The White Planet: The Evolution and Future of Our Frozen World

by Jean Jouzel

  Confident from this success, the drillers of the CRREL went on to Antarctica. There, too, the drilling site, at Byrd Station (Figure 1.2) on the ice cap of West Antarctica, was chosen because of its accessibility from the American McMurdo Base. Nearly 2,000 people live in this true town during the summer and a few hundred the rest of the year. It is located at the base of the Ross Sea a few hundred kilometers from the South Pole, where the United States has constructed a permanent base. It was near McMurdo that, at the beginning of last century, various expeditions started off in the challenging conquest of the South Pole, this somewhat mythical place. Visiting the huts of Scott and Shackleton, which have remained as they were originally, is a very moving moment for anyone who has the opportunity to stay a few days at McMurdo. Byrd Station is located a few hundred kilometers away in a place where the ice cap is a bit more than two kilometers thick. There, too, the rock base was reached in 1968 after only two seasons. This was a great success, even if the age of the ice was discovered to be no more than 80,000 years old.4 Unfortunately the drill remained at the bottom of the hole and we had to wait until 1993 for American drillers to again celebrate the success of a deep drilling.

  Another team then joined the Danish and American pioneers, that of the physicist Hans Oeschger from the University of Bern, to whom we owe the perfection of counters adapted to precisely measure very low-level radioactivity of elements such as tritium and carbon 14. The analysis of tritium was interesting for following the fallout due to nuclear explosions on the ice sheets and for dating the recent layers of snow,5 whereas that of carbon 14 had to be adapted to the dating of older layers. Oeschger and his laboratory were primarily interested in Greenland, where they participated in various campaigns aimed at obtaining recent samples and then brought their contribution to the Byrd program. Enthralled by the complexity of how the climatic system functions and by environmental issues in general, Oeschger made his mark on the relatively recent development of those disciplines in which the Bern lab, now directed by Thomas Stocker, is still very active.

  The research carried out by glaciologists in polar regions in the 1950s and 1960s was not limited to these Danish, American, and Swiss contributions. Other countries, Scandinavia in particular, have been active in Greenland. For Antarctica, the 1957–1958 International Geophysical Year was the point of departure for research activities in which a dozen countries were involved. In 1959, in a spirit of collaboration, they signed the Antarctic Treaty, which devoted the continent to peace and research.

  The properties and the composition of the snow taken from the surface and from shallow drillings were studied. That was the opportunity for an American team to determine the isotopic content of the snow at the South Pole.6 There, too, a relationship with the temperature is very marked. As we might expect, the snow has fewer heavy isotopes (oxygen 18 and deuterium) during the winter than it has during the summer. In the next section we’ll discover what the French teams did in Antarctica and Greenland in the 1950s and 1960s.

  Fifty Years Ago: The French on the Polar Ice

  After the pioneering work of Jules Dumont d’Urville in Antarctica and Jean-Baptiste Charcot in Antarctica and Greenland, French interest in polar regions was renewed through Paul-Émile Victor and his expeditions to Greenland. After his winter stay devoted to the study of the Inuits, he founded the Expéditions Polaires Françaises (EPF) in 1947, which, until 1992, supported scientific missions to the two poles. From 1957 to 1960 he directed the International Glaciological Expedition, which was responsible for studying the Greenland ice sheet following a west-east axis and for installing a wintering station in its center. French researchers participated in this work, but at that time the national research effort was aimed primarily at Antarctica, with the beginning of the International Geophysical Year (IGY) in 1957, which saw twelve countries invest in the study of that vast continent, which was still practically unknown. That IGY produced a wealth of scientific results. Under the aegis of the French Academy of Sciences, research undertaken in Adélie Land benefited from the establishment of the coastal Dumont d’Urville Base and truly took off thanks to three expeditions that occupied this base and that of Charcot (see the drawing on page 95), installed on the glacial ice sheet 320 kilometers to the south, at 2,400 meters in altitude. The climate was only one of the areas studied, and the idea that the polar ice sheets contained unique archives had not gained much support at that time. French glaciologists measured the thickness of the ice with the help of seismic probes, as well as the accumulation of snow and its properties on the surface from shallow drilling, which also enabled them to determine the mean temperatures by placing a thermometer at the bottom of the holes they drilled.

  In Les glaces de l’Antarctique,7 Claude Lorius passionately recounts the adventure of the year he lived in Antarctica in the company of Roland Schlich and Jacques Dubois. From an explorer at the beginning in the 1960s he was transformed into a geochemist. Convinced of the power of the isotopes of water as a tool for reconstituting the climates of polar regions, he devoted his doctoral thesis to this; his primary objective was documenting their distribution in recent snow. He participated in fieldwork that went back and forth over Victoria Land and Adélie Land and took many samples from both areas. At the end of the 1960s, two drillings down to around one hundred meters were undertaken in the coastal regions by a French team.

  But the scientific tools of the EPF were relatively rudimentary. A barge docked on the quays of the Seine served as a laboratory, and it did not have such a sophisticated apparatus as a mass spectrometer. Fortunately the research center of the CEA in Saclay was only about twenty kilometers away. There then began a successful collaboration between isotopists from the CEA and glaciologists, which has produced a wealth of results during almost fifty years of work together. In the CEA, the Laboratoire de Géochimie Isotopique (LGI) directed by Liliane Merlivat within the department of Étienne Roth has been the backbone of the operation. Deuterium mass spectrometers with a unique system of automatic injection were developed at the CEA. The content of that isotope was thus analyzed there in preference over that of oxygen 18. A very strong correlation between deuterium and the mean average temperature of the site was established over the entire zone explored by Claude Lorius. Isotope and temperature varied hand in hand: a cooling of 1°C was accompanied by a decrease in the amount of deuterium by 0.6%.8 This ratio, established in the 1970s, is still the one used to interpret deep drilling carried out in that sector of East Antarctica.

  Dominique Raynaud was the first Ph.D. student of Claude Lorius, who encouraged him to work on a new and promising subject: the composition of the air trapped in polar ice. He started in the 1960s working at the CEA and looking at the CO2 content of the ice. It was a pioneering work, but at that time the methods used for extracting the air from the ice provided inconclusive CO2 results. Finally Raynaud formulated a thesis around a simple idea. Since air pressure decreases the higher one goes in the atmosphere, the amount trapped in the ice must decrease as the altitude of the ice sheet rises. Even if the interpretation of the results is more complicated than it first appears, Raynaud demonstrated that 20,000 years ago, in the Last Glacial Maximum, the glacial ice sheet was thicker than it is now, probably on the order of one kilometer at Camp Century.9

  In 1968 Jean Jouzel was just beginning his doctoral thesis at the LGI. A research topic off the beaten path was proposed to him by Étienne Roth: What can we learn about the formation mechanisms of large hail from their isotopic analysis?10 This was at a time when much hope was placed in the possibility of preventing devastating hail by injecting clouds with silver iodide. Basic research on hail went along with these more applied programs. They were, however, almost abandoned a few years later when rigorous tests of prevention methods proved to be ineffective. But it wasn’t far from the ice of hail to that of glaciers, and Jouzel enthusiastically made the leap.

  The barge at Saint-Cloud was not big enough for the research team that Claude Lorius hoped to create
around his research in polar regions. With the speedboats and other barges traveling on the Seine River, the barge was also not stable enough to establish an analytical lab there! Jacques Labeyrie invited the team to the Centre des faibles radioactivités in Gif-sur-Yvette. The offer was interesting, but Lorius was attracted by the Laboratoire de Glaciologie in Grenoble whose director, Louis Lliboutry, was a brilliant glaciologist. Excited by the modeling of Alpine glaciers, he was less interested in the study of polar ice caps as climatic archives. But he was ready for his laboratory to be involved in it. The goal was quickly established: Lliboutry agreed that Lorius should take the lead on a project to carry out deep drilling at the site of Dôme C, in the heart of the Antarctic continent, at 1,100 kilometers from the Dumont d’Urville Station (Figure 1.2). Unlike Camp Century and Byrd Station, the site was deliberately chosen. The snow that falls on a dome comes down vertically, and, providing that the dome did not move significantly over time, the ice taken from along the length of a core sample is, regardless of the depth, formed from snow that, to a few kilometers, has fallen on the site itself. Thus the interpretation of the results was to be largely facilitated with respect to a site where ice at depth is originated from upflow.

  The First Drilling at Dôme C: Success of the French Team

  The project began with the development of a core drill. There are essentially two systems involved in deep core drilling: a thermal core drill and an electromagnetical core drill. The thermal core drill, equipped on its end with a heating mechanism, penetrates through fusion a thin circle of ice while that circle is cut from the rotation of knives in the electromechanical core drill. In both cases, the ice cores are extracted in a cylindrical core tube and brought up to the surface at the end of each drilling. This tube is equipped with a reservoir that allows debris to be brought up, as well as liquid water and ice chips. A motor, pumps, and associated electronics are all connected to the core drill, which is suspended by a cable that provides energy and signals from the surface where the team of drillers is installed next to a winch, a drilling tower, and a command console. Many tests are necessary before everything is operational, and there is always the risk that either core drill will become blocked and not be able to be brought back up. At Camp Century, the CRREL team had two failures with a thermal core drill. On the third try they used that system at the beginning of the drilling, but at around 600 meters went to an electromechanical drill that allowed them to reach the bedrock. This second system was also used at Byrd, but the decision to drill very long six-meter cores called for an extremely cumbersome system. With a 26-meter-long tube and a winch of close to 20 tons, the apparatus weighed nearly 70 tons.

  In Grenoble, the team of François Gillet opted for a thermal core drill. The idea was to achieve a dry drilling without any filling fluid, which would enable them to avoid the closing of the hole. This reduced the amount of material that needed to be transported to the site but forced them to carry out the drilling in a single season. There was little hope, in the end, of going beyond 1,000 meters because in the absence of fluid the drilling hole could quickly become deformed. In the spirit of cooperation that ruled in Antarctica, McMurdo provided logistical support in the form of C130s that the U.S. Army put at the disposal of the National Science Foundation (NSF). Two planes crashed in 1975 during the first season of reconnaissance, both of which were near tragedies. Despite these setbacks, the NSF maintained its support of the French drilling operation at Dôme C, and three years later there was success; in less than two months the drilling team, under the direction of Daniel Donnou, reached a depth slightly greater than 900 meters. Seven tons of ice were brought back to our labs. We estimated that the deepest ice was about 30,000 years old11 but later revised that dating and now more than 40,000 years of archives are available from the first drilling at Dôme C.

  This was a true godsend for the French teams from Grenoble, Saclay, and Orsay. After several years of research Dominique Raynaud and Robert Delmas, a transfer from Saclay to Grenoble, perfected a method for extracting air bubbles trapped in the ice, which enabled analysis of their concentrations of carbon dioxide. This was also the main objective of Hans Oeschger and the glaciological team of Bernhard Stauffer in Bern. The Swiss team at Byrd and the French at Dôme C had access to ice from the Last Glacial Maximum, and both teams contributed to a major discovery and confirmed the prediction made by S. Arrhenius at the end of the nineteenth century: the concentration of carbon dioxide was indeed at that time about 30% less than that of the preindustrial period before human activity began to change it.12

  The content of dust,13 the size of crystals,14 and the chemistry of the ice15 were realms in which the scientists from Grenoble, under the leadership of Martine de Angelis, Robert Delmas, Paul Duval, Michel Legrand, and Jean-Robert Petit, were to distinguish themselves, thanks to the ice from Dôme C. At Saclay the emphasis was placed on the conjoined analysis of the two isotopes, deuterium and oxygen 18. One or the other can provide access to the temperature, but, on largely theoretical bases, one could expect that a detailed comparison of these two isotopes would provide supplementary information. The wager was won. The comparison gave access to the conditions that prevailed in the ocean regions from which the air masses that generated precipitations came.16 Consequently, the conjoined analysis of deuterium and oxygen 18 has been henceforth systematically carried out on the ice of Antarctica and Greenland. At Orsay, Françoise Yiou and Grant Raisbeck demonstrated that it is possible to measure the concentration of beryllium 10 in polar ice, and analyses done on the ice of Dôme C suggest that there is a way to reconstruct the past variations in the accumulation of snow.17 With this wealth of results, the French entered the very tight circle of nations that had succeeded in deep core drilling in polar regions.

  We are proud of these initial successes. But in this realm of research dedicated to the reconstitution and understanding of past variations in the climate, the high ground was indisputably held by paleoceanographers, whose strength lies in their access to data on variations in sea level provided by the analysis of oxygen 18 in foraminifera. The distribution of the species that find their optimal growth temperature in more or less warm waters further provides access to variations in temperature. And above all, marine sediments enable us to go far back in time; many marine cores cover several climatic cycles of the Quaternary and even beyond it. At the time of this first Dôme C record, we talked in our scientific community about the works already mentioned of Jim Hays, John Imbrie, and Nick Shackleton, which had just established the validity of Milankovitch’s theory. Much remained to be clarified regarding the mechanisms put into play, but to make a contribution glaciologists should necessarily go further back in time.

  Rapid Climate Variations: Initial Inklings

  The Danish and American teams were also attempting to go back in time. With the loss of the core drill at Byrd, the drilling team from CRREL was unable to continue their work. The Copenhagen team took over. Engineers, technicians, and scientists all worked under the direction of Niels Gunderstrup and Sigfus Johnsen. The electromechanical drill Istuk was built and tested during the 1970s. This new drill had a motor driven by rechargeable batteries installed in the drilling tube. Built to drill cores two meters long, it was much less cumbersome and lighter than the one used at Byrd; it was 11.5 meters long and weighed only 180 kilograms. The winch and the drilling tower were scarcely more than a ton because the cable was not very thick.

  Despite these efforts to construct a relatively small, lightweight drilling system, there were logistical constraints that dictated the choice of site for this new drilling project, GISP (Greenland Ice Sheet Project), which the Swiss from Bern joined, along with the Danes and the Americans. The scientists argued in favor of drilling at the center of Greenland at its highest point, convinced that they would reach the oldest ice there. But that region was far from the American bases, Thule to the northwest and Sonderstrom Fjord to the southwest. A site close to the latter, Dye3 in southern Greenland was
ultimately chosen, even though it was far from ideal. The origin of the ice formed upstream from the site was difficult to determine because this coastal region is very hilly. It is also a relatively warm site where summer fusion prevents the reconstruction of variations in the composition of air bubbles, which are very sensitive to fusion. After three seasons (1979–81), the bedrock was reached at a depth of 2,038 meters. The scientists’ fears proved grounded, as the samples did not go beyond the last glacial period, and their analysis was complicated. But this drilling offered an extremely surprising discovery: that glacial period and the deglaciation that followed it were marked by great and very rapid warming that occurred in the span of a few decades, or perhaps even a shorter period of time. These rapid variations were also seen at Camp Century, but these results were not put forward because the scientists feared that the variations were due to the movements of the ice near the base. Documenting them at a second site eliminated any doubt.18 These rapid variations, henceforth known as Dansgaard-Oeschger events, were indeed of climatic origin.

  Vostok: A Collaboration between French and Soviet Teams

  To go back in time is, a priori, more promising in Antarctica than in Greenland. The accumulation of snow there is weak, less than 10 centimeters per year, or around 3.5 centimeters of water, over a large part of the Antarctic plateau, and the ice is thick, often more than three kilometers. In addition, the movement of the ice is very slow throughout the central region. The flipside: accessing it is not easy and the temperature is the coldest on our planet, making fieldwork much more difficult. In spite of everything, the Soviets established a permanent station in this central region at the Vostok site (see Figure 1.2), where the record for the lowest winter temperature ever was recorded (−89.2°C). At the beginning of the 1970s a long-term operation was begun at Vostok—a true epic adventure under the direction of the Leningrad Mining Institute, whose drillers were accustomed to extreme conditions—which, after thirty years, has just been completed.