Changes in redox conditions in deep‐sea sediments of the subarctic North Pacific Ocean: Possible evidence for the presence of North Pacific Deep Water

Cores of upper Quaternary and Holocene sediment from the subarctic North Pacific north of about 48°N contain one or more layers of oxidized brown sediment interbedded within predominantly reduced green sediment. The brown layers are enriched in several trace elements, especially Mn, Mo, Ni, and Co, relative to the green layers. Where multiple oxidized layers are present, the intensity of the brown coloration and the magnitude of trace element enrichment often decrease with depth, suggesting that the oxidized layers are unstable and are being chemically reduced at depth. The oxidized layers represent a change in redox conditions between the North Pacific red clay province and the subarctic biosiliceous green clay province. The redox change may have been caused by an increase in supply of dissolved oxygen to bottom waters during glacial‐interglacial transitions as the result of the periodic formation of a seasonal bottom water mass in the northeastern Pacific Ocean.