Deep flow in the Madagascar-Mascarene Basin over the last 150,000 years

McCave, I. N. and Kiefer, T. and Thornalley, D. J. R. and Elderfield, H. (2005) Deep flow in the Madagascar-Mascarene Basin over the last 150,000 years. Philosophical Transactions of the Royal Society of London A, 363. pp. 81-99. DOI 10.1098/rsta.2004.1480

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Abstract

The SW Indian Ocean contains at least four layers of water masses with different sources: deep Antarctic (Lower Circumpolar Deep Water) flow to the north, midwater North Indian Deep Water flow to the south and Upper Circumpolar Deep Water to the north, meridional convergence of intermediate waters at 500–1500 m, and the shallow South Equatorial Current flowing west. Sedimentation rates in the area are rather low, being less than 1 cm ka−1 on Madagascar Ridge, but up to 4 cm ka−1 at Amirante Passage. Bottom flow through the Madagascar–Mascarene Basin into Amirante Passage varies slightly on glacial–interglacial time-scales, with faster flow in the warm periods of the last interglacial and minima in cold periods. Far more important are the particularly high flow rates, inferred from silt grain size, which occur at warm-to-cold transitions rather than extrema. This suggests the cause is changing density gradient driving a transiently fast flow. Corroboration is found in the glacial–interglacial range of benthic δ18O which is ca. 2 %, suggesting water close to freezing and at least 1.2 more saline and thus more dense glacial bottom waters than present. Significant density steps are inferred in isotope stage 6, the 5e–5d, and 5a–4 transitions. Oxygen isotope data suggest little change by mixing in glacial bottom water on their northward path. Benthic carbon isotope ratios at Amirante Passage differ from glacial Southern Ocean values, due possibly to absence of a local productivity effect present in the Southern Ocean

Item Type: Article
Uncontrolled Keywords: 2005 PUBL 2005 AREP IA47, Part III
Subjects: 01 - Climate Change and Earth-Ocean Atmosphere Systems
Divisions: 01 - Climate Change and Earth-Ocean Atmosphere Systems
06 - Part-III Projects
Journal or Publication Title: Philosophical Transactions of the Royal Society of London A
Volume: 363
Page Range: pp. 81-99
Identification Number: 10.1098/rsta.2004.1480
Depositing User: Sarah Humbert
Date Deposited: 20 Jan 2011 09:45
Last Modified: 09 Jun 2014 16:19
URI: http://eprints.esc.cam.ac.uk/id/eprint/1743

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