HR: 0800h
AN: PP31B-1526    [Abstracts]
TI: Seasonal Variability of Seawater Salinity and the Oxygen Isotopic Composition of Seawater in the Cariaco Basin, Venezuela
AU: * McConnell, M C
EM: mmcconnell@geol.sc.edu
AF: University of South Carolina, Department of Geological Sciences 701 Sumter Street, Columbia, SC 29205
AU: Thunell, R C
EM: thunell@geol.sc.edu
AF: University of South Carolina, Department of Geological Sciences 701 Sumter Street, Columbia, SC 29205
AU: Tappa, E J
EM: tappa@geol.sc.edu
AF: University of South Carolina, Department of Geological Sciences 701 Sumter Street, Columbia, SC 29205
AU: Wright, J D
EM: jdwright@rci.rutgers.edu
AF: Rutgers University, Department of Geological Sciences, Piscataway, NJ 08854
AB: Monthly seawater oxygen isotope measurements (δ¹⁸O_sw) were collected between May 1996- February 1997 and in May 2005 at various water depths in the Cariaco Basin, offshore Venezuela. The δ¹⁸O_sw values are compared with concurrent salinity measurements to assess the δ¹⁸O_sw:salinity relationship in this tropical region and to determine if there is significant seasonal variability in the relationship. The δ¹⁸O_sw values range from 0.83‰ - 1.27‰ smow. The climatology of the region is driven by the seasonal migration of the ITCZ. During the winter and early spring, precipitation is low and upwelling is intense causing salinity to increase to ~37 psu. In contrast, during the Summer and early Fall when the ITCZ migrates to the north, upwelling ceases and precipitation increases causing surface salinities to decrease to ~36.2 psu. Preliminary results indicate that the strongest positive correlation between δ¹⁸O_sw and salinity in the upper 400m occurred during May 2005 (R²= 0.93). However, the salinity:oxygen isotope relationship varies significantly over the course of the year. For example, the lightest δ¹⁸O_sw values occurred during November 1996 possibly due to increased input of Orinoco River water into the Cariaco Basin. The relationships determined from our study will aid our understanding of paleosalinity variations in this region. Magnesium/calcium (Mg/Ca) ratios and the oxygen isotope composition (δ¹⁸O_c) were also measured in two surface dwelling planktonic foraminiferal species Globigerinoides ruber (white and pink variety) and Globigerina bulloides from bi-weekly sediment trap samples collected in the Cariaco Basin between 2003 and 2005. The Mg/Ca ratios range from 3.9-6.9 mmol/mol for G. ruber and 4.7-6.4mmol/mol for G. bulloides. The range in δ¹⁸O_c is 0.96‰ for G. ruber over ~5°C change in sea surface temperature (SST) and 0.50‰ for G. bulloides over ~2.5°C change in SST.
DE: 4900 PALEOCEANOGRAPHY (0473, 3344)
DE: 4924 Geochemical tracers
DE: 4954 Sea surface temperature
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005