Oceanographic Engineering of the Woods Hole Oceanographic Institution and the Massachusetts Institute of Technology, Woods Hole, MA 02543. Oceanographers have long sought to verify the theoretical Ekman transport relation, which predicts that a steady wind stress acting together with the Coriolis force will produce a transport of water to the right of the wind. In situ measurements of wind and ocean currents provide a detailed view of this phenomenon. By separating the wind-driven current from the measured total current and by averaging over a long record, it is found that the observed transport is consistent with theoretical Ekman transport to within about 10 percent. In this case the wind-driven transport is strongly surface trapped, with 95 percent occurring in the upper 25 meters as a result of fair summer weather.

We determine annual rates of net biological oxygen production in the euphotic zone and respiration in the upper thermocline of the subtropical North Pacific ocean using mass balances of oxygen, argon, and nitrogen measured at the U.S. Joint Global Ocean Flux Study time series station ALOHA. Net evasion of nitrogen and argon to the atmosphere caused by warming of surface waters is balanced by supply primarily from cross‐isopycnal transport. Mixing rates between the euphotic zone and the top of the permanent thermocline required to balance the inert gas flux are 1–2 cm2 s−1 when transformed to units of an eddy diffusion coefficient. Application of mixing rates derived from the inert gas mass balance to the oxygen field yields a net annual euphotic zone production rate of 1.4±1.0 moles O2 m−2 yr−1, one half of which is lost to the atmosphere, with most of the rest mixed into the top of the thermocline. Since cross‐isopycnal gradients of dissolved organic carbon (DOC) are about half to those of oxygen, we estimate that at least one quarter of the carbon flux out of the euphotic zone is via DOC. Because surface ocean dissolved organic matter has a relatively high C/N ratio, the stoichiometry among O2, C, and inorganic N in the upper ocean should be different than that observed in deeper waters.

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We have used a simple, one‐dimensional model to simulate the diurnal cycle of the equatorial upper ocean. The model is initialized with the stratification and shear of the Equatorial Undercurrent (EUC) and is driven with heating and wind stress. A surface mixed layer is determined by bulk stability requirements, and a transition layer below the mixed layer is simulated by requiring that the gradient Richardson number be no less than ¼. A principal result is that the nighttime phase of the diurnal cycle is strongly affected by the EUC, resulting in deep mixing and large dissipation at night consistent with observations of the equatorial upper ocean during the 1984 Tropic Heat experiment. The day time (heating) phase of the simulated diurnal cycle is very similar to that seen at mid‐latitudes. Solar heating produces a stably stratified surface layer roughly 10 m thick within which there is little, O(3 × 10−8 W kg−1), turbulent dissipation. For the typical range of conditions at the equator, diurnal warming of the sea surface is 0.2°–0.5°C, and the diurnal variation of surface current (diurnal jet) is 0.1–0.2 m s−1, consistent with observations. The nighttime (cooling) phase of the simulated diurnal cycle is quite different from that seen at mid‐latitudes. As cooling removes the warm, stable surface layer, the wind stress can work directly against the shear of the EUC. This produces a transition layer that can reach to 80 m depth, or nearly to the core of the EUC. Within this layer the turbulent dissipation is quite large, O(2 × 10−7 W kg−1). Thus the simulated dissipation has a diurnal range of more than a factor of 5, as observed in Tropic Heat, though the diumal cycle of stratification and current are fairly modest.

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