[ESS Colloquium] Orsi (Scripps): "Gas isotopes and borehole thermometry in West Antarctica"

Start Date/Time: Thursday, May 05, 2011, 3:30 PM
Location: JHN 102

Anais Orsi, a senior graduate student with Jeff Severinghaus at Scripps, will be giving the ESS colloquium on Thursday, May 5th at 3:30 in Johnson 102.

Anais will speak about her innovative work combining 15N of gas in ice cores with borehole thermometry to obtain a state-of-the art paleotemperature history in Antarctica.

Anais will be around much of the week, and you can contact Eric Steig (steig@uw) if you would be interested in meeting with her.

Abstract:

We present a record of temperature and accumulation at WAIS Divide for the last 1000 years using noble gas isotopes.

The isotopes of nitrogen, argon and krypton in air bubbles reflect changes in the firn thickness as well as temperature gradients between the surface and the depth at which bubbles close. We used krypton and argon isotopes in WDC05A to estimate changes in the firn thickness, which is sensitive to both temperature and accumulation. The results are consistent with estimates of the accumulation rate obtained from layer counting, and they provide a useful constraint on firn densification models. d15N from WDC06A was then corrected and integrated to produce an estimate of surface temperature over time. In addition, observed borehole temperature from the 300m WDC05A hole provides an independent long term surface temperature record. Both methods agree well, and provide a test of the validity of d18Oice as a thermometer. The results show that West Antarctic centennial mean temperature was cooling from 1000 to 1765 (+-20) CE , and has been on a long term warming trend since. There is significant multi-decadal variability in temperature, with an amplitude of at least 0.5C. The recent warming trend of 0.29C/decade since 1958, established by Steig et al (2009) is confirmed by this work, and placed in the broader context of the last millennium.