Dissolved iron in the Australian sector of the Southern Ocean (CLIVAR SR3 section): Meridional and seasonal trends

• Published in: Deep Sea Research Part I: Oceanographic Research Papers
• Main Authors: Sedwick, PN, Bowie, AR, Trull, T
• Format: Article in Journal/Newspaper
• Language: English
• Published: Pergamon-Elsevier Science Ltd 2008
• Subjects: Earth Sciences; Oceanography; Chemical Oceanography; Antarctic; Southern Ocean; The Antarctic; Antarc*; Sea ice
• Online Access: http://www.sciencedirect.com; https://doi.org/10.1016/j.dsr.2008.03.011; http://ecite.utas.edu.au/54685

We report measurements of dissolved iron (dFe, o0.4 mm) in seawater collected from theupper 300m of the water column along the CLIVAR SR3 section south of Tasmania inMarch 1998 (between 421S and 541S) and NovemberDecember 2001 (between 471S and661S). Results from both cruises indicate a general north-to-south decrease in mixed-layerdFe concentrations, from values as high as 0.76 nM in the Subtropical Front to uniformlylow concentrations (o0.1 nM) between the Polar Front and the Antarctic continentalshelf. Samples collected from the seasonal sea-ice zone in NovemberDecember 2001provide no evidence of significant dFe inputs from the melting pack ice, which mayexplain the absence of pronounced ice-edge algal blooms in this sector of the SouthernOcean, as implied by satellite ocean-color images. Our data also allow us to infer changesin the dFe concentration of surface waters during the growing season. South of the PolarFront, a comparison of near-surface with subsurface (150m depth) dFe concentrationsin NovemberDecember 2001 suggests a net seasonal biological uptake of at least 0.140.18 nM dFe, of which 0.050.12nM is depleted early in the growing season(before mid December). A comparison of our spring 2001 and fall 1998 data indicates abarely discernible seasonal depletion of dFe ( 0.03nM) within the Polar Frontal Zone.Further north, most of our iron profiles do not exhibit near-surface depletions, and mixedlayerdFe concentrations are sometimes higher in samples from fall 1998 compared tospring 2001; here, the near-surface dFe distributions appear to be dominated by timevaryinginputs of aerosol iron or advection of iron-rich subtropical waters from the north.