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

Copyright: 2014 European Geosciences Union (EGU). This is an Open Access journal. The journal authorizes the publication of the information herewith contained. Published in Biogeosciences Discuss, vol. 11, pp 4335-4358 The seasonal cycle of primary productivity is impacted by seasonal and intra-seas...

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Bibliographic Details
Main Authors: Joubert, WR, Swart, S, Tagliabue, A, Thomalla, Sandy J, Monteiro, Pedro MS
Format: Article in Journal/Newspaper
Language:English
Published: European Geosciences Union (EGU) 2014
Subjects:
Oceanography
Intra-seasonal dynamics
Climate research
Synoptic scales
Sub Antarctic Zone
SAZ
ÉO2/Ar ratios
Antarctic
Antarc*
Online Access:http://hdl.handle.net/10204/7491
http://www.biogeosciences-discuss.net/11/4335/2014/bgd-11-4335-2014.pdf
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Summary:Copyright: 2014 European Geosciences Union (EGU). This is an Open Access journal. The journal authorizes the publication of the information herewith contained. Published in Biogeosciences Discuss, vol. 11, pp 4335-4358 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 ÉO2/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 (< 45m). 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.

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