More Evidence for the Ice Ages
Another line of evidence confirming that ice ages occurred is contained in sea cores from the North Atlantic. As discussed previously, the oxygen isotope ratios in these cores suggest that the cooling of the oceans lagged behind that of the land by some 3,000 to 5,000 years. This means that at the start of an ice age the North Atlantic was much warmer than at the end. The finding that the Gulf stream wandered north and south during the ice ages is consistent with this. Evidence of this wandering is further described in Time-Life's Ice Ages. Two geophysicists, William F. Ruddiman and Andrew McIntyre, focused on two periods -- the start of the last ice age, some 115,000 years ago, and a particularly frigid episode about 40,000 years later.215
A particular kind of sediment Ruddiman and McIntyre found in the cores documents the warmth of the North Atlantic at the onset of glaciation. These deposits consist of sand and clay particles larger than those carried to sea by ocean currents or wind. The debris was scraped from the surface of the earth by the ice sheets, carried to sea by icebergs that broke free from the glaciers' edges, and then released when the icebergs succumbed to warm water. The location of the deposits, called ice-rafted detritus, shows that when the ice sheets were in the early stages of growth, the icebergs that calved from them melted near the coasts of Greenland and Newfoundland. In later periods, icebergs drifted as much as 1,000 miles farther south, to the latitude of Spain, before meeting water warm enough to melt them....
Oxygen-isotope profiles and the fossil content of ocean cores indicate that when the last two ice ages terminated -- the earlier one some 127,000 years ago and the most recent about 10,000 years ago -- the oceans were still remarkably cold. Just as they had lagged behind the continents in growing cool, they took longer to warm as the ice sheets began to melt....
Sediments deposited while the ice sheets were in retreat disclose that the ocean surface was almost barren of microscopic plankton. Ruddiman and McIntyre think this may have been due to a deluge of fresh water -- the runoff from ice sheets melting rapidly in the summer. Floating on the heavier salt water, the layer of fresh water changed the salinity of the Atlantic's surface so much that plankton were obliterated; they did not return until the meltwater had dispersed, several thousand years later.
"Aha!," a reader might say; "A deluge of fresh water! This is evidence for the Flood." Not at all. This deluge of fresh water wiped out plankton only in the North Atlantic -- they obviously survived elsewhere. But if a deluge of fresh water had inundated the entire earth, where would the plankton have survived? A little thinking on all the other points I've covered will show that this deluge of fresh water is no evidence of The Deluge, but is entirely consistent with the requirement that a huge amount of melt water be released into the oceans at the close of an ice age.
The Antarctic and Greenland ice sheets contain a wealth of information about the ice ages, which has been obtained by drilling cores. Time-Life's Ice Ages explains:216
Although sediments deposited on the sea floor contain some hints about the composition, temperature, and turbulence of the earth's atmosphere during ice ages and interglacials, cores drilled from the great ice sheets that survive in Greenland and Antarctica provide much more detailed information. These sheets -- composites of annual layers of snow compressed and transformed into ice -- provide an unbroken record stretching hundreds of thousands of years into the past. The age of the oldest of this ice has not yet been determined, but scientists think that just above the bedrock of East Antarctica lies ice that was formed 500,000 years ago.
Perhaps most important to understanding the mechanics of ice ages are the ice sheets' component water molecules, which contain the oxygen isotopes that indicate past changes in temperature. But the ice sheets also contain airborne particles -- dust, volcanic debris, sea salts, and various isotopes formed in the atmosphere -- that fell on the snow when it was fresh. In addition, the layers of ice are riddled with tiny air cavities -- remnants of the atmosphere just as it was when the snow fell. These ancient air samples and the other constituents of the ice sheets (with the exception of radioisotopes, which decay with time) remain perfectly preserved as long as they are frozen.
Much as the isotope content of a layer of sea-floor sediment does, the ratio of the heavy O-18 isotope to the lighter O-16 in a layer of ice indicates the temperature at the time it was formed, but with a very important difference. A large proportion of O-18 in sea sediment indicates a colder climate, but just the opposite is true in ice. Since more heat energy is required to vaporize water molecules containing the heavier isotope, a higher proportion of O-18 in an ice layer means that the air temperature was relatively high when that water evaporated from the ocean and later fell as snow. Thus, snow that falls in summer has a higher O-18 content than winter snow. On a much longer time scale, the snows of an interglacial are richer in this isotope than snows deposited during glaciation.
Ice cores have one very significant advantage for scientists trying to establish and refine the chronology of climatic shifts. The top inch or so of sea-floor sediment is frequently stirred by bottom-dwelling creatures; consequently, the layers cannot be dated with precision. But ice layers are not likely to have ever been disturbed by living creatures. Because the concentration of the O-18 isotope generally peaks in summer, declines in winter, then peaks again, the ice between two peaks represents a single year's snowfall. Painstaking measurements of O-18 levels -- in areas where the temperatures are so low all year that the ice layers have not been muddled by melting -- have identified the ice formed each year as far back as 1000 B.C.216a
Of all the cores removed from the Greenland Ice Sheet, the one containing the most ancient ice is the Camp Century core.... The deepest, and hence oldest, layer.... once lay 4,600 feet below the surface of the ice sheet and was probably laid down some 125,000 years ago, before the advent of the Ice Age.... analysis of the O-18 content of the bottom 1,000 feet of the core yielded details of the climatic history of Greenland -- and, by inference, of the earth -- from the end of the last interglacial to the end of the subsequent Ice Age, some 10,000 years ago. The temperature trends signaled by the O-18 levels parallel the changes indicated by sea-floor cores from the Indian Ocean and the North Atlantic.
Here is more recent information on ice cores from National Geographic.217
In 1970 Soviet scientists began drilling at Vostok Station, high on the inland ice cap in East Antarctica.... since 1980 the Vostok ice drillers have bored through more than 2,080 meters of the 3,700 meters (12,140 feet) of the ice under the station.
"The Vostok core is the first to cover, completely and unambiguously, the entire last 150,000 years of earth's ice-age cycle," French glaciologist Claude Lorius reported in 1985, after working with Soviet scientists on the ice core. "It clearly goes back through earth's previous interglacial warm period, called the Eem or Sangamon, and well into the ice age before that.
"That previous interglacial was similar but markedly warmer than our present warm spell, the Holocene,".... "The beginning of the previous warming was as sharp and extensive as was the opening of the Holocene, between about 10,000 and 8,000 years ago."
The Vostok core, somewhat surprisingly to Professor Lorius, does not hold evidence of more volcanic activity on earth during the past glacial age and previous interglacial than in modern times. But the volcanic dust seen there, as in cores taken from the Greenland ice cap, has given a precise and dramatic record of many great volcanic events of the distant past.
In 1980-1981 Danish, Swiss, and American scientists penetrated more than a mile deep at a point named Dye 3 in southern Greenland. From winter-summer variations in the preserved frozen core, the drillers can read year-by-year weather for the past 11,000 years.
The massive eruptions of the volcanoes Laki in Iceland in 1783 and Tambora in the East Indies in 1815 are clearly identifiable near the top of the Dye 3 core. The latter produced the notorious "Year Without a Summer" in New England in 1816, when crops froze and snow fell in July and August.
Sequences of heavy summer melting from A.D. 950 to roughly 1200 confirm the world's warmth during the time that Vikings settled and thrived in Greenland, before the cold of the Little Ice Age froze them out. (From about 1200 until the mid-1800s, world climate was colder than at any time since the last deglaciation.)
Even deeper in the core, volcanic acids show that an eruption must have darkened skies over Rome the year Julius Caesar was killed in 44 B.C. A blast in 1390 B.C. may have been one of several that spelled the end of the volcanic isle of Thera in the Aegean.
On back through time, the Dye 3 core gives absolute dates to unwritten events:
- 4401 B.C. Explosion of Mount Mazama in Oregon created Crater Lake.
- 7911 to 7090 B.C. Seven different great eruptions occurred somewhere on earth.
- From 25,000 down to 10,000 years ago, high amounts of wind-blown continental dust marked the last glacial maximum in the Northern Hemisphere, before the start of global warming in the Holocene.
While some of these dates have been updated since this article was written,218, 219 they have not changed much. Time-Life's Ice Ages says about ice cores:220
The Camp Century core shows that the climate of Greenland became sharply colder, and the Ice Age began there, about 120,000 years ago. The onset of the cold was soon followed by heavy annual snowfalls for the next 5,000 years. ([One geologist, Willi] Dansgaard thinks the heavy snowfalls account for the rapid build-up of the ice sheets and the consequent drop in sea level.) But these Ice Age snow samples contain almost as much O-18 as snow that had fallen thousands of years before, when the climate was milder. Thus the Camp Century core confirms that the North Atlantic near Greenland did indeed remain warm, as Ruddiman and McIntyre concluded from their research, long after the ice sheets had begun to grow.
The Camp Century core also records another drop in temperature and an ice advance some 75,000 years ago. This timing coincides with that calculated by Ruddiman and McIntyre from North Atlantic sediments -- and with the period when, according to the astronomical theory, the Northern Hemisphere was having the cool summers needed for ice-sheet growth.
Particles of clay, volcanic dust and sea salts embedded in ice cores indicated that during the last glaciation, especially toward its end, the atmosphere was turbulent and dirty. In the Camp Century core, Ice Age layers contain 12 times as many such particles as do layers formed during the interglacial that followed....
Besides being stormy and dirty, the Ice Age seems to have had scant snowfall. Around 15,000 years ago, the annual accumulation at Camp Century, as shown by chemical analyses, was only one third to one half the average winter's snowfall there now. This evidence supports the picture developed by Ruddiman and McIntyre after their study of sea-floor sediments -- of a cold, ice-covered ocean from which little moisture evaporated.
Geologists Chester C. Langway and Michael M. Herron have turned up evidence that when the Ice Age finally ended, the climatic transition came about very rapidly -- within a few decades or even less. Segments of two cores, one from Camp Century and the other from the Dye 3 research station in southern Greenland, reveal that the concentration of windborne sea salts fell by about 75 per cent in no more than a century. Apparently, the harsh winds that characterized the Ice Age for thousands of years had died away in the moderating climate of the interglacial.
Another fascinating change that accompanied the end of the Ice Age involved the amount of carbon dioxide in the atmosphere.... it is a key component in the so-called greenhouse effect.... Analysis of air bubbles trapped in three ice cores -- from Camp Century in Greenland and from Antarctica's Byrd Station and Dome C -- has provided a chronology of atmospheric changes from 40,000 years ago up to the present. During the last major glaciation, the amount of carbon dioxide in the atmosphere fell drastically, by about 25 per cent, reaching its lowest level during the last 2,000 years or so of the Ice Age. Why this occurred is not known for certain, but the decline may reflect a reduction of plant life on the icy continents and in the surface waters of the ocean. Then at about the time the interglacial began, carbon dioxide became more abundant.... During the centuries-long transition from glacial to interglacial climate, average global temperatures rose about 4Deg F....
The average global temperature continued to rise for thousands of years.... Temperatures peaked around 4000 B.C. and remained stable for about 2,000 years. During this period -- called the climatic optimum, for its benign conditions -- many regions were about 5Deg F. warmer on the average than they are today, according to calculations based on pollen distribution and the oxygen-isotope ratios in the Greenland ice cores.... Civilizations were flourishing in regions of the world that today are deserts.... After 2000 B.C., temperatures in the Northern Hemisphere began a slow decline. Drought struck in tropical and subtropical areas.... In Egypt, winds piled sand and soil in the dried-up beds of Saharan streams and lakes that for millennia had supplied farmers with water, and the Nile's annual flood level dropped sharply.... While the lower latitudes were experiencing drought, Europe north of the Alps became increasingly cold and wet. Glaciers advanced in mountainous regions, and forests were transformed into bogs. In North America, the Paleo-Eskimos abandoned their high-latitude Arctic hunting grounds and migrated south to Labrador and the Hudson Bay, while glaciers formed in the Rockies south of what is now the Canadian border, for the first time since the Ice Age. Around 450 B.C., temperatures began to rise again, reaching a peak around 1000 A.D. Ever since that time, although they have oscillated up and down, the overall trend has been toward cooler temperatures. The most extreme downward turn occurred around 1500, when a cold period known as the Little Ice Age set in. This neoglacial event, as climatologists call it, persisted into the 19th century.
Perhaps the most significant finding in decades has come to light in ice core drillings completed in the summers of 1992 and 1993. At an ice divide called Summit, in central Greenland, European and American teams of scientists drilled two holes in two-mile-thick ice. There is little flow of ice at such a divide, so the accumulation of snow records climate changes much further back than where the flow rate is higher. The drill sites were calculated to yield ice layers at least 200,000 years old, but have actually yielded 250,000 year old ice.
The European Greenland Ice-core Project (GRIP) hit bedrock July 12, 1992, while the United States Greenland Ice-Sheet Project II (GISP2) hit bedrock July 1, 1993. Workers have directly counted annual layers marked by summer dust and other markers as far back as about 40,000 years ago. During the coldest parts of the last glacial period, snow accumulation was low enough that annual layers are indistinguishable further back than 40,000 years, but they reappear in the Eemian interglacial period which lasted from about 135,000 to 115,000 years ago.
The climate record of the last 40,000 years brought to light by these ice cores is extremely detailed. Preliminary results mostly confirm what has been garnered from earlier ice cores, although anomalies exist. The most surprising results were summarized in a recent Nature article, which said:221
At a time when superlatives are routinely used to describe the mundane, it is difficult to express the importance of two papers in this issue which present results from the new GRIP ice core in central Greenland. The GRIP Project Members and Dansgaard et al. (pages 203 and 218, respectively) give us our first detailed look at the last interglacial period, and it is not what we expected.
As an uncertain climate lies before us, we have been looking warily over our shoulders to see how the climate system has behaved in the past. For 10,000 years, the Earth has enjoyed an interglacial period, a time of steady and dependable climate. Further back, during the last ice age (which lasted about 100,000 years), and in the transitional period, it is now accepted that the climate 'flickered' rapidly. But we could take comfort from the thought that dramatic changes occurring in decades or even years were probably triggered in some way by the massive glaciers or huge extensions of sea ice present at the time.
Now the Greenland Ice-core Project (GRIP) team have removed this sense of security. Using a variety of evidence drawn from the ice core -- stable isotope ratios, chemical and physical properties, and greenhouse gas concentrations in trapped air bubbles -- they demonstrate that very rapid shifts in temperature and greenhouse gases are also possible in interglacial periods.
Our view of climate on the timescale of glacial cycles is shaped by the tools we use to construct that view. Up to now, our ideas of interglacial periods have come from three sources. First and foremost is our knowledge of our own Holocene interglacial, drawn from sources such as tree rings, historical records and pollen samples, to name but a few. Then there are the ocean sediment cores which document numerous interglacials over the past million years. Third, there is the Vostok ice core, until now the only deep core to have yielded easily datable ice from the previous interglacial period (known as the Eemian) which stretched from about 135,000 to 115,000 years ago.
In ocean cores the stirring of the sediment surface by benthic life homogenizes the oceanic record so that the minimum resolution is not better than a thousand years. In the Vostok core, the low accumulation rate of snow and thinning of the annual layers with depth means that climate changes of a century or less are difficult to resolve; flickers may have occurred that cannot now be detected. (There is a compensation: the Vostok core should take the record back to about 500,000 years ago, twice the age of the oldest Greenland ice, and covering several glacial to interglacial cycles.)
The new Greenland ice cores GRIP and GISP2, in contrast, were drilled in regions of high snow accumulation near the centre of the Greenland ice sheet. With these cores, designed to concentrate on the past 200,000 years, we can see climate changes on the timescale of decades or less, even though they occurred a hundred thousand years ago. The indicators of climate change range from local (for example, temperature, deduced from its effect on stable isotope ratios), to regional and hemispheric (such as airborne dust concentrations and chemical composition), to global (greenhouse gas compositions).
The Eemian period falls in the interval from 2,780 to 2,870 m down, well above bedrock. Blurred in the Vostok core, it now comes into focus and it is strikingly different from the Holocene [most recent geological period]. Holocene climate appears to have one, and only one, state, whereas the new results show that the Eemian had three. The middle state matches our own Holocene climate. A significantly colder state and a significantly warmer state existed in the Eemian. On average, temperatures were 2 DegC higher than at present. It apparently took very little time, perhaps less than a decade or two, to shift between the states, and the states appear to be stable sometimes for thousands of years and sometimes for only decades. We don't know which is the norm for interglacial periods: the stable, one-state Holocene or the multiple-state, rapidly changing Eemian. We do know that answering this question will be a priority for global change research.
When evidence from the sister core of GRIP, the GISP2 core, showed earlier this year that aspects of the climate system could shift from glacial conditions to interglacial conditions in a few years, there was always the solace that such changes were characteristic of glacial times, and not really analogues of the future. In our interglacial age, we do not expect the polar front in the North Atlantic rapidly to dip down to Spain with sea ice expanding in behind it, plunging adjacent land, particularly Northern Europe, into glacial-like cold. We do not have massive lakes formed by retreating glaciers, lakes which may catastrophically drain into the North Atlantic, disrupting deep water formation and the transfer of heat northward.
The new ice core results bring rapid climate change to our doorstep: changes of up to 10 DegC in a couple of decades, or perhaps in less than a decade, appear possible in interglacials. Given our ongoing 'global experiment' of increasing greenhouse gas concentrations via fossil fuel burning, is the Eemian warm state a glimpse at our future climate? Whatever the answer to that question, the speed with which the climate system can shift states gives us pause. Adaptation -- the peaceful shifting of food growing areas, coastal populations and so on -- seemed possible, if difficult, when abrupt change meant a few degrees in a century. It now seems a much more formidable task, requiring global cooperation with swift recognition and response.
How unusual is the climate stability of the Holocene? Dansgaard and colleagues investigated one of the possible tracers, the oxygen isotope ratio (a proxy for atmospheric temperature) along the whole of the GRIP core (see figure). Throughout the last glacial period, the Eemian interglacial and the glacial before that, they found rapid oscillations in the isotope ratio. Because of the way that ice thins with age, they could look in detail at the Holocene, and found that the swings have been much smaller, by a factor of 3 to 4, than those earlier flickers. At no time during the Holocene has Eemian-like climate change occurred.
We humans have built a remarkable socio-economic system during perhaps the only time when it could be built, when climate was stable enough to let us develop the agricultural infrastructure required to maintain an advanced society. We don't know why we have been so blessed, but even without human intervention, the climate system is capable of stunning variability. If the Earth had an operating manual, the chapter on climate might begin with a caveat that the system has been adjusted at the factory for optimum comfort, so don't touch the dials.
An accompanying technical article222 contained a graph plotting the oxygen isotope ratio derived from the GRIP core. For all but the last 12,000 years the ratio is quite unstable, but for the latter period makes a sudden large jump, gradually approaches a final value, and then just sits there. The article mentions that the timescale back to 14,500 years ago was derived by direct count of annual layers, and for earlier periods was derived from a mathematical ice-flow model. It said that, apart from a minor deviation, "the record indicates a remarkably stable climate during the past 10 kyr."
Other articles appearing in Nature223, 224, 225, 226 and Science227, 228, 229, 230 during the past few years contain fascinating discussions of technical features of ice core data. This is a very active area of research and there are many more articles, too numerous to mention, appearing in the literature. The articles listed here should give an entry point for further research.
Peat bogs provide more evidence of ice ages. Time-Life's Ice Ages says:231
Additional evidence of the abruptness of the transition from an interglacial to a glacial climate has been found in a peat bog in Alsace, in northeastern France. The bog has remained undisturbed for 140,000 years -- a span that includes all of the last interglacial, the Ice Age and the present interglacial. Genevieve Woillard, a Belgian botanist, examined the pollen in the layers of peat formed some 115,000 years ago, in the final three centuries of the last interglacial. In the oldest layers she found the pollen of trees that flourish in a temperate climate, with firs, oaks, alders and hornbeams especially plentiful. During the next 125 years or so, spruces, which are cooler-climate trees, gradually gained ground over the temperate-forest species and became dominant. In the century that followed, the climate cooled further, the temperate-forest trees became less numerous, and pines began to grow alongside the spruces.
Then, in a very short period -- perhaps no more than 20 years -- there was a radical change in the vegetation. The temperate-climate trees disappeared altogether, along with companion plants such as mistletoe, which requires summer temperatures higher than 60Deg F. to survive, and English ivy, which cannot endure winters during which the temperature stays below 30Deg F. for long periods of time. At the end of the rapid transition, the forest was very much like that of modern-day northern Scandinavia, which lies some 1,400 miles north of the site of the Alsatian bog.
England contains a surprising record of ice age phenomena. The rise and fall of sea level with the glacial cycles is recorded in extensive deposits along the coast of England, especially in alluvial deposits along the River Thames.232 Remains of arctic animals living at the edge of glacial advances shows that ice ages occurred. Polar bear remains were found in upper Thames River deposits,233 along with reindeer, woolly mammoth, woolly rhinoceros and saiga antelope. These remains are often found interbedded with warmer climate species, showing an extreme alternation in climate.
Accompanying the stages of cold climate that caused the falls of sea-level described above were repeated episodes of intensive gelifluction [slow mud flows that subsequently froze].... and some loess deposition. In the estuary [of the Thames] these periglacial deposits commonly rest upon or are interbedded with interglacial terrace deposits and can sometimes be traced down into the buried channels [formed when the Thames cut deep into its channel during low sea-level stages and then buried under alluvium when sea-level rose again].
[At a site 50 kilometers from London] commercial excavations in the early 1980s for chalk .... exposed an overburden of stratified Pleistocene deposits containing a unique sequence of mammalian faunas. The youngest of these, situated only just below ground level, contained remains of hippopotamus, narrow nosed rhinoceros...., elephant, giant deer, bison and water vole. This is a typical Ipswichian [the name of an interglacial period in England] assemblage.... and is referred to that interglacial. Underlying this was a thick deposit of Coombe Rock [gelifluction deposits], interpreted as evidence of periglacial and thus of very cold conditions; and underneath this yet another fossiliferous horizon with mammalian, insect, molluscan, and plant remains, indicating an earlier temperate episode.
During the periods of lowered sea levels, a broad tract of land joined eastern England to Europe, upon which lived a rich community of animals. The area is now covered by the English Channel and the North Sea. Animal remains are pulled up from time to time as a result of fishing and diving operations.
Mammals whose remains have been trawled from the North Sea include woolly mammoth...., woolly rhinoceros, horse, red deer, giant ox, bison, reindeer and giant deer. Bear, spotted hyaena, wolf and beaver are represented by single specimens. The fishing area now known as the Dogger Bank.... has been an especially fruitful source of such finds.
The recovery by trawlers of blocks of Holocene peat, one of them containing an approximately 9000-year-old Mesolithic antler harpoon head.... shows that there was a time lag after the melting of the Devensian ice, when the exposed land was colonized by man, before the sea returned once more to its present level. By this time tundra had been replaced by oak forest. Soon afterwards the Dogger Bank became an island and finally disappeared beneath the sea.234
Another evidence of extremely cold climate at the former margins of ice sheets is
that wide variety of phenomena known as patterned ground. Frost heaving and the annual contraction and expansion of the ground may lead to the most remarkable sorting of rock fragments; often arranged on the surface as polygonal structures. When viewed in section these polygons are seen as a series of vertical wedges, sometimes ice filled.... Collapsed ice wedges are a common feature in many former periglacial areas.235
Several series of ice ages have also occurred in the remote past, as far back as the Paleozoic and Precambrian eras. Time-Life's Ice Ages describes how research in the theory of plate tectonics led to the discovery of one series:236
The theory of continental drift led to one of the most remarkable discoveries in ice age studies. During the 1960s, scientists analyzed the magnetic orientation of rocks from many parts of the world and concluded that North Africa had been located over the South Pole during the Ordovician period, about 450 million years ago. If they were correct, there should be traces of ancient glaciation in the Sahara. At about the same time, French petroleum geologists working in southern Algeria stumbled on a series of giant grooves that appeared to have been cut into the underlying sandstone by glaciers. The geologists alerted the scientific world and assembled an international team to examine the evidence. The team saw unmistakable signs of an ice age: scars created by the friction of pebbles incorporated into the base of glaciers; erratic rocks that had been transported from sources hundreds of miles distant; and formations of sand typical of glacial outwash streams.
One of the scientists, Rhodes Fairbridge of Columbia University, described the effect on the team as "electrifying," and went on to observe: "Here we were privileged, beneath the hot Sahara sun, to see the detailed record of a giant glaciation, precisely dated, and just where it had been predicted to be by the evidence of the paleomagnetists. Our French hosts were not unprepared for the occasion. There was a refrigerator on our supply vehicle, and out of it miraculously emerged a bottle of the finest champagne, ice cold. And so we drank to the health of the discoverers, to the visitors, and to the Ordovician ice age!"
A series of photographs is also presented, showing some of the typical ice age features. A particularly striking one shows the remains of an esker, snaking about 30 miles across the Sahara. Lest the reader think that this is evidence similar to what is being misinterpreted in the most recently glaciated areas of the world, note that these features are not recent. They are not lying on top of everything else in the region, as are the features in North America. Instead, these features have been eroded out of several thousand feet of hardened sediment in which they were buried for hundreds of millions of years. The esker is not composed of sand and gravel, as are eskers in New England -- it is composed of sand and gravel that have turned to stone.
Could the Greenland and Antarctic ice caps have formed after the Flood, 4400 years ago? Evidence from fossil animals in Arctic Ocean sediments show "that at no time over the past several million years has the Arctic Ocean been ice-free."237 A large part of the Antarctic continent is below sea-level, with the rock floor of some ice-buried valleys more than 8200 feet below sea level.238 The Antarctic ice is up to 15,000 feet thick; Greenland ice up to 12,500. How could such a thickness of ice build up in less than 4400 years? How could the ice contain layers that correspond to a year by year accumulation going back hundreds of thousands of years and show detailed evidence of climatic change? How could the build-up be done in such a manner as to depress the Antarctic continent by an average of two thousand feet in such a short time? Remember that, although the earth's crust is ductile, it will flow only over a long time scale, like window glass. Scandinavia and the Hudson Bay area are still rising at significant rates after 7000 to 10,000 years of being ice free. On the other hand, Antarctica is neither rising nor sinking, showing that it is in equilibrium with the rest of the earth's crust. This is consistent with its very low rate of accumulation of snow, which would not have been all that different during an ice age, so that there would not have been much change in ice volume after the ice age had ended and therefore little change in the load on the land. But Canada and Greenland, which are in relatively more temperate regions, would have had a much larger change in total ice volume, and so the load on the land would change a great deal.
Much evidence, some of which I've already presented, shows that continents respond to loading over periods measured in tens of thousands of years. A good account of crustal response to loading by ice is given in Scientific American, February, 1984, "The Earth's Orbit and the Ice Ages." If all the ice in Antarctica formed in less than the time since the Flood, how could the continent come to be in equilibrium? There is no way it could get into equilibrium after 4400 years, after having accumulated up to 3 miles of ice. If you claim the ice caps were around before the Flood, how could they have survived it, given that ice floats? Surely a floating, continent sized ice sheet would break up and the pieces would float all over. Then there should be evidence in the form of ice-rafted erratics and sediment all over the world that this took place. Yet such evidence is not found. And what does this mean for the idea the earth was under hothouse conditions?
Recent findings show that glaciation changed more or less simultaneously all over the world. The caption for an illustration in a recent Scientific American article says:239
Timing of glacial retreat was identical in the Northern Hemisphere and in the Southern Hemisphere. The graphs give the extent of mountain glaciers and ice sheets from the source regions.... and show that in every case dramatic retreat began 14,000 years ago.
The main article uses the term "seasonality" for the astronomical cycles I've already described, and says that
glaciers grew and retreated in the Southern Hemisphere as well. Studies by geologists.... show that during the last ice age, climate changed at the same times and by comparable amounts in the middle latitudes of the Southern Hemisphere -- even though seasonality there varies on a different schedule.
They.... have found, for example, that during the last ice age the earth's mountain glaciers also expanded. The evidence -- from the heaps of debris plowed up by the glaciers, known as moraines -- is as clear in the tropics (New Guinea, Hawaii, Colombia and East Africa) and the southern temperate latitudes (Chile, Tasmania and New Zealand) as it is in northern temperate latitudes (the Cascades, the Alps and the Himalayas). On all the mountains studied so far, regardless of geographic setting or precipitation rate, the snow line descended by about one kilometer, corresponding to a drop in temperature of about five degrees Celsius. [A graph appears on page 51 of the article.]
Where organic material was trapped in the moraines, radiocarbon dating shows that the glaciers advanced and retreated on the same schedule. They fluctuated near their maximum extent between about 19,500 and 14,000 years ago, about the same time as the glaciation of northern continents peaked. Then, just as the northern ice sheet began to shrink, the mountain glaciers underwent a dramatic retreat that sharply reduced their size by about 12,500 years ago.... Isotopic studies of the Greenland and Antarctic [ice] cores show that during the last glaciation both poles cooled -- to as much as 10 degrees C below today's temperatures -- and warmed in step.
This article proposes that a major shift in ocean circulation, caused by the astronomical cycle and interacting with atmospheric circulation, was a major factor in triggering the ice ages. The evidence marshalled in support of this proposition is relevant to our present discussion. Like the north-south swings of the Gulf Stream that were mentioned earlier, there was a jump in the circulation pattern of the North Atlantic. Concerning this circulation the article says:240
The first indications that the ice-age ocean did operate differently came from fossil evidence: changes in the populations of microorganisms that inhabit water masses of specific temperature and salinity.... More recently a geochemical technique pioneered by Edward A. Boyle of the Massachusetts Institute of Technology provided dramatic and direct confirmation that the ocean circulated differently during the last glaciation.... Boyle discovered that.... foraminifera in the present-day ocean.... incorporate cadmium in a constant proportion to its abundance in seawater. He then measured cadmium in sediment cores. The result was exciting: a key signature of the Atlantic's present-day circulation was missing during glacial time, until about 14,000 years ago....
Every winter at about the latitude of Iceland, water of relatively high salinity, flowing northward at intermediate depths...., rises as winds sweep the surface waters aside. Exposed to the chill air, the water releases heat, cooling from 10 degrees C to two degrees. The water's high salinity together with the drop in temperature makes it unusually dense, and it sinks again, this time all the way to the ocean bottom.
The formation of the North Atlantic deep water, as it is called, gives off a staggering amount of heat. Equal to about 30 percent of the yearly direct input of solar energy to the surface of the northern Atlantic, this bonus of heat accounts for the surprisingly mild winters of Western Europe. (The warming is often mistakenly ascribed to the Gulf Stream, which ends well to the south.) The magnitude of the vertical circulation is also immense, averaging 20 times the combined flow of all the world's rivers. Indeed, much of the deep water in the world's oceans ultimately originates here. From its source the water floods the deep Atlantic, curves around the southern tip of Africa and joins the deep current that circles Antarctica and distributes deep water to the other oceans....
[Several microfossil studies showed that the] Atlantic "conveyor," which releases vast quantities of heat to the North Atlantic and sends immense volumes of water into the abyss, was shut down until the last ice age ended 14,000 years ago. In the absence of this key component, worldwide ocean circulation must have looked very different.
The sea and land evidence together points to a simultaneous change in the operation of the ocean and the atmosphere 14,000 years ago. The pattern of ocean circulation shifted dramatically; glaciers in both hemispheres began retreating, signaling global warming; and the carbon dioxide content of the atmosphere started to rise to interglacial levels. We think these events indicate a major reorganization of the joint ocean-atmosphere system -- a jump from a glacial mode of operation to an interglacial mode. Indeed, we believe that abrupt jumps among several ocean-atmosphere modes may underlie glacial cycles in general.
We propose that changes in seasonality are the ultimate causes of these mode shifts. Although we can suggest no simple mechanisms linking seasonality, the ocean-atmosphere system and global climate, we can offer some insights....
.... a gradual shift in atmospheric circulation, by changing salinity in regions such as the North Atlantic, could dramatically alter the global circulation pattern. Indeed, the Atlantic conveyor appears to be the most vulnerable part of the [circulation] system, which may explain why it is Northern Hemisphere seasonality that drives global climatic changes.
A climatic event called the Younger Dryas, which took place several thousand years after the glaciers started to retreat, provides a smoking gun for this part of our case. It vividly illustrates the link between the transport of fresh water -- in this case liquid water and not vapor -- and ocean circulation. About 11,000 years ago the retreat of the glaciers was well under way, and temperatures had risen to their interglacial levels. Suddenly, in as little as 100 years, northern Europe and northeastern North America reverted to glacial conditions. Pollen records show that the forests that had colonized postglacial Europe gave way to arctic grasses and shrubs (including the Dryas flower, for which the period is named), and the Greenland ice core records a local cooling of six degrees C. About 1,000 years later, this cold spell ended abruptly -- in as little as 20 years, recent work by Willi Dansgaard of the University of Copenhagen suggests.
Boyle's cadmium measurements, together with the record of surface-water foraminifera in the North Atlantic, tell what happened. Both indicators return to their glacial state at the onset of the Younger Dryas. The conveyor belt had shut down once again. Deep-water formation had stopped, and so the warm intermediate-depth water that supplies Europe's bonus of heat could no longer flow northward. The chill over the region was dispelled only when the conveyor began running again 1,000 years later.
A massive influx of fresh water from the melting North American ice sheet seems to have killed the conveyor and precipitated the Younger Dryas. The ice sheet started shrinking 14,000 years ago; for the 7,000 years it took to melt away, it must have released fresh water at about the same rate as today's Amazon River. At first nearly all the meltwater from the southern edge of the massive ice sheet flowed down the Mississippi River to the Gulf of Mexico. About 11,000 years ago, however a major diversion sent meltwater in torrents down the St. Lawrence River to the Atlantic.
A vast clearinghouse for meltwater, known as Lake Agassiz, had formed in the bedrock depression at the edge of the retreating ice sheet in what is now southern Manitoba. Until 11,000 years ago the lake, larger than any of the existing Great Lakes, had overflowed a bedrock lip to the south and drained down the Mississippi. Then the retreat of the ice opened a channel to the east. The water level in lake Agassiz dropped by 40 meters as water flowed across the region of the Great Lakes and down the St. Lawrence.
Foraminifera from surface waters of the Gulf of Mexico record this diversion. Their oxygen 18 content had been anomalously low, reflecting the oxygen 16-rich meltwater discharging from the Mississippi. About 11,000 years ago the isotopic ratio increased abruptly as the Lake Agassiz diversion shut off the meltwater flow to the Gulf.
The meltwater, meanwhile, poured into the North Atlantic close to the site of deep-water formation. There it reduced the salinity of surface waters (and hence their density) by so much that, in spite of severe winter cooling, they could not sink into the abyss. The conveyor belt stayed off until 1,000 years later, when a lobe of ice advanced across the western end of the Lake Superior basin and once again blocked the exit to the east. Lake Agassiz rose again by 40 meters, diverting the meltwater back down the Mississippi. The conveyor belt was reactivated, and Europe warmed up again.
The Younger Dryas links freshwater flow, ocean circulation and climate -- but only regional climate. Only around the North Atlantic did the episode bring a sharp cooling; elsewhere its effects were slight or absent. Unlike the glaciations, the Younger Dryas affected only the transport of heat (from low latitudes to the North Atlantic) and not the global climate. How could a change in ocean atmosphere operation during the ice ages have cooled the world as a whole?
The Greenland and Antarctic ice cores suggest part of an answer.... carbon dioxide is a greenhouse gas that warms the earth's surface by trapping solar energy.... Two other changes recorded in the ice cores must also have contributed. Ice-age air contains only half the post-glacial level of methane. Methane, too, is a greenhouse gas.... In addition, dust is about 30 times as abundant in glacial-age ice as in more recent layers, confirming evidence from other sites that the ice-age atmosphere was exceedingly dusty.... The dustiness and low methane content of the ice-age air do suggest that the glacial mode of ocean-atmosphere operation had imposed a dry climate. Dust, after all, blows from areas where vegetation is sparse, whereas methane is produced in swamps. Dry conditions (which are also recorded in ice-age landforms, such as sand dunes, and in pollen deposits) would have had their own effect on global temperatures. Temperature falls more rapidly with increasing altitude in a drier atmosphere; hence, the drying could have contributed to the depression of mountain snow lines....
Clearly, our account of how changes in ocean-atmosphere operation could have cooled the planet is incomplete.... Still, much recent evidence favors our basic proposal: transitions between glacial and interglacial conditions represent jumps between two stable but very different modes of ocean-atmosphere operation. If the earth's climate system does jump between quantized states.... all climate indicators should register a transition simultaneously. In this regard, the evidence from the end of the last ice age is most impressive. The warming of North Atlantic surface waters, the onset of melting in the northern ice sheets and the mountain glaciers of the Andes, the reappearance of trees in Europe and changes in plankton ecology near Antarctica and in the South China Sea -- all took place between 14,000 and 13,000 years ago.
In addition to what this article mentioned, other changes took place at the same time: as recorded in polar ice cores, carbon dioxide and methane increased and dust decreased in the atmosphere; in sea cores oxygen isotope ratios and foraminifera populations changed to indicate that much water that had been tied up in ice was being released into the oceans; sea levels, as recorded all over the globe, increased; loess formation was much reduced worldwide; ice-age lakes such as Lake Bonneville in southwestern United States began to dry up; pollen sequences found in lake varves in Europe and North America showed a radical change in vegetation to warmer climate types.240a All of this is tied together by the Milankovitch astronomical cycles, which together with other evidence, indicates that all these changes happened many times. None of these things can be satisfactorily explained by the Flood.
Final Summary on Ice Ages
Many lines of evidence have been presented, to show that the notion of ice ages is not based on a few flimsy observations. All the lines of evidence give similar answers, both qualitatively and quantitatively. A mathematical theory, based on Newton's laws of motion for the solar system, explains and ties together many of the observations. The notion of The Flood is unable to explain the evidence, and the evidence shows that no Flood occurred -- at least, not one with geologically observable consequences.
The Society's latest attempt to deal with the problem of ice ages, in The Bible: God's Word or Man's?, pages 113-114, is a very incomplete and misleading presentation of evidence. It speaks in sweeping generalities, focusing on only one specific point -- the possible misinterpretation of water activity as glacial. In view of the extensive evidence I've presented, you can see that glacial land forms are only a small part of the picture, but the book ignores all the other evidence. Older publications do no better. I think the Society owes it to its readers to do better. Otherwise, its arguments hold no more weight than those of "scientific creationists," who think that the entire universe was created in six days, and to prove their position use tactics of misdirection, obfuscation and ignoring of evidence they don't want their readers to see.
215 Windsor Chorlton, op cit, pp. 151-152.
216 ibid, pp. 152-154.
216a This material was published in 1983. For results of newer studies that go back about 40,000 years, see the next few paragraphs.
217 "Ice on the World," National Geographic Magazine, pp. 96-99, Washington, D.C., January, 1987.
218 Robert D. Ballard, Exploring Our Living Planet, p. 315, National Geographic Society, Washington, D.C., 1988.
219 Nature, vol. 364, pp. 186, 203-7, 218-20.
220 Windsor Chorlton, op cit, pp. 154-159.
221 J. W. C. White, "Don't Touch That Dial," Nature, vol. 364, p. 186, July 15, 1993.
222 W. Dansgaard, et al., "Evidence for general instability of past climate from a 250-kyr ice-core record," Nature, vol. 364, p. 218.
223 GRIP members, "Climate instability during the last interglacial period recorded in the GRIP ice core," Nature, vol. 364, pp. 203-7.
224 ibid, vol. 362, pp. 495, 527-9, April 8, 1993.
225 ibid, vol. 361, pp. 432-6, February 4, 1993.
226 ibid, vol. 359, pp. 274-5, 311-3, September 24, 1992.
227 Richard A. Kerr, "How Ice Age Climate Got the Shakes," Science, vol. 260, pp. 890-2, May 14, 1993.
228 ibid, vol. 260, pp. 962-8.
229 ibid, vol. 259, pp. 926-34, February 12, 1993.
230 ibid, vol. 258, pp. 220-1, 255-60, 284-7, October 9, 1992.
231 Windsor Chorlton, op cit, p. 166.
232 Antony J. Sutcliffe, On The Track Of Ice Age Mammals, pp. 117-150, Harvard University Press, Cambridge, Massachusetts, 1985.
233 ibid, p. 136.
234 ibid, pp. 142-143.
235 ibid, p. 20.
236 ibid, pp. 141-147.
237 John Imbrie, et al, op cit, p. 67.
238 Frank Press, et al, op cit, p. 242.
239 Wallace S. Broecker and George H. Denton, "What Drives Glacial Cycles?," Scientific American, pp. 52-53, New York, January, 1990.
240 ibid, pp. 53-56.
240a See also chapter 6 of On The Track Of Ice Age Mammals, Antony Sutcliffe, op cit. This chapter adds many other observations to what has been covered here. Note especially the chart on page 64, which graphically depicts the correlation among oxygen isotope ratios from a Pacific sea bottom core, oxygen isotope ratios from a Greenland ice core, vegetational changes during the last 140,000 years from an analysis of plant remains from the deep peat bog at Grand Pile, France, and vegetational changes during the last 120,000 years from an analysis of plant remains from a bog at Tenagi Phillipon, Greece.