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-Melé, 4 L. Vidal, 5
and M. Brownless 6
ABSTRACT
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-Melé, 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.
5Universität
Bremen, Geowissenschaften, Postfach 330440, D-28334 Bremen, Federal Republic of
Germany. Present address: CEREGE, Université 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
