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Studies of the Santa Barbara Basin off the coast of California have linked changes in its bottom-water oxygen content to millennial-scale climate changes as recorded by the oxygen isotope composition of Greenland ice. Through the use of detailed records from a sediment core collected off the Magdalena Margin of Baja California, Mexico, we demonstrate that this teleconnection predominantly arose from changes in marine productivity, rather than changes in ventilation of the North Pacific, as was originally proposed. One possible interpretation is that the modern balance of El Nino–La Nina conditions that favors a shallow nutricline and high productivity today and during warm climate intervals of the past 52 k.y. was altered toward more frequent, deep nutricline, low productivity, El Nino–like conditions during cool climate intervals.