ABSTRACT: The Pacific Decadal Oscillation and the growth and decay of the Cordilleran Ice Sheet during the Last Glacial.

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Late Quaternary growth and decay of the Cordilleran Ice Sheet left substantial terrestrial sedimentary deposits in the American Northwest and although this ice sheet has been the subject of numerous studies, the interaction between global climate and local ice sheet growth and decay is not fully understood. MD02-2496, drilled off the coast of Vancouver Island, Canada, (48 58'N; 127 02'W; 1190m water depth; 38.38m core length) provides the first high resolution Late Quaternary record of northeast Pacific ocean response to climate change that can be precisely correlated with Cordilleran Ice Sheet dynamics. Preliminary results indicate MD02-2496 contains a significant record of climate variability that shares many similarities with Greenland delta{18}O records. From the base of the core to 31.5m terrigenous sediments dominate. Numerous drop stones, high magnetic susceptibility and delta{18}O values suggest glacial conditions From 25-31.5m, higher Corg/terrigenous ratios are suggested by color reflectivity and low magnetic susceptibility similar to that of the core top. delta{18}O values decrease during this interval and demonstrate unprecedented variability similar to the widely documented MIS 3 interstadial events. Magnetic susceptibility increases at 25m prior to an interstadial event (possibly IS 2). The sudden occurrence of bedded turbidite layers at 19.5m appears co-incident with high delta{18}O values suggesting the Last Glacial Maximum. The incidence of turbidites decreases upcore to 7m. A dramatic shift in delta{18}O toward lower values occurs at 9.5m marking the Bolling. The upper 7m of the core contains sediments with the same distinct color reflectivity shift and low magnetic susceptibility seen between 25 and 31.5m. Tentative interpretation of these early results suggests the core bottom (31.5 m +) preserves the first record of a possible MIS 4 glacial advance in the Juan de Fuca lobe. The interstadial events recorded in MIS 3 (25-31.5m) suggest glacial retreat and a return to a high sedimentary Corg/terrigenous ratio. The increase in magnetic susceptibility at 25m appears coincident with regional ice sheet growth, while the turbidite sequence beginning at 19.5m possibly signifies the maximum ice extent (20 ka) with the engulfing of Vancouver Island and ice expansion on the continental shelf. The sudden shift of delta{18}O at 9.5m probably correlates with the B\philling and subsequent rapid decay of the Cordilleran Ice Sheet with modern oceanic conditions returning at 7m.

Bibliography of Canadian Geomorphology