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Contrasting variability in foraminiferal and organic paleotemperature proxies in sedimenting particles of the Mozambique Channel (SW Indian Ocean)
Fallet, U.; Ullgren, J.E; Castañeda, I.S.; van Aken, H.M.; Schouten, S.; Ridderinkhof, H.; Brummer, G.J.A. (2011). Contrasting variability in foraminiferal and organic paleotemperature proxies in sedimenting particles of the Mozambique Channel (SW Indian Ocean). Geochim. Cosmochim. Acta 75(20): 5834-5848. dx.doi.org/10.1016/j.gca.2011.08.009
In: Geochimica et Cosmochimica Acta. Elsevier: Oxford,New York etc.. ISSN 0016-7037, more
Peer reviewed article  

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  • Fallet, U., more
  • Ullgren, J.E, more
  • Castañeda, I.S., more
  • van Aken, H.M., more
  • Schouten, S., more
  • Ridderinkhof, H., more
  • Brummer, G.J.A., more

Abstract
    Accurate sea surface temperature (SST) proxies are important for understanding past ocean and climate systems. Here, we examine material collected from a deep-moored sediment trap in the Mozambique Channel (SW Indian Ocean) to constrain and compare both inorganic (delta O-18, Mg/Ca) and organic (U-37(k'), TEX86) temperature proxies in a highly dynamic oceanographic setting for application in paleoceanography. High-resolution time-series current velocity data from long-term moorings (2003 - present) deployed across the Mozambique Channel reveal the periodic migration of four to six meso-scale eddies through the channel per year. These meso-scale eddies strongly influence water mass properties including temperature and salinity. Despite the dynamic oceanographic setting, fluxes of the surface-dwelling planktonic foraminifera Globigerinoides ruber and Globigerinoides trilobus follow a seasonal pattern. Temperatures reconstructed from G. ruber and G. trilobus delta O-18 and Mg/Ca closely mirror seasonal SST variability and their flux-weighted annual mean SSTs of 28.1 degrees C and 27.3 degrees C are in close agreement with annual mean satellite SST (27.6 degrees C). The sub-surface dwelling foraminifera Neogloboquadrina dutertrei and Globigerinoides scitula recorded high-frequency temperature variations that, on average, reflect conditions at water depths of 50-70 m and 200-250 m, respectively. Concentrations and fluxes of organic compounds (alkenones and crenarchaeol) display no or only moderate seasonality but flux weighted means of the associated temperature signatures, U-37(k'), and TEX86H of 28.3 degrees C and 28.1 degrees C, respectively, also closely reflect mean annual SST. We analyzed all time-series data using multiple statistical approaches including cross-correlation and spectral analysis. Eddy variability was clearly expressed in the statistical analysis of physical oceanographic parameters (current velocity and sub-surface temperature) and revealed a frequency of four to six cycles per year. In contrast, statistical analysis of proxy data from the sediment trap did not reveal a significant coupling between eddy migration and organic compound fluxes or reconstructed temperatures. This is likely a result of the relatively low resolution (21 days) and short (2.5 years) duration of the time series, which is close to the detection limit of the eddy frequency.

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