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

Abstract

AbstractWe 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 PO4 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.