Water-mass relationships and morphologic variability in the benthic foraminifer Bolivina albatrossi Cushman, northern Gulf of Mexico

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Abstract
Morphometric analysis of Bolivina albatrossi from 25 sediment-top samples from the northern Gulf of Mexico reveals a strong correlation between intraspecific morphologic variability and factors related to water-column properties. The test triangularity and pore density of B. albatrossi decrease between 600-800 m water depth, apparently in response to changes in bottom-water dissolved-oxygen concentration. Test lobateness exhibits a progressive, inverse relationship to disolved-oxygen concentration, which may be the result of the reduced surface sculpture of specimens from the oxygen-minimum zone compared to those from deeper, more-oxygenated water. Morphometric end members can be defined in B. albatrossi on the basis of test triangularity and lobateness which vary proportionally with water-mass distribution or with specific water-column properties, such as dissolved oxygen, temperature, and salinity. A better understanding of the factors controlling the morphologic variability of benthic foraminifera in large and small ocean basins could greatly enhance the reliability of paleoceanographic reconstructions of deep and intermediate water-mass properties, which are presently difficult to reconstruct from sediment analyses alone.