Water column iron dynamics in the subarctic North Pacific Ocean and the Bering Sea

Abstract

We measured water-column iron concentrations from west to east along 47°N in the subarctic North Pacific, and in the Bering Sea. In the North Pacific dissolved Fe (D-Fe) showed surface depletion, mid-depth maxima at 1000-1500 m (west, 1.3-1.6 nM; east, 0.9-1.1 nM), and a gradual decrease with depth below 3500-4000 m depth (west, 1.1-1.4 nM; east, 0.6-0.7 nM). D-Fe and total soluble Fe (T-Fe) in deep water showed a decreasing trend eastward. The higher iron concentrations in western deep waters probably result from higher inputs of dissolved Fe through atmospheric deposition or lateral transport. In contrast, D-Fe throughout the Bering Sea showed a consistent depth regime characterized by a rapid increase with depth to mid-depths, a gradual increase with depth in intermediate water to a maximum of 1.6-1.7 nM at 1500-2250 m, and a gradual decrease with depth to 1.3-1.4 nM at 3700 m. Higher iron concentrations and deeper D-Fe maxima in the Bering Sea are likely due to higher biological productivity and greater and deeper D-Fe input from the decomposition of sinking particulate organic matter in deep water. We suggest that the higher concentrations and deeper input of D-Fe as well as PO 4 and humic-type fluorescent dissolved organic matter in the Bering Sea probably results from the longer time for the accumulation of decomposition products resulting from iron supply from the organic-rich downslope sediment along the steep continental slopes and slow replacement of the deep water in the Bering Sea Basin. © 2013. American Geophysical Union. All Rights Reserved.