Modeling the global ocean iron cycle (original) (raw)
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Global Biogeochemical Cycles, 1999
Iron occurs at very low concentrations in seawater and seems to be a limiting factor for primary production in the equatorial Pacific and the Southern Ocean. The global distribution of iron is still not well understood because of a lack of data and the complex chemistry of iron. We develop a 1 O-box model to study the oceanic distribution of iron and its effect on atmospheric CO2 concentration. Subject to our assumptions, we find that a lack of interocean fractionation of deep sea iron concentrations, as suggested by Johnson et al.
Journal of Geophysical Research, 2003
1] Aeolian dust input may be a critical source of dissolved iron for phytoplankton growth in some oceanic regions. We used an atmospheric general circulation model (GCM) to simulate dust transport and removal by dry and wet deposition. Model results show extremely low dust concentrations over the equatorial Pacific and Southern Ocean. We find that wet deposition through precipitation scavenging accounts for 4040% of the total deposition over the coastal oceans and 4060% over the open ocean. Our estimates suggest that the annual input of dissolved Fe by precipitation scavenging ranges from 0.5 to 4 Â 10 12 g yr À1 , which is 4-30% of the total aeolian Fe fluxes. Dissolved Fe input through dry deposition is significantly lower than that by wet deposition, accounting for only 0.6-2.4 % of the total Fe deposition. Our upper limit estimate on the fraction of dissolved Fe in the total atmospheric deposition is thus more than three times higher than the value of 10% currently considered as an upper limit for dissolved Fe in Aeolian fluxes. As iron input through precipitation may promote episodic phytoplankton growth in the ocean, measurements of dissolved iron in rainwater over the oceans are needed for the study of oceanic biogeochemical cycles.
Iron cycling and nutrient-limitation patterns in surface waters of the World Ocean
Deep Sea Research Part II: Topical Studies in Oceanography, 2001
A global marine ecosystem mixed-layer model is used to study iron cycling and nutrient-limitation patterns in surface waters of the world ocean. The ecosystem model has a small phytoplankton size class whose growth can be limited by N, P, Fe, and/or light, a diatom class which can also be Si-limited, and a diazotroph phytoplankton class whose growth rates can be limited by P, Fe, and/or light levels. The model also includes a parameterization of calcification by phytoplankton and is described in detail by Moore et al. (Deep-Sea Res. II, 2002).
Seasonal distributions of aeolian iron fluxes to the global ocean
Geophysical Research Letters, 2001
Among the factors affecting the photosynthetic rate of marine phytoplankton, aeolian iron (Fe) fluxes appear to be critical in several large regions of the global ocean. Here we present an analysis of in situ aerosol iron data obtained from a wide variety of marine locations to quantify the seasonal Fe inputs to the global ocean. When extrapolated to the global ocean, our results indicate strong seasonal variations in aeolian Fe fluxes in different oceanic basins. The predominant fraction of the Fe inputs enters the oceans in the Northern Hemisphere, with the summer flux rates ca. twice those of winter. The high Fe fluxes in the Northern Hemisphere are concentrated in low and mid-latitudes. With the promising new data from MODIS aboard the Terra satellite, the linkage between Fe fluxes and phytoplankton biomass and productivity may be soon further quantified.
Models of iron speciation and concentration in the stratified epipelagic ocean
Geophysical Research Letters, 2011
1] Surface ocean iron speciation is simulated using a timedependent box-model of light-mediated redox cycling over a range of aeolian inputs of soluble iron in the stratified epipelagic ocean. At steady-state, Dissolved iron (DFe) concentration increases with aeolian input of soluble iron up to 0.1 mmol m −2 d −1 , and is limited by the solubility of ferric hydroxide at higher fluxes which causes the formation of colloidal iron. We demonstrate that even in the presence of ample excess ligand, rapid conversion of dissolved iron between oxidized and reduced forms in the tropical surface ocean exposes DFe to colloid formation and scavenging. This result provides an explanation for the much smaller range of interregional variability in DFe measurements (0.05-0.4 nM) than soluble Fe fluxes (0.01-1 mmol m −2 d −1 ) and dust fluxes (0.1-10 g m −2 yr −1 ) predicted by atmospheric models. We incorporate the critical behavior of the full chemical speciation model into a reduced, computationally efficient model suitable for large scale calculations. Citation: Fan, S.-M., and J. P. Dunne (2011), Models of iron speciation and concentration in the stratified epipelagic ocean,
Aeolian input of bioavailable iron to the ocean
Geophysical Research Letters, 2006
Atmospheric deposition of mineral dust supplies much of the essential nutrient iron to the ocean. Presumably only the readily soluble fraction is available for biological uptake. Previous ocean models assumed this fraction was constant. Here the variable solubility of Fe in aerosols and precipitation is parameterized with a two-step mechanism, the development of a sulfate coating followed by the dissolution of iron (hydr)oxide on the dust aerosols. The predicted soluble Fe fraction increases with transport time from the source region and with the corresponding decrease in dust concentration. The soluble fraction is $1 percent near sources, but often 10-40 percent farther away producing a significant increase in soluble Fe deposition in remote ocean regions. Our results may require more rapid biological and physicochemical scavenging of Fe than used in current ocean models. We further suggest that increasing SO 2 emission alone could have caused significant Fe fertilization in the modern northern hemisphere oceans.
Biogeosciences, 2014
We investigated the simulated iron budget in ocean surface waters in the 1990s and 2090s using the Community Earth System Model version 1 and the Representative Concentration Pathway 8.5 future CO 2 emission scenario. We assumed that exogenous iron inputs did not change during the whole simulation period; thus, iron budget changes were attributed solely to changes in ocean circulation and mixing in response to projected global warming, and the resulting impacts on marine biogeochemistry. The model simulated the major features of ocean circulation and dissolved iron distribution for the present climate. Detailed iron budget analysis revealed that roughly 70 % of the iron supplied to surface waters in high-nutrient, low-chlorophyll (HNLC) regions is contributed by ocean circulation and mixing processes, but the dominant supply mechanism differed by region: upwelling in the eastern equatorial Pacific and vertical mixing in the Southern Ocean. For the 2090s, our model projected an increased iron supply to HNLC waters, even though enhanced stratification was predicted to reduce iron entrainment from deeper waters. This unexpected result is attributed largely to changes in gyre-scale circulations that intensified the advective supply of iron to HNLC waters. The simulated primary and export production in the 2090s decreased globally by 6 and 13 %, respectively, whereas in the HNLC regions, they increased by 11 and 6 %, respectively. Roughly half of the elevated production could be attributed to the intensified iron supply. The projected ocean circulation and mixing changes are consistent with recent observations of responses to the warming climate and with other Coupled Model Intercomparison Project model projections. We conclude that future ocean circulation has the potential to increase iron supply to HNLC waters and will potentially buffer future reductions in ocean productivity. * Primary and export production changes integrated over the IRON-DRIVEN AREA.