Iron cycling and nutrient-limitation patterns in surface waters of the World Ocean

Abstract

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).The model reproduces the observed high nitrate, low chlorophyll (HNLC) conditions in the Southern Ocean, subarctic Northeast Pacific, and equatorial Pacific, and realistic global patterns of primary production, biogenic silica production, nitrogen fixation, particulate organic carbon export, calcium carbonate export, and surface chlorophyll concentrations. Phytoplankton cellular Fe/C ratios and surface layer dissolved iron concentrations are also in general agreement with the limited field data. Primary production, community structure, and the sinking carbon flux are quite sensitive to large variations in the atmospheric iron source, particularly in the HNLC regions, supporting the Iron Hypothesis of Martin (Paleoceanography 5 (1990) 1-13). Nitrogen fixation is also strongly influenced by atmospheric iron deposition.Nitrogen limits phytoplankton growth rates over less than half of the world ocean during summer months. Export of biogenic carbon is dominated by the sinking particulate flux, but detrainment and turbulent mixing account for 30% of global carbon export. Our results, in conjunction with other recent studies, suggest the familiar paradigm that nitrate inputs to the surface layer can be equated with particulate carbon export needs to be expanded to include multiple limiting nutrients and modes of export. r

Bathymetry and productivity of the southern Great Basin seaway, Nevada, USA: An evaluation of isotope and trace element chemistry in mid-Carboniferous and modern brachiopods

“…Iron is a limiting micronutrient for diatoms in the waters off California and in other bodies of water (e.g., Bruland et al, 2001;Moore et al, 2002;Bruland et al, 2005). Iron and other nutrients are usually supplied by the upwelling of offshore subsurface waters interacting with organic-rich shelf sediments, whereas it is quite possible for upwelling currents to be iron-deplete if no and/or small plateau/shelf sources of sediment are within the area.…”

“…The coast of Durban, South Africa, unlike the waters off Marseille, has no major river systems and thus offshore fertilization depends largely on offshore blowing winds transporting aeolian material from the arid hinterland (Moore et al, 2002). The shallowerwater brachiopods off Durban are enriched in Fe relative to their deeper water counterparts (Fig.…”

“…In contrast, the influence of seawater productivity on brachiopod abundance and distribution is essentially unstudied, and its application to studies of fossil and paleo-ocean chemistry remains unexplored. Complementary studies on marine phytoplankton give us a clear insight of the impact of macroand micronutrients on population dynamics, individual's sizes and their oceanic distribution (e.g., Broecker and Peng, 1982;Moore et al, 2002;Bruland et al, 2005). These and other studies demonstrated that the micronutrient iron plays a key role in limiting phytoplankton growth rates and the structuring of plankton communities (e.g., Martin et al, 1989;Takeda, 1998;Boyd and Harrison, 1999; others cited in Moore et al, 2002).…”

“…Complementary studies on marine phytoplankton give us a clear insight of the impact of macroand micronutrients on population dynamics, individual's sizes and their oceanic distribution (e.g., Broecker and Peng, 1982;Moore et al, 2002;Bruland et al, 2005). These and other studies demonstrated that the micronutrient iron plays a key role in limiting phytoplankton growth rates and the structuring of plankton communities (e.g., Martin et al, 1989;Takeda, 1998;Boyd and Harrison, 1999; others cited in Moore et al, 2002). Several studies documented considerable variability of Fe/C ratios in phytoplankton relative to Fe availability (e.g., Sunda et al, 1991;Sunda, 1997).…”

A decade of synthesis and modeling in the US Joint Global Ocean Flux Study

“…Although the link between iron limitation and High-Nitrate Low-Chlorophyll (HNLC) regions was identified prior to the SMP, it was not until the SMP era that iron dynamics and iron limitation became a common element of marine ecosystem models (e.g., Moore et al 2002b;Moore et al, 2004;Mongin et al, 2006;Wang et al, 2006;Wiggert et al, 2006). Iron limitation lowers phytoplankton growth rates and alters community structure, tending to shift ecosystems away from the larger diatoms that differentially contribute to vertical export flux.…”