Berkner Island Ice Cores 1994-95

Overview: 12 ice cores were drilled on and around the two main 'dome'
locations on Berkner Island during the 1994/95 field season. These
were drilled in a joint project between British Antarctic Survey (BAS)
and the Alfred Wegner Institue (AWI). BAS were responsible for the
drilling of the cores at the northern location while AWI drilled the
cores at the southern location.

The objective of the Berkner Ice Core Project was to reconstruct a
high resolution record of climate and environmental change on
timescales extending from centuries to several thousand years. Berkner
Island lies adjacent to the Weddell Sea: ice core records from this
island will help elucidate the role of the Weddell Sea in long-term
climate change over West Antarctica.

North Dome: The first phase of drilling took place on Reinwarthhvhe,
the northern dome of Berkner Island. A main core (R1) was drilled from
a shallow pit, covered by a temporary tarpaulin to protect the
drilling operation from excessive sunlight. This main core was 151.4m
in length and 106mm in diameter.

In addition four 10m cores were collected at four sites 5km from the
main borehole in the North, South, East and West directions. Two
other cores were collected of varying length as well as snow pits to
provide additional information.

Traverse: A party of two BAS staff travelled overland to the South
Dome location. On route they drilled two 20m cores and a third at a
later date. These are used to assess the spatial variability of the
ice core records across Berkner Island and to provide a link between
the two domes.

South Dome: The second major phase of drilling took place at a site
5km to the south of Thyseenhvhe, the southern dome of Berkner
Island. The location of the drill site was chosen to avoid the
geographical dome where a future deeper drilling is planned. Two cores
were drilled, the first (R10), 182m in length and 99mm in diameter and
a second, 101m in length was drilled alongside the first and used for
analytical techniques that require full sections of the core.

General findings: Measurements of accumulation rates, reference
horizons (such as the eruptions of Krakatoa and Tambora) and the
annual horizons have given an approximate age for the bottom of both
main cores. The north dome core: 580 years and the south dome core:
1200 years.

10m temperatures were logged in the main deep cores, and the shallower
cores. These indicate a fall of 20C between the northern dome and the
southern dome with intermediate locations lying on the same
trend. Temperatures are close to those measured on the Ronne Ice Shelf
approximately 700m lower. The higher than expected temperatures
probably indicate a persistent temperature inversion over Berkner
Island.

Full borehole temperatures were logged in both the main north dome
hole and the south dome hole. The temperature profiles show a turning
point to warmer temperatures at 70m. This is consistent with an
overall warming of the mean temperature at the site of about 0.50C in
recent decades.