Ice Core Climate Record: Merging the Historical with the Last 1000 Years and Beyond

Sunday, 16 February 2014
Columbus CD (Hyatt Regency Chicago)
Ellen Mosley-Thompson , Ohio State University, Columbus, OH
An ice core drilled to bedrock (448.12 m) in 2010 on the Bruce Plateau (BP) ice field (66.03°S; 64.07°W; 1975.5 masl) in the northern Antarctic Peninsula (AP) is the second ice core to reach bedrock in the AP and thereby capture the entire preserved record. The few multi-century ice core records from the AP extend back at most 500 years. The annual mass accumulation on the BP is high (~1.8 m w.e. from 1900 to 2009) facilitating precise dating by layer counting back to 1400 CE.  Assisted by known volcanic eruptions the annually resolved history is extended back to 1250 CE.

Annually resolved records of stable isotopic content (δ18O and δD) and mass accumulation provide proxy-based histories of temperature and precipitation. Comparisons with regional meteorological observations indicate that the BP δ18O record provides a reliable proxy of mean annual air temperature along the west side of the AP.  The resulting δ18O-inferred air temperatures for the last 600 years reveal multi-decadal scale variability with warm conditions during some periods exceeding that of the last few decades. Extracting the annual accumulation history is complicated by layer thinning at depth.  A Dansgaard-Johnsen model configured for flank flow is used to reconstruct annual layer thicknesses. The resulting record indicates that average annual mass accumulation (precipitation) rises from ~1400 to ~1800 CE (~2.3 m w.e.) and thereafter declines to a minimum (~1.5 m w.e.) around 1950 CE. Accumulation then rises rapidly to its maximum value (~2.6 m w.e.), consistent with recent accumulation increases in several other ice core-derived accumulation records in the AP.

The Antarctic Peninsula is characterized by a sharp west to east gradient in both atmospheric and oceanographic conditions that create a marked trans-Peninsula contrast in precipitation and to a lesser extent in winter temperature.  Thus comparison with the James Ross Island (JRI) ice core drilled to bedrock in 2008 by British scientists offers a unique opportunity to examine the history of regional climate conditions, including the Antarctic Dipole that influences interannual climate variability in the AP.  For example, ENSO brings warmer anomalies to the western side and colder anomalies to the eastern side of the AP.  These regional (west to east) climate differences are further emphasized by the virtual absence of surface melting at the BP site that is concomitant with a recent acceleration of snow melt as recorded in the JRI core.