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

Type Article
Acceptance Date 2021 IN PRESS
Language English
Author(s) Hörstmann Cora1, 2, Raes Eric J1, 3, Buttigieg Pier Luigi4, Lo Monaco Claire5, John Uwe1, 6, Waite Anya M1, 7
Affiliation(s) 1 : Alfred Wegener Institute for Polar and Marine Science, Bremerhaven, Germany
2 : Department of Life Sciences and Chemistry, Jacobs University, Bremen, Germany
3 : CSIRO Oceans and Atmosphere, Hobart, Tasmania, Australia
4 : Helmholtz Metadata Collaboration, GEOMAR, Kiel, Germany
5 : LOCEAN-IPSL, Sorbonne Université, Paris, France
6 : Helmholtz Institute for Functional Marine Biodiversity, Oldenburg, Germany
7 : Ocean Frontier Institute and Department of Oceanography, Dalhousie University, Halifax, NS, Canada
Source Biogeosciences (1726-4189) (Copernicus GmbH) In Press
DOI 10.5194/bg-2021-52

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.

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Hörstmann Cora, Raes Eric J, Buttigieg Pier Luigi, Lo Monaco Claire, John Uwe, Waite Anya M Hydrographic fronts shape productivity, nitrogen fixation, and microbial community composition in the South Indian Ocean and the Southern Ocean. Biogeosciences IN PRESS. Publisher's official version : https://doi.org/10.5194/bg-2021-52 , Open Access version : https://archimer.ifremer.fr/doc/00685/79672/