Title

A high-resolution comparison of late Quaternary upwelling records from the Cariaco Basin and Arabian Sea: Coccolith paleoecology and paleoclimatic investigations

Date of Award

1998

Availability

Article

Degree Name

Doctor of Philosophy (Ph.D.)

First Committee Member

Larry C. Peterson, Committee Chair

Abstract

Coccoliths, the minute calcareous plates produced by photosynthetic algae, were studied in high-resolution, AMS $\sp{14}$C-dated sediment cores from two sites of tropical upwelling located in climatically-sensitive regions, the Cariaco Basin (Venezuela) and the Arabian Sea. The Cariaco Basin is ideally situated to record changes in the strength of upwelling induced by migration of the Intertropical Convergence Zone (ITCZ) in the tropical Atlantic, while the Arabian Sea is strongly influenced by the broader dynamics of the Indian Ocean monsoon.Scanning Electron Microscopy has revealed that two coccolith species, Emiliania huxleyi and Gephyrocapsa oceanica, dominate both assemblages for the last $\sim$30,000 years. Time series of relative abundance for these and other species show large variations that can be related to both local and regional climate changes, including the Younger Dryas cold interval, the onset of anoxia in the Cariaco Basin, and the reduced upwelling strength in the Arabian Sea during the Last Glacial Maximum.Coccolith accumulation rate data, derived from modified direct settling techniques, complement and in some cases improve upon the relative abundance data, while also comparing favorably with modern flux estimates derived from sediment trap studies. Accumulation rates at both locations are on the order of 10$\sp9$ to 10$\sp{11}$ coccoliths/cm$\sp2$/kyr, roughly equivalent to 10$\sp8$-10$\sp9$ coccoliths/m$\sp2$/day. Stable isotope time series from the $<$38$\mu$m sediment fraction in the Cariaco Basin compare favorably with foraminiferal $\delta\sp $O records from the same core and provide further insights into the climatic and oceanographic history of the region. The fine-fraction $\delta\sp $O time series from the Oman margin records large influxes of eolian carbonate dust which overwhelms the glacial-interglacial signal of the coccoliths.Interest in coccolithophore productivity has increased in recent years because of their potential impacts on global climate as producers of DMS and CaCO$\sb3.$ Some species also produce alkenones, which are increasingly extracted from sediments and used as indicators of paleo-sea surface temperatures. The findings from this study have implications relevant to studies of past SST variations, global carbon cycling, and aerosol-induced climate change, in addition to the more direct insights into the climate history of the tropical Atlantic and Arabian Sea.

Keywords

Geology; Paleoecology

Link to Full Text

http://access.library.miami.edu/login?url=http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:9905033