18. Fluctuations in Productivity and Upwelling Intensity at Site 1083 during the Intensification of the Northern Hemisphere Glaciation (2.40-2.65 Ma)1

V.J. Ettwein, 2,3 C.E. Stickley, 2 M.A. Maslin, 2 E.R. Laurie, 2,3 A. Rosell-Melť, 4 L. Vidal, 5 and M. Brownless 6


Coastal upwelling regions play an important role in regulating the partial pressure of CO2, because they are zones of intense productivity and therefore contribute considerably to the drawdown mechanism. One of the major aims of Leg 175 was to develop an understanding of the relationship between wind-driven upwelling intensity and surface water productivity. In this paper, such a relationship during the late Pliocene intensification of the Northern Hemisphere glaciation (INHG) ~2.54 Ma is examined. Surface water productivity is reconstructed using principally diatoms and 15N, but total organic carbon is also used to a lesser extent. Results are compared with "hard" isothermal remnant magnetism, a proxy for wind strength. Lying offshore on the Walvis Ridge, Site 1083 is ideally located for such a study as it is influenced by the center of the Benguela Current upwelling system and is distant from terrestrial sources which may affect the productivity signal. Prior to the INHG, strong frontal systems were found to be operative over the site, with little interglacial-glacial fluctuation in wind intensity and productivity. Following the INHG, the development of trade winds induced the formation of an upwelling regime. However, where wind intensity remained elevated throughout the succeeding glacial periods, productivity levels peaked sharply during the interglacial-glacial transitions before falling again to levels comparable to those of interglacials. Such peaks during the initial stages of the glaciations may provide an important feedback mechanism for the further rapid, intensified cooling of global climate. 15N reconstructions of nutrient utilization, and the abundance of southern-source diatoms transported to the site via the nutrient-bearing Antarctic Intermediate Waters, suggest that productivity may have responded instead to the nutrient content of upwelled waters.

1Ettwein, V.J., Stickley, C.E., Maslin, M.A., Laurie, E.R., Rosell-Melť, A., Vidal, L., and Brownless, M., 2001. Fluctuations in productivity and upwelling intensity at Site 1083 during the intensification of the Northern Hemisphere glaciation (2.40-2.65 Ma). In Wefer, G., Berger, W.H., and Richter, C. (Eds.), Proc. ODP, Sci. Results, 175 [Online]. Available from World Wide Web: <http://www-odp.tamu.edu/publications/175_SR/chap_18/chap_18.htm>. [Cited YYYY-MM-DD]

2Environmental Change Research Centre, Department of Geography, University College London, 26 Bedford Way, London WC1H 0AP, United Kingdom. Correspondence author: v.ettwein@ucl.ac.uk

3Centre for Quaternary Research, Department of Geography, Royal Holloway, University of London, Egham, Surrey TW20 0EX, United Kingdom.

4Quaternary Environmental Change Research Group, Department of Geography, University of Durham, Science Site, South Road, Durham DH1 3LE, United Kingdom.

Present address: ICREA (Catalan Institution for Research and Advanced Studies), Centre of Environmental Studies (CEA) Edifici Cn, Autonomous University of Barcelona, 08193 Bellaterra (Barcelona), Catalonia, Spain.

5Universitšt Bremen, Geowissenschaften, Postfach 330440, D-28334 Bremen, Federal Republic of Germany. Present address: CEREGE, Universitť Aix-Marseille III, Europole de l'Arbois, BP 80, 13545 Aix en Provence, Cedex 04, France.

6Department of Geology, Royal Holloway, University of London, Egham, Surrey TW20 0EX, United Kingdom.

Initial receipt: 22 February 2000
Acceptance: 4 June 2001
Web publication: 10 August 2001
Ms 175SR-227