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| Titel |
Regional impacts of iron-light colimitation in a global biogeochemical model |
| VerfasserIn |
E. D. Galbraith, A. Gnanadesikan, J. P. Dunne, M. R. Hiscock |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1726-4170
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| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 7, no. 3 ; Nr. 7, no. 3 (2010-03-18), S.1043-1064 |
| Datensatznummer |
250004592
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| Publikation (Nr.) |
 copernicus.org/bg-7-1043-2010.pdf |
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| Zusammenfassung |
| Laboratory and field studies have revealed that iron has multiple roles in
phytoplankton physiology, with particular importance for light-harvesting
cellular machinery. However, although iron-limitation is explicitly included
in numerous biogeochemical/ecosystem models, its implementation varies, and
its effect on the efficiency of light harvesting is often ignored. Given the
complexity of the ocean environment, it is difficult to predict the
consequences of applying different iron limitation schemes. Here we explore
the interaction of iron and nutrient cycles in an ocean general circulation
model using a new, streamlined model of ocean biogeochemistry. Building on
previously published parameterizations of photoadaptation and export
production, the Biogeochemistry with Light Iron Nutrients and Gasses (BLING)
model is constructed with only four explicit tracers but including
macronutrient and micronutrient limitation, light limitation, and an
implicit treatment of community structure. The structural simplicity of this
computationally-inexpensive model allows us to clearly isolate the global
effect that iron availability has on maximum light-saturated photosynthesis
rates vs. the effect iron has on photosynthetic efficiency. We find that the
effect on light-saturated photosynthesis rates is dominant, negating the
importance of photosynthetic efficiency in most regions, especially the cold
waters of the Southern Ocean. The primary exceptions to this occur in
iron-rich regions of the Northern Hemisphere, where high light-saturated
photosynthesis rates allow photosynthetic efficiency to play a more
important role. In other words, the ability to efficiently harvest photons
has little effect in regions where light-saturated growth rates are low.
Additionally, we speculate that the phytoplankton cells dominating
iron-limited regions tend to have relatively high photosynthetic efficiency,
due to reduced packaging effects. If this speculation is correct, it would
imply that natural communities of iron-stressed phytoplankton may tend to
harvest photons more efficiently than would be inferred from iron-limitation
experiments with other phytoplankton. We suggest that iron limitation of
photosynthetic efficiency has a relatively small impact on global
biogeochemistry, though it is expected to impact the seasonal cycle of
plankton as well as the vertical structure of primary production. |
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