MIXED-LAYER CIRCULATION DURING EQPAC AND SOME THERMOCHEMICAL IMPLICATIONS FOR THE EQUATORIAL COLD-TONGUE

Surface currents inferred from satellite-tracked drifting buoys were u sed to develop a chronology of surface currents in the central Pacific for the year encompassing the EqPac field program. Salient features o f the chronology are the early months of the program witnessed anomalo us eastward current surges near the equator within the moderate El Nin o event, followed by a period of anomalously strong westward flow near the equator and eastward flow in the North Equatorial Countercurrent that led. in mid-summer, to an eruption of tropical instability waves that continued until the end of the field program. None of these event s was particularly unusual, but they were departures from climatology that influence the interpretation of the biochemical measurements made for EqPac. Results from a semi-quantitative conceptual model indicate that tropical instability waves have more important long-term, as wel l as short-term, consequences for thermochemical properties of the col d tongue than previously recognized. Copyright (C) 1996 Elsevier Scien ce Ltd.