Carbon export in the naturally iron-fertilized Kerguelen area of the Southern Ocean based on the 234Th approach

• Published in: Biogeosciences
• Main Authors: Planchon, Frédéric, Ballas, D., Cavagna, A.-J., Bowie, A. R., Davies, D., Trull, T., Laurenceau-Cornec, E. C., van Der Merwe, P., Dehairs, F.
• Other Authors: Laboratoire des Sciences de l'Environnement Marin (LEMAR) (LEMAR), Institut de Recherche pour le Développement (IRD)-Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER)-Université de Brest (UBO)-Institut Universitaire Européen de la Mer (IUEM), Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS), Analytical, Environmental and Geo- Chemistry, Vrije Universiteit Brussel (VUB), Antarctic Climate and Ecosystems Cooperative Research Centre (ACE-CRC), Institute for Marine and Antarctic Studies Hobart (IMAS), University of Tasmania Hobart, Australia (UTAS), CSIRO Marine and Atmosphere Research Hobart, Commonwealth Scientific and Industrial Research Organisation Canberra (CSIRO), ANR-10-BLAN-0614,KEOPS 2,Kerguelen : Comparaison plateau Ocean2(2010)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2015
• Subjects: NITROGEN UPTAKE; SPRING BLOOM; ACL; PARTICULATE ORGANIC-CARBON; ANTARCTIC POLAR FRONT; PHYTOPLANKTON BLOOM; DISSOLVED IRON; ATLANTIC SECTOR; PARTICLE EXPORT; PLATEAU; REGION; [SDE.BE]Environmental Sciences/Biodiversity and Ecology; [SDU.OCEAN]Sciences of the Universe [physics]/Ocean; Atmosphere; Antarctic; Austral; Kerguelen; Southern Ocean; Antarc*
• Online Access: https://hal.archives-ouvertes.fr/hal-02559414; https://hal.archives-ouvertes.fr/hal-02559414/document; https://hal.archives-ouvertes.fr/hal-02559414/file/bg-12-3831-2015.pdf; https://doi.org/10.5194/bg-12-3831-2015

International audience This study examined upper-ocean particulate organic carbon (POC) export using the 234Th approach as part of the second KErguelen Ocean and Plateau compared Study expedition (KEOPS2). Our aim was to characterize the spatial and the temporal variability of POC export during austral spring (October–November 2011) in the Fe-fertilized area of the Kerguelen Plateau region. POC export fluxes were estimated at high productivity sites over and downstream of the plateau and compared to a high-nutrient low-chlorophyll (HNLC) area upstream of the plateau in order to assess the impact of iron-induced productivity on the vertical export of carbon. Deficits in 234Th activities were observed at all stations in surface waters, indicating early scavenging by particles in austral spring. 234Th export was lowest at the reference station R-2 and highest in the recirculation region (E stations) where a pseudo-Lagrangian survey was conducted. In comparison 234Th export over the central plateau and north of the polar front (PF) was relatively limited throughout the survey. However, the 234Th results support that Fe fertilization increased particle export in all iron-fertilized waters. The impact was greatest in the recirculation feature (3–4 fold at 200 m depth, relative to the reference station), but more moderate over the central Kerguelen Plateau and in the northern plume of the Kerguelen bloom (~2-fold at 200 m depth). The C : Th ratio of large (\textgreater53 μm) potentially sinking particles collected via sequential filtration using in situ pumping (ISP) systems was used to convert the 234Th flux into a POC export flux. The C : Th ratios of sinking particles were highly variable (3.1 ± 0.1 to 10.5 ± 0.2 μmol dpm−1) with no clear site-related trend, despite the variety of ecosystem responses in the fertilized regions. C : Th ratios showed a decreasing trend between 100 and 200 m depth suggesting preferential carbon loss relative to 234Th possibly due to heterotrophic degradation and/or grazing activity. C ...