When they began growing, they were immersed in a "young" water mass that originated in the North Atlantic. The calcite at the base of the coral incorporated carbon from this water, with a proportion of carbon-14 to carbon-12 reflecting its ventilation "age." Then a denser, older water mass from the south rose until it covered these depths. The carbon in this water mass was more depleted in carbon-14, through radioactive decay. Incorporated into the top of the coral skeleton, it makes it appear to be older than than the base. This is confirmed by measurements of the cadmium-to-calcium ratio in one of the corals, which show a progressive twofold rise from the bottom to the top, marking the transition from northern- to southern-source waters. 62
Laminated sediments from the shallow Cariaco Basin show a sharp increase in the ratio of carbon-14 to carbon-12 at the beginning of the Younger Dryas cold period, about 13,000 years ago. Counting the annual laminations reveals a "long, sloping 'plateau' " from 10,600 to 10,000 radiocarbon years ago, "during which radiocarbon ages decrease only 600 yr in 1,600 varve years. The beginning of this sloping 'plateau' coincides with the onset of the climatic Younger Dryas, but continues for an additional 400 varve years after the Younger Dryas termination." 63 Back-calculation shows that the atmospheric ratio of carbon-14 to carbon-12 must have risen 5 to 8 percent in the first 200 years, followed by a gradual decline of the same magnitude over the next 1100 calendar years. (See Fig. 16.) A similar figure was reached by comparing varve counts with radiocarbon ages from Lake Gosciaz in Poland. 64 Over long periods of time, the carbon-14 ratio is affected by various factors, such as the earth's magnetic field strength and solar energy output, but only one thing is capable of producing such a sharp jump in 14C values -- a slowdown or virtual shutdown in the production of North Atlantic Deep Water. Carbon-14 is created by cosmic-ray bombardment high in the atmosphere, and exchanged with carbon atoms in atmospheric carbon dioxide, which readily dissolves in ocean water. The ocean as a whole stores about 60 times as much inorganic carbon as the atmosphere. But only a thin skin, to a depth of about 75 meters, is affected by gas exchange with the atmosphere. The deep ocean "breathes" only through convection. About 80 percent of the carbon-14 entering the deep sea is carried down from the North Atlantic. 65 If the vertical circulation in the North Atlantic were to come to a standstill, carbon-14 would build up rapidly in the atmosphere. And that is just what seems to have happened at the beginning of the Younger Dryas, followed by a recovery over the next millennium.
At almost exactly the same time, as nearly as one can tell, there was a steep 23-percent drop in the atmospheric level of carbon dioxide, followed by a gradual recovery. The evidence comes not from the sea, but from willow leaves in a Norwegian lakebed. Plants breathe through pores on the undersides of their leaves, called stomata. Certain species of plants adjust to the level of carbon dioxide in the air by growing either more, or fewer stomata per unit area -- there is an excellent inverse linear correlation. Willow leaves from Lake Kråkenes in western Norway have been used to reconstruct carbon dioxide levels through the period from about 11,500 to 9,600 radiocarbon years ago. (See Fig. 17.) Over a period of 130 to 200 radiocarbon years beginning just before the Younger Dryas, CO2 levels fell from an estimated 273 parts per million to about 210 ppm. Over the next 800 radiocarbon years, the level recovered to 270 ppm at the end of the Younger Dryas. 66
So while our "flickering switch" often seems to act more like a rheostat, moving over a continuum of possible settings, at times it can shut down almost completely. It should be recognized what is being proposed: It's not just a question of what *triggers* climate jumps, because in an oscillating system, where feedbacks from every part of the system affect every other part, that's a chicken-and-egg question, but rather, which component in the climate system functions as the amplifier. The evidence strongly implicates the ocean conveyor belt. While the conveyor clearly has a tremendous effect on temperatures in the high northern latitudes, it is less obvious how its influence could be communicated so rapidly around the world to the tropics. Nevertheless, many such linkages between weather conditions at places half a world apart are well-known to meteorologists. They are called teleconnections. If we define a weather anomaly as a departure from average seasonal temperature, rainfall, air pressure, or wind conditions persisting for months or years, a teleconnection is a strong correlation, positive or negative, between weather anomalies at different places over great distances. The linkage can be either through the air or the ocean, or both. They tend to oscillate back and forth together as though on a seesaw. William Kessler likens these patterns to the preferred modes of vibration on a drum head. 67 The most familiar of them all is the Southern Oscillation, which brings us alternately El Nino and La Nina.
Normally, a high-pressure area off South America keeps the southeast trade winds blowing hard enough along the equator to pile up the warm surface layer of the ocean to a depth of 150 meters in the western Pacific. Off Peru, where it is only 30 meters deep, offshore winds permit cool water to well up from below, maintaining the high-pressure system. The zone of intense evaporation and rainfall is confined to the western Pacific. During a Nino, the trade winds slacken and the warm surface waters slosh back to the east, suppressing upwelling. The air over the eastern Pacific warms as much as 4-5 degrees Celsius. Intense Ninos may bring torrential rains to Peru and drought to Australia, Indonesia, southeastern Africa, and northeast Brazil, weaken the monsoon in India, and intensify the jet stream over North America, bringing more storms and heavier rainfall to the southern United States.
The Southern Oscillation illustrates how ocean and atmosphere are coupled together on a global scale, causing tremendous changes in the geographic distribution of heat, evaporation, precipitation, and water vapor. A change in the total water-vapor content of the atmosphere would be the most effective way to communicate climate change from the high northern latitudes to the tropics, and the most plausible link is upwelling, which takes place at the other end of the conveyor belt, in the tropics. One hears a great deal these days about the greenhouse warming effects of carbon dioxide. But the most effective greenhouse gas by far is water vapor, because of its presence in much greater concentrations. As Wallace Broecker puts it, "If you wanted to cool the planet by 5 degrees C and could magically alter the water-vapor content of the atmosphere, a 30% decrease would do the job." 68 And in spite of Ginenthal's ignorance on this matter, it is well known that the ice-age climate was much drier than today's, as will be shown in Part VII.
That there should be a link between ice sheet and ocean seems easier to understand, even expected, when they lie next to one another. But the precise nature of that link remains to be clarified. When the same high-frequency climatic oscillations were found in the Dye 3 ice core as at Camp Century, 1400 kilometers away (with a correlation of 0.88 ) 69, it did not immediately set off a rush to find a sea connection. But it sparked Wallace Broecker's interest. In 1988, Broecker and others were asking (the title of their paper), "Can the Greenland Climatic Jumps Be Identified in Records from Ocean and Land?" At that time they could still say: "...we know of only two ocean cores... for which published records are appropriate for documentation of Greenland events." 70 In fact, they already had the answer to their question, in a study published just three months earlier in that same journal, Quaternary Research (but no doubt after their manuscript was submitted). 71 But at the time, it wasn't recognized for what it was, even by the author, Hartmut Heinrich. Even as late as 1989, Broecker and Denton cautioned, "Correlatives of these events have yet to be confirmed outside of Greenland, even in the adjacent northern Atlantic basin." 72
There are several reasons for this. Some of the oscillations in the ice-core record (the Heinrich events) are generally much more conspicuous in ocean sediments than others, which could not be distinguished without much closer sampling intervals than are ordinarily used in the study of marine cores. Given that the ice-core record showed two or three times as many events as the deep-sea record, correlations between the two were uncertain. And without sufficient numbers of radiocarbon dates, the drastic increases in sedimentation rates during ice-rafting episodes went unrecognized, so the abruptness of these events was not fully realized.
Finding the cause of the oscillations was another matter. Broecker was looking for something that might shut down the conveyor. At the height of the last glaciation, more than twice as much ice as today was held in the world's ice sheets and glaciers. Over the course of the next seven or eight thousand years, that excess ice was returned to the oceans -- nearly all of it around the Arctic and North Atlantic basins -- in the form of glacial meltwater. But this was not accomplished in one smooth, steady process. It came in spurts, interrupted by periods of partial glacial readvance. In a 1985 Nature article, Broecker et al. noted that if just three percent of the excess ice were returned in one century, it would be twice as much as the amount of freshwater currently being removed from the Atlantic by evaporation and transferred to the Pacific basin by winds and precipitation. 73 And that might be enough to shut down the conveyor in the North Atlantic, or push it into a weaker mode of operation, bringing on a deep cold spell.
To account for the last such cold spell, the Younger Dryas, Broecker took up a suggestion made tentatively by Claes Rooth some years earlier. At approximately the same time as the onset of the Younger Dryas cooling, the Laurentide ice sheet had retreated far enough northward to permit the waters of proglacial Lake Agassiz to drain eastward into the St. Lawrence valley through Lakes Superior and Huron. By the end of the Younger Dryas, a glacial readvance cut off this outlet and rediverted the outflow from Lake Agassiz southward into the Mississippi valley. It was tempting to conclude that the extra influx of fresh water into the Labrador Sea might have suppressed deep-water formation in the North Atlantic, and Broecker et al. advanced the idea in a Nature article. 74 But this fortuitous set of circumstances could at best explain only one particular event.
The first blow to this hypothesis came less than three months later, with the appearance of Richard Fairbanks' sea-level curve for the past 17,000 years derived from a coral reef off Barbados. 75 The Fairbanks curve showed two periods of rapid sea-level rise interrupted by a slowdown during the Younger Dryas. The rate of sea-level rise at this location can be interpreted as a record of global meltwater discharge from the retreating glacial ice sheets. A plot of inferred meltwater input shows two sharp peaks neatly bracketing the Younger Dryas. The implication is that the discharge from Lake Agassiz during this period would have been minimal.
Another blow was Keigwin and Jones' failure to find a Younger Dryas meltwater spike in the planktonic oxygen-isotope record in a suite of cores taken off Nova Scotia, near the Gulf of St. Lawrence. 76 This, in spite of the fact that Duplessy et al. did find a Younger Dryas salinity minimum further east in the North Atlantic. Yet a further blow was Lasalle and Shilts' discovery that ice readvanced across the St. Lawrence valley near Quebec City during Younger Dryas time, so that Laurentide meltwater would have been prevented from reaching the ocean through this outlet for at least part of this time. 77
Broecker wrote later that it bothered him that if the other cooling "events in the... ice core record were assumed to be akin to the Younger Dryas event then" by logical extension, "each would require a river diversion." 78 His immediate response to the criticism of Fairbanks was to downgrade the role of the diversion to the secondary status of a trigger that pushed the conveyor circulation, already weakened by a surge of meltwater during the preceding warm interval, over the edge. 79 He didn't have it altogether quite right yet. But more pieces were beginning to fall into place.
To bear the quantity of glacial debris seen in the Heinrich layers would require a tremendous volume of ice, melting into the ocean within a comparatively short time. And in fact, the planktonic oxygen-isotope record showed reduced surface-water salinity during Heinrich events. A rough estimate was that mixing one part iceberg meltwater with 30 parts seawater would account for the isotope signal. 80 Not only would this low salinity explain the virtual absence of foraminifera in the Heinrich layers, it would be sufficient to suppress deep convection in the North Atlantic. The trail of debris left by these icebergs as they drifted across the Atlantic can be followed for 2,000 miles, thinning by more than an order of magnitude from west to east. The path they followed would deliver fresh water quite efficiently to the places where convection takes place. The polar front, where subpolar and subtropical water masses meet, lies at the northern edge of the Gulf Stream. In glacial times, it lay somewhat further south, especially in the eastern Atlantic. Icebergs that drift southward to the polar front are turned eastward by the current, and they begin to melt rapidly.
So the location of the meltwater is much more important than the quantity, in its effects on the operation of the ocean conveyor. Meltwater runoff from ice sheets is greatest in warm periods, but it is diluted by seawater long before it reaches the sites of convection. Iceberg calving is greatest in cold periods, and surface currents carry them where their melting will have a disproportionate effect on the sinking of water masses.
Broecker was collaborating with Gerard Bond on the study of a North Atlantic core. It had dried to a uniform, dull gray, but photographs of the fresh core showed color variations on a much shorter time scale than the intervals between Heinrich events. Sampling at the usual coarse spacing would miss such changes. But counting individual grains in every centimeter of core confirmed that in between the Heinrich layers were other, thinner layers of ice-rafted debris, composed of different types of minerals. Cross-comparison with the Greenland ice cores showed an almost perfect match -- all but one stadial in the past 38,000 years corresponds to an ice-rafting peak. 81 The Heinrich layers are composed overwhelmingly of carbonate grains from limestone and dolomite rocks in northern and eastern Canada. The other ice-rafted layers consisted almost entirely of basaltic glass from Iceland and hematite-coated grains of quartz and feldspar. And the Younger Dryas was marked by a carbonate-rich layer similar to, but less pronounced than the Heinrich layers -- so similar that it is often referred to as layer H0, while the Heinrich layers are labelled H1, H2, etc.
So while the picture is getting much more complicated in the details, some things are now much clearer. Heinrich events and other stadials are fundamentally similar: every two to three thousand years there is a surge of icebergs, bringing an influx of fresh water to the North Atlantic, which suppresses deep convection and deepens cooling in the high northern latitudes, with related climatic changes as far away as the tropics.
The increased discharge of icebergs from multiple sources during stadials could be a common response to cooling. But the much more dramatic discharges from North America at longer intervals during Heinrich events seems to involve something more complex -- a brief period of intense ice-stream surging after a long mass buildup. Douglas MacAyeal proposed a model that would explain these "binge/purge" cycles solely in terms of internal ice-sheet dynamics.
The trail of carbonate rock fragments laid down during Heinrich events leads right back to the mouth of Hudson Strait, between Labrador and Baffin Island. The central third of the great Laurentide ice sheet, centered over Hudson Bay, drained through Hudson Strait into the Labrador Sea in glacial times. This part of the ice sheet rested on soft, easily abraded sedimentary rocks. The motion of the ice across this bed built up a thick layer of loose sediment that deforms easily under mechanical stress when saturated with water. It is stable when frozen to the bedrock, but "forms a slippery lubricant when thawed." 82 If an ice sheet grows thick enough, the temperature at its base rises to the pressure melting point, because of the geothermal heat flux. If the base of the ice stream at the mouth of Hudson Strait were to thaw, it would begin to move faster, and frictional heating would melt away more ice. In MacAyeal's model, this triggers a massive runaway surge that doesn't stop until the ice sheet has thinned enough to refreeze at its base. Assuming reasonable values for temperature and accumulation, MacAyeal derives a period of approximately 7,000 years for one cycle, close to what is observed in the record. While MacAyeal shows that the internal dynamics of the Laurentide ice sheet alone could explain the occurrence of Heinrich events, there is more to the story.
Even if these surges take place only when the central part of the Laurentide ice sheet reaches a critical mass, their timing must be partly determined by climate. Wherever this critical threshold lies, it can only be reached under climatic conditions favoring ice-sheet growth. And while the overwhelming bulk of the sediment in Heinrich layers comes from the Laurentide ice sheet, other ice sheets also contribute. Lehman notes:
Cores from the central part of the belt of maximum ice-rafting show an overwhelmingly Canadian strontium signature during Heinrich events. At the eastern end of the belt, the signature veers toward that of Scandinavia, and possibly Britain. Just north of the belt it is increasingly British, and farther north, Scandinavian. 83
The question, then, is, are all these ice sheets responding to a common climatic signal, or does an iceberg discharge from one ice sheet trigger discharges in the others? These possibilities are not mutually exclusive. The answer may turn out to be, "both." One might think that small ice sheets would be more likely to follow the lead of the larger, than the reverse, but that does not seem to be the case. Bond and Lotti find that each discharge of carbonate-rich sediment from Hudson Strait lags slightly behind an initial pulse from other sources. 84 But since smaller ice sheets are expected to have a shorter response time to a climatic change, perhaps this is only to be expected.
John Andrews emphasizes the role of relative sea level in driving these cycles. 85 Cooling climate favors the advance of ice sheets at their tidewater margins. Isostatic adjustment to the increased weight of ice depresses continental shelves. The consequent rise in relative sea level, together with the increase in basal ice temperature, threatens the stability of the ice margin. Once a surge begins, iceberg melting raises general sea level slightly, affecting other ice margins, and perhaps leading to a cascade of nearly synchronous ice-sheet surges. Eventually, removal of the extra ice load leads to isostatic rebound of shelf areas and a drop in relative sea level, stabilizing ice-sheet margins.
Finally, Hunt and Malin suggest that earthquakes caused by the isostatic adjustment to the increased ice load on continental shelves could serve as a trigger for surges. 86
This is a multiplicity of hypotheses, but they are more complementary than contradictory -- it's a matter of the relative timing and magnitude of the effects. Ginenthal dismisses them all with these words: "Of course, the researchers are scrambling to create ad hoc theories to warm up and cool off the Atlantic Ocean again and again for these 100,000 years and more. They have suggested endless floods, icecap breakups on the continents but not for either Greenland or Antarctica, and oceanic current changes every so often -- none of which has ever been observed for such short timespans or ever been conceived to have occurred." 87 This goes beyond irony, coming from someone who makes and discards ad hoc assumptions as casually as Charles Ginenthal. We have returned to the dreary world of the ideologue, where the aim is not to understand the workings of nature, but the manipulation of words for their symbolic and emotional associations. Ginenthal's limited awareness of research in this rapidly progressing area seems to be based on reading a couple of review articles. His "endless floods" may be a distorted echo of the meltwater diversion hypothesis. It is the task of science to explain the phenomena of nature. The various suggestions discussed above are all reasonable, or were at the time they were made. What is not reasonable is to deny the reality of the phenomena observed, as Ginenthal does.
This piece of rhetoric is repeated almost word for word in Ginenthal's Extinction of the Mammoth, written three years later, which I saw just recently. 88 Ginenthal recycles a lot of his verbiage from one title to another, although they are ostensibly about different subjects. But there are major differences, too, and even outright contradictions. The whole delusional system assumes ever more elaborate forms from one incarnation to the next. He has abandoned some of the positions he took up in "Ice Core Evidence," and presented more material to support others we have already discussed. If that paper is considered in isolation, we would miss these developments. So we will stop here to take stock of some of these changes, and deal with others as they arise in the next section, but a full consideration of this later work is beyond the scope of the present project.
One difference of interest at this point is that in this latest mutation of his fantastic scenario, Ginenthal now accepts the existence of Heinrich events, while still denying the reality of the rapid temperature changes recorded in the very same deep-sea cores! He tries to tie this in with his ideas about pole shifts -- a major theme in Extinction of the Mammoth: "If there was a sudden global tilting of the Earth's axis accompanied by massive, sudden crustal motions, than [then] the ice caps would have been shaken and broken loose from their moorings to slide into the seas from the adjacent lands." 89 Actually, a pole shift such as Ginenthal envisions would have much more dramatic and obvious consequences than this, of which more later. He acknowledges the existence of several Heinrich layers: "about six or seven such layers are presently known." 90 Actually, that's only for the last 60,000 to 70,000 years. There have been similar episodic increases in the delivery of ice-rafted debris to the North Atlantic for at least the last one million years. 91 McManus et al. say there have been more than 50 comparable events in the last half million years. 92 So how does Ginenthal explain all those layers? Was there another pole shift for each one, caused by some magical force in a close encounter with another planet on each occasion, at recurrent intervals of 7,000 to 10,000 years? Perhaps he doesn't find such a remarkable coincidence even worthy of mention.
Heinrich events are pretty dramatic. Based on a range of assumptions as to the thickness and concentration of the basal debris layers, the volume of ice calved necessary to produce debris layers of the thickness and extent seen in the North Atlantic has been estimated at anywhere from about 140,000 to 1,400,000 cubic kilometers, released over a time period of anywhere from 50 to more than 2,000 years. 93 The higher figure is half the volume of the Greenland ice sheet -- perhaps five percent of the volume of the Laurentide ice sheet at its maximum. But this isn't big enough to satisfy Charles Ginenthal. For Ginenthal, who always thinks he knows more than the sources on which he is dependent, this can only mean the complete disintegration of all ice sheets -- overnight, of course. Nothing less will do: "In order to explain this continental material by uniformitarian processes, scientists suggest that the base of the ice sheet contained soft muddy material which acted as a lubricant to permit a sudden catastrophic slide." Notice that even when scientists posit catastrophic processes, Ginenthal calls them "uniformitarian". "This process may have occurred in small isolated regions, but the evidence makes it clear that the entire ice sheet moved, as explained by Mark Maslin who pointed out that sediment deposited by icebergs in the Labrador Sea... [contained] rocks of the type found in the middle of the North american continent, as well as at its edge'." 94 A naive reader might be misled by Ginenthal's spin into thinking that Maslin was somehow contradicting the above expressed view. But what Ginenthal does not grasp is that the sedimentary rocks found in the middle of the Laurentide ice sheet, centered on Hudson Bay, ARE the easily deformed and abraded type that form thick, loose sediments -- limestones and dolomites. Around Hudson Bay, including at its seaward edge, is a ring of hard crystalline rock, where the ice was much more firmly bedded.
With inverted logic, Ginenthal claims to find confirmation of his pole-shift ideas in the oddest places: "...why are there no such layers in the oceans in the southern hemisphere closer to Antarctica?," he asks. "The implication is quite clear. The ancient ice cap in Antarctica did not exist at that time." 95 (Remember, this is a guy so confused that he stresses the excellent correlation between the Devil's Hole core and a core drilled through an ice sheet which, according to him, didn't exist at the time -- and he accuses others of catching themselves in contradictions!) An ice sheet doesn't have to disintegrate to announce its presence. Heinrich layers were generated by the spasmodic behavior of a particular part of the Laurentide ice sheet. Although it does not produce thick layers consisting almost entirely of continental detritus, the Antarctic ice sheet has been depositing ice-rafted sediments in the surrounding seas for ages. And like ice sheets in the northern hemisphere, the concentration shows periodic variations. 96
A new Devil's Hole calcite specimen that fills in most of the last 50,000 years previously missing from the record has handed Ginenthal ammunition for another attack in Extinction of the Mammoth, this time not on Milankovitch theory, but on the reality of the abrupt climatic changes first seen in the ice cores:
"...the most important question with respect to our discussion is whether or not these sudden, large, ice core temperature swings were found in the Devil's hole core? And here again Velikovsky's theory is fully supported by this research. Not a single sudden switch in temperature was found to exist, just as with the evidence found in the varve chronology. "According to Isaac J. Winograd, who has been deeply involved with Devil's Hole research... specimens of a core were sampled every five millimeters or so down the length of the core. Because Devil's Hole receives its water from aquifers, it would take several years for a temperature change to register. Therefore, very short-term oscillations in the surface water temperature would not be recorded. However, longer periods of continually averaged temperatures would show themselves. Although even with this five millimeter space sampling, it was estimated that 25 to 35 percent of the climate swings should be evident. Under no reasonable consideration would it, therefore, be probably that not a single temperature oscillation would be found. Nevertheless, after a full examination of every one of the samples, not a single one of these oscillation events was found!" 97
In an excess of generosity, Ginenthal allows that "it would take several years for a temperature change to register" in the isotope record. It is statements like this that mark the difference between a lucid discussion and low farce. The water that reaches Devil's Hole falls on the crests of mountain ranges in the western Great Basin. Most of it comes from the Spring Mountains to the east, but based primarily on the hydraulic gradient and groundwater chemistry, a 1975 study by Winograd and Thordarson 98 estimated that as much as 35% comes from the upper Pahranagat Valley, much further away to the northeast. The residence time of groundwater in the drainage basin is uncertain. It is not easy to judge from direct hydraulic measurements, as the transmissivity of rock along the flow path varies through some four orders of magnitude. Winograd and his coworkers have drastically reduced their earlier estimates. In 1988, they said, "Most likely, it has varied from perhaps just a few thousand years during a full glacial climate to 16,000 years or more during and after transition to interglacial times." 99 In 1992, noting the existence of troughs "as short as 10,000 years duration" in the isotope record, they argued that "A throughput of several volumes of aquifer water would be necessary within 10,000 years in order to preserve these sharply defined delta 18O troughs." From this and other considerations, they concluded that the average transit time might be "less than 10,000 years, and perhaps on the order of several thousand years." 100 A 1996 study by Thomas et al. Used mass-balance modelling of mixing of waters and chemical and isotopic exchanges between the groundwater and the rock to infer flow paths and estimate the travel times of the water. 101 The study concluded that 60% of the water reaching the Devil's Hole area originates in the Spring Mountains, and 40% in the Pahranagat Valley. The preferred model gives an adjusted age of 4100 years for water feeding the springs. But this is only an average. Water from the Pahranagat Valley would be thousands of years older than water from the Spring Mountains.
All this earlier work is called into question by the latest Devil's Hole specimen. Ginenthal says it was sampled every five millimeters. That would be equivalent to about 8,000 years -- far too coarse to reveal events lasting only a thousand years or so. Actually, the sampling interval was 0.25 mm, equivalent to about 400 years. He continues: "Although even with this five millimeter space sampling, it was estimated that 25 to 35 percent of the climate swings should be evident." He doesn't say where he got this specific figure or how it was arrived at. This finer sampling resolution was chosen specifically to look for the millennial-scale climatic oscillations ("Dansgaard-Oeschger events") seen in other climate records, and Winograd expected to see them. What they did find was "Sharp, well-defined," upward and downward, step-like oxygen-isotope shifts of as much as 0.2 to 0.3 parts per thousand within 2,000 years, "anchored by relatively constant values... both prior to and after the shifts." 102 But they are not cyclical, like Dansgaard-Oeschger events.
Obviously, even without such a complex flow regime, there must be considerable mixing of waters of different ages travelling different distances through tortuous channels in the aquifer. And any climatic signal carried by the water must be "smeared out" to some extent, with a reduced amplitude, over a greater apparent time interval. If the isotope shifts Winograd and his co-workers are looking at in the Devil's Hole record are climatic in origin, then they should be able to see any cyclical shifts of equal or greater duration. So while "dispersion in the aquifer" might obliterate "some of the shorter duration D-O events seen in the GRIP and GISP2 ice cores," he reasons, "it seems unlikely for the longer ones (up to several kyr duration) displayed in these cores, for example, interstadials 14, 12, and 8 of GISP2." 103 So for that and other reasons, in 1997 they estimated that average groundwater residence time could be "on the order of 2000 to 3000 yr," or even shorter. 104 Today, Winograd would go even further: "it's certainly less than 2,000 years and probably less than a thousand," and he would argue that the flow system most likely carries water from the Spring Mountains only, and none from the Pahranagat Valley. But his opinion might always change again, given new evidence. 105
In addition to the long list of sites mentioned above on land and sea where abrupt climatic oscillations are seen -- a list that includes the Santa Barbara basin, 260 miles southwest of Devil's Hole -- they are found just across the California border, in the mountains of the Sierra Nevada. Advances and retreats of mountain glaciers register in changes in the type of sediments in nearby lakes. Glacial advances fill the lake with rock flour, iron-rich and high in magnetic susceptibility. A high influx of rock flour suppresses biological productivity in the lake, so sediments laid down during glacial advances are lower in organic carbon. Measurements of these two properties -- magnetic susceptibility and organic carbon -- reveal the rhythm of glacial advances and retreats. At least 20 of these cycles between 52,600 and 14,000 radiocarbon years ago are recorded in the sediments of Owens Lake, 100 miles west of Devil's Hole. 106 This gives an average cycle length of just under 2,000 years -- about the same as the spacing of stadial-interstadial oscillations in Greenland ice cores and North Atlantic sediment cores. The glacial advances seem to have occurred during relatively cold, dry intervals, when lake levels were low. 107 The largest of these advances left moraines in the nearby mountains. Their dates closely match those of Heinrich events H1, H2, H3, and H5. 108 At Mono Lake, 200 miles northwest of Devil's Hole, lake levels show 500- to 1500-year oscillations, with persistent lowstands at longer intervals matching the dates of Heinrich events H1, H2, and H4, within the limits of uncertainty. 109
The travel time of the water at Devil's Hole is still very much an open question. If the sudden shifts in the oxygen isotope record have a non-climatic explanation, such as tectonic movements, for example, then Pahranagat Valley water could be flowing through the aquifer, and the travel time could be long enough to obliterate millennial-scale oscillations.
Devil's Hole is thousands of miles away from Greenland and the North Atlantic. Just because you find one site that doesn't show rapid climatic oscillations doesn't mean that the many others that *do* show them aren't real. What is puzzling is that there are *nearby* sites that *do* show such oscillations. But it has to be borne in mind that they record different kinds of proxies, responding to different climatic variables.
The new Devil's Hole curve has yet to be published, so a detailed comparison with other records is not possible. I will not attempt to offer any specific explanation for this apparent discrepancy between Devil's Hole and the Sierra Nevada, but I have no reason to find fault with the methodology or practice of either team of researchers, or to discard their results. Nature always has a few surprises up her sleeve. These and other interesting developments from Devil's Hole -- including an atmospheric dust record, and a new calcite specimen that extends the record to within a few hundred years of the present -- will be coming out over the next year or two, and when the new findings are published, an informed debate will clarify the issues and the possibilities. As Leroy Ellenberger said, "The Earth itself has only one history and all the evidence attesting to that history should converge on a single scenario when all of it is considered together." 110 And that means all of it -- not just a few isolated bits and pieces that catch one's fancy.
Another interesting change in Ginenthal's scenario is that he has moved the end of the last Ice Age back from 3,500 years ago to 8,500 -- but the most interesting thing about it is that he does it in Velikovsky's name! He writes: "Velikovsky claimed that the Ice Age ended catastrophically about 8,500 years ago by a poleshift..." 111 When I first saw this statement, I thought it was a misprint for 3,500, but it's repeated several times. Velikovsky himself wavered between two dates -- either "twenty-seven centuries ago, or perhaps thirty-five," 112 though he later expressed some misgivings about the permanence of any such pole shift. 113 The axis was supposed to have moved through an arc of 20 degrees, and one polar ice cover melted while another one formed. Ginenthal's innovation is to interpose a 5,000-year period of equable climate with an axis less inclined to the ecliptic, under the influence of a book of Atlantis drivel. It's all tied in with his fantasies about the Hypsithermal. But that must be reserved for another time.
In 1990, in Carl Sagan and Immanuel Velikovsky, Ginenthal states definitely that Velikovsky's date is 3,500 years ago. Again, the statement is repeated several times, and it was reprinted in the 1995 edition. But in 1997, he contradicts himself with an equally definite statement, moving Velikovsky 5,000 years closer to the scientific dating, with the stroke of a pen. And yet Ginenthal complains that the critics are rewriting Velikovsky! It's almost as though he identifies so closely with his intellectual hero that in his mind they have fused, and he has granted himself authority to speak in Velikovsky's name.
1. Ginenthal, I.C.E., Part VIII, near the beginning.
2. Ginenthal, Part VIII.
3. Steven K. Croft, "A First-Order Estimate of Shock Heating and Vaporization in Oceanic Impacts," Geological Society of America Special Paper 190 (1982), pp. 143-152.
4. Ibid., p. 151.
5. Kenneth J. Hsü, e-mail post of February 4, 1998. In a follow-up on February 5 he commented: "I thank you that you cited for my benefit at length the ravings of Ginenthal. If I had known that my writing would be so misused, I would have been much more careful...... I now see that one has to be even more careful when one writes for general readers...... Finally, I might add that I agree whole-heartedly with your comments of the idiot Ginenthal."
6. Hsü, The Great Dying (Harcourt Brace Jovanovich, 1986), p. 184.
7. Robert McQuillin and Nigel Fannin, "Explaining the North Sea's Lunar Floor," New Scientist (July 12, 1979), p. 90.
8. Ginenthal, Part IX, quoting Thomas Gold, Power from the Earth (London, 1987), p. 73.
9. M. Hovland, "The Formation of Pockmarks and their Potential Influence on Offshore Construction," Quarterly Journal of Engineering Geology Vol. 22 (1989), p. 132.
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11. H. J. Melosh, Impact Cratering: A Geologic Process (Tucson, Univ. of Arizona Press, 1988), cited in R. Gersonde et al., "Geological Record and Reconstruction of the Late Pliocene Impact of the Eltanin Asteroid in the Southern Ocean," Nature Vol. 390 (Nov. 27, 1997), p. 362.
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13. Fader, op. cit., p. 1124.
14. J.P. Ellis and W.T. McGuinness, "Pockmarks of the Northwestern Arabian Gulf," Proceedings, Oceanology International, Vol. 6 (1986), pp. 353-367, quoted in Hovland, op. cit., p. 137.
15. Hasiotis et al., op. cit.
16. Henry Savage, Jr., The Mysterious Carolina Bays (Univ. of South Carolina Press, 1982).
17. Scott Lehman, "Ice Sheets, Wayward Winds and Sea Change," Nature Vol. 365 (Sept. 9, 1993) p. 108.
18. Ginenthal, I.C.E., Part IX.
19. Jérôme Chappellaz, Ed Brook, Thomas Blunier, and Bruno Malaizé, "CH4 and Delta 18O of O2 Records from Antarctic and Greenland Ice: A Clue for Stratigraphic Disturbance in the Bottom Part of the Greenland Ice Core Project and the Greenland Ice Sheet Project 2 Ice Cores," Journal of Geophysical Research Vol. 102 (Nov. 30, 1997), p. 26,551.
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21. Ibid., abstract, p. 143.
22. Ibid., p. 145.
23. Wallace Broecker, "Is Earth Climate Poised to Jump again?," Geotimes (November, 1994), p. 16.
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31. Konrad Hughen, e-mail message of March 15, 1998; further details in Konrad A. Hughen, Jonathan T. Overpeck, Scott J. Lehman, Michaele Kashgarian, John R. Southon, and Larry C. Peterson, "A New 14C Calibration Data Set for the Last Deglaciation Based on Marine Varves," Radiocarbon Vol. 40, nos. 1/2 (1998), pp. 483-494. See also Konrad A. Hughen, Jonathan T. Overpeck, Scott J. Lehman, Michaele Kashgarian, John Southon, Larry C. Peterson, Richard Alley, & Daniel M. Sigman, "Deglacial Changes in Ocean Circulation from an Extended Radiocarbon Calibration," Nature Vol. 391 (Jan. 1, 1998), pp. 65-68.
32. Michael Bender, Todd Sowers, Mary-Lynn Dickson, Joseph Orchardo, Pieter Grootes, Paul A. Mayewski, & Debra Meese, "Climate Correlations Between Greenland and Antarctica During the Past 100,000 Years," Nature Vol. 372 (Dec. 15, 1994), p. 663.
33. Hans Oeschger, "Long-Term Climate Stability: Environmental System Studies," in S. Fred Singer, ed., The Ocean in Human Affairs (N.Y., Paragon House, 190), p. 64.
34. Ginenthal, I.C.E., Part IX.
35. Zicheng Yu and Ulrich Eicher, "Abrupt Climate Oscillations During the Last Deglaciation in Central North America," Science Vol. 282 (Dec. 18, 1998), pp. 2235-2238.
36. Richard B. Alley and Michael L. Bender, "Greenland Ice Cores: Frozen in Time," Scientific American (February, 1988), p. 82. There's a good photo of a Z-shaped fold on the previous page.
37. Andreas Fuchs and Markus C. Leuenberger, "Delta 18O of Atmospheric Oxygen Measured on the GRIP Ice Core Document Stratigraphic Disturbances in the Lowest 10% of the Core," Geophysical Research Letters Vol. 23, no. 9 (May 1, 1996), pp. 1049-1052; Chappellaz et al., op. cit., pp. 26,547-26,557.
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39. Ginenthal, I.C.E., Part IX.
40. According to Debra Meese, who led the American side, in her e-mail message of Feb. 18, 1998.
41. Ginenthal, I.C.E., Part IX, "Conclusion."
42. Wallace S. Broecker, "The Great Ocean Conveyor," in B.G. Levi et al., eds., Global Warming: Physics and Facts (AIP Conference Proceedings 247) (N.Y., American Institute of Physics, 1992), p. 146.
43. Wallace S. Broecker and George H. Denton, "What Drives Glacial Cycles?," Scientific American (January, 1990), pp. 49-56; Wallace S. Broecker, "Chaotic Climate," Scientific American (November, 1995), pp. 62-68; Wallace Broecker, "Will Our Ride into the Greenhouse Future be a Smooth One?," GSA Today Vol. 7, no. 5 (May, 1997), pp. 1-7; Stephan Rahmstorf, "Ice-Cold in Paris," New Scientist (Feb. 8, 1997), pp. 26-30.
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48. See also these earlier studies: W.B. Curry and G.P. Lohmann, "Reduced Advection into Atlantic Ocean Deep Eastern Basins During Last Glacial Maximum," Nature Vol. 306 (Dec. 8, 1983), pp. 577-580; Delia W. Oppo and Richard G. Fairbanks, "Variability in the Deep and Intermediate Water Circulation of the Atlantic Ocean During the Past 25,000 Years: Northern Hemisphere Modulation of the Southern Ocean," Earth and Planetary Science Letters Vol. 86 (1987), pp. 1-15.
49. Edward A. Boyle and Lloyd Keigwin, "North Atlantic Thermohaline Circulation During the Past 20,000 Years Linked to High-Latitude Surface Temperature," Nature Vol. 330 (Nov. 5, 1987), pp. 35-40.
50. Thomas M. Marchitto, Jr., William B. Curry, and Delia W. Oppo, "Millennial-Scale Changes in North Atlantic Circulation Since the Last Glaciation," Nature Vol. 393 (June 11, 1998), pp. 557-561.
51. C. Kissel, C. Laj, B. Lehman, L. Labeyrie, & V. Bout-Roumazeilles, "Changes in the Strength of the Iceland-Scotland Overflow Water in the Last 200,000 Years: Evidence from Magnetic Anisotropy Analysis of Core SU90-33," Earth and Planetary Science Letters Vol. 152 (1997), p. 34.
52. M. Moros, R. Endler, K.S. Lackschewitz, H.-J. Wallrabe-Adams, J. Mienert, and W. Lemke, "Physical Properties of Reykjanes Ridge Sediments and their Linkage to High-Resolution Greenland Ice Sheet Project 2 Ice Core Data," Paleoceanography Vol. 12, no. 5 (Oct., 1997), pp. 687-695.
53. C. Hillaire-Marcel, A. de Vernal, G. Bilodeau, & G. Wu, "Isotope Stratigraphy, Sedimentation Rates, Deep Circulation, and Carbonate Events in the Labrador Sea During the Last ~200 ka," Canadian Journal of Earth Sciences Vol. 31 (1994), p. 78.
54. Michael T. Ledbetter and William L. Balsam, "Paleoceanography of the Deep Western Boundary Undercurrent on the North American Continental Margin for the Past 25 000 Yr," Geology Vol. 13 (March, 1985), p. 182.
55. Brian J. Haskell, Thomas C. Johnson, and William J. Showers, "Fluctuations in Deep Western North Atlantic Circulation on the Blake Outer Ridge During the Last Deglaciation," Paleoceanography Vol. 6, no. 1 (February, 1991), p. 21.
56. M.A. Maslin, N.J. Shackleton, and U. Pflaumann, "Surface Water Temperature, Salinity, and Density Changes in the Northeast Atlantic During the Last 45,000 Years: Heinrich Events, Deep Water Formation, and Climatic Rebounds," Paleoceanography Vol. 10, no. 3 (June, 1995), pp. 527-544.
57. M. Sarnthein and A.V. Altenbach, "Late Quaternary Changes in Surface Water and Deep Water Masses of the Nordic Seas and North-eastern North Atlantic: A Review," Geologische Rundschau Vol. 84 (1995), p. 89.
58. J.C. Duplessy, L. Labeyrie, M. Arnold, M. Paterne, J. Duprat, & T.C.E. van Weering, "Changes in Surface Salinity of the North Atlantic Ocean During the Last Deglaciation," Nature Vol. 358 (Aug. 6, 1992), pp. 485-488.
59. Mark R. Chapman and Nicholas J. Shackleton, "Millennial-Scale Fluctuations in North atlantic Heat Flux During the Last 150,000 Years," Earth and Planetary Science Letters Vol. 159 (1998), p. 65
60. Rainer Zahn, Joachim Schoenfeld, Hermann-Rudolf Kudrass, Myong-Ho Park, Helmut Erlenkeuser, and Pieter Grootes, "Thermohaline Instability in the North Atlantic During Meltwater Events: Stable Isotope and Ice-Rafted Detritus Records from Core SO75-26KL, Portuguese Margin," Paleoceanography Vol. 12, no. 5 (Oct., 1997), p. 696.
61. Tine L. Rasmussen, Erik Thomsen, Tjeerd C.E. van Weering, and Laurent Labeyrie, "Rapid Changes in Surface and Deep Water Conditions at the Faeroe Margin During the Last 58,000 Years," Paleoceanography Vol. 11, no. 6 (Dec., 1996), p. 767. See also, by the same authors, "Circulation Changes in the Faeroe-Shetland Channel Correlating with Cold Events During the Last Glacial Period (58-10 ka)," Geology Vol. 24, no. 10 (Oct., 1996), pp. 937-940.
62. Jess F. Adkins, Hai Cheng, Edward A. Boyle, Ellen R. Druffel, & R. Lawrence Edwards, "Deep-Sea Coral Evidence for Rapid Change in Ventilation of the Deep North Atlantic 15,400 Years Ago," Science Vol. 280 (May 1, 1998), pp. 725-728.
63. Konrad A. Hughen, Jonathan T. Overpeck, Scott J. Lehman, Michaele Kashgarian, John Southon, Larry C. Peterson, Richard Alley, & Daniel M. Sigman, "Deglacial Changes in Ocean Circulation from an Extended Radiocarbon Calibration," Nature Vol. 391 (Jan. 1, 1998), pp. 66-67.
64. Tomasz Goslar, Maurice Arnold, Edouard Bard, Tadeusz Kuc, Mieczyslaw F. Pazdur, Magdalena Ralska-Jasiewiczowa, Kazimierz Rozanski, Nadine Tisnerat, Adam Walanus, Bogumil Wicik, & Kazimierz Wieckowski, "High Concentration of Atmospheric 14C During the Younger Dryas Cold Episode," Nature Vol. 377 (Oct. 5, 1995), pp. 414-417.
65. Wallace S. Broecker, "Paleocean Circulation During the Last Deglaciation: A Bipolar Seesaw?," Paleoceanography Vol. 13, no. 2 (April, 1998), p. 119.
66. David J. Beerling, Hilary H. Birks, and Ian F. Woodward, "Rapid Late-Glacial Atmospheric CO2 Changes Reconstructed from the Stomatal Density Record of Fossil Leaves," Journal of Quaternary Science Vol. 10, no. 4 (1995) pp. 379-384.
67. See his web page at: http://www.pmel.noaa.gov/~kessler/occasionally-asked-questions.html?
68. Wallace Broecker, "Will Our Ride into the Greenhouse Future Be a Smooth One?," GSA Today Vol. 7, no. 5 (May, 1997), p. 5.
69. W. Dansgaard, S.J. Johnsen, H.B. Clausen, D. Dahl-Jensen, N. Gundestrup, and C.U. Hammer, "North Atlantic Climatic Oscillations Revealed by Deep Greenland Ice Cores," in James E. Hansen and Taro Takahashi, eds., Climate Processes and Climate Sensitivity, American Geophysical Union Geophysical Monograph 29 (Wash., D.C., 1984), p. 291.
70. Wallace S. Broecker, Michael Andree, Georges Bonani, Willi Wolfli, Hans Oeschger, and Mieczyslawa Klas, "Can the Greenland Climatic Jumps Be Identified in Records from Ocean and Land?," Quaternary Research Vol. 30 (1988), pp. 1-6.
71. Hartmut Heinrich, "Origin and Consequences of Cyclic Ice Rafting in the Northeast Atlantic Ocean During the Past 130,000 Years," Quaternary Research Vol. 29 (1988), pp. 142-152.
72. Wallace S. Broecker and George H. Denton, "The Role of Ocean-Atmosphere Reorganizations in Glacial Cycles," Geochimica et Cosmochimica Acta Vol. 53 (1989), p. 2481.
73. Wallace S. Broecker, Dorothy M. Peteet, & David Rind, "Does the Ocean-Atmosphere System Have More than One Stable Mode of Operation?," Nature Vol. 315 (May 2, 1985), pp. 21-26.
74. Wallace S. Broecker, James P. Kennett, Benjamin P. Flower, James T. Teller, Sue Trumbore, Georges Bonani, & Willy Wolfli, "Routing of Meltwater from the Laurentide Ice Sheet During the Younger Dryas Cold Episode," Nature Vol. 341 (Sept. 28, 1989), pp. 318-321.
75. Richard G. Fairbanks, "A 17,000-Year Glacio-Eustatic Sea Level Record: Influence of Glacial Melting Rates on the Younger Dryas Event and Deep-Ocean Circulation," Nature Vol. 342 (Dec. 7, 1989), pp. 637-642.
76. L.D. Keigwin and G.A. Jones, "The Marine Record of Deglaciation from the Continental Margin off Nova Scotia," Paleoceanography Vol. 10, no. 6 (December, 1995), pp. 973-985.
77. Pierre Lasalle and William W. Shilts, "Younger Dryas-Age Readvance of Laurentide Ice into the Champlain Sea," Boreas Vol. 22 (1993), pp. 25-37.
78. W.S. Broecker, "The Strength of the Nordic Heat Pump," in E. Bard & W.S. Broecker, eds., The Last Deglaciation: Absolute and Radiocarbon Chronologies, NATO ASI Series I Vol. 2 (1992), p. 179.
79. As formulated in Wallace S. Broecker, Gerard Bond, Millie Klas, Georges Bonani, & Willy Wolfli, "A Salt Oscillator in the Glacial Atlantic? 1. The Concept," Paleoceanography Vol. 5, no. 4 (August, 1990), pp. 469-477.
80. Gerard Bond, Hartmut Heinrich, Wallace Broecker, Laurent Labeyrie, Jerry McManus, John Andrews, Sylvain Huon, Ruediger Jantschik, Silke Clasen, Christine Simet, Kathy Tedesco, Mieczyslawa Klas, Georges Bonani, & Susan Ivy, "Evidence for Massive Discharges into the North Atlantic Ocean During the Last Glacial Period," Nature Vol. 360 (Nov. 19, 1992), p. 248.
81. Gerard C. Bond and Rusty Lotti, "Iceberg Discharges into the North Atlantic on Millennial Time Scales During the Last Glaciation," Science Vol. 267 (Feb. 17, 1995), pp. 1005-1010.
82. D.R. MacAyeal, "Binge/Purge Oscillations of thr Laurentide Ice Sheet as a Cause of the North Atlantic's Heinrich Events," Paleoceanography Vol. 8, no. 6 (Dec., 1993), p. 775.
83. Scott Lehman, "True Grit Spells Double Trouble," Nature Vol. 382 (July 4, 1996), p. 25.
84. Bond and Lotti, op. cit.
85. John T. Andrews, "Abrupt Changes (Heinrich Events) in Late Quaternary North Atlantic Marine Environments: A History and Review of Data and Concepts," Journal of Quaternary Science Vol. 13, no. 1 (1998), pp. 3-16.
86. A.G. Hunt and P.E. Malin, "Possible Triggering of Heinrich Events by Ice-Load-Induced Earthquakes," Nature Vol. 393 (May 14, 19998), pp. 155-158.
87. Ginenthal, I.C.E., Part IX.
88. Charles Ginenthal, The Extinction of the Mammoth, special issue of The Velikovskian Vol III, nos. 2/3 (1997), p. 285.
89. Ginenthal, Extinction of the Mammoth, p. 265.
90. Extinction of the Mammoth, loc. cit.
91. M.E. Raymo, K. Ganley, S. Carter, D.W. Oppo, & J. McManus, "Millennial-Scale Climate Instability During the Early Pleistocene Epoch," Nature Vol. 392 (April 16, 1998), pp. 699-702.
92. Jerry F. McManus, Delia W. Oppo, and James L. Cullen, "A 0.5-Million-Year Record of Millennial-Scale Climatic Variability in the North Atlantic," Science Vol. 283 (Feb. 12, 1999), pp. 971-975.
93. J.A. Dowdeswell, M.A. Maslin, J.T. Andrews, & I.N. McCave, "Iceberg Production, Debris Rafting, and the Extent and Thickness of Heinrich Layers (H-1, H-2) in North Atlantic Sediments," Geology Vol. 23, no. 4 (April, 1995), pp. 301-304, Table 1, p. 303.
94. Ginenthal, Extinction of the Mammoth, loc. cit., quoting Mark Maslin, "Waiting for the Polar Meltdown," New Scientist (Sept. 4, 1993), p. 39.
95. Extinction of the Mammoth, loc. cit.
96. Information from Gerard Bond.
97. Extinction of the Mammoth, p. 286.
98. Isaac J. Winograd and William Thordarson, "Hydrogeologic and Hydrochemical Framework, South-Central Great Basin, Nevada-California, with Special Reference to the Nevada Test Site," U. S. Geological Survey Professional Paper 712-C (1975).
99. Isaac J. Winograd, Barney J. Szabo, Tyler B. Coplen, & Alan C. Riggs, "A 250,000-Year Climatic Record from Great Basin Vein Calcite: Implications for Milankovitch Theory," Science Vol. 242 (Dec. 2, 1988), p. 1277.
100. Isaac J. Winograd, Tyler B. Coplen, Jurate M. Landwehr, Alan C. Riggs, Kenneth R. Ludwig, Barney J. Szabo, Peter T. Kolesar, & Kinga M. Revesz, "Continuous 500,000-Year Climate Record from Vein Calcite in Devils Hole, Nevada," Science Vol. 258 (Oct. 9, 1992), pp. 259 and 256.
101. James M. Thomas, Alan H. Welch, and Michael D. Dettinger, "Geochemistry and Isotope Hydrology of Representative Aquifers in the Great Basin Region of Nevada, Utah, and Adjacent States," U. S. Geological Survey Professional Paper 1409-C (1996).
102. I.J. Winograd, T.B. Coplen, K.R. Ludwig, J.M. Landwehr, & A.C. Riggs, "High-Resolution delta 18O Record from Devils Hole, Nevada, for the Period 80 to 19 ka," (abstract), EOS Vol. 77, no. 17 (April 23, 1996), Spring Supplement, p. S169; e-mail and telephone conversations with Isaac Winograd.
103. Isaac Winograd, e-mail message of October 22, 1998.
104. Isaac J. Winograd, Jurate M. Landwehr, Kenneth R. Ludwig, Tyler B. Coplen, & Alan C. Riggs, "Duration and Strucuture of the Past Four Interglaciations," Quaternary Research Vol. 48 (1997), p. 145.
105. Isaac Winograd, telephone conversation of January 15, 1999.
106. Larry V. Benson, Howard M. May, Ronald C. Antweiler, Terry I. Brinton, Michaele Kashgarian, Joseph P. Smoot, & Steve P. Lund, "Continuous Lake-Sediment Records of Glaciation in the Sierra Nevada between 52,600 and 12,500 14C yr B.P.," Quaternary Research Vol. 50 (1998), pp. 113-127.
107. Larry V. Benson, James W. Burdett, Michaele Kashgarian, Steve P. Lund, Fred M. Phillips, & Robert O. Rye, "Climatic and Hydrologic Oscillations in the Owens Lake Basin and Adjacent Sierra Nevada, California," Science Vol. 274 (Nov. 1, 1996), pp. 746-749.
108. Fred M. Phillips, Marek G. Zreda, Larry V. Benson, Mitchell A. Plummer, David Elmore, & Pankaj Sharma, "Chronology for Fluctuations in Late Pleistocene Sierra Nevada Glaciers and Lakes," Science Vol. 274 (Nov. 1, 1996), pp. 749-751.
109. Larry V. Benson, Steve P. Lund, James W. Burdett, Michaele Kashgarian, Timothy P. Rose, Joseph P. Smoot, & Martha Schwartz, "Correlation of Late-Pleistocene Lake-Level Oscillations in Mono Lake, California, with North Atlantic Climate Events," Quaternary Research Vol. 49 (1998), pp. 1-10.
110. E-mail message of October 29, 1998.
111. Extinction of the Mammoth, p. 264.
112. Worlds in Collision, p. 326.
113. Velikovsky, "A Rejoinder to Burgstahler and Angino," Yale Scientific Magazine, April, 1967, p. 22; reprinted as "The Orientation of the Pyramids" in Velikovsky Reconsidered (Doubleday, 1976), pp. 59-60.
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