Preprints
https://doi.org/10.5194/bg-2021-42
https://doi.org/10.5194/bg-2021-42

  01 Mar 2021

01 Mar 2021

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

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

Natasha René van Horsten1,2,3, Hélène Planquette1, Géraldine Sarthou1, Thomas James Ryan-Keogh2, Thato Nicholas Mtshali4, Alakendra Roychoudhury3, and Eva Bucciarelli1 Natasha René van Horsten et al.
  • 1Univ Brest, CNRS, IRD, Ifremer, LEMAR, F-29280 Plouzane, France
  • 2SOCCO, CSIR, Lower Hope road, Cape Town, South Africa, 7700
  • 3TracEx, Department of Earth Sciences, Stellenbosch University, Stellenbosch, South Africa, 7600
  • 4Department of Environment, Forestry and Fisheries, Oceans and Coast, Foretrust Building, Martin Hammerschlag Way, Cape Town, South Africa, 8001

Abstract. 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.

Natasha René van Horsten et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on bg-2021-42', Frank Dehairs, 19 Mar 2021
  • RC2: 'Comment on bg-2021-42', Stéphanie Jacquet, 26 Apr 2021
  • RC3: 'Comment on bg-2021-42', J.K.B. Bishop, 05 May 2021

Natasha René van Horsten et al.

Natasha René van Horsten et al.

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Short summary
The remineralisation proxy, barite, was measured along 30° E in the Southern Indian Ocean during early austral winter. To our knowledge this is the first reported Southern Ocean winter study. Concentrations throughout the water column were comparable to observations during spring to autumn. By linking satellite primary production to this proxy a possible annual timescale is proposed. These findings also suggest possible inference of carbon remineralisation from satellite data on a basin scale.
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