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• W943716509 abstract "Global ocean circulation affects climate through its influence on transport and thecarbon cycle. Past changes in global ocean circulation may have played an importantrole in past glacial-interglacial cycles. This study examines changes in deep-watercirculation and carbonate chemistry in the Southwest Pacific sector of the SouthernOcean over the past 160 kyrs using benthic foraminiferal stable isotopes andcarbonate dissolution proxy records. Two sediment cores (located at 3310 m and4002 m water depths) are the focus of this research and are positioned south of theSubtropical Front south of Australia in modern Circumpolar Deep Water. Thechronostratigraphy of the cores is established by accelerator mass spectrometry(AMS) 14C dates, benthic and planktonic foraminiferal δ180 and lithostratigraphy.Results of this study provide new, deep-water Southern Ocean δ13C values from sitesunlikely to be impacted by productivity effects and establishes that glacial (LastGlacial Maximum (LGM); 18-24 kyrs and Stage 6.2; 134-137 kyrs) benthicforaminifera (Cibicidoides spp.) δ13C values are depleted compared to interglacial(Holocene; 0-10 kyrs and Stage 5.5; 118-124 kyrs) values. Previously, depletedSouthern Ocean glacial δ13C values have implied a reduced contribution of northernsource deep-water input into the Southern Ocean [Oppo and Fairbanks, 1987; Oppoet al., 1990; Charles and Fairbanks, 1992; Ninnemann and Charles, 2002].However, the global δ13C reconstruction in this study, suggests Southern Ocean δ13Cvalues were lower than northern source deep-water values and greater than or equalto Pacific δ13C values, implying there was no 'shut down' of deep-water circulationpatterns during the glacial intervals over the past 160 kyrs.Comparisons between LGM δ13C records from the South Tasman Rise (STR) andpublished records from Atlantic, Pacific, Indian and Southern Oceans suggests: ( 1)horizontal δ13C gradients were maintained in the LGM between the Atlantic, Pacificand Southern Oceans above ,..,3500 m, (2) LGM Southern Ocean δ13C valuesresemble LGM Pacific b13C values at water depths below ,..,3500 m, and (3) LGMbottom waters in the Atlantic, Pacific and Southern Ocean converge to similar δ13Cvalues below ,..,4000 m. A criterion to exclude benthic δ13C records possibly affectedby productivity overprints (Δδ13CcIb-DIc> -0.2 %0) enabled this interpretation. Planktonic foraminiferal shell weights for Globorotalia injlata (355-425 μm and300-355 μm) and Globerigina bulloides (355-425 μm) are calibrated to depthnormalisedcarbonate ion concentrations. LGM shell weights estimate the deep-watercarbonate ion concentration ([C03=]) at the STR was ,...,10-13 μmol/kg greater thanduring the Holocene. Together with a revised shell weight calibration in theequatorial Atlantic and Pacific, the LGM deep-water [C03 =] reconstruction suggests:(1) Southern Ocean [C03=] were intermediate to Atlantic and Pacific [C03=] above,...,4000 m and, (2) LGM bottom waters in the Atlantic, Pacific and Southern Oceanconverge to similar [C03=] below ,...,4000 m, suggesting a similar deep-water source.Carbonate preservation indices (%CaC03 and %whole planktonic foraminifera) atthe STR indicate three dissolution maxima at ,_,159 kyrs, ,....,66 kyrs (Stage 4), and ,...,27kyrs. The dissolution records display similar timing to those recorded in the deepequatorial Pacific [Le and Shackleton, 1992] and deep South Atlantic [Hodell et al.2001]. The synchroneity between the carbonate dissolution events at the STR, theequatorial Pacific and the deep South Atlantic 'lndo-Pacific' carbonate stratigraphy[Hodell et al. 2001], along with a similar deep-water [C03=] for these basins below,_,4000 m, suggest a similar deep-water source at these locations during glacialintervals.The oxygen and carbon isotopic records were obtained from Globigerina bulloides(300-355 μm) at MD972106 and GC34. The two cores are located close to themodem calcite saturation horizon in modern Circumpolar Deep Water (CPDW),providing a test of the effects of carbonate dissolution on G. bulloides stable isotopiccomposition. There are differences between the stable isotopic compositions (δ180and δ13C) between the two cores, particularly during interglacial intervals. G.bulloides δ180 and shell weights are tightly correlated to each other and toatmospheric pC02 , and are most likely due to the combined effects of the selectivedissolution of foraminiferal shell calcite and calcification rates of G. bulloides.Isotopic and shell weight gradients between the two cores show large changes atglacial-interglacial transitions. The complex relationship between post-depositionaldissolution and calcification rates of G. bulloides suggest both influence its stableisotopic composition. It is difficult to isolate the effects of each process on G.bulloides δ180 and δ13C records at both sites." @default.
• W943716509 created "2016-06-24" @default.
• W943716509 creator A5079720275 @default.
• W943716509 date "2005-01-01" @default.
• W943716509 modified "2023-09-27" @default.
• W943716509 title "Late pleistocene palaeoceanographic and geochemical evolution of the South Tasman Rise" @default.
• W943716509 hasPublicationYear "2005" @default.
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