Project: Characterizing the Formation, Nature, and Export of Weddell Sea Bottom Water using Noble Gases and Transient Tracers

NSF Award Abstract:

Intellectual Merit: It is commonly accepted that since at least the last glacial maximum, the substantial millennial-timescale changes in global climate have been caused by, or at least associated with abrupt changes in the oceanic Meridional Overturning Circulation (MOC). There is the lingering suspicion that perhaps the ultimate trigger of the climate transients may lie in the southern hemisphere. Dense waters formed by buoyancy modification on Antarctic shelf regions leave the shelves and sink to comprise the major water mass complex known as Antarctic Bottom Water (AABW). AABW, the coldest and densest water to play a role in the MOC, in turn enters all of the major ocean basins and thereby closes the southern end of the MOC loop. The Weddell Sea features prominently in the production of AABW, where interaction between seawater and the floating ice-shelves produces a unique pre-cursor to AABW by a combination of processes, including) strong heat extraction at ice-edge polynyas, sea-ice formation and export, melting of glacial ice at the grounding line, and formation and deposition of sub-marine sea-ice. These processes not only produce oceanographically and climatically significant injections of fresh water into the AABW pre-cursor, but are hypothesized to have significant impact on its dissolved noble gas composition. We propose to use high precision measurements of the latter as a diagnostic tool of the magnitude of these processes.

The investigator will participate in a British research cruise ANDREX which is a section connecting the CLIVAR (CLImate VARiability and predictability Program) repeat line I6S with the Antarctic Peninsula in early 2009. The cruise follows the northern rim of the Weddell Sea gyre, and is ideally situated to study the exchange of water masses across the Antarctic Circumpolar Current. A combination of noble gases, transient tracers (tritium and radiocarbon) along with CFCs, stable isotopes, 3He, and traditional hydrographic measurements will be used to place constraints on an oceanographically and climatically important region.

Broader Impacts: This project involves the development and use of novel oceanographic tracers and the application of more traditional tracers in new ways to characterize water mass transformation processes that are of fundamental importance in the operation of the global climate system. The new insights into these processes will provide valuable guidance in the design and construction of the next generation of coupled ocean-atmosphere climate models, which will be of strategic importance in facing the broad range of economic, policy, and societal issues created by climate change. The data set produced in this work will be submitted to the appropriate data centers/repositories to be made available to modelers and climate scientists to guide future research efforts and to evaluate or test existing and future climate models.