A 700-Year Record of Atmospheric Circulation Developed from the Law Dome Ice Core, East Antarctica

A 700-year, high-resolution, multivariate ice core record from Dome Summit South (DSS) (66degrees46'S, 112degrees48'E; 1370 m), Law Dome, is used to investigate sea level pressure (SLP) variability in the region of East Antarctica. Empirical orthogonal function (EOF) analysis reveals that the first EOF (LDEOF1) of the combined glaciochemical, oxygen isotope ratio, and accumulation rate record from DSS represents most of the variability in sea salt seen in the record. LDEOF1 is positively correlated (at least 95% confidence level) to instrumental June mean SLP across most of East Antarctica. Over the last 700 years, LDEOF1 levels at Law Dome were the highest during the nineteenth century, suggesting an increase in intensification of winter circulation during this period. The Law Dome DSS oxygen isotope ratio series also indicates that the nineteenth century had the coldest winters of any century in the record. In contrast, LDEOF1 levels were the lowest at Law Dome during the eighteenth century, suggesting a significant shift in the patterns and/or intensity of East Antarctic atmospheric circulation between the eighteenth and the nineteenth centuries. The LDEOF1 sea salt record is characterized by significant decadal-scale variability with a strong 25-year periodic structure.

Post-Depositional Movement of Methanesulphonic Acid at Law Dome, Antarctica, and the Influence of Accumulation Rate

A series of ice cores from sites with different snow-accumulation rates across Law Dome, East Antarctica, was investigated for methanesulphonic acid (MSA) movement. The precipitation at these sites (up to 35 km apart) is influenced by the same air masses, the principal difference being the accumulation rate. At the low-accumulation-rate W20k site (0.17 in ice equivalent), MSA was completely relocated from the summer to winter layer. Moderate movement was observed at the intermediate-accumulation-rate site (0.7 in ice equivalent), Dome Summit South (DSS), while there was no evidence of movement at the high-accumulation-rate DE08 site (1.4 in ice equivalent). The main DSS record of MSA covered the epoch AD 1727-2000 and was used to investigate temporal post-depositional changes. Co-deposition of MSA and sea-salt ions was observed of the surface layers, outside of the main summer MSA peak, which complicates interpretation of these peaks as evidence of movement in deeper layers. A seasonal study of the 273 year DSS record revealed MSA migration predominantly from summer into autumn (in the up-core direction), but this migration was suppressed during the Tambora (1815) and unknown (1809) volcanic eruption period, and enhanced during an epoch (1770-1800) with high summer nitrate levels. A complex interaction between the gradients in nss-sulphate, nitrate and sea salts (which are influenced by accumulation rate) is believed to control the rate and extent of movement of MSA.