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Importance of E kman transport and gyre circulation change on seasonal variation of surface dissolved iron in the western subarctic N orth P acific
Author(s) -
Nakanowatari Takuya,
Nakamura Tomohiro,
Uchimoto Keisuke,
Nishioka Jun,
Mitsudera Humio,
Wakatsuchi Masaaki
Publication year - 2017
Publication title -
journal of geophysical research: oceans
Language(s) - English
Resource type - Journals
eISSN - 2169-9291
pISSN - 2169-9275
DOI - 10.1002/2016jc012354
Subject(s) - ocean gyre , subarctic climate , ekman transport , oceanography , upwelling , environmental science , advection , phytoplankton , mixed layer , geology , biogeochemical cycle , annual cycle , climatology , atmospheric sciences , subtropics , nutrient , chemistry , ecology , physics , organic chemistry , biology , thermodynamics , environmental chemistry
Abstract Iron (Fe) is an essential nutrient for marine phytoplankton and it constitutes an important element in the marine carbon cycle in the ocean. This study examined the mechanisms controlling seasonal variation of dissolved Fe (dFe) in the western subarctic North Pacific (WSNP), using an ocean general circulation model coupled with a simple biogeochemical model incorporating a dFe cycle fed by two major sources (atmospheric dust and continental shelf sediment). The model reproduced the seasonal cycle of observed concentrations of dFe and macronutrients at the surface in the Oyashio region with maxima in winter (February–March) and minima in summer (July–September), although the simulated seasonal amplitudes are a half of the observed values. Analysis of the mixed‐layer dFe budget indicated that both local vertical entrainment and lateral advection are primary contributors to the wintertime increase in dFe concentration. In early winter, strengthened northwesterly winds excite southward Ekman transport and Ekman upwelling over the western subarctic gyre, transporting dFe‐rich water southward. In mid to late winter, the southward western boundary current of the subarctic gyre and the outflow from the Sea of Okhotsk also bring dFe‐rich water to the Oyashio region. The contribution of atmospheric dust to the dFe budget is several times smaller than these ocean transport processes in winter. These results suggest that the westerly wind‐induced Ekman transport and gyre circulation systematically influence the seasonal cycle of WSNP surface dFe concentration.