Biogeosciences www.biogeosciences.net 1726-4170 1726-4189 4 4 2007 10.5194/bg-4-689-2007 http://www.biogeosciences.net/4/689/2007/ http://www.biogeosciences.net/4/689/2007/bg-4-689-2007.html http://www.biogeosciences.net/4/689/2007/bg-4-689-2007.pdf 689 706 2007-08-23 Iron profiles and speciation of the upper water column at the Bermuda Atlantic Time-series Study site: a model based sensitivity study L. Weber llw@noc.soton.ac.uk C. Völker A. Oschlies H. Burchard National Oceanography Centre, Southampton, UK Alfred-Wegener-Institut für Polar- und Meeresforschung, Bremerhaven, Germany Leibniz-Institut für Meereswissenschaften, Kiel, Germany Institut für Ostseeforschung Warnemünde, Germany A one-dimensional model of the biogeochemistry and speciation of iron is coupled with the General Ocean Turbulence Model (GOTM) and a NPZD-type ecosystem model. The model is able to simulate the temporal patterns and vertical profiles of dissolved iron (dFe) in the upper ocean at the Bermuda Atlantic Time-series Study site reasonably well. Subsurface model profiles strongly depend on the parameter values chosen for the loss processes for iron, colloidal aggregation and scavenging onto particles. Estimates for these parameters based on observations in particle-rich waters result in depletion of dFe. A high stability constant of iron-binding organic ligands is required to reproduce the observed degree of organic complexation below the mixed layer. The scavenging residence time for iron in the model is shortest in spring and summer, because of the larger abundance of particles, and increases with depth towards values on the order of a hundred years. A solubility of atmospherically deposited iron higher than 2% lead to dFe concentrations incompatible with observations. 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