Reduced Agulhas Leakage during the Last Glacial Maximum inferred from an integrated provenance and flux study

Surface and intermediate waters from the Indian Ocean enter the Cape Basin in the southeast Atlantic by the "Agulbas Leakage", which adds heat and salt to the Atlantic Ocean, and may act as a positive feedback for the formation of North Atlantic Deep Water (NADW). In order to assess the role of the Agulhas Leakage in past climate change, it is important to constrain whether there was change in its flux in association with warmer and colder global climate intervals. This study uses the radiogenic isotope compositions of strontium and neodymium and the rubidium, strontium, samarium and neodymium concentrations of the terrigenous fraction of sediments from the oceans surrounding South Africa as tracers of sediment provenance, and the initial excess Thorium-230 of the bulk sediments as a constant flux proxy. The purpose is to assess the relationship between sediment sources around southern Africa and Agulhas Current flow for the Holocene and Last Glacial Maximum (LGM). Results point to the Agulhas Current as a major source of sediment to the southern Cape Basin during the Holocene, and show that the surface currents have an important control on the distribution of sediments in the South Atlantic. The Cape Basin data can be explained with three end-member mixing of particulates carried by (1) the Agulhas Current, (2) the South Atlantic or Antarctic Circumpolar Current (SAC or ACC) and (3) locally derived sediments from southern Africa. The composition of each end-member does not change significantly between the LGM and the Holocene. Comparison of the two time-slices show that a smaller fraction of sediment deposited in the Cape Basin is derived from the Agulhas Current during the LGM. The ACC and SAC were more sediment laden during the LGM and western sources were major contributors to the Cape Basin sediments. The data also indicate a much reduced Agulhas contribution to sediments deposited south and southeast of Africa beneath the present-day Agulhas Current flow, indicating a reduced transport of the Agulhas Current and reduced Agulhas Leakage during the LGM. (c) 2006 Elsevier B.V. All rights reserved.