Just out @ Paleoceanography
The intensity of the Oxygen Minimum Zone (OMZ) of the Eastern North Pacific (ENP) experienced strong variations during the last Glacial, mirroring changes in the balance between export production (O2-consumption) and water mass ventilation (O2-renewal). In this paper we present a new benthic foraminiferal assemblages record from Core MD02-2508, recovered from the Pacific slope off Baja California, Mexico. The record reflects oxygen conditions at the northern limit of the OMZ during the last 80 kyr. We statistically identified three assemblages, characteristic of dysoxic, suboxic and oxic conditions, which we used to produce the first semi-quantitative reconstruction of [O2] for the northeastern Pacific Ocean. Our results show that the estimated [O2] co-varies with δ18O records from the North Greenland Ice Core Project [NGRIP, Johnsen et al., 2001]. Oxygen concentrations overall exhibit moderate values (~1 ml.L-1) during stadials, reaching ~ 2 ml.L-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-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 [O2] during interstadials (stadials), suggesting a relationship between both parameters during these intervals. The influence of ventilation on oxygenation is also a key player. O2-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 modelling-based oceanic circulation reconstructions.
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