Site Selection | Borehole Locations | Site Characteristics

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.

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 Drilled	Drill Used	Diameter (cm)	TopDepth (m)	BottomDepth (m)	Latitude, Longitude	Altitude (ft)	Remarks
WDC06A	2007/08	DISC	12.2	114	580	79o28.058'S, 112o05.189'W	~5927	Deep core
WDC06A	2006	4" drill	10	0	114	79o28.058'S, 112o05.189'W	~5927	Deep core
WDC06B	2006	4" drill	10	0	130	79o28.048'S, 112o05.160'W	~5927	Allocation to be determined
WDC05A	2005	4" drill	10	0	~299	79o27.777'S, 112o07.506'W	~5927	Collected for gas analysis
WDC05B	2005	3" Eclipse drill	7.5	0	~75	79o27.775'S, 112o07.422'W	~5927	Hole drilled for firn gas sampling; core will be used for chemistry method development
WDC05C	2005	3" Eclipse drill	7.5	0	~80	79o27.777'S, 112o07.362'W	~5927	Hole drilled for firn gas sampling; core will be used for chemistry method development
WDC05Q	2005	4" drill	10	0	~130	79o28.052'S, 112o05.137'W	~5927	Drilled at the arch pit; used for chemistry and isotopes
WDC05E	2005	4" drill	10	0	~32	79o27.777'S, 112o07.506'W	~5927	Collected for firn structure studies

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Site Characteristics

Longitude:	112.085oW
Latitude:	79.467oS
Surface elevation:	1,759 m
Distance from current flow divide:	24 km
Current ice-accumulation rate:	22 cm/yr
Current average annual surface temperature:	-31oC
Age at 90% of total depth1:	98-105 ka
Age at 96% of total depth1:	175-236 ka
Age by which annual layers have thinned to a thickness of 1 cm2:	45-46 ka
Age of the ice in the depth range when the ice is brittle3:	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:	300-500 years

Notes:
¹ Calculated with the expected high and low geothermal heat flux.
² 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.
³ Core quality will be lower in this age range.