Surface and deep-water variability on the southern Agulhas Plateau: Interhemispheric links over the past 2 Ma

Jens.Gruetzner [ at ]


The Southern Ocean is involved in setting the state of global climate through its role in redistributing heat and salt through the world ocean and its control on atmospheric CO2. Utilising sediment core sites on the southern Agulhas Plateau (AP) in the southwest Indian Ocean, we present new records of ice-rafted debris mass accumulation rate (IRDMAR), intermediate and benthic oxygen and carbon isotope, sortable silt mean grain size and bulk sediment chemistry (XRF) spanning the past 2 Ma. The AP is situated at the southern extent of the Indian-Atlantic Ocean Gateway (I-AOG); the upper water column is dominated by Indian Ocean waters not leaked into the South Atlantic and instead flowing eastward as the Agulhas Return Current. South of the AP, the relatively cold and fresh waters of the Sub-Antarctic Zone (SAZ) meet their northern limit and steep meridional property gradients occur. The AP region is therefore highly sensitive to variations in both the Sub-Antarctic Zone (SAZ) to the south and the Agulhas Current System to the north. IODP Site U1475 (41°25.61’S; 25°15.64’E, 2669 m water depth), was recovered from a contourite drift deposit on the southern AP, situated close to the modern-day subtropical front. Together with complementary data from sediment core MD02-2588 from the same location, our results indicate that during glacial periods there was a persistent influence of a well-ventilated water mass within the I-AOG with a carbon isotope signature similar to present-day Northern Component Water (NCW). The records of chemical ventilation and near-bottom flow vigour closely reflect changes in the advection of NCW and meridional variability in the location of the Antarctic Circumpolar Current and its associated fronts, as recorded by IRDMAR. We suggest that equatorward expansions of the circum-Antarctic frontal system, occurring relatively early in the glacial sequence, are central in triggering this glacial overturning circulation, hence modulating global climate. On orbital timescales, the SAZ represents a window through which external forcing may be translated into the global climate system; likely relevant for the enigmatic Mid-Pleistocene Transition.

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Conference (Invited talk)
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AGU Fall Meeting 2019, 09 Dec 2019 - 13 Dec 2019, San Francisco, U.S.A..
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Hall, I. R. , Starr, A. , Hemming, S. R. , Barker, S. , van der Lubbe, J. , Sierra, A. C. , Berke, M. A. , Gruetzner, J. , Jiménez-Espejo, F. J. , Knorr, G. , LeVay, L. J. , Lathika, N. and Robinson, R. S. , IODP Expedition 361 Scientists (2019): Surface and deep-water variability on the southern Agulhas Plateau: Interhemispheric links over the past 2 Ma , AGU Fall Meeting 2019, San Francisco, U.S.A., 9 December 2019 - 13 December 2019 .

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