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Biogeosciences An interactive open-access journal of the European Geosciences Union
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https://doi.org/10.5194/bg-2019-15
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/bg-2019-15
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 01 Feb 2019

Research article | 01 Feb 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Biogeosciences (BG).

Long chain diols in settling particles in tropical oceans: insights into sources, seasonality and proxies

Marijke W. de Bar1, Jenny Ullgren2, Robert C. Thunnell, Stuart G. Wakeham3, Geert-Jan A. Brummer4,5, Jan-Berend W. Stuut4,5, Jaap S. Sinninghe Damsté1,6, and Stefan Schouten1,6 Marijke W. de Bar et al.
  • 1NIOZ Royal Netherlands Institute for Sea Research, Department of Marine Microbiology and Biogeochemistry, and Utrecht University, P.O. Box 59, 1790 AB Den Burg, Texel, the Netherlands
  • 2Runde Miljøsenter, Runde, Norway
  • 3Skidaway Institute of Oceanography, University of Georgia, 10 Ocean Science Circle, Savannah, USA
  • 4NIOZ Royal Netherlands Institute for Sea Research, Department of Ocean Systems, and Utrecht University, P.O. Box 59, 1790 AB Den Burg, Texel, the Netherlands
  • 5Vrije Universiteit Amsterdam, Faculty of Science, Department of Earth Sciences, De Boelelaan 1085, 1081HV Amsterdam, the Netherlands
  • 6Department of Earth Sciences, Faculty of Geosciences, Utrecht University, the Netherlands
  • deceased

Abstract. In this study we have analyzed sediment trap time series from five tropical sites to assess seasonal variations in concentrations and fluxes of long-chain diols (LCDs) and associated proxies with emphasis on the Long chain Diol Index (LDI). For the tropical Atlantic, we observe that generally less than 2 % of LCDs settling from the water column are preserved in the sediment. The Atlantic and Mozambique Channel traps reveal minimal seasonal variations in the LDI, similar to the TEX86 and U37. However, annual mean LDI-derived temperatures are in good agreement with the annual mean satellite-derived sea surface temperatures (SSTs). In the Cariaco Basin the LDI shows larger seasonal variation, as do the TEX86 and U37. Here, the LDI underestimates SST during the warmest months, which is likely due to summer stratification and the habitat depth of the diol producers deepening to around 20 to 30 m. Surface sediment LDI temperatures in the Atlantic and Mozambique Channel compare well with the average LDI-derived temperatures from the overlying sediment traps, as well as with decadal annual mean SST. Lastly, we observed large seasonal variations in the Diol Index, as indicator of upwelling conditions, at three sites, potentially linked to Guinea Dome upwelling (Eastern Atlantic), seasonal upwelling (Cariaco Basin) and seasonal upwelling and/or eddy migration (Mozambique Channel).

Marijke W. de Bar et al.
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Marijke W. de Bar et al.
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Short summary
We have analyzed sediment traps from the Cariaco Basin, tropical Atlantic and Mozambique Channel to evaluate seasonal imprints in the concentrations and fluxes of long-chain diols, and the LDI proxy (sea surface temperature proxy) and Diol Index (upwelling indicator). Despite significant degradation, LDI-derived temperatures are very similar for the sediment traps and seafloor sediments, and correspond with annual mean SST.
We have analyzed sediment traps from the Cariaco Basin, tropical Atlantic and Mozambique Channel...
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