Date of Award

Fall 12-1-2005

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Geography, Geology, and Anthropology

First Advisor

Anthony E. Rathburn

Second Advisor

Sandra Brake

Third Advisor

James Speer

Abstract

Analyses ofliving (Rose Bengal stained) deep-sea benthic foraminifera collected on the Southern California margin reveal temporal and spatial changes in foraminiferal assemblages related to changes in sea-surface productivity. Samples were collected from two sites in May, August, and October 1996. Results show that foraminiferal microhabitats are not static at these sites, and some species ( e.g., Bolivina spissa and Uvigerina peregrina) responded to the change in seasons with a change in their vertical distribution profiles, which is indicative of microhabitat preferences. Species such as Buliminella tenuata changed sediment depth in different stages of their life cycles, which has implications for assessments of fossil assemblages and geochemistry, both of which are used for paleoceanographic analyses. Many species, such as Uvigerina peregrina and Globobulimina pacifica, had density maxima in May or October, when surface productivity is inferred to be higher than in August. These maxima suggest food supplies for these species that may be linked with seasonal variations. These changes have implications for food preferences of foraminifera as well as resulting geochemical signatures. In the total populations of foraminifera, temporal changes related to organic flux are well established in the >63 μm size fraction at the more productive, northern site 83-55, but not within the > 150 μm fraction at site 83-55, nor within the smaller size fraction at site 90-60. In addition, foraminiferal abundances in the > 150 μm fraction have a negative correlation with productivity in this area, while the foraminiferal abundances in the >63 μm fraction positively reflect productivity in this area of the ocean. This study indicates that the assessment of temporal changes and paleoproductivity along productive continental margins should be based upon changes in species distributions and abundances, total abundances in the >63 micron fraction, and comparisons between the > 150, 63-150, and >63 micron fractions.

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