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Abstract Dissolved iron (dFe) plays an important role in regulating marine productivity. In high nutrient, low chlorophyll regions (>33% of the global ocean), iron is the primary growth limiting nutrient, and elsewhere iron can regulate nitrogen fixation by diazotrophs. The link between iron availability and carbon export is strongly dependent on the phytoplankton iron quotas or cellular Fe:C ratios. This ratio varies by more than an order of magnitude in the open ocean and is positively correlated with ambient dFe concentrations in field observations. Representing Fe:C ratios within models is necessary to investigate how ocean carbon cycling will interact with perturbations to iron cycling in a changing climate. The Community Earth System Model ocean component was modified to simulate dynamic, group‐specific, phytoplankton Fe:C that varies as a function of ambient iron concentration. The simulated Fe:C ratios improve the representation of the spatial trends in the observed Fe:C ratios. The acclimation of phytoplankton Fe:C ratios dampens the biogeochemical response to varying atmospheric deposition of soluble iron, compared to a fixed Fe:C ratio. However, varying atmospheric soluble iron supply has first order impacts on global carbon and nitrogen fluxes and on nutrient limitation spatial patterns. Our results suggest that pyrogenic Fe is a significant dFe source that rivals mineral dust inputs in some regions. Changes in dust flux and iron combustion sources (anthropogenic and wildfires) will modify atmospheric Fe inputs in the future. Accounting for dynamic phytoplankton iron quotas is critical for understanding ocean biogeochemistry and projecting its response to variations in atmospheric deposition.
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A meta-analysis on environmental drivers of marine phytoplankton C : N : P
Abstract. The elemental stoichiometry of marine phytoplankton plays a critical role in global biogeochemical cycles through its impact on nutrient cycling, secondary production, and carbon export. Although extensive laboratory experiments have been carried out over the years to assess the influence of different environmental drivers on the elemental composition of phytoplankton, a comprehensive quantitative assessment of the processes is still lacking. Here, we synthesized the responses of P:C and N:C ratios of marine phytoplankton to five major drivers (inorganic phosphorus, inorganic nitrogen, inorganic iron, irradiance, and temperature) by a meta-analysis of experimental data across 366 experiments from 104 journal articles. Our results show that the response of these ratios to changes in macronutrients is consistent across all the studies, where the increase in nutrient availability is positively related to changes in P:C and N:C ratios. We found that eukaryotic phytoplankton are more sensitive to the changes in macronutrients compared to prokaryotes, possibly due to their larger cell size and their abilities to regulate their gene expression patterns quickly. The effect of irradiance was significant and constant across all studies, where an increase in irradiance decreased both P:C and N:C. The P:C ratio decreased significantly with warming, but the response to temperature changes was mixed depending on the culture growth mode and the growth phase at the time of harvest. Along with other oceanographic conditions of the subtropical gyres (e.g., low macronutrient availability), the elevated temperature may explain why P:C is consistently low in subtropical oceans. Iron addition did not systematically change either P:C or N:C. Overall, our findings highlight the high stoichiometric plasticity of eukaryotes and the importance of macronutrients in determining P:C and N:C ratios, which both provide us insights on how to understand and model plankton diversity and productivity.
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- Award ID(s):
- 1827948
- PAR ID:
- 10257331
- Date Published:
- Journal Name:
- Biogeosciences
- Volume:
- 17
- Issue:
- 11
- ISSN:
- 1726-4189
- Page Range / eLocation ID:
- 2939 to 2954
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.5194/bg-17-2939-2020
