Gomez Nunatak

18th November 2009: Update: This study is now published as:

Thomas, E.R., Dennis, P.F., Bracegirdle, T.J. and Franzke, C., 2009, Ice core evidence for significant 100-year regional warming on the Antarctic Peninsula. Geophysical Review Letters, 36, L20704

A PDF of this paper is available for download below.
The individual sample oxygen isotope data (2314 analyses) and associated core depths are available as a CSV file below.

The Antarctic Peninsula (AP) region has experienced dramatic changes in climate over the period of the observational record: the past 50 years. It is essential to determine whether this strong late 20th century warming in the AP region reflects, in part, a response to anthropogenically driven, globally averaged warming, or if it is consistent with past climate variability in the region. The necessary time perspective can be constructed from proxy records based on the chemical and physical properties preserved in the regional ice cover.

In early 2007 a new medium depth ice core (136m) was drilled in a high accumulation site (73.59oS, 70.36oW) on the south-western Antarctic Peninsula (Thomas et al., 2008). The core extends back more than 150 years in time to 1855.

During 2008 we have measured the 18-O and 2-H composition of ice from Gomez, sampled at 7cm intervals. In all more than 2000 analyses were completed  giving a resolution of better than monthly throughout the whole core. The annual cyclicity in the oxygen isotope signal is excellently preserved allowing us to date individual layers with a precision to better than +/- 1 year for most of the cores length.

In the figure below I have plotted the annual mean oxygen isotope composition as a function of the year of precipitation. Results for individual years are plotted as the dashed line, and a 10-year running mean as the solid line. It is clear that there is significant structure and cyclicity to the data with a multi-decadal wavelength. Moreover, there is a trend towards more 18-O enriched compositions that matches the warming temperature trend that has previously reported. We expect to see an increase of 0.5 per mille per degree C in the mean annual average isotope composition with warming temperatures. Thus our data translates to an approximate 3 degree C warming.

We are busy analysing and interpreting the data. Our preliminary work shows that the isotope compositions are strongly correlated with i) The accumulation rate at Gomez and ii) the 50 year record of temperatures recorded from Faraday Station. Analysis of the accumulation rate by Thomas et al. (2008) shows a strong and temporally stable relationship with the Southern Annual Mode (SAM). The SAM mode has become more positive during the austral summer and autumn (Thompson and Solomon, 2002; Marshall, 2003). The resultant increase in westerlies is believed to be a primary cause of enhanced warming in the north-east peninsula. It is too early to say yet if the warming recorded at Gomez is the result of anthropogenic effects.

Paul Dennis,
Nov 19, 2009, 9:21 AM
Paul Dennis,
Jun 13, 2012, 10:47 AM
Paul Dennis,
Nov 19, 2009, 9:21 AM