Northeastern Pacific oxygen minimum zone variability over the past 70 kyr: Impact of biological production and oceanic ventilation

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.