Early winter barium excess in the Southern Indian Ocean as an annual remineralisation proxy (GEOTRACES GIPr07 cruise)

Type Article
Acceptance Date 2021 IN PRESS
Language English
Author(s) Van Horsten Natasha René1, 2, 3, Planquette Helene1, Sarthou Geraldine1, Ryan-Keogh Thoams James2, Mtshali Thato Nicholas4, Roychoudhury Alakendra3, Bucciarelli Eva5
Affiliation(s) 1 : Univ Brest, CNRS, IRD, Ifremer, LEMAR, F-29280 Plouzane, France
2 : SOCCO, CSIR, Lower Hope road, Cape Town, South Africa
3 : TracEx, Department of Earth Sciences, Stellenbosch University, Stellenbosch, South Africa
4 : Department of Environment, Forestry and Fisheries, Oceans and Coast, Foretrust Building, Martin Hammerschlag Way, Cape Town, South Africa
Source Biogeosciences (1726-4189) (Copernicus GmbH) In Press
DOI 10.5194/bg-2021-42

The Southern Ocean is of global importance and processes such as mesopelagic remineralisation that impact the efficiency of the biological carbon pump in this region is of substantial interest. During this study the proxy barium excess which is utilised to shed light on mesopelagic remineralisation was measured at seven stations along 30° E in the Southern Indian Ocean during early austral winter of 2017. To our knowledge this is the first reported winter study utilising this proxy in the Southern Ocean. Concentrations of 59 to 684 pmol L−1 were comparable to those observed throughout other seasons, indicating that this proxy has a longer timescale than previously thought. Background barium excess values observed in deep waters were also similar to previous studies, not having declined down to an expected true Southern Ocean background value. It is apparent that processes driving the mesopelagic barium excess signal are still underway during early winter. Indicating that continuous remineralisation is sustained at levels comparable to summer, well after bloom termination. Moreover, linking integrated remote sensing primary production to the mesopelagic barium excess signal reiterates a longer timescale. The significant positive correlations obtained in the Antarctic and Subantarctic zones suggest that mesopelagic barium excess stock can be used as a remineralisation proxy on an annual timescale and possible inference of carbon remineralisation from remote sensing data on an annual and basin scale.

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Van Horsten Natasha René, Planquette Helene, Sarthou Geraldine, Ryan-Keogh Thoams James, Mtshali Thato Nicholas, Roychoudhury Alakendra, Bucciarelli Eva Early winter barium excess in the Southern Indian Ocean as an annual remineralisation proxy (GEOTRACES GIPr07 cruise). Biogeosciences IN PRESS. Publisher's official version : https://doi.org/10.5194/bg-2021-42 , Open Access version : https://archimer.ifremer.fr/doc/00683/79485/