Description: Siderophore type chelates were isolated from nutrient enriched seawater collected from coastal and near shore environments and detected using a novel high performance liquid chromatography-electrospray ionisation-mass spectrometric technique. Seawater was enriched with added glucose, ammonia and phosphate, and incubated for four days. Seven different siderophore type compounds were detected in the extracted supernatants and tentatively identified based on mass numbers and spectra. The compounds comprised two groups, the ferrioxamines and the amphibactins. They were produced at typical coastal iron concentrations (total dissolved iron=2.9±1.4 and 2.2±0.1 nM) both in the presence and absence of the iron chelating ligand ethylene diamine-N,N′-diacetic acid. © 2004 Elsevier B.V. All rights reserved.

Description: Iron and other trace metals (Al, Co, Ni) were measured through the upper water column during two north-south transects of the Atlantic Ocean (approximately 50°N-50°S), from the United Kingdom (UK) to the Falkland Islands (September/October 1996) and from South Africa to the UK (May/June 1998). Total dissolvable iron (TD-Fe) concentrations in the surface layers (〈200 m) of the open Atlantic Ocean averaged 0.95±0.67 nM (n = 142) during the 1996 cruise and 1.08±0.59 nM (n = 160) during the 1998 cruise, with increased values in shelf waters at both extremes of the transects. Iron enrichments, fingerprinted via correlation with other trace metals, macronutrients and hydrography, correlated well with dry aerosol deposition off the west African continent and wet deposition in the Inter-Tropical Convergence Zone (ITCZ), with levels 〉 2.2 nM observed in surface waters in these regions. Benthic fluxes provided a significant amount of Fe (2-38 nM) to the base of the water column in Coastal zones. In addition, samples collected from one Atlantic Meridional Transect (AMT) expedition were re-analysed after a 16 month acidification period and showed significant increases over shipboard analyses (average values increasing to 2.26±1.50nM), indicating the extended release of Fe from leachable particulate material in the stored samples. Detailed profiling through the euphotic zone revealed TD-Fe distributions that exhibited strong relationships with biological uptake, regeneration and water column hydrography. In equatorial and tropical North Atlantic waters, trace elemental distributions showed evidence of recent atmospheric deposition through a history of stratified mixed layers. © 2002 Elsevier Science Ltd. All rights reserved.

Description: Iron plays an important role in oceanic biogeochemistry and is known to limit biological activity in certain ocean regions. Such regions have a replete complement of major nutrients but low primary production of phytoplankton due to low ambient iron concentrations. The determination of iron in seawater is a major challenge, although much progress has been made during the last two decades. Techniques for total dissolved iron and iron speciation have been developed in order to rationalise its biogeochemical cycling and better understand its role in limiting phytoplankton growth. In this paper, a critical review of historical and current analytical methods for the determination of iron in seawater is presented and their capabilities evaluated. The need for standard protocols for the clean sampling and storage of low-level (〈1 nM) iron seawater in order to maintain sample integrity is emphasised. The importance of laboratory and shipboard intercomparison exercises to distinguish between environmental variability and operationally measured fractions is also considered. © 2001 Elsevier Science B.V. All rights reserved.

Description: The first Southern Ocean Iron RElease Experiment (SOIREE) was performed during February 1999 in Antarctic waters south of Australia (61°S, 140°E), in order to verify whether iron supply controls the magnitude of phytoplankton production in this high nutrient low chlorophyll (HNLC) region. This paper describes iron distributions in the upper ocean during our 13-day site occupation, and presents a pelagic iron budget to account for the observed losses of dissolved and total iron from waters of the fertilised patch. Iron concentrations were measured underway during daily transects through the patch and in vertical profiles of the 65-m mixed layer. High internal consistency was noted between data obtained using contrasting sampling and analytical techniques. A pre-infusion survey confirmed the extremely low ambient dissolved (0.1 nM) and total (0.4 nM) iron concentrations. The initial enrichment elevated the dissolved iron concentration to 2.7 nM. Thereafter, dissolved iron was rapidly depleted inside the patch to 0.2-0.3 nM, necessitating three re-infusions. A distinct biological response was observed in iron-fertilised waters, relative to outside the patch, unequivocally confirming that iron limits phytoplankton growth rates and biomass at this site in summer. Our budget describing the fate of the added iron demonstrates that horizontal dispersion of fertilised waters (resulting in a quadrupling of the areal extent of the patch) and abiotic particle scavenging accounted for most of the decreases in iron concentrations inside the patch (31-58 and 12-49 of added iron, respectively). The magnitude of these loss processes altered towards the end of SOIREE, and on days 12-13 dissolved (1.1 nM) and total (2.3 nM) iron concentrations remained elevated compared to surrounding waters. At this time, the biogenic iron pool (0.1 nM) accounted for only 1-2 of the total added iron. Large pennate diatoms (〉 20 μm) and autotrophic flagellates (2-20 μm) were the dominant algal groups in the patch, taking up the added iron and representing 13 and 39 of the biogenic iron pool, respectively. Iron regeneration by grazers was tightly coupled to uptake by phytoplankton and bacteria, indicating that biological Fe cycling within the bloom was self-sustaining. A concurrent increase in the concentration of iron-binding ligands on days 11-12 probably retained dissolved iron within the mixed layer. Ocean colour satellite images in late March suggest that the bloom was still actively growing 42 days after the onset of SOIREE, and hence by inference that sufficient iron was maintained in the patch for this period to meet algal requirements. This raises fundamental questions regarding the biogeochemical cycling of iron in the Southern Ocean and, in particular, how bioavailable iron was retained in surface waters and/or within the biota to sustain algal growth. © 2001 Elsevier Science Ltd.

Description: The development of a highly sensitive system for the shipboard determination of dissolved iron at the sub-nM level is presented. The technique is based on a flow injection method coupled with luminol chemiluminescence detection. Dissolved Fe(II+lII) levels are determined after Fe(III) reduction using sulphite and in-line matrix elimination/preconcentration on an 8-hydroxyquinoline (8-quinolinol) chelating resin column. The detection limit (3s) is 40 pM when 1.5 ml of sample is loaded onto the column, and the relative standard deviation is 3.2 (n=5) for a 1.0 nM Fe sample. One analytical cycle can be completed in 3 min. The automated method proved reliable when employed on-board the RRS James Clark Ross during Autumn 1996, mapping dissolvable Fe(II+III) levels along the Atlantic Meridional Transect from 50°N to 50°S. Data from vertical profiles through the upper water column are presented.