Modeling the global ocean iron cycle

Abstract

[1] We describe a model of the ocean transport and biogeochemical cycling of iron and the subsequent control on export production and macronutrient distributions. Ocean transport of phosphorus and iron are represented by a highly idealized six-box ocean model. Export production is parameterized simply; it is limited by light, phosphate, and iron availability in the surface ocean. We prescribe the regional variations in aeolian deposition of iron and examine three parameterizations of iron cycling in the deep ocean: (1) net scavenging onto particles, the simplest model; (2) scavenging and desorption of iron to and from particles, analogous to thorium; and (3) complexation. Provided that some unknown parameter values can be set appropriately, all three biogeochemical models are capable of reproducing the broad features of the iron distribution observed in the modern ocean and explicitly lead to regions of elevated surface phosphate, particularly in the Southern Ocean. We compare the sensitivity of Southern Ocean surface macronutrient concentration to increased aeolian dust supply for each parameterization. Both scavenging-based representations respond to increasing dust supply with a drawdown of surface phosphate in an almost linear relationship. The complexation parameterization, however, asymptotes toward a limited drawdown of phosphate under the assumption that ligand production does not respond to increased dust flux. In the scavenging based models, deep water iron concentrations and, therefore, upwelled iron continually increase with greater dust supply. In contrast, the availability of complexing ligand provides an upper limit for the deep water iron concentration in the latter model.

Biological data assimilation for parameter estimation of a phytoplankton functional type model for the western North Pacific

“…Shortwave radiation input and dust flux were the same as those of a global climate model (Model for Interdisciplinary Research on Climate, MIROC; Watanabe et al, 2011). A part of the dust flux (3.5 %; Shigemitsu et al, 2012) was regarded as iron dust, and 1 % of the iron dust was assumed to dissolve into the sea surface (Parekh et al, 2004). The other iron dust was transported to the lower layers and dissolved, which was the same process as shown in Shigemitsu et al (2012).…”

Overview of the mechanisms that could explain the ‘Boundary Exchange’ at the land–ocean contact

“…For example, it was assumed for years that dissolution from mineral dust was the main source of dissolved iron to the open ocean [3,77]. Therefore, most of the biogeochemical models of the early 2000s included only a dust source for dissolved iron (see [78] and references therein). In addition, coarse grid resolutions at that time prevented the detection of sedimentary iron sources when suspected [79].…”

Iron-binding ligands and their role in the ocean biogeochemistry of iron

“…[11,12,117] To further guide the development of these models, we need to have more detailed answers to the questions raised above.…”

“…[11][12][13][14] Our intention [102] Upwelling and downwelling oceanic fluxes of dissolved Fe are based on average concentrations of <0.1 and 0.7 × 10 −9 M for surface and deep water respectively [40] and a water exchange rate of 1.1 × 10 15 m 3 year −1 . [118] The biological pump flux is based on the IPCC 2001 carbon cycle [119] and a Fe : C ratio of ∼5 µmol mol −1 .…”