Global nutrient cycling
What controls the uptake and cycling of nutrients in the ocean? Answering this question is key for a whole range of issues, including managing global fisheries and understanding the concentration of atmospheric carbon dioxide.
We have recently developed a simplified model of global biogeochemical cycling. To learn more about this model go here.
Dunne, J.P., R.A. Armstong, A. Gnanadesikan and J. L Sarmiento, 2005: Empirical and mechanistic models for the particle export ratio, Global Biogeochemical Cycles, 19, GB4026, doi: 10.1029/2004GB002390. PDF
This paper looks at how much biological productivity within the upper ocean is recycled locally and how much gets converted into sinking particle material. This latter flux drives deep ocean chemical cycles, and is likely related to the flow of energy to higher trophic levels like fish.
Dunne, J.P., J.L. Sarmiento and A. Gnanadesikan, 2007: A synthesis of global particle export from the surface ocean and cycling through the ocean interior and on the sea floor, Global Biogeochemical Cycles, 21, GB4006, doi:10.1029/2006GB2907.PDF
We use satellite-based estimates of ocean primary productivity with algorithms for export and remineralization to calculate estimates for the global-scale fluxes of organic carbon, silica and calcium carbonate through the ocean. This work highlights the potential importance of coastal regions for carbon burial and suggests that lithogenic material may be important in ballasting export of carbon to the deep.
Gnanadesikan, A., J.P. Dunne, R M Key, K Matsumoto, J. L Sarmiento, R. D. Slater, and P. S. Swathi, 2004: Oceanic ventilation and biogeochemical cycling: Understanding the physical mechanisms that produce realistic distributions of tracers and productivity, Global Biogeochemical Cycles, 18, GB4010, doi:10.1029/2003GB002097.PDF
Here we examine the relationship between the distribution of turbulent mixing and the patterns of tracers and biological productivity that result.
Marinov, I., A. Gnanadesikan, J.L. Sarmiento, J.R. Toggweiler, M. Follows and B. Mignone, 2008: Impact of ocean circulation on biological carbon storage in the ocean and the atmospheric pCO2, Global Biogeochemical Cycles, 22, GB3007, doi:10.1029/2007GB002958. PDF
This paper explains how changes in the mean circulation can change the biological storage of carbon in the ocean, essentially by changing how "leaky" the ocean is to stored biological carbon.
Palter, J.B., J.L. Sarmiento, A. Gnanadesikan, J. Simeon and R.D. Slater, Fueling primary productivity: Nutrient return pathways from the deep ocean and their dependence on the meridional overturning circulation, Biogeosciences, 7, 3549-3568, 2010. PDF
This paper quantifies the role of Subantarctic Mode Waters in supplying new nutrients to the low-latitude pycnocline, and demonstrates that it is more dominant as mixing becomes lower (a presumably more realistic state of affairs).
Gnanadesikan, A., J.P. Dunne and J. John, What ocean biogeochemical models can tell us about bottom-up control of ecosystem variability, rev. for ICES J. Mar. Science, PDF
We show that interannual variability in our modeled ecosystems is dominated by ENSO in low latitudes and changes in spring bloom timing in high latitudes. We show that there are at least four extratropical regimes 1. Nutrient-limited, temperature stratified, in which cold winters result in higher spring biomass. 2. Light-limited, temperature stratified mode water formation regions, where the timing of restratification is controlled by winds as well as heat fluxes. 3. Light-limited, ice covered regions, where high temperatures correspond to high biomass because the ice has melted back. 4. Light-limited, salt-stratified regions, where lower temperatures may actually correspond to higher biomass because less heat has been supplied from below during the winter.
Marinov, I. and A. Gnanadesikan,Changes in ocean circulation and carbon storage are decoupled from air-sea CO2 fluxes, Biogeosciences Discussions, 7, 7985-8000, 2010. PDF
Here we show that the magnitude of carbon storage in the ocean is decoupled from air-sea fluxes of carbon, for reasons similar to that discussed in Gnanadesikan and Marinov, 2008.
