Oceanographic conditions of the Eastern tropical Pacific

The eastern Pacific warm pool supports reef-building corals, as well as distinct communities of plankton, fishes, marine mammals and birds. This habitat is characterized by warm, low-salinity surface water lying on top of a strong, shallow thermocline. It is bounded by the South Equatorial Current and equatorial cold tongue to the south, cooler and more saline subtropical water to the northwest, and cold eastern boundary currents to the north and south (California and Peru Currents). The continental boundary influences atmospheric forcing by gap winds during winter and by causing the rainy Intertropical Convergence Zone to be located north of the equator and over the warm pool. Patterns of waves, tides and tropical cyclones impinging on coral reefs are described. The structure and variability of water masses and circulation are determined by solar and atmospheric processes, both within and outside of the region. To the west of the Galápagos, surface circulation is predominantly the east-west equatorial currents. Near the coast, surface circulation is modified by the coastal boundary, local winds, eddies, and interaction with eastern boundary currents. Primary productivity depends on oceanic upwelling along the equator and local centers of upwelling and wind mixing in coastal waters. Eastern tropical Pacific surface waters are moderately productive. Phytoplankton productivity is limited by a lack of the micronutrient dissolved iron, except where local coastal processes provide a source, so that macronutrients such as nitrate are never depleted. Seasonal changes in solar forcing, winds, rainfall, surface temperature and salinity, and other environmental characteristics are described, although seasonality in this region is not as pronounced as at higher latitudes. In contrast, interannual variations caused by the El Niño-Southern Oscillation across the entire tropical Indo-Pacific are very important in this region (Chap. 4). Oxygen depletion is extreme below the sharp thermocline, with consequences for mesopelagic and subthermocline benthic organisms. Surface waters are relatively low pH and marginally carbonate-saturated. Climate change is predicted to lead to future oceanographic changes in this region: warming and acidification of surface waters, increased stratification and reduced productivity, and upwelling/mixing of hypoxic waters into the surface layer. These changes are likely to affect organisms and populations living in the eastern tropical Pacific.

Fiedler P. C. & Lavín M. F., 2017. Oceanographic conditions of the Eastern tropical Pacific. In Glynn P. W., Manzello D. P. & Enochs I. C. (Eds.), Coral Reefs of the Eastern Tropical Pacific: Persistence and Loss in a Dynamic Environment – Coral Reefs of the World 8:59-83. Book chapter (subscription required).

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