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Biogeosciences An interactive open-access journal of the European Geosciences Union
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https://doi.org/10.5194/bgd-11-4335-2014
© Author(s) 2014. This work is distributed under
the Creative Commons Attribution 3.0 License.
https://doi.org/10.5194/bgd-11-4335-2014
© Author(s) 2014. This work is distributed under
the Creative Commons Attribution 3.0 License.

Submitted as: research article 18 Mar 2014

Submitted as: research article | 18 Mar 2014

Review status
This discussion paper is a preprint. It has been under review for the journal Biogeosciences (BG). The revised manuscript was not accepted.

The sensitivity of primary productivity to intra-seasonal mixed layer variability in the sub-Antarctic Zone of the Atlantic Ocean

W. R. Joubert1,2, S. Swart1, A. Tagliabue1,2,3, S. J. Thomalla1, and P. M. S. Monteiro1,2 W. R. Joubert et al.
  • 1Southern Ocean Carbon and Climate Observatory, Council for Scientific and Industrial Research, Jan Cilliers Street, Stellenbosch, 7600, South Africa
  • 2Department of Oceanography, University of Cape Town, Rondebosch, 7700, South Africa
  • 3School of Environmental Sciences, University of Liverpool, Liverpool L69 3GP, UK

Abstract. The seasonal cycle of primary productivity is impacted by seasonal and intra-seasonal dynamics of the mixed layer through the changing balance between mixing and buoyancy forcing, which regulates nutrient supply and light availability. Of particular recent interest is the role of synoptic scale events in supplying nutrients, particularly iron, to the euphotic zone in the Sub Antarctic Zone (SAZ), where phytoplankton blooms occur throughout summer. In this study, we present high resolution measurements of net community production (NCP) constrained by ΔO2/Ar ratios, and mixed layer depth (MLD) in the Atlantic SAZ. We found a non-linear relationship between NCP and MLD, with the highest and most variable NCP observed in shallow MLDs (< 45 m). We propose that NCP variability in the SAZ may be driven by alternating states of synoptic-scale deepening of the mixed layer, leading to the entrainment of iron (dFe), followed by restratification, allowing rapid growth in an iron replete, high light environment. Synoptic iron fluxes into the euphotic zone based on water column dFe profiles and high resolution glider MLD data, reveal a potentially significant contribution of "new iron" which could sustain NCP throughout summer. Future process studies will help elaborate these findings further.

W. R. Joubert et al.
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W. R. Joubert et al.
W. R. Joubert et al.
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