An iron budget during the natural iron fertilisation experiment KEOPS (Kerguelen Islands, Southern Ocean)

• Published in: Biogeosciences
• Main Authors: Chever, F, Sarthou, G, Bucciarelli, E, Blain, S, Bowie, AR
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Gesellschaft MBH 2010
• Subjects: Earth Sciences; Oceanography; Chemical Oceanography; Heard Island; Indian; Kerguelen; Kerguelen Islands; Southern Ocean
• Online Access: http://www.agu.org/; https://doi.org/10.5194/bg-7-455-2010; http://ecite.utas.edu.au/67538

Total dissolvable iron (TDFe) was measured in thewater column above and in the surrounding of the KerguelenPlateau (Indian sector of the Southern Ocean) during theKErguelen Ocean Plateau compared Study (KEOPS) cruise.TDFe concentrations ranged from 0.90 to 65.6 nmol L−1above the plateau and from 0.34 to 2.23 nmol L−1 offshoreof the plateau. Station C1 located south of theplateau, near Heard Island, exhibited very high values (329770 nmol L−1). Apparent particulate iron (Feapp), calculatedas the difference between the TDFe and the dissolved ironmeasured on board (DFe) represented 955% of the TDFeabove the plateau, suggesting that particles and refractorycolloids largely dominated the iron pool. This paper presentsa budget of DFe and Feapp above the plateau. Lateral advectionof water that had been in contact with the continentalshelf of Heard Island seems to be the predominantsource of Feapp and DFe above the plateau, with a supply of9.73.6106 and 8.311.6103 mol d−1, respectively. Theresidence times of 1.7 and 48 days estimated for Feapp andDFe respectively, indicate a rapid turnover in the surface water.A comparison between Feapp and total particulate iron(TPFe) suggests that the total dissolved fraction is mainlyconstituted of small refractory colloids. This fraction doesnot seem to be a potential source of iron to the phytoplanktonin our study. Finally, when taking into account the lateralsupply of dissolved iron, the seasonal carbon sequestrationefficiency was estimated at 154 000 molC (mol Fe)−1,which is 4-fold lower than the previously estimated value inthis area but still 18-fold higher than the one estimated duringthe other study of a natural iron fertilisation experiment,CROZEX.