18O
record indicates intensified bottom-current activity during the Younger Dryas
and stadials of marine isotope Stage 3. This result strongly supports the
hypothesis of Kennett and his colleagues.Intensification of North Pacific Intermediate Water during the Younger Dryas and stadials of the last glacial episode has been advocated by Kennett and his colleagues based on studies of ventilation history in Santa Barbara Basin. Because Santa Barbara Basin is a semi-isolated marginal basin, this hypothesis requires testing in sequences on the upper continental margin facing the open-ocean of the Pacific.
Ocean Drilling Program
Site 1017 is located on the upper slope of southern California off Point
Conception close to the entrance of Santa Barbara Basin, an ideal location to
test the hypothesis of late Quaternary switching in intermediate waters. We
examined chemical and mineral composition, sedimentary structures, and grain
size of hemipelagic sediments representing the last 80 k.y. at this site to
detect changes in behavior of intermediate waters. We describe distinct
compositional and textual variations that appear to reflect changes in grain
size in response to flow velocity fluctuations of bottom waters. Qualitative
estimates of changes in degree of pyritization indicate better ventilation of
bottom water during intervals of stronger bottom-water flow. Comparison between
variations in the sediment parameters and the planktonic 18O
record indicates intensified bottom-current activity during the Younger Dryas
and stadials of marine isotope Stage 3. This result strongly supports the
hypothesis of Kennett and his colleagues.
Our investigation also suggests strong grain-size control on organic carbon content (and to less extent carbonate carbon content). This, in turn, suggests the possibility that organic carbon content of sediments, which is commonly used as an indicator of surface productivity, can be influenced by bottom currents.
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]
2Geological Institute, University of Tokyo, 7-3-1 Hongo, Tokyo 113-0033, Japan. ryuji@tsunami.geol.s.u-tokyo.ac.jp
3Department of Earth and Planetary Sciences, Hokkaido University, Kita-10, Nishi-8, Kitaku, Sapporo, 060-0810, Japan.
4Department of Geological Science and Marine Science Institute, University of California, Santa Barbara, Santa Barbara CA 93106, USA.
Date of
initial receipt: 16 October 1998
Date of acceptance: 27 April 1999
Ms 167SR-222
