Archive for January, 2008

Multimodel analysis of the response of the coccolithophore Emiliania huxleyi to an elevation of pCO2 under nitrate limitation

Large scale precipitation of calcium carbonate in the oceans by coccolithophorids is a phenomenon that plays an important role in atmospheric CO2 trapping. However, recent experiments revealed that the associated fluxes may be slow down by an increase in atmospheric CO2 concentration. In this paper we design models to account for the decrease in calcification and photosynthesis rates observed after an increase of pCO2 in Emiliania huxleyi chemostat cultures. Since the involved mechanisms are still not completely understood, we consider various models, each of them being based on a different hypothesis. These models are kept at a very general level, by maintaining the growth and calcification functions in a generic form, i.e. independent on the exact shape of these functions and on parameter values. The analysis is thus performed using these generic functions where the only hypothesis is an increase of these rates with respect to the regulating carbon species. As a result, each model responds differently to a pCO2 elevation. Surprisingly, the only models whose behaviour is in agreement with the experimental results correspond to carbonate as the regulating species for photosynthesis. Finally we show that a model where pH is the regulating factor can also properly predict the measured shifts.

Continue reading ‘Multimodel analysis of the response of the coccolithophore Emiliania huxleyi to an elevation of pCO2 under nitrate limitation’

[Ocean] Acidification

The uptake of anthropogenic change within part of the climate system that can be attributed to human action, rather than natural causes. carbon since 1750 has led to the oceans becoming more acidic with an average decrease in pH of 0.1 units. Surface ocean and UK coastal water pH will continue to rapidly decline in the future as they take up more atmospheric CO2.

Although the effects of the current reduction in pH on the marine biosphere are as yet undocumented this is due, in part, to lack of research in this area. However, unless we substantially and urgently reduce CO2 emissions, experiments, observations and modelling indicate that future reductions in ocean acidity will have major negative impacts on aragonitic and calcitic (shell/skeleton) forming organisms this century and their dependent species. There is growing evidence that the physiology (e.g. growth and reproduction) of adults, larvae and juveniles of some species are sensitive to acidification. Impacts of decreasing pH on key biogeochemical processes other than calcification is theoretically possible and serious (e.g. impact on nutrient speciation, primary production and nutrient, carbon and sulphur cycling,) but there has been little research on this. The knock-on effects of ocean acidification on marine ecosystems, biogeochemical cycles, food webs and biodiversity could be considerable but difficult to quantify. Reducing CO2 emissions is the only way of reducing ocean acidification.

Nearly half of the CO2 derived from burning fossil fuel has already been absorbed by the surfaces of our seas and oceans and more will be absorbed in the future as we continue to increase our CO2 emissions to the atmosphere. The ocean uptake of CO2 is effectively buffering even more serious climate change than that predicted by clear evidence-based scientific consensus. Continued acidification will reduce the ability of the ocean to take up CO2 from the atmosphere, which will have feedbacks to future climate change, further accelerating the accumulation of CO2 in the atmosphere.

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A comparison of future increased CO2 and temperature effects on sympatric Heterosigma akashiwo and Prorocentrum minimum

Very little is known about how global anthropogenic changes will affect major harmful algal bloom groups. Shifts in the growth and physiology of HAB species like the raphidophyte Heterosigma akashiwo and the dinoflagellate Prorocentrum minimum due to rising CO2 and temperature could alter their relative abundance and environmental impacts in estuaries where both form blooms, such as the Delaware Inland Bays (DIB). We grew semi-continuous cultures of sympatric DIB isolates of these two species under four conditions: (1) 20 °C and 375 ppm CO2 (ambient control), (2) 20 °C and 750 ppm CO2 (high CO2), (3) 24 °C and 375 ppm CO2 (high temperature), and (4) 24 °C and 750 ppm CO2 (combined). Elevated CO2 alone or in concert with temperature stimulated Heterosigma growth, but had no significant effect on Prorocentrum growth. PBmax (the maximum biomass-normalized light-saturated carbon fixation rate) in Heterosigma was increased only by simultaneous CO2 and temperature increases, whereas PBmax in Prorocentrum responded significantly to CO2 enrichment, with or without increased temperature. CO2 and temperature affected photosynthetic parameters α, Φmax, Ek, and Click to view the MathML source in both species. Increased temperature decreased and increased the Chl a content of Heterosigma and Prorocentrum, respectively. CO2 availability and temperature had pronounced effects on cellular quotas of C and N in Heterosigma, but not in Prorocentrum. Ratios of C:P and N:P increased with elevated carbon dioxide in Heterosigma but not in Prorocentrum. These changes in cellular nutrient quotas and ratios imply that Heterosigma could be more vulnerable to N limitation but less vulnerable to P-limitation than Prorocentrum under future environmental conditions. In general, Heterosigma growth and physiology showed a much greater positive response to elevated CO2 and temperature compared to Prorocentrum, consistent with what is known about their respective carbon acquisition mechanisms. Hence, rising temperature and CO2 either alone or in combination with other limiting factors could significantly alter the relative dominance of these two co-existing HAB species over the next century.

Continue reading ‘A comparison of future increased CO2 and temperature effects on sympatric Heterosigma akashiwo and Prorocentrum minimum’

Climate-mediated changes to mixed-layer properties in the Southern Ocean: assessing the phytoplankton response

Concurrent changes in ocean chemical and physical properties influence phytoplankton dynamics via alterations in carbonate chemistry, nutrient and trace metal inventories and upper ocean light environment. Using a fully coupled, global carbon-climate model (Climate System Model 1.4-carbon), we quantify anthropogenic climate change relative to the background natural interannual variability for the Southern Ocean over the period 2000 and 2100. Model results are interpreted using our understanding of the environmental control of phytoplankton growth rates – leading to two major findings. Firstly, comparison with results from phytoplankton perturbation experiments, in which environmental properties have been altered for key species (e.g., bloom formers), indicates that the predicted rates of change in oceanic properties over the next few decades are too subtle to be represented experimentally at present. Secondly, the rate of secular climate change will not exceed background natural variability, on seasonal to interannual time-scales, for at least several decades – which may not provide the prevailing conditions of change, i.e. constancy, needed for phytoplankton adaptation. Taken together, the relatively subtle environmental changes, due to climate change, may result in adaptation by resident phytoplankton, but not for several decades due to the confounding effects of climate variability. This presents major challenges for the detection and attribution of climate change effects on Southern Ocean phytoplankton. We advocate the development of multi-faceted tests/metrics that will reflect the relative plasticity of different phytoplankton functional groups and/or species to respond to changing ocean conditions.

Continue reading ‘Climate-mediated changes to mixed-layer properties in the Southern Ocean: assessing the phytoplankton response’

Climate-mediated changes to mixed-layer properties in the Southern Ocean: assessing the phytoplankton response

Concurrent changes in ocean chemical and physical properties influence phytoplankton dynamics via alterations in carbonate chemistry, nutrient and trace metal inventories and upper ocean light environment. Using a fully coupled, global carbon-climate model (Climate System Model 1.4-carbon), we quantify anthropogenic climate change relative to the background natural interannual variability for the Southern Ocean over the period 2000 and 2100. Model results are interpreted using our understanding of the environmental control of phytoplankton growth rates – leading to two major findings. Firstly, comparison with results from phytoplankton perturbation experiments, in which environmental properties have been altered for key species (e.g., bloom formers), indicates that the predicted rates of change in oceanic properties over the next few decades are too subtle to be represented experimentally at present. Secondly, the rate of secular climate change will not exceed background natural variability, on seasonal to interannual time-scales, for at least several decades – which may not provide the prevailing conditions of change, i.e. constancy, needed for phytoplankton adaptation. Taken together, the relatively subtle environmental changes, due to climate change, may result in adaptation by resident phytoplankton, but not for several decades due to the confounding effects of climate variability. This presents major challenges for the detection and attribution of climate change effects on Southern Ocean phytoplankton. We advocate the development of multi-faceted tests/metrics that will reflect the relative plasticity of different phytoplankton functional groups and/or species to respond to changing ocean conditions.

Continue reading ‘Climate-mediated changes to mixed-layer properties in the Southern Ocean: assessing the phytoplankton response’

Benefits of plankton disrupted by acid?

SAN FRANCISCO (Map, News) – Oceans have grown more acidic as rising levels of carbon dioxide have filled the Earth’s air, prompting a trio of UC San Francisco researchers to investigate whether marine plankton will continue to produce much of the globe’s oxygen as its wet world grows more hostile.

Massive blooms of microscopic phytoplankton are sometimes visible from space. Unlike other types of tiny, fast-growing plankton, phytoplankton grow using energy from the sun.

Phytoplankton feed ocean ecosystems, fighting global warming by turning carbon dioxide into protective shells that are eaten by other creatures or sink to the sea floor.

“They’re bringing the carbon dioxide down into the deeper water,” UC San Francisco biology professor Ed Carpenter said, “so they’re helping to slow global warming.”

Continue reading ‘Benefits of plankton disrupted by acid?’

Ocean Acidification: Towards an Interagency Approach

The Town Hall on Ocean Acidification which is titled: Ocean Acidification: Towards an Interagency Approach is being held at the Ocean Sciences Meeting (http://aslo.org/orlando2008/town_hall.html) Tuesday March 4, 2008 from 7:30 to 9:30 in Rm W108.

Continue reading ‘Ocean Acidification: Towards an Interagency Approach’

Killing Earth’s largest organism

Five times in the history of life on Earth, the corals have died out. Each time they have taken tens of millions of years to evolve anew from simpler creatures. Leading Australian marine scientist Dr J.E.N. “Charlie” Veron argues we are at the brink of a sixth mass extinction – and that the killers of the largest living organism on the planet, the Great Barrier Reef, will be none other than ourselves.

In “A Reef in Time”, published by Harvard University Press, Dr Veron traces the story of the GBR from beginning to what he sees as its probable demise towards the end of the present century.

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Atmospheric CO2, ocean acidification, and ecological changes in planktonic calcifying organisms

The European Science Fondation (EuroCLIMATE Programme) sponsored a workshop on Atmospheric CO2, ocean acidification, and ecological changes in planktonic calcifying organisms with 45 international participants both from the EuroCLIMATE programme as well as externally invited experts.

Continue reading ‘Atmospheric CO2, ocean acidification, and ecological changes in planktonic calcifying organisms’

Atmospheric CO2, ocean acidification, and ecological changes in planktonic calcifying organisms

The European Science Fondation (EuroCLIMATE Programme) sponsored a workshop on Atmospheric CO2, ocean acidification, and ecological changes in planktonic calcifying organisms with 45 international participants both from the EuroCLIMATE programme as well as externally invited experts.

Continue reading ‘Atmospheric CO2, ocean acidification, and ecological changes in planktonic calcifying organisms’


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