Abstract: The distribution of reactive Al and Fe was determined in surface water samples collected by hand from ice flees and by shipboard rosette at 28 stations occupied during the 1994 US-Canadian Arctic Ocean Section. The data show significant variations in the concentration of both species over short spatial scales superimposed on a general trend of higher values in the Canada Basin and lower values in the Eurasian Basin. Detailed examination of the distributions indicates that the highest concentrations correspond to regions in which shipboard observations indicate the presence of significant amounts of sea-ice containing entrained sediments dirty ice. In many of these regions, strong vertical gradients in trace element concentrations are also observed. The observed correlation of high trace element concentrations and dirty ice suggests that ice-rafted sediment may be an important transport mechanism for supplying reactive trace elements such as Al and Fe to the surface waters of the central Arctic Ocean. Input of this sedimentary material through seasonal ice melt into strongly stratified surface waters leads to enrichment of properties in near surface layers which may have biogeochemical consequences for organisms living on the undersides of ice flees. Extreme concentration gradients in the upper 1-2 m though are likely to be missed or destroyed by conventional shipboard rosette sampling.

Abstract: The concentration of dissolved Fe was determined in upper ocean waters along 170°W between 53 and 72°S during four cruises between October 1997 and March 1998 as part of the US-JGOFS Southern Ocean Antarctic Polar Frontal Zone cruises. Fe concentrations were extremely variable in both space and time as a result of advection of meso-scale eddys through the region. Observed values ranged from a maximum of 0.34 nM at 64°S in November next to the retreating ice-edge to 0.075 nM in March at 71°S in the northern Ross Sea gyre. In general, the highest average mixed-layer Fe concentrations and the largest seasonal changes were observed in the two frontal zones at similar to 60°S and similar to 64°S. Formation of deep mixed layers during winter and the entrainment of sub-surface waters enriched in Fe is the primary source of this element to surface waters in this region of the Southern Ocean. Additionally, upwelling of circumpolar deep water in the circumpolar current along its northern boundary at the Polar Front and its southern boundary at the Southern Antarctic Circumpolar Current Front is an important mechanism supplying Fe to surface waters in these areas throughout the summer. Comparison of integrated Fe concentrations and Th-derived POC export and N drawdown all suggest that the maximum changes in these properties are comparable to those that would be predicted by Fe availability. Fe concentrations determined by shipboard Flow Injection Analysis (Measures et al., Mar. Chem. 50 (1995) 3) were significantly higher than those found in replicate samples determined by shored based flameless atomic absorption spectrophotometry after pre-concentration by chelation-solvent extraction (Johnson et al., Mar. Chem. 57 (1997) 137). The concentration differences, which appear to be restricted to the upper 200-300 m, do not appear to arise from different sampling or handling processes but instead are believed to result from the different sensitivity of the methods to organic fractions of Fe in seawater.

Abstract: Concentrations of dissolved Al and Fe in the surface mixed layer were measured during: five cruises of the 1995 US JGOFS Arabian Sea Process Study, Concentrations of both Al and Fe were relatively uniform between January and April, the NE Monsoon and the Spring Intermonsoon period, ranging from 2 to 11 nM Al (mean 5.3 nM) and 0.5 to 2.4 nM Fe (mean 1.0 nM). In July/August, after the onset of the SW Monsoon, surface water Al and Fe concentrations increased significantly (Al range 4.5-20.1 nM; mean = 10 nM, Fe range 0.57-2.4 nM; mean = 1.3 nM), particularly in the NE part of the Arabian Sea, as the result of the input and partial dissolution of eolian dust. Using the enrichment of Al in the surface waters, we estimate this is the equivalent to the deposition of 2.2-7.4 g m-2 dust, which is comparable to values previously estimated for this region. Approximately one month later (August/September), surface water concentrations of both Al and Fe were found to have decreased significantly (mean Al 7.4 nM, mean Fe 0.90 nM) particularly in the same NE region, as the result of export of particulate material from the euphotic zone. Fe supply to the surface waters is also affected by upwelling of sub-surface waters in the coastal region of the Arabian Sea during the SW Monsoon. Despite the proximity of high concentrations of Fe in the shallow sub-oxic layer, freshly upwelled water is not drawn from this layer and the NO3/Fe ratio in the initially upwelled water is below the value at which Fe limitation is through to occur. Continued deposition of eolian Fe into the upwelled water as it advects offshore provides the Fe required to raise this ratio above the Fe limitation value.

Abstract: A towed surface sampling device coupled to two automated flow injection analysis (FIA) systems is described. The towed system permits uncontaminated sampling of seawater from research vessels while underway at full speed. Coupling the sampler to the FIA systems permits automatic determination of Al and Fe in surface waters at natural levels at 5 min intervals, equivalent to similar to 1.5 km spacing at a ship speed of 10 knots (5 m s-1). Results from the tropical Atlantic indicate significant (50%) variation in concentrations of both Al and Fe on space scales of less than 90 km. The combined system facilitates surface mapping of large regions of the ocean for dissolved Al and Fe, thus identifying the sites and magnitude of eolian deposition to the surface ocean. In combination with the determination of nutrients and other biological parameters this permits the investigation of the role that eolian deposition plays in modifying surface water biogeochemical cycles.

Abstract: A highly sensitive method for the shipboard determination of A1 in seawater by flow injection analysis (FIA) has been developed. The method employs in-line pre-concentration of A1 onto a column of resin-immobilized 8-hydroxyquinoline. The AI is subsequently eluted into the FIA system from the resin with acidified seawater. The eluted AI reacts with lumogallion to form a chelate, which is detected by its fluorescence. The fluorescence is enhanced -5-fold by the addition of a micelleforming detergent, Brij-35. The method has a detection limit of -0.15 nM and a precision of 1.7% at 2.4 nM. The method has a cycle time of -3 min and can be readily automated. The speed, ease of use, and relative freedom from contamination artifacts makes this method ideal for shipboard determination of AI in seawater.