What causes the inverse relationship between primary production and export efficiency in the Southern Ocean?

Frédéric A.C. Le Moigne (1) , Stephanie Henson , Emma Cavan , Clément Georges (2) , Katsiaryna Pabortsava , Eric Achterberg (3) , Elena Ceballos-Romero , Mike Zubkov , Richard Sanders

1 NOC - National Oceanography Centre [Southampton]
2 LOG - Laboratoire d’Océanologie et de Géosciences (LOG) - UMR 8187
3 GEOMAR - Helmholtz Centre for Ocean Research [Kiel]

The ocean contributes to regulating atmospheric CO 2 levels, partly via variability in the fraction of primary production (PP) which is exported out of the surface layer (i.e., the e ratio). Southern Ocean studies have found that contrary to global-scale analyses, an inverse relationship exists between e ratio and PP. This relationship remains unexplained, with potential hypotheses being (i) large export of dissolved organic carbon (DOC) in high PP areas, (ii) strong surface microbial recycling in high PP regions, and/or (iii) grazing-mediated export that varies inversely with PP. We find that the export of DOC has a limited influence in setting the negative e ratio/PP relationship. However, we observed that at sites with low PP and high e ratios, zooplankton-mediated export is large and surface microbial abundance low suggesting that both are important drivers of the magnitude of the e ratio in the Southern Ocean.

Domaines: Océan, Atmosphère

Frédéric A.C. Le Moigne, Stephanie Henson, Emma Cavan, Clément Georges, Katsiaryna Pabortsava, et al.. What causes the inverse relationship between primary production and export efficiency in the Southern Ocean?. Geophysical Research Letters, 2016, 43 (9), pp.4457-4466. ⟨10.1002/2016GL068480⟩. ⟨hal-02345498⟩