Variations with depth of oceanographic properties along the equator in the Pacific

Abstract

The vertical distribution along the equator in the Pacific of temperature, salinity, density, oxygen, and phosphate, from the sea surface to 1000 meters, and the anomaly of the dynamic height of the sea surface and other isobaric surfaces above the 700‐decibar surface are shown. In each of the figures, the available data have been partitioned according to the date of the observation into two periods, July to December and January to June, which are designated in the text as summer and winter, respectively. The figures include data from stations within one degree of latitude north or south of the equator between 110°W and 135°E longitude. The surface of the sea, relative to the 700‐db surface, slopes upward, east to west, approximately 0.8 dynamic meters; the value for the slope is 5.0 × 10−8 during both summer and winter. The longitudinal pressure gradient does not extend much below the layer of relatively large vertical density gradient. At the depth of σ = 26.5, 250–300 m, relatively little east‐west slope is evident. In the surface layer (sea surface to top of the thermocline), temperatures along the equator are lower in the eastern Pacific during both periods; the thermocline is comparatively level west of the 180th meridian, sloping upward to the east of this longitude. Temperatures are appreciably lower and concentrations of inorganic phosphate are higher in the surface layer in the eastern Pacific during the summer, both reflecting the temporal and longitudinal variations in divergence and upwelling. The oxygen minimum, centered at a depth of approximately 450 m, is a continuous feature from 100°W longitude (eastern limit of the profiles) to near 170°E longitude, with the lowest concentrations in the east (≤ 0.5 ml/L) increasing to 1.5 to 2.0 at the westward limit. West of 170°E longitude, concentrations at 450 m rapidly increase to 3.0 ml/L.

The mixed layer of the western equatorial Pacific Ocean

“…Therefore the mixed layer waters formed near the date line are saltier than those formed further to the west, but are of nearly the same temperature [Reynolds, 1982]. Austin [1958] Figure 13 is found, surfaces be-tween 160 ø and 170øE, according to Levitus [1982]. Austin [1958] Figure 13 is found, surfaces be-tween 160 ø and 170øE, according to Levitus [1982].…”

On the baroclinic response of the zonal pressure gradient in the equatorial Atlantic Ocean

“…One important consequence is that over a portion of the basin, following the abatement of easterly wind stress, the baroclinic response by the isopycnals reverses from a westward directed force to an eastward one. Adding this part to the surface slope results in a larger eastward directed pressure gradient force at the depth In the Pacific Ocean the mean gradient computed west of, say, 110øW [Austin, 1958;Knauss, 1966;Taft et al, 1974;Halpern, 1980;Manglum and Hayes, 1984;Bryden and Brady, 1985] decreases from a maximum at the surface to zero by about 200 m. Tsuchiya [1979] found no significant gradients at and below 100 m between approximately 130øW and 95øW in seven surveys conducted throughout the year. The decreasing depth of zero gradient from west to east coincides with the shoaling of the thermocline and the EUC core from around 120 m at 150øW to around 60 m at 110øW.…”

The vertical structure of the zonal pressure gradient in the eastern equatorial Pacific

“…Discussion of the vertical structure of p,, has been somewhat limited [Austin, 1958;Montgomery and Palm•n, 1940; Letoasson and Piton, 1968]. Sea level measurements, of course, only provide a measure of the surface topography fluctuations.…”