two cruises were conducted in the central equatorial Pacific to determine the effects of the El Nifio/Southern Oscillation (ENSO) event on the sea-air exchange of CO2. Measurements of total carbon dioxide, pCO2, total alkalinity, freon-l l, salinity, temperature, oxygen, nutrients, and wind and current velocities were made along three meridional transects (158øW, April 1983; 150øW, March 1984; 170øW, April 1984). The cessation of upwelling during the ENSO event caused pCO2 concentrations in surface waters to decrease to near-saturation levels along the equator. The calculated net flux of CO2 across the sea-air interface was essentially negligible in the eastern equatorial Pacific during this period. However, when normal trade winds and consequent upwelling returned in late 1983 and early 1984, the equatoriai region returned to a pCO2 condition of highly supersaturated •urface waters in the region between 8øN and 8øS along the 150 ø and 170øW transects. The calculated post-ENSO sea-air flux of CO2 exceeded 6.0 mmol CO2 m-2d -•. The mean annual CO2 flux in the equatorial Pacific was estimated to be 0.02 Gt of carbon during the 1982-1983 ENSO event as compared with 0.6 Gt during 1984. the year-to-year changes in the atmospheric growth rate of CO2 tended to reach a minimum of near-zero growth during the summer-fall period of 1982 followed by an anomalously high growth rate of•approximately 2-3 ppm yr -• during the summer-fall period of 1983. They suggested that the striking variations during the strong 1982-1983 ENSO event were due in part to variations in upwelling-induced CO2 exchange along th e equator. All of these earlier studies have been limited by a lack of pCO2 data for equato,rial surface waters which could be utilized to determine the variability of the rate of exchange of carbon dioxide between the ocean and the atmosphere. In this paper we describe the distributions of physical and chemical properties along the equator during and after the 1982-1983 ENSO event with a view toward assessing the physical factor• controlling the variability of CO2 upwelling and exchange in the eastern equatorial Pacific. Detailed measurements of the distribution of pCO2 in surface waters of the equatorial Pacific have been limited to a single time series study and a number of individual cruises over the past 25 years. The earlies• data were obtained on various ScriPps Institution of Oceanography (SIO) cruises, and the results were summarized in several papers by Keeling and coworkers [Keeling et al., 1965; Keeling, 1968]. Supersaturations of pC02 of UP to approximately 30% were observed in an equatorial zone between 10øN and 20øS. The GEOSECS data for 1973 showed similar pCO2 supersaturations along 150øW [Takahashi et al., 1980]. The only time series measurements were made by Weiss et al. [1982] during the 1979-1980 First Global Geophysical. Experiment expedition, during which pCO2 measurements were taken along 150øW on a bimonthly basis for a period of one year. The preliminary results, reported by Keeling [1983], indicated...

Sea surface temperature (SST) maps and imagery derived from the NOAA 6 satellite Advanced Very High Resolution Radiometer (AVHRR) for June and July 1981 in the eastern tropical Pacific portray the wavelike structure of the cool water along the equator from 93°W to 125°W. Cusped waves of approximately 1000‐km zonal wavelength and 25‐day period propagated westward with a phase speed of 40 km/day. The observed meridional extent between the crest and trough of the waves is about 300 km. Details in the imagery show cooler water at the cusps advected north and then east with the north equatorial countercurrent (NECC), consistent with the suggestion of a series of anticyclonic eddies occupying the shear zone between the NECC and the westward flowing south equatorial current. Absolute SST estimates from the AVHRR data agree to within 0.6°C with shipboard data taken along 110° W between 5°N and 5°S. The wavelike structures in the SST maps are also in agreement at the surface with a vertical expendable bathythermograph temperature section made along the equator between 93°W and 125°W, which shows the phase of the waves tilting westward with increasing depth over the upper 75 m. Such a phase shift, if it extended 100–200 km meridionally in either direction from the equator, would be associated with an equatorward flux of heat. Similar phase shifts appear in temperature time series at depths of 20 and 50 m, from a mooring at 0°33′N, 110°30′W. Near‐surface currents measured at this and a second mooring on the equator at 109°40′W indicate a regular pattern of northward advection when wave cusps pass them, followed by southwest flow during the passage of wave troughs, again consistent with an equatorward flux of heat, as well as with earlier theoretical and drift buoy findings.

No abstract

During the SEASAT repeat‐orbit period, a CTD and deep (1800 m) XBT hydrographic experiment was conducted across the Kuroshio to obtain cotemporaneous surface topography measurements for comparison with the altimeter‐derived surface height measurements. The results showed that the altimeter could detect and measure the change in sea surface topography caused by movement of the Kuroshio and the cold rings that were found in the hydrographic data. After compensation for the small differences in the time of the measurements, the altimeter measured changes in the surface topography that matched those measured by the hydrographic sections with an average difference of 9.6 cm for the 41 comparison points.

Abstruct-Downward-looking RD Instruments acoustic Doppler current profilers (ADCPs) are presently mounted on surface moorings along the Pacific equator as part of the Tropical Ocean-Global Atmosphere Program. In the equatorial region, the South Equatorial Current/Equatorial Undercurrent system creates high vertical shear in the zonal velocity. ADCP skew error is known to occur in high vertical shear regimes due to the misposition of the ADCP tracking filter with respect to the frequency of backscattered sound energy. Skew errors in the moored ADCP current measurements from the eastern equatorial Pacific are particularly troublesome in the first bin below the surface. The filter position for the first bin is set by the values measured from previous pings according to the E-command setup. Calculations of the expected skew error from typical mean zonal shears in the equatorial region were made prior to deployment of the moored array using equations provided by RD Instruments. However, the skews calculated from the mean curve only account for about 1/3 of the velocity errors observed in a moored ADCP system at O", llOoW in spring 1991. This underestimate of error is due to the fact that the skew must be computed on a ping-to-ping basis, incorporating the vertical and horizontal velocity changes that occur each ping. A model for surface wave induced skew error i s presented which includes ping-to-ping velocity changes in the skew calculation. In high shear regimes, such as the equatorial region, the model calculates skew errors of equal magnitude to those observed in the data. Alternative ADCP setup commands, tested with shipboard data, are presented to minimize tracking filter skew errors in future measurements.