HR: 17:45h
AN: PP24A-08    [Abstracts]
TI: The Growth and Decay of the Southern Lobe of the Cordilleran Ice Sheet
AU: * Hendy, I L
EM: ihendy@umich.edu
AF: University of Michigan, 2534 CC Little Building 425 E University Ave, Ann Arbor, MI 48109-1063 United States
AU: Cosma, T
EM: tcosma@umich.edu
AF: University of Michigan, 2534 CC Little Building 425 E University Ave, Ann Arbor, MI 48109-1063 United States
AB: During the last glacial, the relatively small, ephemeral Cordilleran Ice Sheet lay between the moisture source of the North Pacific Ocean and the extensive Laurentide Ice Sheet on North America. A number of important climate considerations have resulted from studies of this ice sheet including: the apparent asynchroneity of ice sheet advance around the rim of the northwest Pacific Ocean and the incredible speed of Cordilleran ice accumulation and retreat. Terrestrial records of glacial sediments have previously been the only means of evaluating the growth and decay of the Ice Sheet in response to global climate forcing. MD02-2496 (48\deg 58' N; 127\deg 02' W; 1190 meters water depth; 38.38m core length) cored on the slope of Vancouver Island, British Columbia is the first well-dated high resolution record of climate forcing and ice sheet response on the southern lobe of the Cordilleran Ice Sheet during the last glacial cycle. Evidence from magnetic susceptibility and color reflectance at MD02-2496 demonstrate that the continental slope is highly sensitive to glacially derived sediment delivery. At the same time the oxygen isotope record of surface dwelling planktonic foraminifera {\it G. Bulloides } resembles the temperature record of the Greenland Ice Sheet and provides a local themometer. At 20 cm resolution, many rapid climate events are identifiable including the Younger Dryas, Allerod and interstadial events. The presence of glacial-marine sediments in the core is demonstrated by large increases in magnetic susceptibility and concurrent shifts in sediment color from olive to grey. These indicators suggest glacial-marine sedimentation began to diminish around 15 Ka, with two small bursts of activity around 13.8 Ka and 12-12.5 Ka. Glacial marine sedimentation ceased at 10.5 Ka. This interval of glacial-marine sedimentation began around 31 Ka, with apparent ice-free conditions in southern British Columbia for much of Marine Isotope Stage (MIS) 3. A large increase in sedimentation rate occurred at 18 Ka suggesting maximum extent of the southern limb of the Cordilleran Ice Sheet at that time. Modern glacier distribution in the North Pacific is primarily controlled by topography and precipitation. Presently abundant moisture along the west coast of North America accompanies the dominant position of the jet stream by defining the main path of Pacific storms (low pressure systems). Potentially, the rapid growth of the Cordilleran Ice Sheet along the North Pacific rim was the product of precipitation from a storm track controlled by the jet stream. The data indicate that despite MIS 2 cooling by the Last Glacial Maximum (LGM; 21 Ka) the Cordilleran Ice Sheet had not yet achieved maximum extent in southern British Columbia. The maximum ice sheet growth in the region appears to require the Aleutian Low to be positioned far to the south of its present location. Rapid decay of the southern lobe of ice sheet probably occurred as storm tracks followed the jet stream northward with global climate warming. Changes in the position of the jet stream as it enters the North American continent would result from shifts in the positions and strengths of the Aleutian Low and North Pacific High, as well as growth of the Laurentide Ice Sheet.
DE: 9355 Pacific Ocean
DE: 4267 Paleoceanography
DE: 3022 Marine sediments--processes and transport
DE: 1040 Isotopic composition/chemistry
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting