Preprints
https://doi.org/10.5194/bg-2021-105
https://doi.org/10.5194/bg-2021-105

  23 Apr 2021

23 Apr 2021

Review status: this preprint is currently under review for the journal BG.

Distribution of coccoliths in surface sediments across the Drake Passage and calcification of Emiliania huxleyi morphotypes

Nele Manon Vollmar1, Karl-Heinz Baumann1, Mariem Saavedra-Pellitero2, and Iván Hernández-Almeida3 Nele Manon Vollmar et al.
  • 1University of Bremen, Department of Geosciences, P.O. Box 33 04 40, 28334 Bremen, Germany
  • 2University of Birmingham, School of Geography, Earth and Environmental Sciences, Birmingham B15 2TT, UK
  • 3ETH Zürich, Geological Institute, Department of Earth Science, Sonneggstrasse 5, 8092, Zürich, Switzerland

Abstract. The Southern Ocean is experiencing rapid and profound changes in its physical and biogeochemical properties that may influence the distribution and composition of pelagic plankton communities. Coccolithophores are the most prolific carbonate-producing phytoplankton group playing an important role in Southern Ocean biogeochemical cycles. However, knowledge is scarce about the record of (sub-)fossil coccolith assemblages in the Southern Ocean, which are constituting invaluable indicators for paleoenvironmental reconstructions. This study investigates coccolith assemblages preserved in surface sediments of southernmost Chile and across the Drake Passage that were retrieved during R/V Polarstern Expedition PS97. We focused on the coccolith response to steep environmental gradients across the frontal system of the Antarctic Circumpolar Current and to hydrodynamic and post-depositional processes occurring in this region. We used statistical analyses to explore which environmental parameters influenced the coccolith assemblages by means of Cluster and Redundancy Analyses. We specifically assessed the morphological diversity of the dominant taxa, i.e. Emiliania huxleyi, emphasizing biogeographical variability of morphotypes, coccolith sizes and calcite carbonate mass estimations.

High coccolith abundances and species diversity compared to studies in the same area and in other sectors of the Southern Ocean occur, with a high species richness especially south of the Polar Front. While the surface sediments offshore Chile and north of the Polar Front provide suitable material to reconstruct overlying surface ocean conditions, further factors such as temporary thriving coccolithophore communities in the surface waters or transport of settling coccoliths via surface and bottom currents and eddies are influencing the (sub-)fossil coccolith assemblages south of the Polar Front. Additionally, deeper samples in the southern part of the study area are particularly affected by selective carbonate dissolution.

We identified five E. huxleyi morphotypes (A, A overcalcified, R, B/C and O), and estimated coccolith carbonate masses on the basis of scanning electron microscope images. E. huxleyi morphologies reflect diverging biogeographical distributions, trending towards smaller and lighter coccoliths to the south and emphasizing the importance of documenting those morphologies in relation to changing environmental conditions to assess their response to projected environmental change in the SO.

Nele Manon Vollmar et al.

Status: open (until 12 Jun 2021)

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Nele Manon Vollmar et al.

Nele Manon Vollmar et al.

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Short summary
We studied the most recent (sub-)fossil remains of one type of algae (coccolithophores) off southernmost Chile and across the Drake Passage, adding to the scarce knowledge that exists in the Southern Ocean, a rapidly changing environment. We found that those can be used to reconstrunct the surface ocean conditions in the north, but not in the south. We also found variations in shape in the dominant species depending on the location, indicating subtle adaptations to environmental conditions.
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