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https://doi.org/10.5194/bg-2019-125
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/bg-2019-125
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 20 May 2019

Research article | 20 May 2019

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

Organic carbon rich sediments: benthic foraminifera as bio-indicators of depositional environments

Elena Lo Giudice Cappelli1, Jessica L. Clarke1,2, Craig Smeaton1, Keith Davidson3, and William E. N. Austin1,3 Elena Lo Giudice Cappelli et al.
  • 1School of Geography and Sustainable Development, University of St Andrews, St Andrews, KY16 9AL, Scotland, UK
  • 2School of Natural and Environmental Sciences, Newcastle University, Newcastle, NE1 7RU, UK
  • 3Scottish Association for Marine Science, Scottish Marine Institute, Oban, PA37 1QA, Scotland, UK

Abstract. Fjords have been described as hotspots for carbon burial, potentially playing a key role within the carbon cycle as climate regulators over multiple timescales. Nevertheless, little is known about the long-term fate of the carbon that may become stored in fjordic sediments. One of the main reasons for this knowledge gap is that carbon arriving on the seafloor is prone to post-depositional degradation, posing a great challenge when trying to discriminate between an actual change in carbon deposition rate and post depositional carbon loss. In this study, we evaluate the use of modern benthic foraminifera as bio-indicators of carbon content in six voes (fjords) on the west coast of Shetland. Benthic foraminifera are sensitive to changes in carbon content in the sediments, and changes in their assemblage composition therefore reflect synchronous variations in the quantity and quality of carbon reaching the seafloor. We identified four environments based on the relationship between benthic foraminiferal assemblages and carbon content in the sediments: 1) Land-locked regions influenced by riverine/freshwater inputs of organic matter, namely the head of fjords with a restricted geomorphology; 2) Stressed environments with a heavily stratified water column and sediments rich in organic matter of low nutritional value; 3) Depositional environments with moderate organic content and mild or episodic current activity; 4) Marginal to coastal settings with low organic content, such as fjords with an unrestricted geomorphology. We conclude that foraminifera potentially provide a tool to disentangle primary carbon signals from post-depositional degradation and loss of carbon because of their environmental sensitivity and high preservation potential in the sedimentary record.

Elena Lo Giudice Cappelli et al.
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Elena Lo Giudice Cappelli et al.
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Short summary
Fjords are known sinks of organic carbon (OC); however, little is known about the long-term fate of the OC stored in these sediments. The reason of this knowledge gap is due to post-depositional degradation of OC. This study uses benthic foraminifera (microorganisms with calcite shells) to discriminate between post-depositional OC degradation and actual OC burial and accumulation in fjordic sediments, as foraminifera would only preserve the latter information in their assemblage composition.
Fjords are known sinks of organic carbon (OC); however, little is known about the long-term fate...
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