Articles | Volume 8, issue 2
Biogeosciences, 8, 227–237, 2011
Biogeosciences, 8, 227–237, 2011

Research article 01 Feb 2011

Research article | 01 Feb 2011

The influence of iron and light on net community production in the Subantarctic and Polar Frontal Zones

N. Cassar1,*, P. J. DiFiore1, B. A. Barnett1, M. L. Bender1, A. R. Bowie2, B. Tilbrook2,3, K. Petrou4, K. J. Westwood5, S. W. Wright5, and D. Lefevre6 N. Cassar et al.
  • 1Department of Geosciences, Princeton University, Princeton, NJ 08544, USA
  • 2Antarctic Climate and Ecosystems CRC, University of Tasmania, Private Bag 80, Hobart, Tasmania 7001, Australia
  • 3Commonwealth Scientific and Industrial Research Organisation (CSIRO), Marine and Atmospheric Research, Hobart, Tasmania 7001, Australia
  • 4Plant Functional Biology and Climate Change Cluster (C3), University of Technology, Sydney, P.O. Box 123, Broadway NSW 2007, Australia
  • 5Australian Antarctic Division and Antarctic Climate and Ecosystem Cooperative Research Center, Kingston, Tasmania 7050, Australia
  • 6Université de la Méditerranée, Laboratoire de Microbiologie Géochimie et Ecologie Marines (LMGEM) CNRS/INSU, UMR 6117, Centre d'Océanologie de Marseille, Campus de Luminy, Case 901, 13 288 Marseille Cedex 9, France
  • *now at: Division of Earth and Ocean Sciences, Nicholas School of the Environment, Duke University, Durham, NC 27708, USA

Abstract. The roles of iron and light in controlling biomass and primary productivity are clearly established in the Southern Ocean. However, their influence on net community production (NCP) and carbon export remains to be quantified. To improve our understanding of NCP and carbon export production in the Subantarctic Zone (SAZ) and the northern reaches of the Polar Frontal Zone (PFZ), we conducted continuous onboard determinations of NCP as part of the Sub-Antarctic Sensitivity to Environmental Change (SAZ-Sense) study, which occurred in January–February 2007. Biological O2 supersaturation was derived from measuring O2/Ar ratios by equilibrator inlet mass spectrometry. Based on these continuous measurements, NCP during the austral summer 2007 in the Australian SAZ was approximately 43 mmol O2 m−2 d−1. NCP showed significant spatial variability, with larger values near the Subtropical front, and a general southward decrease. For shallower mixed layers (<50 m), dissolved Fe concentrations and Fe sufficiency, estimated from variable fluorescence, correlated strongly with NCP. The strong correlation between NCP and dissolved Fe may be difficult to interpret because of the correlation of dissolved Fe to MLD and because the concentration of iron may not be a good indicator of its availability. At stations with deeper mixed layers, NCP was consistently low, regardless of iron sufficiency, consistent with light availability also being an important control of NCP. Our new observations provide independent evidence for the critical roles of iron and light in mediating carbon export from the Southern Ocean mixed layer.

Final-revised paper