Late Quaternary High-Frequency Variations in Sedimentary Oxygenation on the Vancouver Island Margin

Core MD02-2496 collected from the Vancouver Island margin (48 58.47' N and 127 02.14' W, 1243 m water depth) contains a high-resolution paleoenvironmental record that extends to 50 kyr BP, well beyond any other core previously recovered from the region. Hence, this core provides a unique opportunity for exploring the paleoproductivity, upwelling and sediment redox histories along the Vancouver Island margin that can then be compared to records from other cores recovered along the North American margin. Detailed records of d15N, d13C, organic C, carbonate C, and opal indicate that productivity was higher during the Holocene and Marine Isotope Stage (MIS) 3 relative to the Last Glacial Maximum (LGM). Intervals of heavy d15N, interpreted to reflect upwelling of isotopically heavy nitrate to the surface waters, correlate with d15N records from ODP Site 1017 off the southern California coast during Dansgaard-Oeschger (interstadial) events particularly in MIS 3. This suggests that heavy nitrate initially generated by denitrification in the Eastern Tropical North Pacific is carried as far north as central Vancouver Island via the California Undercurrent. Analysis of major and minor elements indicates broad scale fluctuations influenced mainly by sediment grain size and mineralogy. However, redox sensitive and/or chalcophile elements (Ag, Cd, Mo and U) show slight increases in concentration during interstadials of MIS 3, on par with slight increases in organic C and shifts toward heavier d15N. Sedimentary redox conditions on the Vancouver Island margin during the interstadials, at roughly 1.2 km water depth, may therefore reflect increased export production, consequent depletions of O2 in near-surface pore waters (and bottom water?), as well as elevated pore-water sulphide concentrations.