15 Mar 2021

15 Mar 2021

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

Hydrographic fronts shape productivity, nitrogen fixation, and microbial community composition in the South Indian Ocean and the Southern Ocean

Cora Hörstmann1,2, Eric J. Raes3,1, Pier Luigi Buttigieg4, Claire Lo Monaco5, Uwe John1,6, and Anya M. Waite7,1 Cora Hörstmann et al.
  • 1Alfred Wegener Institute for Polar and Marine Science, Bremerhaven, Germany
  • 2Department of Life Sciences and Chemistry, Jacobs University, Bremen, Germany
  • 3CSIRO Oceans and Atmosphere, Hobart, Tasmania, Australia
  • 4Helmholtz Metadata Collaboration, GEOMAR, Kiel, Germany
  • 5LOCEAN-IPSL, Sorbonne Université, Paris, France
  • 6Helmholtz Institute for Functional Marine Biodiversity, Oldenburg, Germany
  • 7Ocean Frontier Institute and Department of Oceanography, Dalhousie University, Halifax, NS, Canada

Abstract. Biogeochemical cycling of carbon (C) and nitrogen (N) in the ocean depends on both the composition and activity of underlying biological communities and on abiotic factors. The Southern Ocean is encircled by a series of strong currents and fronts, providing a barrier to microbial dispersion into adjacent oligotrophic gyres. Our study region straddles the boundary between the nutrient-rich Southern Ocean and the adjacent oligotrophic gyre of the South Indian Ocean, providing an ideal region to study changes in microbial productivity. Here, we measured the impact of C- and N- uptake on microbial community diversity, contextualized by hydrographic factors and local physico-chemical conditions across the Southern Ocean and South Indian Ocean. We observed that contrasting physico-chemical characteristics led to unique microbial diversity patterns, with significant correlations between microbial alpha diversity and primary productivity (PP). However, we detected no link between specific PP (PP normalized by chlorophyll a concentration) and microbial alpha and beta diversity. Prokaryotic alpha and beta diversity were correlated with biological N2 fixation, itself a prokaryotic process, and we detected measurable N2 fixation to 60° S. While regional water masses have distinct microbial genetic fingerprints in both the eukaryotic and prokaryotic fractions, PP and N2 fixation vary more gradually and regionally. This suggests that microbial phylogenetic diversity is more strongly bounded by physical oceanographic features, while microbial activity responds more to chemical factors. We conclude that concomitant assessments of microbial diversity and activity is central in understanding the dynamics and complex responses of microorganisms to a changing ocean environment.

Cora Hörstmann et al.

Status: open (until 30 Apr 2021)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on bg-2021-52', Anonymous Referee #1, 17 Apr 2021 reply

Cora Hörstmann et al.

Data sets

Nitrogen and carbon processes in the South Indian Ocean and the French Southern and Antarctic Lands Hörstmann, Cora, Raes, Eric, and Waite, Anya

Cora Hörstmann et al.


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Short summary
Microbes are the main drivers of productivity and nutrient cycling in the ocean. We present a combined approach assessing C- and N- uptake and microbial community diversity across ecological provinces in the Southern Ocean and South Indian Ocean. Provinces showed distinct genetic fingerprints, but microbial activity varied gradually across regions, correlating with nutrient concentrations. Our study advances the biogeographic understanding of microbial diversity across C- and N- uptake regimes.