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Free Content Simulations of phytoplankton species and carbon production in the equatorial Pacific Ocean 2. Effects of physical and biogeochemical processes

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A one-dimensional multi-component lower trophic level ecosystem model that includes detailed algal physiology is used to investigate the response of phytoplankton community and carbon production and export to variations in physical and biochemical processes in the Cold Tongue region of the equatorial Pacific Ocean at 0N, 140W. Results show that high-frequency variability in vertical advection and temperature is an important mechanism driving the carbon export. Filtering out low frequency physical forcing results in a 30% increase in primary production and dominance of high-light adapted Prochlorococcus and autotrophic eukaryotes. Sensitivity studies show that iron availability is the primary control on carbon export and production; whereas, algal biomass concentration is largely regulated by zooplankton grazing. Recycled iron is an important component of the ecosystem dynamics because sustained growth of algal groups depends on remineralized iron which accounts for 40% of the annual primary production in the Cold Tongue region. Sensitivity studies show that although all algal groups have a considerable effect on simulated phytoplankton carbon biomass, not all have a strong effect on primary production and carbon export. Thus, these sensitivity studies indicate that it may not be necessary to represent a broad spectrum of algal groups in carbon cycle models, because a few key groups appear to have a large influence on primary production and export variability. Combining the low-light adapted Prochlorococcus, high-light adapted Prochlorococcus and Synechococcus groups as a single group and using a three algal group model may be sufficient to simulate primary production and export variability in the tropical Pacific waters. The results from this modeling study suggest that the net effect of increased stratification and temperature conditions is a decrease in carbon export in the Cold Tongue region and a shift in the phytoplankton community towards smaller algal forms (e.g., Prochlorococcus spp. and Synechecoccus). Increased stratification can result in decreased iron concentration and reduced vertical velocities, both of which contribute to decreased carbon export. Also, stratified conditions enhance the remineralization rate of nutrients (e.g., iron), which enhances carbon production. Thus, inclusion of iron dynamics in climate models may be needed to fully represent the effect of climate variability on equatorial Pacific ecosystems.

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Document Type: Research Article

Publication date: 2007-03-01

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  • The Journal of Marine Research publishes peer-reviewed research articles covering a broad array of topics in physical, biological and chemical oceanography. Articles that deal with processes, as well as those that report significant observations, are welcome. In the area of biology, studies involving coupling between ecological and physical processes are preferred over those that report systematics. Authors benefit from thorough reviews of their manuscripts, where an attempt is made to maximize clarity. The time between submission and publication is kept to a minimum; there is no page charge.
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