Resumen del producto

Eastern Tropical North Pacific have showed evidence of millennial-scale variabil-ity of the oxygen minimum zone in relation to abrupt climate variability as observed inthe North Atlantic Ocean with oxygen depletion occurring during interstadial events, andinterglacial rather than stadials, Heinrich events, and last glacial. Changes in marine pro-ductivity, induced by wind-driven upwelling variations, and ventilation of the water column(dissolved oxygen transport by oceanic advection via North Pacific Intermediate Water orSouthern Ocean) have been proposed to modulate past oxygen minimum zone variabil-ity through oxygen consumption and inputs. In this study, we present new stable isotoperecords for two sites spanning the 550-700 m depth range along the southwestern margin ofBaja California. Hence, the multicores collected were present allow us to constrain the den-itrification of the last 1400 years (Medieval Climate Anomaly, Little Ice Age and Present)from Soledad Basin and Magdalena margin. The results indicate that both areas the den-itrification was similar during the Medieval Warming. In the Little Ice Age, Magdalenamargin showed a decrease in denitrification with respect to Soledad basin. The variabilityin the sedimentary d15N was a product of denitrification in the water column and not byearly diagenesis. The biogenic silica content in both sites was very similar during the LittleIce Age, so that primary productivity was not the causative mechanism of denitrification.This suggests that denitrification differential between the two sites was due to the ventila-tion of the water column in the range of 550 to 700 m depth. Thus both export productionand intermediate water ventilation play a role in oxygen minimum zone processes on theEastern Tropical North Pacific.

Palabras clave: Little Ice Age; Eastern Tropical North Pacific; Medieval Warming; oxygen minimum zone; denitrification

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