Ice core methodology - Ice Ages and Interglacials: Measurements, Interpretation, and Models - page 108

The site chosen had a flat basal topography to avoid the flow distortions that
rendered the bottoms of the GRIP and GISP cores unreliable. Thus, the NGRIP
data extended back further in time, reaching the Eemian interglacial period prior
to the most recent ice age, which indicated that temperatures during that
interglacial period were comparable with those existing today.
A number of ice cores have also been drilled at Antarctica. They provide
longer term records than Greenland and have recently been extended to about
800,000 ybp . However, the annual layers are very narrow and dating is therefore
more dicult.
The Vostok ice core at Antarctica provided data for 420,000 years and
revealed four past glacial cycles. Drilling stopped just above Lake Vostok.
However, the Vostok core was not drilled at a summit, hence ice from deeper
down had flowed from upslope, complicating dating and interpretation.
The EPICA Dome C core in Antarctica was drilled at 75 S (560 km from
Vostok) at an altitude of 3,233m, near Dome C. The ice thickness there is 3,309m
and the core was drilled to 3,190m. Present day annual average air temperature is
54.5 C and snow accumulation is 25mm/year. The core went back 800,000 years
and revealed eight previous glacial cycles.
Two deep ice cores were drilled near the Dome F summit (77 S) at an altitude
of 3,810m. The first core (1995-1996) covered a period back to 320,000 years. The
second core (2003-2007) extended the climatic record of the first core to about
720,000 years.
The West Antarctica Ice Sheet Divide (WAIS Divide) is a U. S. deep-ice
coring project in West Antarctica. The purpose of the WAIS Divide project is to
collect a deep ice core from the flow divide in central West Antarctica in order to
develop a unique series of interrelated climate, ice dynamics, and biologic records
focused on understanding interactions among global Earth systems. The WAIS
Divide ice core will provide Antarctic records of environmental change with the
highest possible time resolution for the last 100,000 years and will be the
Southern Hemisphere equivalent of the Greenland GISP2, GRIP, and North
GRIP ice cores. The most significant and unique characteristic of the WAIS
Divide project will be the development of climate records with an absolute
annual-layer-counted chronology for the most recent 40,000 years. It is
believed that the WAIS Divide record will have only a small offset between
the ages of the ice and the air trapped in the ice. The combination of high
time resolution and this small age offset will allow interactions between climate
variations and atmospheric composition to be studied at a level of detail pre-
viously not possible in deep long Antarctic ice core records. As such, it is intended
that the WAIS Divide ice core will enable detailed comparison of environmental
conditions between the Northern and Southern hemispheres, and the study of
greenhouse gas concentrations in the paleo-atmosphere, at a greater level of detail
than previously possible. It is hoped thereby to determine (a) the role of green-
house gases in ice ages and (b) whether initiation of climate changes occurs
preferentially in the south or the north. Drilling was completed in 2011 to a depth
of 3,405m.