Hydrography and geostrophy around Easter Island

A series of hydrographic stations north and south of Easter Island (27′10′S, 109′20′W), Chile, were sampled between 22 and 23 May, 1994. The hydrography measured was consistent with basin-scale studies and showed a surface mixed layer that ranged between 80 and 115 m depth and had temperature and salinity values typical of autumn subtropical waters (22′C in temperature and 35.85 in salinity). The hydrography indicated the presence of two water masses in the vicinity of the island: the eastern South Pacific Central Water and the Antarctic Intermediate Water. Nutrient concentrations in general were lowest at the surface, over a layer that was deeper than the density mixed layer, and increased with depth. The appearance of salt fingers within the eastern South Pacific Central water mass was suggested by the positive vertical gradients of temperature and salinity, by the rough steps in the temperature and salinity profiles, and by the low and positive density ratios combined with Turner angles between 70′ and 80′. The density field indicated the development of geostrophic flows that were consistent with the eastern portion of the subtropical gyre of the South Pacific and with the surface dynamic topography of the period of observations. Due to the presence of the island, the large-scale north-northwestward geostrophic flows were reversed at spatial scales comparable to the size of the island.