Equatorial Pacific Ocean Horizontal Velocity, Divergence, and Upwelling*

Abstract

Upper-ocean horizontal velocity and divergence were estimated from shipboard observations taken from 1991 to 1999 in the equatorial Pacific between 170ЊW and 95ЊW. Mean transports were estimated for the zonal currents at the mean longitude of the sections, 136ЊW. Mean meridional currents for the entire longitude range included poleward surface flows reaching Ϫ0.09 m s Ϫ1 in the south and 0.13 m s Ϫ1 in the north as well as equatorward flow within the thermocline reaching 0.05 m s Ϫ1 in the south and Ϫ0.04 m s Ϫ1 in the north near 23ЊC (85 m). Vertical velocity was diagnosed by integrating horizontal divergence estimated for the entire region down from the surface. Equatorial upwelling velocities peaked at 1.9 (Ϯ0.9) ϫ 10 Ϫ5 m s Ϫ1 at 50 m. The upwelling transport in the area bounded by 3.6ЊS-5.2ЊN, 170ЊW-95ЊW was 62 (Ϯ18) ϫ 10 6 m 3 s Ϫ1 at 50 m. Strong downwelling was apparent within the North Equatorial Countercurrent. An asymmetry in the meridional flows suggested that on the order of 10 ϫ 10 6 m 3 s Ϫ1 of thermocline water from the Southern Hemisphere was upwelled at the equator and moved into the Northern Hemisphere as surface water. This interhemispheric exchange path could be part of the route for water from the Southern Hemisphere to supply the Indonesian Throughflow.

The dynamics of waves interacting with the Equatorial Undercurrent

“…v ≡ 0 and ∂/∂ y ≡ 0. Observations given by Johnson and McPhaden (2001) show that meridional speeds near the Equator are much smaller than the zonal speeds. However, it is known that, in some circumstances, the amplitudes of the eddy perturbations can be roughly the same size in all three directions and, occasionally, larger than the mean flow.…”

“…The thermocline itself is at a depth of 120 m, the total depth of the ocean is 4 km, and below 240 m we have the abyssal region of stationary water; see the data provided by Johnson and McPhaden (2001). Indeed, we may use our model to fit the observations for other regions of the equatorial flow; for example, the choice of 120 m for the depth of the thermocline is actually appropriate for the 6000 km stretch between about 140 • E and 150 • W (see Fedorov and Brown 2009).…”

Inshore Fishes of Howland Island, Baker Island, Jarvis Island, Palmyra Atoll, and Kingman Reef

“…Calculations from direct measurements of current velocities by acoustic Doppler current profiler surveys in this region estimated mean meridional sea-surface current velocities of 0-13 cm s -1 , with strong divergence at the equator and convergence from 5°N to 9°N (Johnson et al, 2001; averaged to the mean longitude in their study-135°W). These velocities are considerably less than the average zonal sea-surface velocities of 0-50 cm s -1 and almost an order of magnitude less than the EUC zonal velocities of 1-90 cm s -1 at 50-200 m. Nevertheless, meridional transport mechanisms may be influential for biogeography because of the shorter latitudinal distances between islands in this region compared to their longitudinal distances.…”

“…Wyrtki and Kilonski (1984) suggested that the northward surface water transport is minimal in the Intertropical Convergence Zone (ICZ) region of 4°N (the doldrums), but more pronounced to the south and north. Johnson et al (2001) found empirical evidence that the northward water transport north of the equator was greater than was predicted by wind patterns. They explained this, in part, by suggesting that the strong shears between the zonal currents of the region reduce the effective Coriolis parameter below its calculated value, allowing enhanced Ekman transport.…”

ENSO related variations in biogeochemistry of AA and HA in settling particles along the equatorial Pacific Ocean

“…The collected samples were filtered through a 0.45 µm represents site number without the prefix MT. Hatched area represents NINO 4 region, while shaded area represents equatorial upwelling area (Johnson et al, 2001). WPWP is defined by 28°C isotherm (Yan et al, 1992).…”