Dissolved and particulate Fe in the western and central North Pacific: Results from the 2002 IOC cruise

[1] The goals of the 2002 Intergovernmental Oceanographic Commission (IOC) cruise were to examine the variability in dissolved and particulate Fe over the cruise track, relate this variability to atmospheric aerosol Fe input, and examine the relationships between Fe, nitrate, and dust deposition with regards to Fe limitation particularly in the subarctic North Pacific. Dissolved Fe in the surface waters was quite variable, ranging from 0.10 nM to 0.30 nM. Dissolved Fe in the vertical profiles showed significant variability, the most prominent feature being an Fe maximum (similar to 1.5 nM Fe) associated with a broad nitrate maximum at 400 - 1000 m in the western subarctic gyre. Deep water Fe values in the subarctic region ranged from 0.8 nM to 1.1 nM. Subtropical gyre surface water dissolved Fe values were also quite variable, ranging from similar to 0.15 nM to 0.4 nM. Intermediate and deep water Fe values were on the order of 0.6 - 0.9 nM. Significant differences were observed between total dissolvable Fe and dissolved Fe (TDFe-DFe) in surface waters over the course of the cruise track, and these differences are discussed in terms of particulate Fe and possible sources of Fe to surface waters. Finally, nitrate: Fe ratios in the western subarctic gyre, atmospheric dust flux estimates based on surface water aluminum concentrations, and aerosol Fe fluxes from ship-based aerosol collections are used to evaluate the relative importance of atmospheric and/or continental Fe input versus upwelling fluxes of Fe to the surface waters of the subarctic gyre.