Deep mixed layers dominate the upper ocean where Subantarctic Mode Water (SAMW) and Antarctic Intermediate Water (AAIW) are formed in the southeastern (SE) Pacific north of the Subantarctic Front (SAF). The cold thick layers have low salinity and high gas content that fills almost all of the southern hemisphere and tropical oceans at lower thermocline to intermediate depths. SAMW/AAIW formation has a major impact on the oceanic sink for anthropogenic CO2, whose largest uncertainty is at intermediate depths. However, AAIW is probably the only intermediate-depth, large-scale water mass that has not been studied in winter at its major source.
In this project, researchers from the University of Miami Rosenstiel School of Marine & Atmospheric Science and the University of California-San Diego Scripps Institute of Oceanography will study the processes responsible for the formation of SAMW/AAIW in the SE Pacific. Though the overall goal of the project is to characterize carbon and tracer properties in the thick SAMW/AAIW layers in the SE Pacific formation region, measurements of carbon system parameters and chlorofluorocarbons (CFCs) also be taken to: 1) map wintertime carbon system and CFC properties in the major SAMW/AAIW formation region; 2) compare the observed wintertime air-sea CO2 disequilibrium to the average disequilibrium terms estimated using the ?C* approach; 3) investigate the possible relationship of upper ocean features (e.g., convection, eddies, interleaving, currents) to the carbon and tracer characteristics of newly formed deep mixed layers of SAMW/AAIW; and 4) estimate CFC ages and a local AAIW formation rate to assess the relative effects of advection versus mixing of newly formed AAIW. The results yielded from this US and Chilean collaboration will fill an important and large gap in global ocean observations, both for physical processes that impact long-term climate change and for processes governing the carbon cycle. The results will be disseminated broadly to enhance scientific and technological understanding and will be available for use in models of processes that control the uptake and transport of anthropogenic CO2 into the ocean interior.
