1,721,086 research outputs found
Report on a desk study to identify likely sources of error in the measurements of carbonate system parameters and related calculations, particularly with respect to coastal waters and ocean acidification experiments. Supplement to DEFRA contract ME4133 “DEFRApH monitoring project”
Full text linkThe relative influences of nitrogen and phosphorus on oceanic primary production
No full textA simple model has the potential to resolve the long-running debate amongst oceanographers over whether nitrogen or phosphorus exerts overall control on oceanic primary production. A representation of the competition between nitrogen-fixing and other phytoplankton is inserted into a two-box global model of the oceanic nitrogen and phosphorus cycles. Homeostatic regulation of both nitrate and phosphate concentrations results, with surface waters more deficient in nitrate than phosphate in the steady state, but with external phosphate inputs controlling longer-term primary production in the global ocean
Book review: Introduction to the Modelling of Marine Ecosystems, by W. Fennel and T. Neumann, Elsevier, 2004, 230pp
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Anthropogenic modification of the oceans
No full textHuman activities are altering the ocean in many different ways. The surface ocean is warming and, as a result, it is becoming more stratified and sea level is rising. There is no clear evidence yet of a slowing in ocean circulation, although this is predicted for the future. As anthropogenic CO2 permeates into the ocean, it is making sea water more acidic, to the detriment of surface corals and probably many other calcifiers. Once acidification reaches the deep ocean, it will become more corrosive to CaCO3, leading to a considerable reduction in the amount of CaCO3 accumulating on the deep seafloor. There will be a several thousand-year-long interruption to CaCO3 sedimentation at many points on the seafloor. A curious feedback in the ocean, carbonate compensation, makes it more likely that global warming and sea-level rise will continue for many millennia after CO2 emissions cease
Calcium carbonate cycling in future oceans and its influence on future climates
No full textIn the last few years, evidence has accumulated that calcifying organisms are likely to be affected by ocean acidification. Therefore, the production of calcium carbonate will probably decline, although conversely global warming, increasing stratification and sea level rise may also stimulate increases in global calcification. As acidification reaches the deep ocean, it will cause pronounced shallowing of the lysocline depths for calcite and aragonite, leading most probably to an almost complete cessation of deep-sea calcium carbonate burial for some centuries. Here, I briefly review the consequences of these and other changes on future ocean calcium carbonate cycling, and the consequences of this for future climate. Associated climate impacts are not likely to be significant over the next few centuries, but will become increasingly important thereafter. After the carbonate compensation response to acidification has run its course, extra CO2 is expected to be left behind in the atmosphere, protecting against future ice ages
The role of diatoms in regulating the ocean's silicon cycle
No full textAmong phytoplankton the diatoms are strong competitors and contribute significantly to total global primary production. Aspects of their life history, notably their high sinking rates, make them important to the export flux of carbon into the ocean interior. Unlike the majority of other phytoplankton, they utilize silicic acid (=silicate) to construct their cell walls and are controlled by its availability and distribution. Here a simple model is developed to study the relationship between the diatoms and the ocean's silicon cycle. The ecological component of this model pits the slightly superior diatoms against all other algae, with both groups competing for phosphate while the diatoms additionally require silicic acid. The model agrees reasonably with observed distributions of nutrients and with their biogeochemical fluxes. While theoretically superior, the diatoms are held in check by the availability of silicic acid, allowing the persistence and numerical dominance of the other algae. The concentrations of both nutrients are homeostatically controlled by the phytoplankton, and resist perturbations. Analysis finds that primary production in the model is ultimately controlled by phosphate, with silicic acid abundance controlling the fraction of the total produced by diatoms. Sensitivity analyses using more ecologically detailed variants of the model find that these results are generally robust. The model's treatment of the “silica pump" hypothesis [Dugdale and Wilkerson, 1998] is also examined
Short review of chemical and biological consequences of ocean acidification
No full textCommissioned Report for Meteorological Office, AVOID project. ICP product number 7.2, report number 4, DECC/Defra (GA01101), MoD (CBC/2B/0417_Annex C5
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