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Climate of the Past An interactive open-access journal of the European Geosciences Union
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Preprints
https://doi.org/10.5194/cp-2020-115
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/cp-2020-115
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  29 Sep 2020

29 Sep 2020

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This preprint is currently under review for the journal CP.

Nutrient utilization and diatom productivity changes in the low-latitude SE Atlantic over the past 70 kyr: Response to Southern Ocean leakage

Katharine Hendry1, Oscar Romero2,3, and Vanessa Pashley4 Katharine Hendry et al.
  • 1University of Bristol, School of Earth Sciences, Wills Memorial Building, Queen’s Road, Bristol, BS8 1RJ, UK
  • 2MARUM–Center for Marine Environmental Sciences, Leobener Str. 8, University of Bremen, 28359 Bremen, Germany
  • 3Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, 27568 Bremerhaven, Germany
  • 4Geochronology and Tracers Facility, British Geological Survey, Keyworth, NG12 5GG, UK

Abstract. Eastern Boundary Upwellings (EBUs) are some of the key loci of biogenic silica (opal) burial in the modern ocean, representing important productive coastal systems that extraordinarily contribute to marine organic carbon fixation. The Benguela Upwelling System (BUS), in the low-latitude SE Atlantic, is one of the major EBUs, which is under the direct influence of nutrient-rich Southern Ocean waters. Quantification of past changes in diatom productivity through time, in response to Late Quaternary climatic change, feeds into our understanding of the sensitivity of EBUs to future climatic perturbations. Existing sediment archives of silica cycling include: opal burial fluxes, diatom assemblages and opaline silicon isotopic variations (denoted by d30Si). Burial fluxes and siliceous assemblages are limited to recording the remains reaching the sediment (i.e. export), and d30Si variations are complicated by species-specific influences and seasonality. Here, we present the first species-specific d30Si record from the BUS, encompassing full glacial conditions to the Holocene. In addition to export, our new data allows us to reconstruct utilisation of dissolved Si in surface waters in an area with strong input from Southern Ocean waters. Our new archives show that there was enhanced upwelling of Southern Ocean Si-rich water, and accompanied strong silicic acid utilisation by coastal dwelling diatoms, during Marine Isotope Stage 3 (60–40 kyr). This pulse of strong silicic acid utilisation was followed by a weakening of upwelling and coastal diatom Si utilisation into MIS2, before an increase in pelagic diatom Si utilisation across the deglaciation. We combine our findings with mass balance model experiments to show that changes in surface water silica cycling through time are a function of both upwelling intensity and utilisation changes, illustrating the sensitivity of EBUs to climatic change on glacial-interglacial scales.

Katharine Hendry et al.

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Short summary
Productive Eastern boundary upwelling systems (EBUs) are characterised by abundant siliceous algae, diatoms, and play a key role in carbon fixation. Understanding past shifts in diatom production is critical for predicting the impact of future climate change. We combine existing sediment archives from the Benguela EBU with new diatom isotope analyses and modelling to reconstruct Late Quaternary silica cycling, which we suggest depends on both upwelling intensity and surface utilisation.
Productive Eastern boundary upwelling systems (EBUs) are characterised by abundant siliceous...
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