Posts Tagged 'modeling'

Climate change could drive marine food web collapse through altered trophic flows and cyanobacterial proliferation

Global warming and ocean acidification are forecast to exert significant impacts on marine ecosystems worldwide. However, most of these projections are based on ecological proxies or experiments on single species or simplified food webs. How energy fluxes are likely to change in marine food webs in response to future climates remains unclear, hampering forecasts of ecosystem functioning. Using a sophisticated mesocosm experiment, we model energy flows through a species-rich multilevel food web, with live habitats, natural abiotic variability, and the potential for intra- and intergenerational adaptation. We show experimentally that the combined stress of acidification and warming reduced energy flows from the first trophic level (primary producers and detritus) to the second (herbivores), and from the second to the third trophic level (carnivores). Warming in isolation also reduced the energy flow from herbivores to carnivores, the efficiency of energy transfer from primary producers and detritus to herbivores and detritivores, and the living biomass of detritivores, herbivores, and carnivores. Whilst warming and acidification jointly boosted primary producer biomass through an expansion of cyanobacteria, this biomass was converted to detritus rather than to biomass at higher trophic levels—i.e., production was constrained to the base of the food web. In contrast, ocean acidification affected the food web positively by enhancing trophic flow from detritus and primary producers to herbivores, and by increasing the biomass of carnivores. Our results show how future climate change can potentially weaken marine food webs through reduced energy flow to higher trophic levels and a shift towards a more detritus-based system, leading to food web simplification and altered producer–consumer dynamics, both of which have important implications for the structuring of benthic communities.

Continue reading ‘Climate change could drive marine food web collapse through altered trophic flows and cyanobacterial proliferation’

Assessing carbon dioxide removal through global and regional ocean alkalization under high and low emission pathways

Atmospheric CO2 levels continue to rise, increasing the risk of severe impacts on the Earth system, and on the ecosystem services that it provides. Artificial Ocean Alkalization (AOA) is capable of reducing atmospheric CO2 concentrations, surface warming and addressing ocean acidification. Here we simulate global and regional responses to alkalinity addition (0.25 PmolAlk/year) using the CSIRO-Mk3L-COAL Earth System Model in the period 2020–2100, under high (RCP8.5) and low (RCP2.6) emissions. While regionally there are large changes associated with locations of AOA, globally we see only a very weak dependence on where and when AOA is applied. We see that under RCP2.6, while the carbon uptake associated with AOA is only ~ 60 % of the total under RCP8.5, the relative changes in temperature are larger, as are the changes in pH (1.4×) and aragonite saturation (1.7×). The results of this modelling study are significant as they demonstrate that AOA is more effective under lower emissions, and the higher the emissions the more AOA required to achieve the same reduction in global warming and ocean acidification. Finally, our simulations show AOA in the period 2020–2100 is capable of offsetting global warming and ameliorating ocean acidification increases due to low emissions, but regionally the response is more variable.

Continue reading ‘Assessing carbon dioxide removal through global and regional ocean alkalization under high and low emission pathways’

Simulated effect of carbon cycle feedback on climate response to solar geoengineering

Most modeling studies investigate climate effects of solar geoengineering under prescribed atmospheric CO2, thereby neglecting potential climate feedbacks from the carbon cycle. Here we use an Earth system model to investigate interactive feedbacks between solar geoengineering, global carbon cycle, and climate change. We design idealized sunshade geoengineering simulations to prevent global warming from exceeding 2°C above preindustrial under a CO2emission scenario with emission mitigation starting from middle of century. By year 2100, solar geoengineering reduces the burden of atmospheric CO2 by 47 PgC with enhanced carbon storage in the terrestrial biosphere. As a result of reduced atmospheric CO2, consideration of the carbon cycle feedback reduces required insolation reduction in 2100 from 2.0 to 1.7 W m−2. With higher climate sensitivity the effect from carbon cycle feedback becomes more important. Our study demonstrates the importance of carbon cycle feedback in climate response to solar geoengineering.

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Influence of diatom diversity on the ocean biological carbon pump

Diatoms sustain the marine food web and contribute to the export of carbon from the surface ocean to depth. They account for about 40% of marine primary productivity and particulate carbon exported to depth as part of the biological pump. Diatoms have long been known to be abundant in turbulent, nutrient-rich waters, but observations and simulations indicate that they are dominant also in meso- and submesoscale structures such as fronts and filaments, and in the deep chlorophyll maximum. Diatoms vary widely in size, morphology and elemental composition, all of which control the quality, quantity and sinking speed of biogenic matter to depth. In particular, their silica shells provide ballast to marine snow and faecal pellets, and can help transport carbon to both the mesopelagic layer and deep ocean. Herein we show that the extent to which diatoms contribute to the export of carbon varies by diatom type, with carbon transfer modulated by the Si/C ratio of diatom cells, the thickness of the shells and their life strategies; for instance, the tendency to form aggregates or resting spores. Model simulations project a decline in the contribution of diatoms to primary production everywhere outside of the Southern Ocean. We argue that we need to understand changes in diatom diversity, life cycle and plankton interactions in a warmer and more acidic ocean in much more detail to fully assess any changes in their contribution to the biological pump.

Continue reading ‘Influence of diatom diversity on the ocean biological carbon pump’

Socioeconomic risk from ocean acidification and climate change impacts on Atlantic Canadian fisheries

Ocean acidification (OA) is an emerging consequence of anthropogenic carbon dioxide emissions. The full extent of the biological impacts are currently not well understood. However, it is expected that invertebrate species that rely on the mineral calcium carbonate will be among the first and most severely affected. Despite the limited understanding of impacts there is a need to identify potential pathways for human societies to be affected by OA. Research on these social implications is a small but developing field of literature. This thesis contributes to this field by using a risk assessment framework, informed by a biophysical model of future species distributions, to investigate Atlantic Canadian risk from changes in shellfish fisheries. New Brunswick and Nova Scotia are expected to see declines in resource accessibility. While Newfoundland and Labrador and PEI are more socially vulnerable to losses in fisheries, they are expected to experience relatively minor changes in access.

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Past and future evolution of the carbonate system in a coastal zone of the Northern Antarctic Peninsula


• Anthropogenic carbon concentrations are estimated within the mixed layer using three different methods.
• There is a large increasing rate of anthropogenic carbon penetration in the deep waters.
• Undersaturated aragonite saturation state at sea surface could be reached before year 2060.
• An alternative method for calculating anthropogenic carbon is purposed for regions with low carbonate system datasets.


It is arduous to gather a good spatial and temporal dataset of marine carbonate properties, especially in the Southern Ocean. In this study, we have reconstructed the carbonate system in the Gerlache Strait, a coastal zone of the Northern Antarctic Peninsula. We also analyzed the impact of ocean acidification by calculating the tipping points of the calcium carbonate saturation states and pH (i.e., when saturation state and pH goes below one and 7, respectively). Hydrographic and carbonate data from three distinct data sets (GOAL – 2013 to 2016, FRUELA – 1996, and World Ocean Database – 1965 to 2004) have been joined and used to reconstruct the carbonate system from the past 50 years. Temporal annual mean trends were determined depending on the water column depth-layer. The northern Gerlache Strait showed a significant increasing trend of CT concentrations (1.0024 ± 0.34 µmol kg–1) and related pH decreasing trend (–0.0026 ± 0.0009 sws) in the surface mixed layer (> 60 m). The properties variability is relatively different (magnitudes and signs) between the northern and southern sectors of the Gerlache Strait, which indicate that adjacent regions to the Gerlache Strait to the southwest and north, respectively, may major influence the regional carbonate dynamics. Results also show that episodic under-saturation conditions, in relation to aragonite within the surface mixed layer, may already occur, especially in regions close to large glaciers.

Continue reading ‘Past and future evolution of the carbonate system in a coastal zone of the Northern Antarctic Peninsula’

Impacts of ocean acidification in the coastal and marine environments of Caribbean Small Island Developing States (SIDS)

Oceans have absorbed one third of the carbon dioxide (CO2) released to the atmosphere from human activities causing the seawater pH to decrease by 0.1 units since the Industrial Revolution. There is certainty that ocean acidification caused by anthropogenic activities is currently in progress and will increase in accord with rising atmospheric CO2. There is medium confidence that these changes with significantly impact marine ecosystems. Throughout the Caribbean small islands, ocean acidification effects could be exacerbated due to local processes within coastal zones. Ocean surface aragonite saturation state (Ωarg) has declined by around 3% in the Caribbean region relative to pre-industrial levels potentially already impacting tropical marine calcifying organisms. In addition to the effect on living organisms, ocean acidification is likely to diminish the structural integrity of coral reefs through reduced skeletal density, loss of calcium carbonate, and dissolution of high-Mg carbonate cements which help to bind the reef. This would make coastal areas of the Caribbean small islands increasingly more vulnerable to the action of waves and storm surge. This is likely to have knock-on effects to the tourism sector, fisheries and coastal infrastructure. More studies about the present and projected impacts of ocean acidification on Caribbean small islands are necessary in order to evaluate alternative adaptive strategies accounting for the different island’s environmental, socioeconomic, and political settings.

Continue reading ‘Impacts of ocean acidification in the coastal and marine environments of Caribbean Small Island Developing States (SIDS)’

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Ocean acidification in the IPCC AR5 WG II

OUP book