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We report measurements of dissolved iron (dFe, o0.4 mm) in seawater collected from the upper 300m of the water column along the CLIVAR SR3 section south of Tasmania in March 1998 (between 421S and 541S) and November–December 2001 (between 471S and 661S). Results from both cruises indicate a general north-to-south decrease in mixed-layer dFe concentrations, from values as high as 0.76 nM in the Subtropical Front to uniformly low concentrations (o0.1 nM) between the Polar Front and the Antarctic continental shelf. Samples collected from the seasonal sea-ice zone in November–December 2001 provide no evidence of significant dFe inputs from the melting pack ice, which may explain the absence of pronounced ice-edge algal blooms in this sector of the Southern Ocean, as implied by satellite ocean-color images. Our data also allow us to infer changes in the dFe concentration of surface waters during the growing season. South of the Polar Front, a comparison of near-surface with subsurface (150m depth) dFe concentrations in November–December 2001 suggests a net seasonal biological uptake of at least 0.14–0.18 nM dFe, of which 0.05–0.12nM is depleted early in the growing season (before mid December). A comparison of our spring 2001 and fall 1998 data indicates a barely 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 mixedlayer dFe concentrations are sometimes higher in samples from fall 1998 compared to spring 2001; here, the near-surface dFe distributions appear to be dominated by timevarying inputs of aerosol iron or advection of iron-rich subtropical waters from the north.

Item Type:	Refereed Article
Keywords:	Iron, Southern Ocean, Antarctic Zone, Sea ice, Polar waters
Research Division:	Earth Sciences
Research Group:	Oceanography
Research Field:	Chemical Oceanography
Objective Division:	Environment
Objective Group:	Physical and Chemical Conditions of Water
Objective Field:	Physical and Chemical Conditions of Water in Coastal and Estuarine Environments
Author:	Sedwick, PN (Dr Peter Sedwick)
Author:	Bowie, AR (Associate Professor Andrew Bowie)
Author:	Trull, T (Professor Thomas Trull)
ID Code:	54685
Year Published:	2008
Web of Science® Times Cited:	55
Deposited By:	IASOS
Deposited On:	2009-02-26
Last Modified:	2009-07-27
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