Rüggeberg, Andres (2000) Late Quaternary paleoceanography in the South Tasman Region : implications of benthic foraminifers and grain size analysis. (Diploma thesis), Christian-Albrechts-Universität zu Kiel, Kiel, Germany, 78, XVI pp.

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Abstract

This Thesis was compiled as part of the TASQWA project, which is an international project for reconstructing the variability of the water masses in the southern Tasman Sea and the Southern Ocean (SW Pacific Sector) of the late Quaternary. The paleoclimatic and paleoceanographic reconstructions are concentrated on micropaleontological, mineralogical and sedimentological analyses. The studied area is the South Tasman Rise (STR), which is located in the southern extension of Tasmania/ Australia. This still poorly investigated area is thought to play a major role as a part of the "Global Ocean Conveyor Belt" for the global ocean circulation. The goal of this thesis was to perform micropaleontological and sedimentological investigations of two sediment cores (SO136-124 and SO136-155), retrieved during cruise SO 136 at the STR. The two sediment cores were studied for its benthic foraminiferal assemblages and grain sizes of the bulk silt-sized fraction (2-63 μm). Late Quaternary sediment Core SO136-155 presents a distribution into oxygen isotope Stages 1 to late 6. Epistominella exigua is dominating the assemblage of the most important factor, revealed by multivariate statistics. Its accumulation rate (BFAR = Benthic Foraminiferal Accumulation Rate) shows peaks during glacial Stages 2, 4 and 6 and indicates short-term fluxes of fresh organic matter to the sea floor. This correlates well with the distribution of the subfraction 4.5 - 9 μm, consisting of coccoliths, coccolithophorids and to a minor degree of diatoms. These features indicate a northward shift of the frontal system and the influence of the nutrient-rich Subantarctic Surface Water, which induced plankton-blooms during glacial periods. The faunal assemblage of Pullenia quinqueloba and Pullenia bulloides dominates a second factor and suggests a continuous organic matter supply during interglacial Stages 1 and 5 (in particular in Substage 5.5). The distribution of the silt fraction shows maxima in subfraction 2 - 4 μm ( dominantly consisting of individual coccoliths) and a moderate presence of subfraction 15 - 31 μm (dominantly planktic foraminiferal fragments and juvenile planktic foraminifers). These features are related to the influence of the Subantarctic Front during peak interglacials, indicating a less variable, but continuously enhanced organic matter supply to the sea-floor. Sediment Core SO136-124 shows a low resolution for the sub-division into isotopic stages. The horizon of Mn-nodules at 36 cm core depth suggests a Tertiary age of the sediments downcore. At least a distribution into three "warm" and two "cold" periods is presented. Factor 1 of the faunal analysis indicates presumably "warmer" periods with a high and continuous organic matter flux from the sea-surface, dominated by Globocassidulina subglobosa and Epistominella exigua. This correlates well with the subfraction 2 - 6 μm, consisting of coccoliths, which can be related to indicate a higher organic matter supply to the sea-floor. Factors 2 and 3, described by agglutinated tube fragments and Nuttalides umbonifer, observe the influence of the Antarctic Bottom Water (AABW). Factor 2 occurs during the "cold" periods and also indicates a stronger carbonate dissolution, which is responsible for the highly dissolved coccoliths and may have produced the conglomerations of subfraction 14 - 28 μm, consisting of coccoliths and fragments of foraminiferal tests. The most dominant Factor 3, described by Nuttalides umbonifer, is related to indicate the influence of the AABW only, but not the dissolution of carbonate, because the species Oridosalis umbonatus, Epistominella exigua and Globocassidulina subglobosa also represent this factor. No clear relation between the components of the subfractions and Factor 3 is observed.

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