Deep‐Sea Benthic Foraminiferal Assemblage Response to a Surface Ocean Productivity Gradient: A Test

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Abstract
A transect of samples from the eastern equatorial Pacific, where surface ocean productivity is the only changing environmental variable, was used to test the response of benthic foraminiferal assemblages to an open‐ocean productivity gradient. The transect runs along the East Pacific Rise from the highly productive waters near the equator to the oligotrophic South Pacific subtropical gyre. Surface sediment benthic assemblages show progressive change along the transect with strong compositional shifts corresponding to the rapid productivity gradient near the equator and to the position of the southern convergence, near 18°–19°S. The relationship of the assemblages to surface ocean productivity was tested by statistical regression of quantitative estimates of productivity on the assemblage principal component scores calculated for each sampling location. The regression yielded an r‐squared of 0.87, demonstrating a clear relationship between surface ocean productivity and deep‐sea benthic foraminiferal assemblage composition. The species most important to this relationship display a consistent response to oceanic productivity for long stretches of geologic time. This conservative behavior and the results of the regression analysis indicate that benthic foraminiferal assemblages can be used to estimate surface ocean productivity for the geologic past.