HR: 16:45h
AN: GC44A-04    [Abstracts]
TI: Response of Thermohaline Circulation to Freshwater Forcing under Present Day and LGM Conditions
AU: * Hu, A
EM: ahu@ucar.edu
AF: National Center for Atmospheric Research, 1850 Table Mesa Dr., Boulder, CO 80021, United States
AU: Otto-Bliesner, B L
EM: ottobli@ucar.edu
AF: National Center for Atmospheric Research, 1850 Table Mesa Dr., Boulder, CO 80021, United States
AU: Meehl, G A
EM: meehl@ucar.edu
AF: National Center for Atmospheric Research, 1850 Table Mesa Dr., Boulder, CO 80021, United States
AU: Han, W
EM: whan@colorado.edu
AF: University of Colorado at Boulder, Campus Box 311, Boulder, CO 80309, United States
AU: Morrill, C
EM: carrie.morrill@noaa.gov
AF: NOAA National Climatic Data Center, 325 Broadway, Boulder, CO 80305, United States
AU: Brady, E C
EM: brady@ucar.edu
AF: National Center for Atmospheric Research, 1850 Table Mesa Dr., Boulder, CO 80021, United States
AU: Briegleb, B
EM: bruceb@ucar.edu
AF: National Center for Atmospheric Research, 1850 Table Mesa Dr., Boulder, CO 80021, United States
AB: Responses of the thermohaline circulation (THC) to freshwater forcing (hosing) in the subpolar North Atlantic Ocean under present day and the last glacial maximum (LGM) conditions are investigated using the National Center for Atmospheric Research Community Climate System Model versions 2 and 3. Three sets of simulations are analyzed, with each set including a control run and a freshwater hosing run. The first two sets are under present day conditions with an open and closed Bering Strait. The third one is under LGM conditions, which has a closed Bering Strait. Results show that the THC nearly collapses in all three hosing runs when the freshwater forcing is turned on. The full recovery of the THC, however, is at least a century earlier in the open Bering Strait run than the closed Bering Strait and LGM runs. This is because the excessive freshwater is diverged almost equally towards north and south from the subpolar North Atlantic when the Bering Strait is open. A significant portion of the freshwater flowing northward into the Arctic exits into the North Pacific via a reversed Bering Strait throughflow, which accelerates the THC recovery. When the Bering Strait is closed, this Arctic to Pacific transport is absent and freshwater can only be removed through the southern end of the North Atlantic. Together with the surface freshwater excess due to precipitation, evaporation, river runoff, and melting ice in the closed Bering Strait experiments after the hosing, the removal of the excessive freshwater takes longer, and this slows the recovery of the THC. Although the background conditions are quite different between the present day closed Bering Strait run and the LGM run, the THC responds to the freshwater forcing added in the North Atlantic in a very similar manner.
DE: 1605 Abrupt/rapid climate change (4901, 8408)
DE: 1620 Climate dynamics (0429, 3309)
DE: 1626 Global climate models (3337, 4928)
DE: 4901 Abrupt/rapid climate change (1605)
DE: 8408 Volcano/climate interactions (1605, 3309)
SC: Global Environmental Change [GC]
MN: 2007 Fall Meeting