Title

Decadal- to century scale climate variability in the tropical north Atlantic as recorded in sediments from the anoxic Cariaco Basin, Venezuela

Date of Award

1998

Availability

Article

Degree Name

Doctor of Philosophy (Ph.D.)

Department

Marine Geology and Geophysics

First Committee Member

Larry C. Peterson, Committee Chair

Abstract

Laminated sediments of the anoxic Cariaco Basin record a detailed history of trade wind-induced coastal upwelling off northern South America, a seasonal phenomenon related to the meridional motion of the Intertropical Convergence Zone (ITCZ). The ability to construct paleoenvironmental time-series with near-annual resolution in the most recently deposited sediments allows for calibration to instrumental records, and extrapolation into the past. Results of high-resolution analyses of box core and piston core sediments are reported that provide a record of upwelling variability spanning the last 825 yrs, and during the Bolling-Allerod/Younger Dryas (BA/YD) transition, respectively, and links are explored to tropical and extratropical phenomena as recorded in instrumental data.Continuous sampling of well-dated box core sediments at 1-mm intervals yields a record with a temporal resolution of 1-3 yrs for the period of 1990-1165 AD. Over the interval of data overlap, a high correlation on decadal time scales between abundance of the upwelling-sensitive foraminifer Globigerina bulloides and local zonal wind velocities strongly suggests that G. bulloides accurately records upwelling and trade wind variability. Correlation of G. bulloides in the Cariaco Basin with global sea-surface temperature (SST) data show the strongest correlations with high latitude North Atlantic SST (50$\sp\circ$-60$\sp\circ$N). Together, these relationships indicate that upwelling and trade wind intensities over the Cariaco Basin are stronger at times of colder SST in the northern North Atlantic region. This pattern of observation can perhaps be explained by decadal-scale fluctuations in the Atlantic's "conveyor belt" circulation. Over the pre-instrumental portion of the record, G. bulloides abundance continues to show evidence of large decadal- to century-scale variability, with dominant periods close to well-known solar periodicities, suggesting a possible sun-ocean-atmosphere climate link.In contrast to the record of the last 825 yrs, decadal variability is largely reduced over the BA/YD transition, indicating differences in the ITCZ/trade wind system during this time. This may be the result of a more southerly ITCZ and reduced sensitivity of the Cariaco Basin to changes in its position.

Keywords

Geology; Physical Oceanography; Biology, Oceanography; 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:9905027