HR: 09:15h
AN: PP21E-06    [Abstracts]
TI: The Freshening of Surface Waters in High Latitudes: Effects on the Thermohaline and Wind-driven Circulations
AU: * Fedorov, A
EM: alexey.fedorov@yale.edu
AF: Department of Geology and Geophysics, Yale University, KGL, New Haven, CT 06511 United States
AU: Philander, G
EM: gphlder@Princeton.edu
AF: AOS, Department of Geosciences, Princeton University, Sayre Hall, Princeton, NJ 08544 United States
AU: Pacanowski, R
EM: Ronald.Pacanowski@noaa.gov
AF: GFDL, Forrestal Campus, Princeton, NJ 08544 United States
AU: Boccaletti, G
EM: gbocca@mit.edu
AF: Earth, Atmospheric and Planetary Sciences, MIT, 77 Massachusetts Ave, Cambridge, MA 02139 United States
AB: The impacts of a freshening of the surface waters in high latitudes on the deep, slow, thermohaline circulation have received enormous attention, especially the possibility of a "shut-down" in the meridional overturning that involves sinking of surface waters in the northern Atlantic. A recent study (Fedorov et al 2004) has drawn attention to the effects of a freshening on the other main component of the oceanic circulation - the swift, shallow, wind-driven circulation with which is associated the ventilated thermocline and which can vary on decadal timescales. That circulation too involves meridional overturning with surface waters sinking in certain subduction zones, but its "shut-down" affects mainly the tropics. A freshening can deepen the equatorial thermocline to such a degree that temperatures along the equator become as warm in the eastern as western part of the basin, so that the zonal SST gradient virtually disappears and permanently warm (El Niño-like) conditions prevail in the tropics. In a model that has both the wind-driven and thermohaline components of the circulation, which factors determine the relative effects of a freshening on the two components and its impact on climate? Studies using an idealized oceanic GCM to address this question find that the vertical diffusivity of a model is a critical parameter: for large values the impact is mainly on the thermohaline component, for small values mainly on the wind-driven circulation. The spatial structure of the surface freshwater forcing and imposed meridional temperature gradients are other important factors.
DE: 4263 Ocean predictability and prediction (3238)
DE: 4532 General circulation (1218, 1222)
DE: 4962 Thermohaline
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005