Clim. Past Discuss., 9, 3209-3238, 2013
www.clim-past-discuss.net/9/3209/2013/
doi:10.5194/cpd-9-3209-2013
© Author(s) 2013. This work is distributed
under the Creative Commons Attribution 3.0 License.
Review Status
This discussion paper has been under review for the journal Climate of the Past (CP). Please refer to the corresponding final paper in CP.
Salinity changes in the Agulhas leakage area recorded by stable hydrogen isotopes of C37 alkenones during Termination I and II
S. Kasper1, M. T. J. van der Meer1, A. Mets1, R. Zahn2, J. S. Sinninghe Damsté1, and S. Schouten1
1NIOZ Royal Netherlands Institute for Sea Research, Department of Marine Organic Biogeochemistry, P.O. Box 59, 1790 AB Den Burg (Texel), the Netherlands
2Universitat Autònoma de Barcelona, Institut de Ciència i Tecnologia Ambientals, 08193 Bellaterra, Spain

Abstract. At the southern tip of the African shelf, the Agulhas Current reflects back into the Indian Ocean causing so called "Agulhas rings" to spin off and release relatively warm and saline water into the South Atlantic Ocean. Previous reconstructions of the dynamics of the Agulhas current, based on paleo sea surface temperature and sea surface salinity proxies, inferred that Agulhas leakage from the Indian Ocean to the South Atlantic is reduced as a consequence of changes in wind fields related to a northwards migration of ice masses and the subtropical front during glacial stages. Subsequently, this might have led to a build-up of warm saline water in the southern Indian Ocean. To investigate this latter hypothesis, we reconstructed sea surface salinity changes using alkenone δ D, and paleo sea surface temperature using TEXH86 and UK'37, from two sediment cores (MD02-2594, MD96-2080) located in the Agulhas leakage area during Termination I and II. Both UK'37 and TEXH86 temperature reconstructions infer an abrupt warming during the glacial terminations, which is different from the gradual warming trend previously reconstructed based on Mg/Ca ratios of Globigerina bulloides. These differences in temperature reconstructions might be related to differences in the growth season or depth habitat between organisms. A shift to more negative δ Dalkenone values of approximately 14‰ during glacial Termination I and approximately 13‰ during Termination II is also observed. Approximately half of these shifts can be attributed to the change in global ice volume, while the residual isotopic shift is attributed to changes in salinity, suggesting relatively high salinities at the core sites during glacials, with subsequent freshening during glacial terminations. Approximate estimations suggest that δ Dalkenone represents a salinity change of ca. 1.7–2 during Termination I and ca. 1.5–1.7 during Termination II. These estimations are in good agreement with the proposed changes in salinity derived from previously reported combined planktonic foraminifera δ18O values and Mg/Ca-based temperature reconstructions. Our results show that the δ D of alkenones is a potentially suitable tool to reconstruct salinity changes independent of planktonic foraminifera δ18O.

Citation: Kasper, S., van der Meer, M. T. J., Mets, A., Zahn, R., Sinninghe Damsté, J. S., and Schouten, S.: Salinity changes in the Agulhas leakage area recorded by stable hydrogen isotopes of C37 alkenones during Termination I and II, Clim. Past Discuss., 9, 3209-3238, doi:10.5194/cpd-9-3209-2013, 2013.
 
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