Climatically related millennial-scale fluctuations in strength of California margin oxygen-minimum zone during the past 60 k.y.

A strong oxygen-minimum zone (OMZ) currently exists along the California ma rgin because of a combination of high surface-water productivity and poor i ntermediate-water ventilation. However, the strength of this OMZ may have b een sensitive to late Quaternary ocean-circulation and productivity changes along the margin, Although sediment-lamination strength has been used to t race ocean-oxygenation changes in the past, oxygen levels on the open margi n are not sufficiently low for laminations to form. In these regions, benth ic foraminifera are highly sensitive monitors of OMZ strength, and their fo ssil assemblages can be used to reconstruct past fluctuations. Benthic fora miniferal assemblages from Ocean Drilling Program Site 1017, off Point Conc eption, exhibit major and rapid faunal oscillations in response to late Qua ternary millennial-scale climate change (Dansgaard-Oeschger cycles) on the open central California margin. These faunal oscillations can be correlated to and are apparently synchronous with those reported from Santa Barbara B asin. Together they represent major fluctuations in the strength of the OMZ which were intimately associated with global climate change-weakening, per haps disappearing, during cool periods and strengthening during warm period s. These rapid, major OMZ strength fluctuations were apparently widespread on the Northeast Pacific margin and must have influenced the evolution of m argin biota and altered biogeochemical cycles with potential feedbacks to g lobal climate change.