Glacial-interglacial variability in upwelling and bioproductivity off NW Mexico: Implications for quaternary paleoclimate

Sedimentary accumulation of biogenic components (organic carbon, opal, and biogenic barium) on the northwestern Mexican margin declined during every g lacial interval of the past 140 kyr, indicating decreases in upwelling-indu ced productivity during cold periods. The glacial-interglacial contrasts in upwelling on this margin are attributed to reversals in land-ocean thermal contrast, the waxing and waning of the Laurentide Ice Sheet, and consequen t responses of the western hemisphere wind fields. This scenario is consist ent with three independent lines of evidence: terrestrial paleoclimatic dat a, general circulation model results, and our marine records. This pattern of glacial interglacial variability in upwelling off NW Mexico is opposite to that observed in other low-latitude and midlatitude upwelling areas, suc h as the eastern equatorial Pacific. These results add to a growing pool of observations that the response of oceanic upwelling to glacial climatic fo rcing has been regionally variable.