National Oceanic and
Atmospheric Administration
United States Department of Commerce


FY 1990

Anomalous nutrient distribution in the equatorial Pacific in April 1988: evidence for rapid biological uptake

Bender, M., and M.J. McPhaden

Deep-Sea Res., 37(7), 1075–1084, doi: 10.1016/0198-0149(90)90051-V (1990)

Nutrients in the central equatorial Pacific are normally enriched at the Equator, with concentrations gradually falling to the north and south. This pattern reflects input by equatorial upwelling, with slow removal as waters flow poleward. In April 1988, we observed minima in SiO2 and NO3– + NO2– concentrations near the Equator. [SiO2] in particular dropped to minima at 2.5°N and 1-2.5°S, rose to maxima at 3°N and 3-6°S, then fell off in the normal pattern. Such minima are unusual features not clearly evident in data from other equatorial Pacific transects. A period of anomalous hydrographic conditions preceded the time of our chemical observations. Between February 1988 and April 1988, the anomalously warm conditions which characterized the equatorial Pacific during the 1986–1987 El Niño/Southern Oscillation event ended, and the thermocline shoaled sharply. We speculate that the anomalous nutrient distributions we observed in April are related to the regional hydrography of the preceding months. Physical forcing may have triggered rapid biological SiO2 and NO3– removal, producing the anomalous nutrient distribution we observed.

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