Southern Ocean sourced waters modulate Eastern Equatorial Pacific denitrification during the Mid-Pleistocene transition

Abstract

The Eastern tropical Pacific holds extensive oxygen minimum zone (OMZ) areas where pelagic denitrification occurs. Sedimentary nitrogen isotopes are believed to record their denitrification history, which provides indirect evidence for the past extent of the upper ocean oxygen depletion. We present a new high-resolution sedimentary δ15N record of ODP Site 1242 located in the Eastern Equatorial Pacific during the Mid-Pleistocene Transition. The sedimentary record shows increased (decreased) denitrification during interglacial (glacial) periods and a substantial 41 kyr power. Comparing the sedimentary nitrogen signal with proxies for organic carbon supply and paleoxygenation indicates a decoupling of the denitrification from local productivity and bottom water oxygenation. We claim that this feature is a response to the extratropical ventilation of the subthermocline waters. Increased glacial AAIW influence might have provided the EEP with oxygenated and nutrient-rich waters, explaining the decreased glacial denitrification rates observed in Site 1242 and other OMZs records. Qualitative inferences about the vertical oxygen structure depict an extensive deoxygenated glacial EEP. This scenario might have contributed to the storage of the carbon captured during the glacials of the MPT.