The White Planet: The Evolution and Future of Our Frozen World
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A depth of 2,755 meters was reached in January 1994; the core samples then covered two climatic cycles. Then 3,350 meters was reached in January 1996—600 additional meters, which doubled the period with an estimated age of 420,000 years at 3,310 meters. We were disappointed because data suggested that below that level the layers of ice, as in the center of Greenland, were disturbed. Core drilling continued, but we decided that it should be stopped a bit beyond 3,600 meters because radar measurements taken from the surface had revealed the existence of a huge subglacial lake the size of Lake Ontario or Corsica, with a depth of 600 meters, directly below Vostok Station. It was obviously essential to avoid contaminating that water, which could have been more than a million years old. Core drilling was stopped in December 1998 at around 120 meters above Lake Vostok and close to thirty years after the operations began.
Since then our Russian colleagues have been extremely motivated by sampling liquid water from Lake Vostok, an undertaking that raised a great deal of concern among the international glaciological community because of the high risk of polluting the lake water. The Russian drillers claimed that such contamination would be avoided—or at least very limited—because of the overpressure at the lake surface when it would be reached. They convinced their authorities and were given permission to proceed. Under their initiative, drilling of the core resumed in 2009 by a deviation of the hole reaching a depth of 3,720 meters in December 2011. Nonstop drilling operations began on January 2, 2012, and continued until February 6 under the leadership of the Russian chief driller, Nikolay Vasiliev. The last flight ending the summer season at Vostok was scheduled for February 6. We summarize here a report of the last day of operation by our Russian colleague Volodya Lipenkov, who was part of this field party: “the drill hit the surface of Lake Vostok in the morning of that same day at a depth of 3769.3 meters. Due to the high water pressure at the surface of the lake, liquid water surged up the borehole, and one minute after the penetration the kerosene used as drilling fluid began outflow through the top of the hole. This shows that we had reached and broached the main water body of the lake without contaminating it. This outflow persisted for about five minutes and about 1.5 cubic meters of drilling fluid was forced out the top of the casing. According to our estimate the water rose to about 600 meters above the lake surface. The last drilled core was mostly frozen and was sampled for biological and isotopic analyses just a few hours before we left the station with the last flight.” Lipenkov added, “Such was the end of the 5G drilling but hopefully not the end of the Vostok project.” Next season (2012–13), the Russian team plans to come back to the station to start coring the lake water frozen in the hole.
Other Core Drilling in Antarctica
The decade of the 1990s was full of other coring activity in Antarctica. The Japanese were initiated in coring methods through contact with Europeans during the GRIP coring. Evenings under their tent, which was set up a few hundred meters from the main dome, were congenial and warm. Their participation in the GRIP campaigns was fruitful since they built their own drill inspired by Istuk, which quickly became operational. The project initiated by Okitsugu Watanabe was ambitious: to reach the bedrock at Dôme Fuji, an ideal site on the other side of East Antarctica from Dôme C. As at Vostok, it was decided to drill throughout the year in spite of winter temperatures below −70°C. In two years, 1995 and 1996, the Japanese drillers were at 2,503 meters. The level of the drilling liquid was then much lower than what it should have been. Perhaps that was the reason the drill became blocked; despite every effort it was impossible to bring it up. There was success, however, because the deepest ice was around 330,000 years old, and three complete climatic cycles were recorded. But there were also many regrets because we now know that the extraction of the 500 remaining meters would have allowed the record held by Vostok to be broken. The Japanese did everything they could to resume drilling from the surface, and that new operation was crowned with success at the beginning of 2006 when they obtained a 3,035-meter-deep core covering more than 700,000 thousand years.22
Other teams chose more modest projects, aiming to drill on one of the small domes that exist in the coastal regions. There is a good deal of snow precipitation there, which helps in dating the ice because the years can be counted. There is also an advantage for the interpretation of records contained in the air bubbles because, due to this high accumulation, the uncertainty about the difference in age between these bubbles and the ice that contains them is much less than in regions on the Antarctic plateau with little accumulation. The drillings on small domes, whose depth generally did not go beyond 1,500 meters, were in fact very well adapted for the study of the relatively recent climate, say the last 20,000 years, a period that covers the Last Glacial Maximum, the deglaciation, and the Holocene. Some of those ice cores cover all of the last glacial/interglacial period and even beyond.
Above all, these small domes are located in regions that are relatively accessible and thus required limited logistical support. For example, the Australians did not have the necessary logistical support to mount an operation far from their base, Casey, but they were fortunate to have a little ice dome, Law Dome, near that station. A single summer season (1996–97) was necessary for a 1,200 meter long core to be extracted, which was particularly interesting. More recently, drillers from Grenoble, with the support of the IPEV under the direction of Gérard Jugie (Institut français polaire Paul-Émile-Victor, the new name of the IFRTP since the beginning of 2002), developed a new core drill, light and easily transportable, used in collaboration with the British Antarctic Survey (Cambridge) to carry out an operation on Berkner Island; the drilling, 948 meters deep, reached the bedrock in January 2005. The same drill was then used to obtain, within the framework of an international project coordinated by Italy, a core of about 1,500 meters at Talos Dome, a site close to the Terra Nova Bay Station. The goal was reached at the end of 2007.23 At the beginning of 2008, there was also success on James Ross Island, to the east of the Antarctic Peninsula, whose glacial ice sheet was drilled down to the bedrock.
It is somewhat surprising that the logistical means the NSF could devote to glacial drilling were, in fact, rather limited. That organization, unlike the IPEV, did not have the means to transport materials overland, and the transport of all supplies in Antarctica was dependent on the use of large C130 transport planes from McMurdo Base. But those aerial means were primarily devoted to transporting the material necessary for the reconstruction of the permanent base on the South Pole and for an experiment aiming to count the very rare solar neutrinos using the ice as a detector. The glaciologists were therefore forced to concentrate on sites that were easily accessible from McMurdo. Two core drillings were thus carried out at Taylor Dome between 1991 and 1994 and at Siple Dome, where the bedrock was reached in January 1999. Those drillings were primarily interesting in terms of the study of the last 100,000 years. The Americans then decided to launch a large-scale operation in West Antarctica, a region particularly interesting in which to check the assumption put forward by some scientists who had feared that it had been unstable in the past. Deep core drilling in the central regions of this part of Antarctica would enable a better evaluation of this hypothesis. But our colleagues needed a lot of patience because, at the beginning of the 2000s, logistical support still was largely devoted to activities in the South Pole. Drilling operations of the West Antarctic Ice Sheet (WAIS) ice core began in 2008, 160 kilometers from the location of the Byrd ice core. A depth of 2,561 meters was reached in January 2010 and the drilling was completed on December 31, 2011. The final core was collected at a depth of 3,405 meters: the WAIS team could not have asked for a better reason to celebrate the New Year. Due to the high accumulation at this site,24 the core does not extend beyond the last 62,000 years, but it will allow scientists to obtain records of very high accumulation.
The Glaciers of the Andes and the Himalaya
We are indebted to an American team, that of Lonnie Thompson of Ohio St
ate University, for having been the first to launch extensive ice drilling projects in other regions. He was the first to believe in the scientific value of cores extracted from tropical glaciers, which many of us doubted, and to drill above 6,000 meters in altitude in the Andes and the Himalaya. Of course, just as in the coastal zones of Antarctica, the scale of time was limited to tens of thousands of years, but the Andean glaciers are excellent archives of the past rhythm of the El Niños and the Himalayan glaciers of that of monsoons. In addition, some of those glaciers are shrinking in volume at a dangerous rate and quite simply risk disappearing under the effect of global warming. It is worth pursuing this area of study, but there are difficulties in drilling even if the thickness of the ice to be cored never goes beyond 200 meters and in retrograding the ice in the laboratories. Light drills that run on solar energy have been developed, but everything must be transported by foot from the last accessible base. And once the cores are extracted, they have to be brought back down as quickly as possible to avoid melting. Lonnie Thompson overcame all those difficulties, and we are indebted to him for an entire series of ice cores from those tropical glaciers.
Other teams have followed in his footsteps: that of Paul Mayewski in the United States and a Franco-Swiss consortium led by glaciologists at the Institut de Recherche et Développement (IRD). This consortium, in which on the French side the Laboratoire des Sciences du Climat et de l’Environnement (LSCE) Saclay and the LGGE Grenoble collaborate, has succeeded in extracting a core in Chimborazo, just south of the equator at more than 6,000 meters in altitude. But the most amazing project is that of the Chinese: to extract an ice core from the Muztagh Ata, on the roof of the world, at more than 7,500 meters in altitude. Closer to home, in the Alps, there is little hope of going back to past climates from glaciers because they are generally places of surface fusion and percolation, phenomena that blur the signals recorded by the snow. On the other hand, these temperate glaciers provide an excellent means for reconstructing the increase in pollution connected to the advent of the industrial era in Western Europe.
A Return to Greenland
There were other drilling projects in the 1990s. The Danes were very disappointed that the core samples from the center of Greenland, GRIP and GISP2, did not reliably allow them to go back further than 100,000 years. There was still hope, however, because it was possible that the mixture of layers observed at the base of these cores was linked to the fact that the subglacial relief was very tortured in that zone. It would therefore suffice to locate a region with a flatter relief to be able to go back further in time. In 1994, reconnaissance missions were organized in the northern part of Greenland. A zone located 200 kilometers north of GRIP appeared a priori favorable. The team from Copenhagen assumed the leadership of a new coring project baptized North GRIP, in which we participated alongside German, American, Belgian, Japanese, Scandinavian, and Swiss teams. The camp was established in 1995, and core drilling began successfully in 1996. Everything was going well, but the following season the drill was blocked at a bit more than 1,400 meters.
Nothing could be done; neither the efforts undertaken that year nor those undertaken the following season could bring the Istuk drill back to the surface. The team decided in 1999 to start again from the surface. In two seasons a depth of 2,931 meters was reached, but the drilling was subsequently greatly slowed down. Indeed, the geothermal flow was higher than anticipated, and the temperature of the ice was closer to the point of fusion than was predicted by flow models. To drill into that ice, which is called “warm,” required enormous precautions, and procedures had to be put into place to ensure the drill did not get stuck. Three seasons were needed to reach the bedrock; this occurred in 2003. More specifically, the drilling ended in a subglacial “river” present under 3,085 meters of ice, with as a consequence the rise of 45 meters of that water, subjected to very strong pressure, before it froze.
The presence of liquid water at the base of the glacier had a beneficial consequence because the relatively great fusion at the base of the North GRIP drilling contributes to making the deep layers disappear. The thinning of the layers of ice within the ice sheet was reduced and, with that, the risk of a perturbation due to the ice flow like those that affected the last 300 meters of the GRIP and GISP2 drilling. The age of the deepest ice was estimated at 123,000 years, probably the warmest time of the last interglacial period.25 The drilling thus did not go back as far as had initially been hoped for, but the disadvantage was largely compensated by the absence of perturbations linked to the ice flow. In a rather unanticipated way, we thus went from obtaining deep cores of which approximately the deepest 10% were practically unusable from a climatic point of view (in both Antarctica and Greenland) to a completely unperturbed record.
Empowered by that success, the Copenhagen team, with their usual partners, initiated a new drilling project at a site located farther north, between North GRIP and Camp Century. New teams (Canadian, Chinese, and Korean) joined the project, which began in 2007 with the establishment of the camp and ended in 2010 with a core drilling that reached the bedrock on July 27 at a depth of 2537.36 meters. The hope was to cover the entire previous interglacial period, but unlike for North GRIP the bottom part is perturbed by ice flow below about 2.2 kilometers. However, available data show that a correct time sequence can be reconstructed back 129,000 thousand years, extending the North GRIP record over a large part of the last interglacial period.26
The European EPICA Drilling: A Double Success beyond All Hopes
The years 1997 and 1998 were extremely trying for all the drilling teams with the loss of the drills both at Dôme Fuji and at North GRIP. And the EPICA Dôme C project wasn’t spared either. The first season (1997–98) was difficult because it was the true baptism by fire for the EPICA drill. Drilling resumed the following year and was satisfactory, but after a few weeks the drill was stuck at a depth of 780 meters. Despite all the attempts made by the drillers brought in by Laurent Augustin from Grenoble, it was impossible to recover the drill and to resume operations. It was a huge disappointment for everyone because they had to begin again from the surface, and that solution didn’t appeal to the drillers, the scientists, or the institutes and organizations that had helped finance EPICA. In spite of everything, the drilling operation was resumed during the 2000–2001 season, and it was henceforth proven that the decision to resume drilling after that failure was a good one.
After the 1999–2000 season, which was devoted to putting new tubing into place and testing the changes made to the drill, the success of the two following campaigns exceeded all expectations. A depth of 1,459 meters was reached at the end of January 2001, and the final following season saw a doubling of the depth at 2,871 meters. A comparison of the records of electrical conductivity indicated an age older than that of 420,000 attained at that site. The objective of obtaining 500,000-year-old ice had, in fact, already been surpassed. However, the increase in temperature, due to the influence of the geothermal flux as one went farther into the ice sheet, made the drilling conditions increasingly difficult. In spite of these difficulties, more than 300 meters of ice were extracted during the 2002–2003 season, and drilling was finally stopped at a depth of 3,201 meters. After stopping for a season, the EPICA Dôme C drilling reached the bedrock at 3,260 meters in January 2005. Ice drilling at Vostok kept the world record of depth, but even if the measurements taken from the deepest ice indicated that the last 60 meters had been perturbed, the Dôme C drilling was enormously satisfying, allowing us to go beyond 800,000 years.27 For a time, the Japanese hoped that the second drilling at Dôme Fuji would contain ice that was one million years old, but that estimation was lowered and the age close to the bedrock was on the order of 700,000 years. Dôme C thus holds the record for the longest climatic sequence, a record that will likely remain unbroken for several years.
The second EPICA (Kohnen) drilling was undertaken in 2001–2, the season during which a depth of 450 meters was reached; it continued without d
ifficulties and reached a depth of 2,565 meters in 2004. The ice there was around 200,000 years old. That drilling, which should have enabled us to obtain extremely detailed records over an entire climatic cycle, reached the bedrock during the 2005–6 season, at a depth of 2,760 meters. This double success opened the door to an entire series of articles describing our climate and our environment during the last 800,000 years and to a group of new results bearing on the climatic interactions between the Northern and the Southern hemispheres. This wealth of results earned EPICA the honor of being one of three projects to receive the prestigious Descartes Prize for Science given by the European Union in 2008.