HR: 0800h
AN: PP31A-0903    [Abstracts]
TI: The Impact of the Opening of the Bering Strait on the Atlantic Fresh Water Budget and Climate
AU: * Sandal, C K
EM: sandal@ocean.fsu.edu
AF: Department of Oceanography, Florida State University, 0102 OSB, West Call Street, Tallahassee, FL 32306-4320 United States
AB: It is often suggested that reorganizations of the overturning circulation is the cause of abrupt climate changes. Such a re-organization probably happened in the early Holocene when mean Greenland temperatures suddenly increased. We hypothesize that the abruptness of the temperature change in the early Holocene, and the increase in mean temperature is due to the opening of the Bering Strait (BS), which plays a pivotal role in the re-organization. With a present day depth of merely 50 meters, the strait opens and closes with deglaciation/glaciation (which cause changes of as much as 140 meters in the sea level). We use laboratory experiments and climate models to examine this idea. Assuming that the oceans are in a state of the Last Glacial Maximum (LGM) and that the BS Strait is initially closed, deglaciation starts melting continental ice sheets. This melt water finds its way to the North Atlantic creating a low salinity surface layer, which inhibits convection. Since the BS is closed, this anomaly cannot be flushed out of the system quickly, and convection would recover only after a few hundred or thousand years (via processes such as diffusion). However, as deglaciation continues, global sea level rises and eventually opens the BS. The pressure head created on the Atlantic side by the Southern Ocean winds attempts to flush this low salinity layer out into the Pacific. As it does this, icebergs in the vicinity of the BS move towards the strait creating a temporary dam, because the water level is too shallow to allow them to pass through. Global temperatures continue to rise and eventually the pressure head on the Arctic side is able to break this temporary dam, flushing the low salinity layer into the Pacific and kick starting convection in the North Atlantic. A simple laboratory box model is used to investigate this temporary dam and it's subsequent release. This experiment was done for five different strait widths, using polyethylene balls as icebergs. For each width we see the temporary damming effect, as mentioned earlier, releasing abruptly once the pressure head on the Arctic side is large enough to force both balls and water through. Increasing the width of the strait decreases the number of temporary dam occurrences as well as the length of each occurrence. The transition from LGM to Holocene conditions is examined using the University of Victoria Earth System Climate Model (Uvic ECSM). Specific focus is placed on recreating (1) a reversal of flow through the Bering Strait, (2) an increase in mean atmospheric and oceanic temperature in the North Atlantic and (3) a resumption of convection in the North Atlantic.
DE: 4267 Paleoceanography
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting