Evidence for a stronger oxygen-minimum zone off central California during late Pleistocene to early Holocene

Of 31 deep-sea cores collected along the central California continental slope, 18 have distinctly laminated sediment at depth, but none have laminations in the top few centimetres. The cores with laminated facies are restricted to water depths between 508 and 1508 m, but not all cores taken from this depth interval have laminated facies. ¹⁴C dates yield an extrapolated age of 4700 B.P. for the top of the uppermost laminated unit. Comparisons of the diatom flora in the laminated couplets with diatom floras in a 13-month sediment-trap record suggest that the laminations are varvelike couplets of seasonal sedimentation. The laminated facies represent a period from the last global deglaciation to early Holocene when the oxygen-minimum zone along the northeastern Pacific Ocean was stronger than at present. A stronger oxygen-minimum zone during this time is inferred to be the result of intensified upwelling.