sea-surface
temperature (SST) estimates obtained at ~2.5-k.y. resolution from Ocean Drilling
Program Site 1020 show glacial-interglacial cyclicity with an amplitude of 7°-10°C
over the last 780 k.y. This record shows a similar pattern of variability to
another alkenone-based SST record obtained previously from the Santa Barbara
Basin. Both records show that oxygen isotope Stage (OIS) 5.5 was warmer by ~3°C
relative to the present and that glacial
temperatures warm in advance of deglaciation, as inferred from benthic
18O
records. The alkenone-based SST record at Site 1020 is longer than previously
published work along the California margin. We show that warmer than present
interglacial stages have occurred frequently during the last 800 k.y. Alkenone
concentrations, a proxy for coccolithophorid productivity, indicate that
sedimentary marine organic carbon content has also varied significantly over
this interval, with higher contents during interglacial periods. A baseline
shift to warmer SST and greater alkenone content occurs before OIS 13.
We compare our results with those from previous multiproxy studies in this region and conclude that SST has increased by ~5°C since the last glacial period (21 ka). Our data show that maximum alkenone SSTs occur simultaneously with minimum ice volume at Site 1020, which is consistent with data from farther south along the margin. The presence of sea ice in the glacial northeast Pacific, the extent of which is inferred from locations of ice-rafted debris, provides further support for our notion of cold surface water within the northern California Current system, averaging 7°-8°C cooler during peak glacial conditions. The cooling of surface water during glacial stages most likely did not result from enhanced upwelling because alkenone concentrations and terrestrial redwood pollen assemblages are consistently lower during glacial periods.
1Lyle, M., Koizumi, I., Richter, C., and Moore, T.C., Jr. (Eds.), 2000. Proc. ODP, Sci. Results,167 [Online]. Available from World Wide Web: <http://www-odp.tamu.edu/publications/167_SR/167sr.htm>. [Cited YYYY-MM-DD]
2Department of Geological Sciences, Box 1846, Brown University, Providence RI 02912, USA. Correspondence author: timothy_herbert@brown.edu
Date of
initial receipt: 27 October 1998
Date of acceptance: 25 August 1999
Ms 167SR-213