The California Current and associated coastal upwelling have changed with the growth and decay of the North American ice sheets since 2.5 Ma. Because the coastal upwelling has a close relationship with biogenic productivity in surface water, analyses of biogenic components in sediments of the upwelling region enable us to reconstruct the past changes of the productivity and/or the current systems.
In this study, we analyzed biogenic silica and carbonate as well as organic carbon in sediments from the northern California margin, Hole 1020B. The results show that terrigenous-free content of biogenic silica is high during interglacial periods since 800 ka and varies in correspondence with 100-k.y. glacial-interglacial cycles. On the other hand, terrigenous-free content of biogenic carbonate is high during glacial periods. These temporal variations may have been caused by changes in the origin of deep water.
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 Earth and Planetary Sciences, Hokkaido University, Kita 10, Nishi 8, Sapporo 060-0810, Japan. Correspondence author: kuro@ep.sci.hokudai.ac.jp
Date of
initial receipt: 19 October 1998
Date of acceptance: 25 August 1999
Ms 167SR-232