Abstract
Iron (Fe) is well known as a limiting factor to control primary productivity especially in high-nutrient and low chlorophyll area such as the subarctic Pacific. The solubility of Fe is believed to be controlled by its complexation with natural organic ligands, while the distribution of organic ligands is poorly understood. Here, we report that dissolved (< 0.2 µm) organic ligands were unevenly distributed between the western and eastern stations in the subarctic Pacific. The concentration of dissolved organic ligands around the lower part of subarctic Pacific intermediate water was higher in the western station, suggesting that Fe complexation with these organic ligands supports a lateral transport within the water mass. However, a more detailed size-fractionated treatment indicated no significant difference in the soluble (< 1000 kDa) ligands’ distribution between the western and eastern stations. These results suggest that organic and inorganic colloid formations are potentially essential for Fe transport mechanisms in the subarctic Pacific.
Highlights
Iron (Fe) is well known as a limiting factor to control primary productivity especially in high-nutrient and low chlorophyll area such as the subarctic Pacific
In seawater, dissolved Fe is predominantly complexed with a heterogeneous natural organic ligands pool[2], which regulates both the dissolved Fe concentration ([D-Fe]) and its bioavailability for phytoplankton[3]
The subarctic Pacific is characterized by low salinity surface waters that result in significant stratification between surface waters and intermediate waters[6]
Summary
Iron (Fe) is well known as a limiting factor to control primary productivity especially in high-nutrient and low chlorophyll area such as the subarctic Pacific. High excess ligand concentrations (> 3.9 nM) with low D-K′Fe′L (< 1011.0) were detected in the lower NPIW density range at Stn. CL2.
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