Journal cover Journal topic
Biogeosciences An interactive open-access journal of the European Geosciences Union
Biogeosciences, 11, 1981-2001, 2014
https://doi.org/10.5194/bg-11-1981-2014
© Author(s) 2014. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
09 Apr 2014
Sedimentary and atmospheric sources of iron around South Georgia, Southern Ocean: a modelling perspective
I. Borrione1, O. Aumont2, M. C. Nielsdóttir3,*, and R. Schlitzer1 1Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, Columbusstrasse, 27568 Bremerhaven, Germany
2Laboratoire de Physique des Océans Institut Européen de la Mer, 29280 Plouzané, France
3University of Southampton, National Oceanography Centre, European Way, SO14 3ZH, Southampton, UK
*now at: Old Dominion University, Department of Ocean, Earth and Atmospheric Sciences, 4600 Elkhorn Avenue, Norfolk VA 23529, USA
Abstract. In high-nutrient low-chlorophyll waters of the western Atlantic sector of the Southern Ocean, an intense phytoplankton bloom is observed annually north of South Georgia. Multiple sources, including shallow sediments and atmospheric dust deposition, are thought to introduce iron to the region. However, the relative importance of each source is still unclear, owing in part to the scarcity of dissolved iron (dFe) measurements in the South Georgia region. In this study, we combine results from a recently published dFe data set around South Georgia with a coupled regional hydrodynamic and biogeochemical model to further investigate iron supply around the island. The biogeochemical component of the model includes an iron cycle, where sediments and dust deposition are the sources of iron to the ocean. The model captures the characteristic flow patterns around South Georgia, hence simulating a large phytoplankton bloom to the north (i.e. downstream) of the island. Modelled dFe concentrations agree well with observations (mean difference and root mean square errors of ~0.02 nM and ~0.81 nM) and form a large plume to the north of the island that extends eastwards for more than 800 km. In agreement with observations, highest dFe concentrations are located along the coast and decrease with distance from the island. Sensitivity tests indicate that most of the iron measured in the main bloom area originates from the coast and very shallow shelf-sediments (depths < 20 m). Dust deposition exerts almost no effect on surface chlorophyll a concentrations. Other sources of iron such as run-off and glacial melt are not represented explicitly in the model, however we discuss their role in the local iron budget.

Citation: Borrione, I., Aumont, O., Nielsdóttir, M. C., and Schlitzer, R.: Sedimentary and atmospheric sources of iron around South Georgia, Southern Ocean: a modelling perspective, Biogeosciences, 11, 1981-2001, https://doi.org/10.5194/bg-11-1981-2014, 2014.
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