Oxygen history off Baja California over the last 80 kyr: A new foraminiferal-based record: Oxygen History in the California Margin

The intensity of the Oxygen minimum zone (OMZ) of the eastern North Paci fi c (ENP) experienced strong variations during the last glacial, mirroring changes in the balance between export production (O 2 consumption) and water mass ventilation (O 2 renewal). In this paper we present a new benthic foraminiferal assemblages record from Core MD02-2508, recovered from the Paci fi c slope off Baja California, Mexico. The record re fl ects oxygen conditions at the northern limit of the OMZ during the last 80kyr. We statistically identi fi ed three assemblages, characteristic of dysoxic, suboxic, and oxic conditions, which we used to produce the fi rst semiquantitative reconstruction of [O 2 ] for the northeastern Paci fi c Ocean. Our results show that the estimated [O 2 ] covaries with δ 18 O records from the North Greenland Ice Core Project. Oxygen concentrations overall exhibit moderate values (~1mL.L (cid:1) 1 ) during stadials, reaching ~2 mL.L (cid:1) 1 during stadials corresponding to Heinrich events in the Atlantic Ocean. Conversely, bottom waters at the core location were strongly depleted in oxygen ( < 0.5 mL.L (cid:1) 1 ) during interstadials. Benthic foraminiferal abundance increased with higher export production as recorded by geochemical tracers (Cd/Al ratio). This export production signal increases (decreases) with a fall (rise) in [O 2 ] during interstadials (stadials), suggesting a relationship between both parameters during these intervals. The in fl uence of ventilation on oxygenation is also a key player. O 2 pulses suggested by the downcore records of serial/spiral test ratio and abundance of oxic species may be explained by enhanced ventilation during Heinrich stadials, in agreement with latest modeling-based oceanic circulation reconstructions.