Preprints
https://doi.org/10.5194/bg-2022-127
https://doi.org/10.5194/bg-2022-127
 
14 Jul 2022
14 Jul 2022
Status: this preprint is currently under review for the journal BG.

Unique benthic foraminiferal communities (stained) in diverse environments of sub-Antarctic fjords, South Georgia

Wojciech Majewski1, Witold Szczuciński2, and Andrew J. Gooday3,4 Wojciech Majewski et al.
  • 1Institute of Paleobiology, Polish Academy of Sciences, Twarda 51/55, 00-818 Warszawa, Poland
  • 2Geohazards Research Unit, Institute of Geology, Adam Mickiewicz University, Bogumiła Krygowskiego 12, 61-680 Poznań, Poland
  • 3National Oceanography Centre, European Way, Southampton SO14 3ZH, UK
  • 4Life Sciences Department, Natural History Museum, Cromwell Road, London SW7 5BD, UK

Abstract. Sub-Antarctic fjords are among the environments most affected by the recent climate change. In our dynamically changing world, it is essential to monitor changes in these vulnerable settings. Here, we present a baseline study of “living” (rose Bengal stained) benthic foraminifera from fjords of South Georgia, including fjords with and without tidewater glaciers. Their distribution is analyzed in the light of new fjord water and sediment property data, including grain size and sorting, total organic carbon, total sulfur, and δ13C of bulk organic matter. Four well-defined foraminiferal assemblages are recognized. Miliammina earlandi dominates in the most restricted, near-shore and glacier-proximal habitats, Cassidulinoides aff. parkerianus in mid-fjord areas, and Globocassidulina aff. rossensis and Reophax subfusiformis in the outer parts of fjords. Miliammina earlandi can tolerate strong glacial influence, including high sedimentation rates in fjord heads and sediment anoxia, as inferred from sediment color and total organic carbon/sulfur ratios. This versatile species thrives both in the food-poor inner reaches of fjords that receive mainly refractory petrogenic organic matter from glacial meltwater, and in shallow-water coves where it benefits from an abundant supply of fresh, terrestrial and marine organic matter. A smooth-walled variant of C. aff. parkerianus, apparently endemic to South Georgia, is the calcareous rotaliid best adapted to inner fjord conditions characterized by moderate glacial influence and sedimentation rates and showing no preference for particular sedimentary redox conditions. The outer parts of fjords with clear, slightly warmer bottom water, are inhabited by G. aff. rossensis. Reophax subfusiformis dominates in the deepest-water settings with water salinities ≥ 33.9 PSU and temperatures 0.2–1.4 °C, characteristic for Winter Water and Upper Circumpolar Deep Water. The inner- and mid-fjord foraminiferal assemblages seem specific to South Georgia, although with continued warming and deglaciation they may become more widespread in the Southern Ocean.

Wojciech Majewski et al.

Status: open (until 26 Aug 2022)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on bg-2022-127', Katrine Husum, 03 Aug 2022 reply
    • AC1: 'Reply on RC1', Wojciech Majewski, 04 Aug 2022 reply
      • RC2: 'Reply on AC1', Katrine Husum, 08 Aug 2022 reply

Wojciech Majewski et al.

Wojciech Majewski et al.

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Short summary
We studied foraminifera living in fjords of South Georgia, a sub-Antarctic island sensitive to climate change. As conditions in water and on the seafloor vary, different associations of these microorganisms dominate far inside, in the middle, and near fjord openings. Assemblages in inner and middle parts of fjords are specific to South Georgia but they may become widespread with anticipated warming. These results are important for interpretation of fossil records and monitoring future change.
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