12. Stable Isotope Record of the Last 500 k.y. at Site 1087 (Southern Cape Basin)¹

C. Pierre,² J.F. Saliege,² M.J. Urrutiaguer,² and J. Giraudeau³

ABSTRACT

High-resolution planktonic and benthic stable isotope records from Ocean Drilling Program Site 1087 off southeast Africa provide the basis for a detailed study of glacial-interglacial (G-IG) cycles during the last 500 k.y. This site is located in the Southern Cape Basin at the boundary of the coastal upwelling of Benguela and close to the gateway between the South Atlantic and the Indian Oceans. It therefore monitors variations of the hydrological fronts associated with the upwelling system and the Atlantic-Indian Ocean interconnections, in relation to global climate change. The coldest period of the last 500 k.y. corresponds to marine isotope Stage (MIS) 12, when surface water temperature was 4°C lower than during the last glacial maximum (LGM) as recorded by the surface-dwelling foraminifer Globigerinoides ruber. The warmest periods occurred during MISs 5 and 11, a situation slightly different to that observed at Site 704, which is close to the Polar Front Zone, where there is no significant difference between the interglacial stages for the past 450 k.y., except the long period of warmth during MIS 11.

The planktonic and benthic carbon isotope records do not follow the G-IG cycles but show large oscillations related to major changes in the productivity regime. The largest positive ¹³C excursion between 260 and 425 ka coincides with the global mid-Brunhes event of carbonate productivity. The oxygen and carbon isotopic gradients between surface and deep waters display long-term changes superimposed on rapid and high-frequency fluctuations that do not follow the regular G-IG pattern; these gradients indicate modifications of the temperature, salinity, and productivity gradients due to changes in the thermocline depth, the position of the hydrological fronts, and the strength of the Benguela Current.

¹Pierre, C., Saliege, J.F., Urrutiaguer, M.J., and Giraudeau, J., 2001. Stable isotope record of the last 500 k.y. at Site 1087 (Southern Cape Basin). 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_12/chap_12.htm>. [Cited YYYY-MM-DD]

²Université Pierre and Marie Curie, Laboratoire d'Oceanographie Dynamique et de Climatologie, 4 Place Jussieu, 75252 Paris Cedex 05, France. Correspondence author: cat@lodyc.jussieu.fr

³Université de Bordeaux I, DGO, avenue des Facultés, 33405 Talence, France.

Initial receipt: 20 March 2000
Acceptance: 14 September 2000
Web publication: 17 April 2001
Ms 175SR-230