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196 CHAPTER 6. FORSCHUNGSSTELLE “RADIOMETRIE” 6.1.6 Reconstruction of the 10 Be-production based on deep sea sediments from the North Atlantic Participating scientist Boris Schulze, M. Christl, F. Bernsdorff, A. Mangini, D. Wagenbach, P. W. Kubik (Zürich) Abstract The 10 Be-production is inversely related with the Earth‘s magnetic field strength. A highly resolved record of 10 Be-production is produced based on highly accumulating deep sea sediments from Bermuda Rise. The data support the idea of using 10 Be as a global matching-tool and as a proxy for geomagnetic paleointensity. Figure 6.5: 10 Be deposition rate, transport corrected by 230 Th-normalization. Compared are data from ODP Sites 1063 (North Atlantik; red) and 1089 (South Atlantic; blue). Background Cosmogenic 10 Be is produced by the interaction of galactic cosmic rays with oxygen and nitrogen atoms in the upper atmosphere of the Earth. Thus, 10 Be-production is inversely related with the Earth‘s magnetic field strength. After different processes of transport, the variations of the 10 Be-production eventually are conserved as varying 10 Be-deposition fluxes in different archives (ice cores, marine and terrestrial sediments). Knowing the past production rate of 10 Be, it should be possible to synchronize chronologies of different archives by comparison of the reconstructed 10 Be-deposition fluxes. Funding DFG Schwerpunktprogramm: Antarktisforschung mit vergleichenden Untersuchungen in arktischen Gebieten (SPP 1158) Methods and results A high-resolution record of 10 Be-production is produced based on highly accumulating deep sea sediments from Bermuda Rise (ODP Site 1063). To correct for marine transport signals, the 230 T hexcess normalisation technique is applied. The 10 Be -concentration (measured at the ETH-Zürich) and the activity of Th/U-isotopes (by alpha-spectroscopy) were determined in sediments of the past 100 kyr. The comparison of the 230 T h-normalized 10 Be-flux at Site 1063 with other records ( 10 Be-fluxes, atmospheric ∆ 14 C, and paleointensity) revealed a very good interhemispheric correlation. Thus, the results of this work strongly support the idea of using 10 Be as a global matching-tool for the synchronisation of marine, terrestrial, and ice-core chronologies and as a proxy for geomagnetic paleointensity. Outlook/Future work The 10 Be and U/Thdataset of the deep sea sediments from ODP Site 1063 will be further expanded and compared to the data from ODP Sites 983 (North Atlantic) and 1089 (South Atlantic). Main publication Schulze [2005]; Christl et al. [2005]
6.1. RADIOMETRIC DATING OF WATER AND SEDIMENTS 197 6.1.7 U/Th dating of deep-water corals from the North Atlantic Participating scientist Andrea Schröder-Ritzrau, A. Mangini, A. Freiwald (Tübingen), G. Hoffman (Zürich) Abstract Coupled uranium-series and radiocarbon measurements on deep-water corals are a proxy to estimate intermediate water ages. 17 intermediate water ages were estimated on deep-water corals from the eastern North Atlantic. These data give strong evidence for periodic reduced ventilation in the North Atlantic during the LGM/Holocene transition. 600 400 � 14 C ‰ 200 0 � C Cariaco Basin; Hughen et al. 2004 14 � 14 C model/atm; Laj et al. 2002 � 14 C atm INTCAL; Reimer et al. 2004 � 14 C marin INTCAL; Hughen et al. 2004 -200 0 4000 8000 12000 16000 20000 24000 age (years BP) Figure 6.6: ∆ 14 Cintermediate water (red data points) compared to various ∆ 14 C records and models (see references in the Fig.). Data are plotted without error bars for clarity - except for the deep-water coral data. Background Thermohaline circulation in the world ocean has a major influence on climate. Hence, changes of thermohaline circulation and water mass distribution especially in the North Atlantic during climate transitions are of major interest for paleoceanographic and climatic reconstructions. It is suggested that at terminations the intermediate water has a larger component of poorly ventilated SSW (Southern Source Water) compared to interglacials and full glacials. The 14 C/ 12 C ratio of dissolved inorganic carbon is a powerful tracer for reconstructing the pathways of deep- and intermediate water in the ocean. Coupled AMS- 14 C- and Th/U- (TIMS) measurements on coral carbonate, deliver a snapshot of the 14 C-concentration of deep- or intermediate water at the time and place the coral lived [Mangini et al. 1998]. Funding DFG and EU Methods and results Intermediate water ages were calculated via the method of 14 C projection ages [Adkins and Boyle, 1997]. Radiocarbon dates (measured at the ETH-Zurich and at the Leibniz-Laboratory in Kiel) and uranium series ages (via TIMS in HD) were used to calculate the ∆ 14 Cintermediate water of the former sur- rounding intermediate water the coral lived in. Assuming closed system radiocarbon decay and no further exchange with atmospheric radiocarbon, the calculated ∆ 14 Cintermediate water of the coral (Fig. 6.6) can be backtracked to the crossover-point with the (∆ 14 C past/atm) [Reimer et al., 2004]. This ratio (∆ 14 C past/coral) is the ratio of the water that had equilibrated with the past atmosphere. This value was applied in the equation for the ventilation age [Mangini et al., 1998] where non-reservoir-corrected ventilation ages (intermediate water ages) are determined. A total of 69 deep-water corals were investigated and 17 intermediate water ages were calculated. Our data document short periods of reduced conveyor circulation associated with increasing influence of SSW at intermediate water depth at the end of Heinrich I and the end of the Younger Dryas event. These periods are associated with meltwater discharge (MPIA and B). A similar event in the early Holocene has to be verified. Outlook/Future work none in this case, the project is finished Main publication Schröder-Ritzrau et al. [2003]; Schröder-Ritzrau et al. [2005]
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Contents 1 Introduction/Overview of
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CONTENTS 7 3.2.1 Glaciological pilo
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Overview Summary Atmospheric resear
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2.3. RADIATIVE TRANSFER 45 2.3 Radi
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2.3. RADIATIVE TRANSFER 47 Funding
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2.7. CARBON CYCLE GROUP 111 2.7.4 I
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3.2. ICE AND CLIMATE 137 3.2 Ice an
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3.2. ICE AND CLIMATE 139 regions) a
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