Site Selection

The WAIS Divide site location was chosen based on the following site requirements:

  1. Relatively smooth bed topography and minimal horizontal ice flow.
  2. Individually identifiable annual layers of at least 1cm thickness in ice 40,000 years old.
  3. Ice-accumulation rate sufficient to reduce the age difference between the gases in the ice and the ice itself to less than 500 years.
  4. Well-behaved stratigraphy to an age of at least 80,000 years.

Map of WAIS Divide

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:

  1. bedrock topography is relatively smooth at km scales;
  2. internal layers are flat and undisturbed;
  3. 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;
  4. annual layers will be detectable (1 cm thick) to at least 40,000 years;
  5. ice from deglacial period will not be brittle;
  6. gas-age ice-age difference is ~200 years for the Holocene and ~300 to ~500 years for the last glacial period.

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Borehole Locations

Hole Year
Drill Used Core
Lat, Long Altitude
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

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Site Characteristics

Longitude: 112.085 °W
Latitude: 79.467 °S
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.

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