Benthic Current Observations at DOMES Sites A, B, and C in the Tropical North Pacific Ocean

Abstract

Benthic current measurements are reported from three locations (A: 8°27′N, 150°49′W; B: 11°42′N, 138°24′W; C: 14°38′N, 125°29′W) in the eastern tropical Pacific. Near-bottom stratification was weak at all sites. The measurements were of 4- to 6- month duration. Mean currents were small and to the northwest; however, low frequency fluctuations dominated the records. These fluctuations had dominant periods for the meridional component of 2 months at all sites; the zonal component had periods varying from 2 months at the easternmost site to about 5 months at the other sites. Low frequency kinetic energy increased from west to east. Vertically, the low frequency motions were coherent over the bottom 200 m. A small speed increase was observed from 200 m to 30 m off the bottom; below this the speed decreased. Interpretation of these data in terms of an Ekman layer showed counterclockwise (looking down) veering between 30- to 6-m levels, which was consistent with the expected layer thickness of 25 m.

High frequency inertial-internal wave oscillations were also investigated. The inertial oscillations were intermittent and showed evidence for downward energy propagation. Mean energy level and lack of correlation between low frequency currents and internal wave energy suggests that the bottom topography is not a strong source of high frequency internal wave energy in our data.