Freshwater Export from the Weddell Gyre: Magnitude, Variability and Impacts

Freshwater is a key component of the climate system around Antarctica. In general, the fresher seawater is, the less dense it is, and so the injection of freshwater into the ocean controls a range of processes that include deep water formation and ocean circulation. This has implications for global and regional climate, and recent studies have shown that injecting freshwater into regions such as the Weddell Sea (adjacent to Antarctica) can influence climate as far north as the equator and beyond on timescales of just a few years. Climate models indicate that the freshwater budget at high latitudes will change as global warming progresses, but the consequences of these changes are largely unknown. Indeed, due to the difficulties of sampling the Southern Ocean, even detecting such a change here is challenging. We propose to take advantage of an already-scheduled research cruise to make comprehensive measurements of oxygen isotopes around the rim of the Weddell Gyre in the Southern Ocean. Under present climate conditions, the Weddell Gyre is a site of strong deep and bottom water formation, and also a region of strong freshwater export. The measurements of oxygen isotopes will enable us to determine the sources of the freshwater separately, with the contributions of glacial ice melt and precipitation (snow) being distinguished from the contribution of sea ice melt. By combining these measurements with ocean current speed calculations being derived separately, we will provide a benchmark quantification of the freshwater export in different layers of the Weddell Gyre. We will compare our measurements with historical measurements to determine change in any or all of the freshwater components, and interpret these changes in the context of known and expected large-scale climate change, including the changing hydrological cycle. This work is strongly collaborative, and includes workers from Florida State University, Texas A&M University and Woods Hole Oceanographic Institution in the United States. These scientists will provide access to research cruise logistics over and above those provided by UK ships alone, and will also make measurements of noble gases to complement our isotope measurements. This work thus has the potential to make very significant contributions to international science programmes, as well as being strongly relevant to UK science priorities.