VENTILATION CHANGES IN THE NORTHEAST PACIFIC DURING THE LAST DEGLACIATION

Under present climate conditions, convection at high latitudes of the North Pacific is restricted to shallower depths than in the North Atla ntic. To what extent this asymmetry between the two ocean basins was m aintained over the past 20 kyr is poorly known because there are few u nambiguous proxy records of ventilation from the North Pacific. We pre sent new data for two sediment cores from the California margin at 800 and 1600 m depth to argue that the depth of ventilation shifted repea tedly in the northeast Pacific over the course of deglaciation. The ev idence includes benthic foraminiferal Cd/Ca, O-18/O-16, and C-13/C-12 data as well as radiocarbon age differences between benthic and plankt onic foraminifera. A number of features in the shallower of the two co res, including an interval of laminated sediments, are consistent with changes in ventilation over the past 20 kyr suggested by alternations between laminated and bioturbated sediments in the Santa Barbara Basi n and the Gulf of California [Keigwin and Jones, 1990; Kennett and Ing ram, 1995; Behl and Kennett, 1996]. Data from the deeper of the two Ca lifornia margin cores suggest that during times of reduced ventilation at 800 m, ventilation was enhanced at 1600 m depth, and vice versa. T his pronounced depth dependence of ventilation needs to be taken into account when exploring potential teleconnections between the North Pac ific and the North Atlantic.