Mixed layer circulation during EqPac and some thermochemical implications for the equatorial cold tongue

Surface currents inferred from satellite-tracked drifting buoys were used to develop a chronology of surface currents in the central Pacific for the year encompassing the EqPac field program. Salient features of the chronology are the early months of the program witnessed anomalous eastward current surges near the equator within the moderate El Niٌo 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 events 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 well as short-term, consequences for thermochemical properties of the cold tongue than previously recognized.