Increased Subduction of Subantarctic Mode Water and Antarctic Intermediate Water during the LGM, Using NCAR-CCSM3
Abstract
Presently, Subantarctic Mode Water (SAMW) and Antarctic Intermediate Water (AAIW) are large-volume intermediate water masses that transport climatically important properties such as heat, freshwater, and CO2 equatorward into the Southern Hemisphere subtropical gyres. Some of the freshest and coldest SAMW and AAIW formed in today's oceans are found in the southeast Pacific. The objective of this study was to understand how subduction of SAMW and AAIW may have changed between the Last Glacial Maximum (LGM) and preindustrial (PI) period in the South Pacific. The LGM, in particular, is characterized by increased sea-ice cover and increased westerly wind stress, which directly influence subduction of SAMW and AAIW. The NCAR-CCSM3 PI and LGM simulations (~ 21 kyr) were used to quantify the heat and buoyancy flux contributions to subduction of SAMW and AAIW. Mean annual subduction rates were calculated by evaluating contributions to a buoyancy budget that includes heat and freshwater fluxes, and Ekman advection of density in both the vertical and horizontal. During the LGM simulation, SAMW and AAIW exhibit increased subduction rates, almost double the PI rates. Increased subduction during the LGM was due to a substantial contribution from changes between the PI and LGM in Ekman heat transport. Changes in buoyancy fluxes of both heat and freshwater over the outcropping regions of SAMW and AAIW also make an important contribution to the increased subduction rates during the LGM. Despite model limitations, these results agree well with the limited paleo evidence available within the South Pacific. The model results can provide a better understanding of the processes controlling the subduction of SAMW and AAIW during different climatic periods.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2011
- Bibcode:
- 2011AGUFMPP14B..07H
- Keywords:
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- 4512 OCEANOGRAPHY: PHYSICAL / Currents;
- 4928 PALEOCEANOGRAPHY / Global climate models