Antarctic control on tropical western Indian Ocean sea surface temperature and productivity during the late Pleistocene


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Sarah.Romahn [ at ] awi.de

Abstract

We reconstructed water column structure and surface productivity in the tropical western Indian Ocean to identify to what extent changes in surface water temperature and paleoproductivity are atmospherically controlled by the East African monsoon system or controlled by the ocean via subsurface water masses of Antarctic origin. For this purpose we analyzed proxy records of a 14C-AMS dated sediment Core GeoB12615-4 off Tanzania (07°08.30’S / 39°50.45’W, 446 m water depth) that spans the last 40 kyr. The hydrography at this site is influenced by a northwestern branch of the South Equatorial Current, the East African Coastal Current, which receives its water mainly via the Indonesian Throughflow and by equatorial upwelling of Subantarctic Mode Water (SAMW) at 5-10°S [Schott and McCreary, 2001]. The East African Monsoon may affect primary productivity and water mass stratification via nutrient and fresh water influx, respectively, from Rufiji River into the Indian Ocean. We used Mg/Ca ratios of the planktic foraminifer Globigerinoides ruber white (s.s.) for past sea surface temperature (SST) reconstructions and stable carbon isotope ratios of G. ruber white (s.s.) and the benthic foraminifer Planulina ariminensis for paleoproductivity calculations. We find strong correlations between paleoproductivity and SST. In addition, high δ13C values of bottom water coincide with low SST on centennial timescales. Most important, however, the SST pattern during the deglaciation resembles temperature records from continental Antarctic ice cores, with an early SST increase at ∼19 kyr BP and a distinct temperature setback, simultaneous to the Antarctic Cold Reversal. We suggest SAMW to be the most likely thermal link between western tropical Indian and Antarctic Oceans during the past 40 kyr and, moreover, to be the main control on marine primary productivity. Our conclusion corroborates earlier studies suggesting the SST in the Western Indian Ocean to be controlled by SAMW and thereby modulated by Antarctic temperature [Kiefer et al., 2006; Naidu and Govil, 2010]. Kiefer, T. McCave, I.N. and Elderfield, H. (2006). Antarctic control on tropical Indian Ocean sea surface temperature and hydrography, Geophys. Res. Lett, 33, L24612. Naidu, P. D., and P. Govil (2010). New evidence on the sequence of deglacial warming in the tropical Indian Ocean, Journal of Quaternary Science, 25(7), 1138-1143. Schott, F. A., and J. P. McCreary (2001). The monsoon circulation of the Indian Ocean, Progress In Oceanography, 51(1), 1-123.



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Conference (Poster)
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Not peer-reviewed
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Published
Event Details
The Agulhas System and its Role in Changing Ocean Circulation, Climate, and Marine Ecosystems - American Geophysical Union Chapman Conference, 08 Oct 2012 - 12 Oct 2012, Stellenbosch, South Africa.
Eprint ID
33058
Cite as
Romahn, S. , Mackensen, A. , Pätzold, J. and Groeneveld, J. (2012): Antarctic control on tropical western Indian Ocean sea surface temperature and productivity during the late Pleistocene , The Agulhas System and its Role in Changing Ocean Circulation, Climate, and Marine Ecosystems - American Geophysical Union Chapman Conference, Stellenbosch, South Africa, 8 October 2012 - 12 October 2012 .


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