HR: 14:25h
AN: OS23F-04    [Abstracts]
TI: Variable Subduction Rates of North Atlantic Salinity Maximum Water
AU: * Fine, R A
EM: rfine@rsmas.miami.edu
AF: University of Miami, Rosenstiel Schol of Marine and Atmospheric Science, 4600 Rickenbacker Causeway, Miami, FL 33149-1098 United States
AU: Willey, D A
EM: dwilley@rsmas.miami.edu
AF: University of Miami, Rosenstiel Schol of Marine and Atmospheric Science, 4600 Rickenbacker Causeway, Miami, FL 33149-1098 United States
AU: Happell, J
EM: jhappell@rsmas.miami.edu
AF: University of Miami, Rosenstiel Schol of Marine and Atmospheric Science, 4600 Rickenbacker Causeway, Miami, FL 33149-1098 United States
AB: Data from programs back to 1982, and most recently the 2003-04 Repeat Hydrography, Tracer, CO$_{2}$ program are used to highlight the role tracer data can have in monitoring decadal variability of ocean circulation. The CFC data are used to document changes in thermocline ventilation, and specifically the affect increased thermocline salinity is having, if any, on Salinity Maximum Water (SMW) subduction rates in the North Atlantic Ocean. Hydrobase data show a long term trend of increasing salinity in the North Atlantic thermocline since the 1950s, and in particular in SMW. SMW is located in the subtropical/tropical north Atlantic under the evaporation minus precipitation maximum. Since SMW are the most saline of the thermocline waters, no source for additional salt exists within the ocean. Subduction rates have been calculated for SMW from 1982-2004 CFC data at stations where there was a subsurface salinity maximum present. The subduction rate for an isopycnal projected back to its outcrop, is calculated from the inverse tracer age gradient corrected for vortex stretching. Subduction rates vary from 10 to 40 m/year. The results show a pattern of changing subduction rates that correlate well with the NAO index. Since salinity seems to have been steadily increasing, though at different rates, it appears that local fresh water variability is not the major forcing effect on the subduction process. The 1990s rise in evaporation rate coincided with a prolonged high state of the North Atlantic Oscillation index (NAO). The associated increase in trade winds will have enhanced both evaporation and Ekman pumping of waters into the upper ventilated thermocline. Consistent with model results, the observational based calculations suggest that increased (decreased) wind stress curl accompanying an increased (decreased) NAO has the major forcing effect on SMW subduction variability.
DE: 4500 OCEANOGRAPHY: PHYSICAL
DE: 4512 Currents
DE: 4532 General circulation
DE: 4572 Upper ocean processes
DE: 4599 General or miscellaneous
SC: Ocean Sciences [OS]
MN: 2004 AGU Fall Meeting