Dr. Xiaojun Yuan
Earth Institute Contact: Dr. Xiaojun Yuan
The goal of this study is to examine impacts of surface processes such as sea ice export, sea ice concentration variability, ice shelf breakups, and changes in surface wind and air temperature on the interannual variability of the Antarctic Bottom Water (AABW) exports in the Weddell Sea, which have been observed by deep sea moorings in the western Weddell Gyre for six years.
The global abyssal ocean is filled with cold, dense water that originated from the Antarctic marginal seas. This water is called the Antarctic Bottom Water (AABW), which is formed by the near surface water on the continental shelf mixing while sinking along the continental slope. The Weddell Sea has the largest amount of the AABW production around Antarctica each year. By spreading into the deep part of the world’s oceans, the AABW links surface climate variability in the Polar Regions with lower latitudes, affecting global circulation.
To observe the changes in properties and strength of the outflow of Weddell Sea Deep and Bottom Waters, three deep-sea moorings have been deployed in the Western Weddell Sea, measuring temperature, salinity and current since 1999. Six years of data (April 1999 to April 2005) reveal that the production of the Weddell Sea AABW varies seasonally and interannually. The coldest pulses occurred in the winters of 1999 and 2002, while 2000 winter lacked a cold event. During this period, the Larsen B ice shelf breakups occurred mainly in two periods: from 15 February 1998- 18 March 1999, and from January 31 to March 7, 2002. Observed coldest pulses in the AABW followed the Larsen B ice shelf breakups, indicating the impact from the breakups on the bottom water formation. A numbers of questions arise. How does the Larsen B ice shelf breakup affect surface processes that influence the bottom water formation? What are the roles of surface winds and air temperature in the formation processes of the AABW? Do ice shelf breakups affect sea ice distribution in the Weddell Sea? Is the sea ice export from the Weddell Gyre an indicator of the bottom water formation? Is any surface process related to the lack of a cold event in 2000?
We plan to use a set of data ranging from surface weather stations / automatic weather station data, satellite observed sea ice concentration / sea ice drift data, and ECMWF surface winds and air temperature data to address these questions. An undergraduate student can participate this project by establishing the relationships between sea ice export and the AABW variability, between surface winds/air temperature and AABW properties, and between Larsen B ice shelf breakups and variability in sea ice concentration/sea ice export in the Weddell Gyre. Since most data exist in local computers, the student can finish the project in nine weeks. Yuan will be available most of time during the nine-week period.