We determined alkenone concentrations (µg/g dry sediment) and unsaturation indices (Uk´37) on 280 samples from Ocean Drilling Program Hole 1002C over the last full glacial cycle (marine oxygen isotope Stages [MIS] 1-6). Alkenone concentrations vary dramatically in relation to glacial-interglacial cycles, with high concentrations typical of interglacial stages, high sea level, inferred high surface productivity, and bottom-water anoxia. Our reconstruction of low productivity during the last glacial maximum is consistent with previous reports of a sharp decline in the foraminiferal species Neogloboquadrina dutertrei, an upwelling index. Alkenone paleotemperatures show little cooling at both the last glacial maximum and MIS 6. Variations of as much as 4°C occurred during the earlier part of MIS 3 and MIS 4 as well as the latter part of MIS 5. The absence of cooling during glacial maxima determined from alkenone paleothermometry is consistent with faunal reconstructions for the western Caribbean but requires that much of the oxygen isotopic record of the planktonic foraminifer Globigerinoides ruber be influenced by salinity variations rather than temperature.
1Leckie, R.M., Sigurdsson, H., Acton, G.D., and Draper, G. (Eds.), 2000. Proc. ODP, Sci. Results, 165 [Online]. Available from World Wide Web: <http://www-odp.tamu.edu/publications/165_SR/165TOC.HTM>. [Cited YYYY-MM-DD]
2Department of Geological Sciences, Box 1846, Brown University, Providence, RI 02912, U.S.A. timothy_herbert@brown.edu
3GEOMAR Research Center, University of Kiel, Wischhofstrasse 1-3, Building 4, D-24148 Kiel, Federal Republic of Germany.
Date of
initial receipt: 27 July 1998
Date of acceptance: 29 April 1999
Ms 165SR-030