Site information and initial results from deep ice drilling on Law Dome, Antarctica

TLDR

The study aimed to drill deep ice at Law Dome’s summit to obtain a high‑resolution core for Holocene and Last Glacial Maximum climatic and environmental analyses. They drilled to 1196 m in the cold, high‑accumulation ice divide, employing annual‑layer counting, sulphate and conductivity measurements, and an ice‑flow model to date the core. The 1196‑m core, drilled in 1993, contains basal rock fragments and continuous annual‑layer dating to 399 m (AD 1304); sulphate and conductivity data confirm volcanic eruptions and support dating of others, while ice‑fabric and δ18O analyses show a 7.0‰ LGM/Holocene shift and a 250‑to‑14 mm² crystal‑size reduction, indicating Law Dome remained an independent ice cap during the glacial.

Abstract

Abstract The aim of deep ice drilling on Law Dome, Antarctica, has been to exploit the special characteristics of Law Dome summit, i.e. low temperature and high accumulation near an ice divide, to obtain a high-resolution ice core for climatic/environmental studies of the Holocene and the Last Glacial Maximum (LGM). Drilling was completed in February 1993, when basal ice containing small fragments of rock was reached at a depth of 1196 m. Accurate ice dating, obtained by counting annual layers revealed by fine-detail δ 18 О, peroxide and electrical-conductivity measurements, is continuous down to 399 m, corresponding to a date of AD 1304. Sulphate concentration measurements, made around depths where conductivity tracing indicates volcanic fallout, allow confirmation of the dating (for Agung in 1963 and Tambora in 1815) or estimates of the eruption date from the ice dating (for the Kuwae, Vanuatu, eruption ~1457). The lower part of the core is dated by extrapolating the layer-counting using a simple model of the ice flow. At the LGM, ice-fabric measurements show a large decrease (250 to 14 mm 2 ) in crystal size and a narrow maximum in c -axis vertically. The main zone of strong single-pole fabrics however, is located higher up in a broad zone around 900 m. Oxygen-isotope (δ 18 O) measurements show Holocene ice down to 1113 m, the LGM at 1133 m and warm (δ 18 O) about the same as Holocene) ice near the base of the ice sheet. The LGM/Holocene δ 18 O shift of 7.0‰, only ~1‰ larger than for Vostok, indicates that Law Dome remained an independent ice cap and was not overridden by the inland ice sheet in the Glacial.