Size-fractionated iron distribution on the northern Gulf of Alaska



[1] Concentrations of soluble (<0.025 μm), dissolved (<0.4 μm) and total (unfiltered) iron (Fe) were measured over the continental shelf and slope of the northern Gulf of Alaska (GoA) during spring-summer. Large cross-shelf gradients of surface water Fe concentrations were observed in these productive shelf waters during both seasons. Most of the particulate (>0.4 μm) and colloidal (0.025–0.4 μm) Fe size fractions were removed from surface waters within the inner and mid shelf. As a result the contribution of soluble Fe to the total Fe concentration increased from the inner shelf to the shelf break/slope waters. Surface water dissolved Fe concentrations on the northern GoA continental slope were higher than those previously observed in the central GoA gyre. Variations in surface water Fe concentrations from spring through summer appear to result from the changes in freshwater discharge and physical processes on the shelf.