The WAIS Divide site location was chosen based on the following site requirements:
- Relatively smooth bed topography and minimal horizontal ice flow.
- Individually identifiable annual layers of at least 1cm thickness in ice 40,000 years old.
- Ice-accumulation rate sufficient to reduce the age difference between the gases in the ice and the ice itself to less than 500 years.
- Well-behaved stratigraphy to an age of at least 80,000 years.
High-resolution, grid-based airborne geophysical surveys of the Ross/Amundsen ice divide region were conducted during 1994-1996 and identified several sites with favorable surface topography, ice thickness, accumulation rate, and bedrock topography characteristics. On-ice site reconnaissance started in 1995/1996 with exploratory traverses into the area and the drilling of three shallow firn cores to confirm the preservation of climatic signals in the snow and ice. Ice flow modeling and temperature calculations were applied to the candidate sites to predict time scales and annual layer resolution. This was then followed by two seasons of ground-based geophysical surveys to further investigate the candidate sites.
The chosen WAIS Divide site is favored because:
- bedrock topography is relatively smooth at km scales;
- internal layers are flat and undisturbed;
- location is ~24 km downsloap of the flow divide (but within 10 ice thicknesses of the divide) to insure that no divide migration has compromised the stratigraphy;
- annual layers will be detectable (1 cm thick) to at least 40,000 years;
- ice from deglacial period will not be brittle;
- gas-age ice-age difference is ~200 years for the Holocene and ~300 to ~500 years for the last glacial period.
|WDC12A||Jan ~13, 2012||Eclipse||81||0||121.5||79°27.86' S, 112°06.69' W||~5927||The top 2 meters of the hole is cased and the casing extends to 2 meters above the current snow surface. An additional 1.5 meters of casing is being stored in the Arch for extension in the future.|
|WDC06A||2011/12||DISC||122||3331||3405||79°28.058' S, 112°05.189' W||~5927||Deep core|
|WDC06A||2010/11||DISC||122||2564||3331||79°28.058' S, 112°05.189' W||~5927||Deep core|
|WDC06A||2009/10||DISC||122||1514||2564||79°28.058' S, 112°05.189' W||~5927||Deep core|
|WDC06A||2008/09||DISC||122||580||1514||79°28.058' S, 112°05.189' W||~5927||Deep core|
|WDC06A||2007/08||DISC||122||114||580||79°28.058' S, 112°05.189' W||~5927||Deep core|
|WDC06A||Dec 9, 2006||4-Inch||104||0||114||79°28.058' S, 112°05.189' W||~5927||Deep core|
|WDC06B||Dec 1, 2006||4-Inch||104||0||130||79°28.048' S, 112°05.160' W||~5927||Allocation TBD|
|WDC05A||Dec 19, 2005||4-Inch||104||0||~299||79°28' S, 112°05' W||~5927||Collected for gas analysis|
|WDC05B||2005||Eclipse||81||0||~75||79°27.775' S, 112°07.422' W||~5927||Hole drilled for firn gas sampling; core will be used for chemistry method development|
|WDC05C||2005||Eclipse||81||0||~80||79°27.777' S, 112°07.362' W||~5927||Hole drilled for firn gas sampling; core will be used for chemistry method development|
|WDC05Q||2005||4-Inch||104||0||~130||79°28.052' S, 112°05.137' W||~5927||Drilled at the arch pit; used for chemistry and isotopes|
|WDC05E||2005||4-Inch||104||0||~32||79°27.777' S, 112°07.506' W||~5927||collected for firn structure studies|
|Surface elevation1:||1,766 m|
|Distance from current flow divide:||24 km|
|Current ice-accumulation rate:||22 cm/year|
|Current average annual surface temperature:||-30°C|
|Age at 90% of total depth2:||98-105 ka|
|Age at 96% of total depth2:||175-236 ka|
|Age by which annual layers have thinned to a thickness of 1 cm 3:||45-46 ka|
|Age of the ice in the depth-range when the ice is brittle4:||1.8-9.4 ka|
|Ice thickness:||3,465 m|
|Ice age-gas age difference in Holocene:||200 years|
|Ice age-gas age difference in the glacial period:||500 years|
1 Determined from pole measurements using processed GPS data at the site. Note that this elevation is referenced to WGS84. Source: Conway and Rasmussen, 2009.
2 Calculated with the expected high and low geothermal heat flux.
3 Calculated with the expected high and low geothermal heat flux. This is approximately how far back the core can be dated by counting annual layers.
4 Core quality will be lower in this age range.