Australia: The Land Where Time Began

A biography of the Australian continent 

Rapid Climate Change Events (RCCEs) "Rickies"

Prior to the GISP2 ice core it had been found that a warm period, an interglacial, occurred about 120,000 BP that lasted about 10,000 years. In North America it was called the "Sangamon Interglacial" and in Europe it was called the Eemian Interglacial, a period during which the global temperature was slightly higher than at present. This was followed very rapidly by a period that was relatively long called the Wisconsin Glacial in North America and the Wurm Glacial in Europe, the change to a glacial climate occurring so rapidly that it has been called a climate termination. The following period was the Holocene that covers the last 10,000 years.

Prior to 1993 it was believed that glacial climate changed only slowly, with the Holocene being a quite time for the global climate, up until the beginning of the present round of global warming. The results of the study of the GIPS2 ice cores contradicted this view. The Camp Century ice drilling expedition in the northern part of Greenland had provided a clue to the rich data that would eventually be gathered from drilling completely through the summit of the Greenland ice sheet to bedrock. In southern Greenland the "Dye 3" ice coring expedition also produced results that indicated that Rickies might be much more common than previously believed. The results of these 2 earlier ice coring expeditions indicated that the climate had moved from warm to cold in a very short period, possibly as little as a decade (Dansgaard et al., 1989).

These results were challenged by other researchers on the grounds that the bedrock beneath these sites was extremely bumpy, and because of the uneven nature of the rock the layers of the ice were not necessarily preserved in the order in which they formed, the oldest layer on the bottom and the youngest on the top. The ice in the cores was twisted and some layers had been completely flipped over as the glacier flowed over the uneven bed, no unequivocal proof that the ice cores from these sites contained an original record in the order in which the layers were deposited, as the effects of the nature of the bedrock can be translated well above the bedrock. The best part of the ice sheet to core in order to get ice layers in the order in which they formed was the summit of the ice sheet. It had been demonstrated that the bedrock at the point where they GISP2 ice core was drilled is relatively flat, and the ice core was taken from what was literally the summit of the Greenland ice sheet; a location at which all the snow that falls continues vertically, and with no lateral flow, almost to the bedrock (Hodge et al., 1990). The research was aimed at confirming or disproving the fast climate events, Dansgaard/Oeschger events. They are one of the types of rapid climate change that is indicated in the GISP2 ice core, that have been called Rapid Climate Change Events (RCCEs), often referred to by the author1 as Rickies.

Ice Cores - Stable isotope Measurements of Water

Ice Cores - Chemical Measurements

The GRIP ice core was drilled 30 km (about 19 miles) from the GISP2 site, allowing it to prove conclusively if flow of the ice had been responsible for the interpretations of data obtained from earlier ice drilling projects that proved to be very surprising. According to the author1 as the 2 drilling sites were in different flow regimes if the same record was seen in both ice cores it would indicate that the events recorded must be true climate events and not events that were flow developed. The 2 ice cores have since been shown to record the same events to a remarkable degree.

The results from both ice cores, that were well-dated, demonstrated that the earlier view that variability of climate operates on slow time scales was incorrect, they actually change rapidly.

There are many sources for the chemical species that are eventually deposited with snow on glaciers, each of which indicates either the strength of its emission from its source or the source and the direction from which it arrived at the glacier in the air mass that carried that particular chemical species.

Chemical species that are carried in the ocean do so either as seasalt (ss, typically as ssNA, ssCl, ssK, ssMg, and ssSO4) or as biological emissions from the surface of the ocean (methanesulphonate, MS, or exSO4). As wind blows across the surface of the ocean the ocean chemistry is incorporated into the atmosphere, incorporating sea spray, or as gases are emitted from the surface of the ocean by organisms.

The histories of volcanic events can be developed from ice cores because gases are emitted from volcanoes that are often rich in exSO4, where ex refers to "in excess of seasalt SO4" and non-seasalt chlorine (nssCl).

Dusts, in the form of nssK, nssCa, and nssMg, are incorporated into the atmosphere when wind blows across land, more dust being picked up by stronger winds and/or under arid conditions, then eventually being trapped in the ice cores.

Levels of NH4, NO3 and nssK in ice cores allow the tracing of biological emissions from terrestrial plants, soils and animals.

In a wide variety of chemicals, including exSO4 released by the burning of fossil fuels, and NO3 in emissions from car engines, as well as trace metals that include mercury, cadmium, and lead, the ice cores demonstrate the inclusion in the ice of byproducts of human activities (Hans Oeschger of Bern University in Switzerland).

The levels of both marine and terrestrial sourced chemicals are increased during glacial periods as the results of generally increased wind strength. In the oceans this results from increased turnover caused by the increased speed of the surface winds, and on the land glacial periods are times when there is less vegetation to bind the soil, allowing more to be picked up as a result of the increased force of the wind. Methanesulphonate produced by marine organisms increases as a result of the increased ocean turnover as the winds get stronger, more nutrients being brought to the surface from greater depths of the oceans. There is usually a decrease in the amount of ammonium from the land as a result of the general reduction of terrestrial vegetation that occurs in glacial periods. Atmospheric circulation patterns can be reconstructed by use of the chemical species previously mentioned as the chemistry is like a marker for the air mass.

According to the author1 RCCEs have been shown by the data from the Greenland ice cores to actually occur, and also that their occurrence is much more frequent than previously suspected, and it was also discovered from the data that even in conditions that are relatively mild  RCCEs can occur such as the interglacials of the Holocene. As a result of this the Holocene has been shown to be a time of many climatic changes that occurred rapidly and at ushered in very dramatic changes in climate.

The Greenland ice core data have provided a history of the climatic changes that have occurred and show just how variable the climate can be over decades to centuries, the most rapid changes recorded in the cores being on the scale of years to seasons.

From 70,000-10,000 years ago, the time of the last glacial phase, with vast ice sheets in the Northern Hemisphere providing positive feedback, or reinforcement, to the climate system, the cold of the time being amplified still further. The  RCCEs, that have been described as extremely massive reorganisation of the climate system, achieved their most extreme levels during the period of glaciation. The albedo of the ice sheets resulted in positive feedback, with other factors that are seen as positive feedback being the smoothness of ice sheets and their elevation.

Ice sheet albedo - the fraction of the incoming solar radiation that is reflected back into space. If the surface was absolutely white 100 % of the solar radiation would be reflected, and if it was absolutely black, 100 % would be absorbed. As the ice sheets are very white they would have reflected a high proportion of the incoming solar radiation into space with the result that they were effectively huge cooling devices, cooling the air above them.

Ice sheet elevation - In Europe and America the central regions of the ice sheets reached as much as 2 miles above sea level. As temperatures decrease with increasing height in the troposphere the elevation of the central parts of the ice sheets would act as a positive feedback, the colder air being denser would flow down the ice sheets to their edges and the coast.

Ice sheet surface smoothness - The cold, dense air flowing off the ice sheets would lead to strong winds that would intensify the patterns of atmospheric circulation. As the surfaces of the ice sheets are relatively smooth, when compared with the surface in mountainous areas and even the surface of the ocean with its surface that is rarely free of waves, the overall strength of the atmospheric circulation is further reinforced by the relative smoothness of the ice sheet surface, as would the strength of the wind, and the strength of the wind would be maintained as it flowed off the glacier into surrounding areas.  

The Younger Dryas, a classic RCCE.

Sources & Further reading

  1. Mayewski, Paul Andrew @ White, frank, 2002, The Ice Chronicles: The Quest to Understand Global Climate Change, University Press of New England.
Author: M. H. Monroe
Last Updated 31/01/2013

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