Skip navigation


You are in:  Home » Publications » Reports » Report 13

SCAR Report No. 13, November 1996 

SCAR Group of Specialists on Global Change and the Antarctic (GLOCHANT)

Report of the 1995 bipolar meeting of the GLOCHANT / IGBP-PAGES
Task Group 2 on Palaeoenvironments from Ice Cores (PICE)

Members of the PICE Group present: Dr. D. Raynaud (Chairman, France), Dr. D. Peel (Secretary, U.K.), Dr. J. White (U.S.A.), Mr. V. Morgan (Australia), Dr. V. Lipenkov (Russia), Dr. J. Jouzel (France), Dr. H. Shoji (Japan, proxy for Prof. O. Watanabe).

Apologies: Prof. O. Watanabe (Japan).

Other participants: Prof. P. Mayewski (U.S.A.), Prof. B. Stauffer (Switzerland), Dr. H. Zimmerman (PAGES), Prof. C. Hammer (Denmark), Prof. S. Johnsen (Denmark), Dr. H. Miller (Germany).

1. Introduction

1.1 H. Zimmerman briefly outlined the relationship between IGBP-PAGES (Past Global Changes) & SCAR-GLOCHANT. PAGES is designed to focus on the past global changes over the last 250 k yr. It has joined with the SCAR-GLOCHANT to formulate a coherent bipolar approach to the future strategies for polar ice-core drilling. We require a bipolar science plan which establishes the relationship between national ice-core drilling projects, and a framework for continental scale analyses of palaeoenvironmental changes.

1.2 D. Raynaud briefly reviewed the history of the group. Following the Col de Porte meeting of the GLOCHANT Planning Group on Palaeoenvironmental records (24-25 February, 1994), a draft Antarctic ice-coring strategy document had been prepared. A new document was now needed to make a much stronger case, and should especially emphasize bipolar aspects. An update of factual information is needed.

2. Update of Major Antarctic Drilling Projects

2.1 Vostok (V. Lipenkov)

Deep ice coring was initiated at Vostok Station in 1970; the latest borehole, Hole 5G was started in 1990 with a thermal drilling system and is now continuing with an electromechanical drill. Since 1989, drilling has been carried out as a joint Russian-French-American project. The aim of the project is to obtain high resolution climatic records covering approximately the past 500 k yr. These data are needed to validate the predictive climatic models, as well as to establish the interrelationships between climate change in Antarctica and climate changes over the Southern Ocean (registered in marine cores) and in the Northern hemisphere. The project also aims to elucidate the external forcing mechanisms and internal dynamics of the Earth's environmental systems.

Drilling reached a depth of 3100 m in September 1995, where the estimated age of the ice is 320 k yr BP. Drilling was then stopped over winter owing to a shortage of the densifier for the hole liquid. Drilling continued during the 1995/96 field season, and was intended to continue through the 1996 winter. In the event, it was decided to close the station for the 1996 winter, when the drilling had reached 3349.68 m depth in January 1996. According to guide-lines recommended by the SCAR and Lake Vostok Workshop (Cambridge, May 1995), drilling should be stopped at a point ~25 m above the surface of the subglacial lake beneath Vostok (at ~3,650 m depth). To confirm the existence of the lake as well as to determine the thickness of the ice, water layer and lake sediments in the vicinity of the station, a seismic survey was undertaken during the 1995–96 field season in an area about 2 km2 around the borehole. Plans have been made to reopen the station for the 1996–97 summer season. It was pointed out that modelling has not yet taken account of the lake, and dating is becoming more problematic.

The group congratulated all who had made this project such an outstanding success.

2.2 Dome FUJI (H. Shoji, O. Watanabe)

A new deep drilling programme commenced in 1994 at Dome Fuji, the highest point of the eastern Queen Maud Land ice sheet. At the centre of ice sheet flow, the deposited layers suffer minimal horizontal deformation by ice motion, and it is expected that an ice core from this site will clarify the climatic and environmental changes over the past 150,000 to 200,000 years.

Preparations for a deep ice coring operation at Dome Fuji started in 1991 and were completed with a successful camp construction by the JARE-35 party in 1995. The mean annual temperature at the site is -58°C, with a minimum of -78.1°C. The JARE-36 party started deep ice core drilling by extending the JARE-34 pilot hole from a depth of 112.6 m. Drilling has been continued by JARE-37, and by end of March 1996 had reached 840 m depth. The core quality is reported to be excellent and drilling is proceeding. A portion of the recovered core will be brought back to Japan by the JARE-36 party at the end of the field season. It is planned to reach 2500 m depth in 1997.

Once drilling is completed the focus will shift to mass balance studies in the Shirase drainage basin (1997-2001). The JARE-38 and -40 parties plan to drill several 100 m depth ice cores around the Dome Fuji site and along a flowline from Dome Fuji to Shirase Glacier, near the coast, and along an ice divide between the Shirase and Lambert drainage basins. These will be used to identify changes in surface mass balance during the past 200 years. These will investigations will contribute to the GLOCHANT-ITASE project. The shallow drillings will be coordinated with radio echo sounding and satellite remote sensing observations. There are also plans to perform atmospheric chemistry work after deep drilling is completed.

2.3 US Antarctic Drilling Programmes (J. White, P. Mayewski)

WAISCORES (West Antarctic Ice Sheet Program, ice cores)

WAISCORES, the ice coring part of WAIS (West Antarctic Ice Sheet Program), will address several fundamental questions concerning the nature and causes of climate change, the past variability of climate, and the stability of the West Antarctic ice sheet

The goals of WAIS are:

The WAISCORES project proposes that two deep ice cores be drilled in West Antarctica. The first ice-core will be drilled at Siple Dome to a depth of 1000 m. This is a coastal dome in a location at the base of the main ice streams currently draining the southern part of the West Antarctic ice sheet, to the Siple Coast. This location is believed to be sensitive to potential changes in the extent of the West Antarctic ice sheet. It is expected to yield a precisely datable stratigraphic record, and enable a detailed interhemispheric comparison of prominent Holocene climatic features. Several research programmes have been funded to recover and analyse core from the Siple Dome site. Camp construction and shallow-drilling will commence in 1996-97. Reconnaissance surface studies, including stable isotopes, chemistry and accumulation rate, were conducted around Siple Dome in 1994-95 and around the Byrd region in 1995-96. As a strategy, there will be minimal field personnel - most scientists will go to national core lab at Denver to analyse the core. Drilling is due to start in 1997/98 and surface work in 1996/97. The scientific proposals have been reviewed scientifically but the schedule for drilling has still to be decided. Some surface studies have been done at Siple Dome. Radio echo sounding shows absolutely horizontal layering and well defined visible stratigraphic layering. The expected age of the core is 40-70 k yr with 7-11 cm ice/yr accumulation. The site shows good promise for a high resolution Holocene record, and evidence for several glacial age rapid climate change events. The second ice-core drilling site will be located in the centre of the West Antarctic ice sheet along the ice divide, near Byrd station. It is planned to drill one 2000 m deep core at this site. Accumulation rates of snow at this location are comparable to those in central Greenland, and hence it is believed to be a good location for replicating the high resolution Greenland palaeoenvironmental records in Antarctica. The ultimate age at this site is currently unknown, but is expected to be at least 100,000 years. It is hoped that the Siple Dome drilling may start in 1997. Currently, drilling on the Inland core is scheduled to begin in 1999.

In East Antarctica, an ~550 m core has been drilled to bedrock at Taylor Dome, near McMurdo Sound. The length of the record is ~140 k yr with +/- 350 yr error at the time of the Younger Dryas. Comparisons with the Vostok and GISP2 cores have been conducted and have revealed notable bipolar similarities.

2.4 EPICA (J. Jouzel)

EPICA is a long-term (ca seven years) European deep ice-core drilling project in Antarctica, to derive high resolution records of climate and atmospheric composition through several glacial-interglacial cycles. To achieve EPICA's goals it is planned to drill at two sites, in order to achieve the required resolution of the climate and gas records on different timescales, and an adequate continent-wide perspective.

The first four-years phase (1996-2000) will focus on a deep (3500 m) drilling at Dome C, East Antarctica with the aim to characterise the major climate shifts during the past several glacial-interglacial cycles. A core from this location, which is ideally placed to secure an undisturbed long record, will allow examination of the relative phasing of climate and climate-forcing parameters associated with these major climate-change events. The core location is also optimal to put the Antarctic record into a global context and to produce a record for comparison with the ocean, continental and Greenland ice-core records. The project has been accepted by the European Union (EU) and funding approved for the first three years at the level of 90% of the original request.

During the second phase of the project, starting around 2000, a core will be obtained from Dronning Maud Land, an area of Antarctica most strongly influenced by the Atlantic ocean, and a region of somewhat greater annual snowfall rate and thinner ice cover, that will enable records of higher time resolution during the Holocene and last glaciation. This phase of the project is designed to focus specifically on the rapid climate oscillations, the Dansgaard/Oeschger events, that have been detected across Greenland especially during the later stages of the last glaciation.

Dronning Maud Land is also one of the least explored sectors of Antarctica, hence a large-scale framework of basic geophysical and geochemical survey will be undertaken during the first phase of the project, to gather the essential information that will be needed to locate an optimal deep drilling site, and to characterise the pattern of climate change across the region during the past centuries, and its representation in the ice-core record.

The direct costs for Phase 1 of EPICA, which will start in 1996, will be shared by ten national partners (Belgium, Denmark, France, Germany, Great Britain, Italy, Netherlands, Norway, Sweden and Switzerland) and by funding from the Framework 4 Programme of the EU. There may be opportunities for involvement of other countries, eg Russia and Australia, but extra money would be needed.

2.5 Australian Deep Drilling Programmes (V. Morgan)

Analysis of the 1200 m core from Law Dome Summit South (DSS) is continuing. The very high snow accumulation at DSS allows precision dating by layer-counting for a large part of the Holocene, however, the rapid thinning required to balance the accumulation leads to a layer thickness of only about 9 mm in the transition from the Last Glacial Maximum (LGM). There is 6 m of clear, isotopically warm ice at the bottom of the core above the silty basal ice. In 1995/96 an unsuccessful attempt was made to obtain silty ice from the bottom of the DSS borehole, due to slight borehole closure at depth. The borehole was successfully relogged to obtain vertical strain rates.

The record is ideal to extend the instrumental climate record for East Antarctica and to characterise in detail the climate during periods of important climatic fluctuations of large scale significance that have been documented in other parts of the world, such as the so-called European Little Ice Age and the Mediaeval warm period.

Field work to be carried out during the 1995–96 season covers:

Plans are being developed for future deep drilling on the ice sheet inland of Law Dome. At a site some 600 km inland, ice thickness exceeds 4000 m, and a core to near bedrock could be expected to produce a record going back more than 400,000 years, before bedrock effects make the timescale unreliable. The area lies on the flank of the ice sheet, and the deep ice could come from near either the Dome C or Vostok depending on the exact location. Site surveys would be made around 1998, and drilling could start about 2002. The project does not have national support at this stage.

3. Upate of Major Greenland Drilling Projects

3.1 GISP2 (P. Mayewski) AND GRIP (B. Stauffer)

The GISP2 and GRIP deep ice core drilling projects in central Greenland collected parallel ice cores, each extending more than 3 k m deep and 110,000 years past. Findings have been detailed in roughly 200 refereed publications so far. A recent joint workshop (Wolfeboro, New Hampshire, September 1995) hosted by the US GISP2 project was designed to exchange data and ideas, finalize arrangements for a special joint issue of JGR Oceans and Atmospheres (due out in 1996), and to plan future analyses and ice-coring projects.

The earth has experienced large, rapid, regional-to-global climate oscillations throughout most of the last 110,000 years, of a scale that agricultural and industrial humans have not faced. A few of these stadial/interstadial oscillations, such as the Younger Dryas (YD) event, had been known for decades or longer from pollen and other records. Many more were found in the first Greenland deep ice cores, but most of the oscillations occurred in ice from close to the bed where ice flow may have disturbed the climatic record. These events are recorded far enough above the bed in the new cores that ice flow is unlikely to have altered the climatic record. Indeed, the new cores show an almost perfect match back to 110,000 years ago.

These millenial-scale events, which frequently begin or end rapidly, represent quite large climate deviations: probably many degrees C in temperature, twofold changes in snow accumulation; order-of-magnitude changes in wind-blown dust and sea-salt loading, roughly 100 ppbv in methane concentration, etc., with cold, dry, dusty, and low-methane conditions correlated.

The events also are regional to global: they are observed in local climatic indicators such as snow accumulation rate and the isotopic composition of snow linked to temperature; in regional climatic indicators such as wind-blown sea salt and continental dust, and in regional-to-global indicators such as atmospheric concentrations of methane, nitrate and ammonium. Some events are readily identified in the ocean-sediment record in regions critical to global ocean circulation. Furthermore, new correlation techniques involving the gaseous composition of the atmosphere demonstrate that the major events also are recorded in the isotopic temperature record of the Vostok core from central East Antarctica.

The latest investigations, based on an analysis of borehole temperatures, suggest that ice-age temperatures in central Greenland were roughly 20°C colder than today. This verifies the commonly held belief that climate changes are amplified in polar regions. Independent estimates based on the stable isotope analysis of the ice indicate that the calibration of the isotope thermometer may be non-linear in Greenland over glacial to interglacial timescales, with a considerably smaller ∂18O/T gradient in glacial times compared with the gradient calculated for the modern period.

Initial interpretation of the GRIP ice-core data indicated that the large, rapid climate oscillations that dominate the record of the last 110,000 years also persisted through the previous warm period, The Eemian interglacial. Careful physical examination of the cores shows that significant structural disturbances from ice flow occur at or slightly above the depth where the climate records from the two cores diverge. Details of the gas records and of the chemistry indicates that some Eemian ice is probably present but that the stratigraphic sequence is probably disturbed. Ultimately, just as these cores were needed to validate the rapid oscillations observed in older cores, a new core or cores from sites where the Eemian ice is further from the bedrock, and thus less sensitive to flow disturbance, will provide the best answer.

GISP2 has produced ~150 peer-reviewed papers to date covering a wide range of topics such as: site survey; analytical and statistical techniques; physical processes of snow and ice; ice core drilling design and operation; transfer functions (eg., snow/atmosphere); unique events (eg., volcanism, biomass burning, anthropogenic emissions); palaeoenvironmental reconstructions; and bipolar, Arctic and GISP2/GRIP comparisons.

The work on GRIP has left several major important questions:

The 'lead parameter' ∂18O

Recent studies have indicated that the δ /T ratio may be strongly affected by changes in the moisture source. Now two new papers analysing the GRIP & GISP2 borehole T profiles indicate much smaller ratios in glacial times, with the implication that glacial-interglacial changes were much larger than previously deduced from isotopic profiles.

CH4 record

Must be a global record. The Younger Dryas (YD) signal in CH4 has to be a global and Vostok & Summit profiles overall agree well over YD, but there are quantitative differences in the early Holocene.

CO2 record

There are problems in Greenland - with significant differences between the Greenland and Antarctic records during 1000-1600 AD, diverging with depth.

The Eemian

The GISP2 and GRIP records of the Eemian interglacial period disagree, most probably due to disturbances in the stratigraphy at one or both sites. Such disturbances, some 300 m above the bedrock, were unexpected. The series of rapid climate shifts in the last glacial, which were first detected within 50 m of bedrock in the Camp Century and Dye 3 records, were fully verified only halfway through the ice sheet in both Summit records. Understanding the causes of the disturbances in the deepest parts of the Summit records must be a priority.

3.2 North GRIP (C. Hammer)

Although both Summit cores in Greenland show an almost perfect correspondence in palaeoclimate system parameters, they differ markedly in the bottom 300 m. Thus it remains an open question, whether the last interglacial was characterized by rapid climate fluctuations as was determined from the GRIP core. Because of the far reaching consequences for our understanding of the climate system this question must be resolved. A further deep ice core is therefore necessary, preferably in a location where ice of Eemian age is further away from bedrock and less disturbed by bedrock undulations than is the case for the Summit cores. Denmark has secured national funding to drill a new deep core at such a site in North Greenland. The area has a lower precipitation than Summit, consequently Eemian ice may be 300 m above bedrock. Presite survey work, including German radio echo sounding of the North GRIP area has been carried out and drilling is planned to start in 1996. This core will, provide further evidence on Eemian climate, yield much information on spatial variability of past climate conditions in Greenland and extend the presently available Greenland climate record further back in time.

The primary aim of the drilling will be to obtain Eemian ice. It will be a low budget operation, cutting down on the science in the field. Some scientists from other nations will be invited, although they will have to obtain funding. Planning is mapped over five years, but funding is for three years in the first instance. The EPICA drill test (to 300 m) will be carried out near the site next season. Drilling of the North GRIP core is planned for 1997-98.

4. ITASE (P. Mayewski)

The broad aim of ITASE is to establish how the modern atmospheric environment (climate and atmospheric composition) is represented in the upper layers of the Antarctic ice sheet. Primary emphasis will be placed on the last ~200 years of the record through the recovery of closely spaced (~100 km) ice cores. This time period was chosen for study because it is relatively simple to recover many ice cores covering this period and to develop a spatially significant study. Further, this time period encompasses the onset of major anthropogenic influence on the atmosphere and the end of the Little Ice Age, two notable complexities in climate change records. Specific objectives include:

Scientific guide-lines for ITASE have been established by the ITASE Steering Committee. Traverse routes have been proposed in order to sample the broad range of geographic, glaciological and meteorological conditions that characterise the Antarctic ice sheet. These traverse routes are the product of several international planning meetings attended by the international representatives of ITASE.

A joint IGBP-PAGES and SCAR-GLOCHANT ITASE Workshop is scheduled for the 2-3 August, prior to the XXIV SCAR meeting to update ITASE activities and develop a Science and Implementation plan. A national US ITASE meeting is to be held in late May 1996.

5. The GLOCHANT Bipolar Document–Discussion

There was a general discussion on updating and developing the GLOCHANT document on an international strategy for ice-core drilling.

The document should make a much stronger case for the need for multiple deep drillings in Antarctica&emdash;especially why there was a need for 3+ holes in East Antarctica and 2+ holes in West Antarctica. It should demonstrate how work in Antarctica is related to work in the north and generally emphasize the justifications for a bipolar approach. Modelling efforts in relation to site selection and core interpretation should be included, and the contribution of ice-core work to understanding the stability of the west Antarctic ice sheet highlighted.

A structure for the new document was agreed and contributions for the component sections were drafted. Progress reports for the individual projects were submitted and partly updated in April, 1996.

6. The GLOCHANT Bipolar Document–Preparation

First drafts for the document were criticized and a revised structure for the document agreed. The following authorships for producing the final document were agreed:

Actions

Future meetings

It was agreed that a meeting should continue to be held each year.
The composition of the group could be adapted to reflect the area of expertise needed.
The setting up of a workshop (GLOCHANT-PAGES) for ITASE could be a suitable focus for 1996.

David Peel

18 March, 1996