Northeastern Pacific oxygen minimum zone variability over the past 70 kyr: Impact of biological production and oceanic ventilation
Résumé
During the last glacial period, the Oxygen Minimum Zone (OMZ) within the northeastern Pacific Ocean strengthened and weakened on a millennial time scale, demonstrating a tight linkage with northern high latitude climate, although the precise mechanisms responsible remain unknown. Core MD02-2508, retrieved off Baja California, was analyzed for major and trace elements (Br, Ca, Ti, Fe, Mn, and Sr) using a XRF scanner and redox-sensitive trace elements (Cu, Ni, Cd, As, V, Cr, Mo, and U) using the ICP-MS. The trace element content, the Fe/Ti ratio, and Br-based organic carbon exhibit higher values during the Holocene and during warm Dansgaard-Oeschger events than during the Last Glacial Maximum (LGM), stadials, and Heinrich (H) events. A principal component analysis of the element/Al ratio indicated that the following two main factors controlled the chemical composition of the sediments: (1) export production, as represented by organic carbon, that was lower during cold periods; and (2) regional intermediate water oxygenation, as represented by U and Mo variability, that was not supported by a change in export production. The latter suggests that intermediate water oxygenation improved during H events, but slightly deteriorated during late Marine Isotope Stage (MIS) 3 and MIS 2. A local biogeochemical effect, forced by atmospheric processes, impacted the LGM and H events in the same manner. Whereas regional intermediate oceanic circulation varied in an opposite manner during the LGM and H events, possibly as a result of the global reorganization of intermediate water circulation during the LGM.
Domaines
Océan, Atmosphère
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