US Global Ice Core Research Program
West Antarctica and Beyond

4.2.1 Long Paleoenvironmental Records: Antarctica.

The emphasis for the US Antarctic ice core program should be on West Antarctica. This was the consensus of the 1988 University of New Hampshire Ice Core Research Workshop. There are several reasons for this choice:

· The stability of the West Antarctic ice sheet under a projected global greenhouse warming is unknown. The sea level rise that would result from a collapse is a major factor of uncertainty in the evaluation of the effects of a greenhouse warming. A core in West Antarctica that contains ice from the previous interglacial and the preceding glacial period will answer crucial questions on a possible collapse of the West Antarctic ice sheet during the warm interglacial period about 125,000 years ago.

A long Antarctic core record with a resolution comparable to the GISP-2/GRIP records now being collected at the summit of the Greenland ice sheet is needed.

This will allow detailed interhemispheric comparison of the critical timing and phase relationship of climatic and atmospheric changes. Although East Antarctica has provided excellent ice core records, e.g. Vostok and Dome C, the accumulation and, therefore, the resolution near the centers of outflow on the East Antarctic plateau is an order of magnitude lower than in Greenland. The northern flow divide area of West Antarctica has a suitable accumulation rate and may preserve a seasonal record as indicated by the results obtained at Siple Station.

· The West Antarctic ice core record(s) will complement the data on configuration, mass balance and ice flow obtained under the US Siple Coast Project. The Siple Coast Project will benefit from the identification of marker horizons in the ice and from the physical properties measured along the core and in the bore hole as well as from data on past ice sheet size and climatic forcing. The understanding of ice flow in the area, obtained by the Siple Coast Project, is of crucial importance for the interpretation of the core record.

· The Solid Earth Geophysics Initiative planned to start in 1990 involves extensive radar. Surveying of the bedrock under the West Antarctic ice sheet. The data gathered by this project will provide an invaluable database for drill site selection in West Antarctica. Conversely, core data on the chemical composition and physical properties of the ice as wen as access to bedrock provided by a deep core, will benefit the Geophysics program.

· The planned program Cenozoic Paleoclimates will benefit from access to subglacial strata provided by deep and intermediate core holes.

· An ice core program in West Antarctica, where the US has a long ongoing research program, complements programs in East Antarctica where research by the USSR, France, Australia, and Japan has produced valuable records, and in the Antarctic Peninsula where Great Britain focuses its Antarctic research.

A disadvantage of West Antarctica is the uncertainty whether a long (>105 yr) record can be recovered. This depends on the stability of the ice sheet during the previous warm interglacial period and on the geothermal flux from the underlying bedrock. Model calculations indicate that for a heat flux near the low end of the normal range most of the West Antarctic ice sheet win be frozen to its bed so we can retrieve a long record, but with a flux at the high end the ice will be melting at the bed. Radar is an imperfect but highly useful sensor for basal melting and data should be collected in potential drill areas to look for melting.

The deep core part of the West Antarctic ice core research project should start with an airborne ice radar survey to determine the general bedrock topography and whether the ice is locally frozen to the bed or melting. Paleoenvironmental records with minimum disturbance due to ice flow can be expected along the ice divides and from ice domes. For West Antarctica these are the Ross Sea-Pine Island Bay and the Pine Island Bay-Weddell Sea divides, the area between Mt. Woollard and the Whitmore Mountains, the area between the Whitmore Mountains and Hercules Dome, Hercules Dome, Siple Dome and Dome BC (Appendix C). For Siple Dome and Dome BC radar survey data are already available. The Ross Sea-Pine Island Bay and Pine Island Bay-Weddell Sea divides are interesting because they have a high accumulation rate (20-30 cm/yr) and are partly over bedrock plateaus which promises simple ice flow near the bottom. These areas are the first choice for the first Antarctic deep core project and should be the starting point for the ice radar survey. Integration of this ice radar survey with the planned Geophysics ice radar activities is feasible and should be undertaken.

More detailed ice radar sounding and study of the preservation of environmental information in snow pits and shallow cores should start at sites found promising in a first analysis of the airborne ice radar data the field season following airborne surveying. Site selection for deep and intermediate drilling can then be based on the field data and the scientific questions to be answered by the core (possibly at a workshop organized by the ICWG). If the airborne ice radar survey is field season 1, then drilling could start in field season 4. This long lead time makes it obvious that airborne ice radar and surface-based surveys of potential core areas should continue for other sites after the first core site has been selected, to provide a database for future site selection for a second Antarctic deep core. Potential goals for a second deep core could be to obtain a very long paleoenvironmental record, or to document the disappearance and regrowth of the West Antarctic ice sheet in case the first core in West Antarctica failed to obtain ice older than about 100,000 years. A core through e.g. Hercules Dome, situated in East Antarctica where the East Antarctic ice sheet adjoins the West Antarctic ice sheet, may be expected to show significant changes in ice flow and surface elevation in case the adjacent West Antarctic ice disappeared. A decision on the second core should be based on the preliminary results of the first West Antarctic core as well as on the information provided and the questions raised by global change research in general and by other deep and intermediate ice cores in particular.

Optimum use of the existing US ice core research and ice core drilling capabilities could be obtained if Antarctic deep drilling could start one or two years after completion of the drilling of the Greenland Summit deep core of the GISP-2 program. This would target the 1994-95 Antarctic field season to start deep drilling in West Antarctica.

Intermediate and shallow Antarctic core projects may be completed within a single field season. These can be developed and proposed by a single PI. Drilling at McMurdo Dome has been proposed for 1991-92. Two other sites with potential for an intermediate (- 1000 m) core are Dome BC and Siple Dome between ice streams B and C, and between C and D respectively. These cores tie in directly with the Siple Coast Project. A core through such a local outflow center will be a sensitive indicator of changes in ice thickness and flow in the West Antarctic ice sheet along this part of the Siple Coast. The core records can be compared with those of nearby Byrd Station and J-9 to evaluate spatial variability.

The full range of important paleoenvironmental indicators should be analyzed in the intermediate and shallow cores. This optimizes use of the environmental information contained in the cores and promotes comparison between different cores. Analysis of a wide range of core properties can be accomplished by a collaboration initiated by the PI or by DPP inviting suitable proposals to complement analyses already proposed. One or two intermediate and/or shallow core projects in West Antarctica should precede the first deep drilling project. This will augment the database available to interpret a deep long record and also build experience in Antarctic deep drilling thereby increasing its chances of success.

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