Distributions of dissolved and particulate iron in the sub-Antarctic and Polar Frontal Southern Ocean (Australian sector)

• Main Authors: Lannuzel, Delphine, Bowie, Andrew, Remenyi, Tomas, Lam, Phoebe, Townsend, Ashley T, Ibisanmi, Enitan, Butler, Edward CV, Wagener, Thibaut, Schoemann, Véronique
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2011
• Subjects: Océanographie biologique; Océanographie physique et chimique; Biogeochemistry; Distributions; Iron; Macro-nutrients; Southern Ocean; Antarctic; Austral; Pacific; Antarc*; North Atlantic
• Online Access: http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/161057; https://dipot.ulb.ac.be/dspace/bitstream/2013/161057/1/Elsevier_146553.pdf

This paper presents iron (Fe) profiles in the upper 1000m from nine short-term (transect) stations and three long-term (process) stations occupied in the Australian sector of the Southern Ocean during the SAZ-Sense expedition in austral summer (January-February) 2007. Strong vertical and horizontal gradients in Fe concentrations were observed between the 18 sampled profiles (i.e. 0.09-0.63nmol/l dissolved Fe (dFe)). Average dFe concentrations in surface gggwaters in the northern Sub-Antarctic Zone (SAZ-N) West (station P1) were 0.27±0.04nmol/l. This is lower in the SAZ-N East region (station P3 and around) where average dFe values in the mixed layer were 0.48±0.10nmol/l. The Polar Front (PF) station (P2) exhibited the lowest average surface Fe values (i.e. 0.22±0.02nmol/l). Iron concentrations in deep waters down to 1000m were more uniform (0.25-0.37nmol/l dFe), which is in accordance with values reported elsewhere in remote waters of the Southern Ocean, but lower than those observed in the North Atlantic and North Pacific basins. A strong decoupling was observed between dFe and nutrient cycles at all stations. Particulate Fe levels were generally very low for all SAZ stations (<0.08-1.38nmol/l), with higher values observed at stations collected near Tasmania and in the SAZ-N East region. The intrusion of subtropical waters, enriched with Fe from sediments or dust further north, is thought to mediate Fe input to the SAZ-N and STZ areas, while input from below would be the main source of Fe in the PF region. We applied the tracer Fe * (Fe *= [dFe]-R Fe:P×[PO 4 3-], where R Fe:P is the algal uptake ratio) to estimate the degree to which the water masses were Fe limited. In this study, Fe * tended to be negative and decreased with increasing depths and latitude. Positive Fe * values, indicating Fe sufficiency, were observed in the (near-)surface waters collected in the SAZ-N East and near continental sources, where primary production was higher and ultimately limited by the lack of macro-nutrients, not Fe. ...