Dissolution of abiogenic and biogenic calcium carbonate under ocean acidification conditions

Under ocean acidification conditions, the chemistry of the seawater will change including a decrease in pH, a decrease in carbonate ion concentration and a decrease in the calcium carbonate saturation state of the water (Ω). This has implications for solid marine calcium carbonates including calcifying organisms and carbonate sediments. The dissolution kinetics of marine carbonates are poorly understood, therefore modelling of the future ocean under ocean acidification scenarios is hampered. The goal of this research was to provide an increased understanding of the kinetics of marine carbonate dissolution, including dependence of the dissolution rate of calcium carbonate mineral phases (calcite, calcite-aragonite, low Mg-calcite) on conditions relevant to ocean acidification, and then to apply this to biogenic samples (Pāua, kina and oyster). The effects of saturation state (Ω), surface area, and temperature were studied. Two methods were refined and used to collect and analyze the dissolution data – a pH-stat method and a pH free-drift method, with manipulation of the carbonate chemistry by addition of NaHCO3 and HCl. A LabVIEW® based program was developed for instrument control and automation and for data acquisition. The empirical equation R = k(1-Ω)n, was used to determine the reaction rates (R), the rate constants (k) and the reaction orders (n) for the each of the mineral phases and shellfish species.

Continue reading ‘Dissolution of abiogenic and biogenic calcium carbonate under ocean acidification conditions’

As oceans acidify, shellfish farmers respond

Scientists collaborate to mitigate climate impacts in the Northwest

Taylor Shellfish Farm’s Quilcene hatchery perches on a narrow peninsula that juts into the sinuous waterways of Washington’s Puget Sound. On the July day I visited, the hatchery and everything surrounding it seemed to drip with fecundity. Clouds banked over darkly forested hills on the opposite shore, and a tangy breeze blew in from across the bay. But the lushness hid an ecosystem’s unraveling.

Climate change is altering the very chemistry of surface seawater, causing ocean acidification, a chemical process that is lowering the amount of calcium marine organisms can access. Acidification is a relative term; the oceans are not actually turning into acid and will not melt surfboards or sea turtles anytime soon. Still, with enough acidification, seawater becomes corrosive to some organisms. Hardest hit are calcifiers, which use aragonite, a form of the mineral calcium carbonate, to make shells, skeletons and other important body parts. Examples of calcifiers include crabs, sea urchins, sea stars, some seaweeds, reef-forming corals, and a type of tiny floating marine snail, or pteropod, called a sea butterfly. Shellfish, including oysters and clams, are also seriously affected. With the disappearance of many of these sea creatures, oceanic food webs will be irrevocably altered by century’s end.

Continue reading ‘As oceans acidify, shellfish farmers respond’

Alaska ferry to host long-distance ocean acidification study (audio)

The Alaska Marine Highway System ferry Columbia will be part of an international science experiment starting this fall when it resumes its weekly run between Bellingham, Wash., and Southeast Alaska.

Equipment has been installed to continuously measure the ocean’s acidity along the ferry’s nearly 2,000-mile route. The goal is to better understand how acidification affects regional fisheries.

Continue reading ‘Alaska ferry to host long-distance ocean acidification study (audio)’

Variable metabolic responses of Skagerrak invertebrates to low O2 and high CO2 scenarios

Coastal hypoxia is a problem that is predicted to increase rapidly in the future. At the same time we are facing rising atmospheric CO2 concentrations, which are increasing the pCO2 and acidity of coastal waters. These two drivers are well studied in isolation however; the coupling of low O2 and pH is likely to provide a more significant respiratory challenge for slow moving and sessile invertebrates than is currently predicted. The Gullmar Fjord in Sweden is home to a range of habitats such as sand and mud flats, seagrass beds, exposed and protected shorelines, and rocky bottoms. Moreover, it has a history of both natural and anthropogenically enhanced hypoxia as well as North Sea upwelling, where salty water reaches the surface towards the end of summer and early autumn. A total of 11 species (Crustacean, Chordate, Echinoderm and Mollusc) of these ecosystems were exposed to four different treatments (high/low oxygen and low/high CO2; varying pCO2 of 450 and 1300 ppm and O2 concentrations of 2–3.5 and 9–10 mg L−1) and respiration measured after 3 and 6 days, respectively. This allows us to evaluate respiration responses of species of contrasting habitats and life-history strategies to single and multiple stressors. Results show that the responses of the respiration were highly species specific as we observed both synergetic as well as antagonistic responses, and neither phylum nor habitat explained trends in respiratory responses. Management plans should avoid the generalized assumption that combined stressors will results in multiplicative effects and focus attention on alleviating hypoxia in the region.
Continue reading ‘Variable metabolic responses of Skagerrak invertebrates to low O2 and high CO2 scenarios’

Divergent responses in growth and nutritional quality of coastal macroalgae to the combination of increased pCO2 and nutrients

Highlights

  • Growth rates and tissue quality of two common macroalgal species were assessed under conditions of high pCO2 and nutrient loading under monoculture and biculture.
  • Ephemeral macroalgae exhibited significant increases in growth under high pCO2 and high nutrients.
  • Growth rates of perennial macroalgae were unaffected by environmental treatments.
  • Tissue quality of both species increased via decreases in C:N when nutrients were increased.
  • Biculture appears to impact resource acquisition of perennial macroalgae as evidence of higher tissue C:N when compared to monoculture tissue.

Abstract

Coastal ecosystems are subjected to global and local environmental stressors, including increased atmospheric carbon dioxide (CO2) (and subsequent ocean acidification) and nutrient loading. Here, we tested how two common macroalgal species in the Northwest Atlantic (Ulva spp. and Fucus vesiculosus Linneaus) respond to the combination of increased CO2 and nutrient loading. We utilized two levels of pCO2 with two levels of nutrients in a full factorial design, testing the growth rates and tissue quality of Ulva and Fucus grown for 21 days in monoculture and biculture. We found that the opportunistic, fast-growing Ulva exhibited increased growth rates under high pCO2 and high nutrients, with growth rates increasing three-fold above Ulva grown in ambient pCO2 and ambient nutrients. By contrast, Fucus growth rates were not impacted by either environmental factor. Both species exhibited a decline in carbon to nitrogen ratios (C:N) with elevated nutrients, but pCO2 concentration did not alter tissue quality in either species. Species grown in biculture exhibited similar growth rates to those in monoculture conditions, but Fucus C:N increased significantly when grown with Ulva, indicating an effect of the presence of Ulva on Fucus. Our results suggest that the combination of ocean acidification and nutrients will enhance abundance of opportunistic algal species in coastal systems and will likely drive macroalgal community shifts, based on species-specific responses to future conditions.

Continue reading ‘Divergent responses in growth and nutritional quality of coastal macroalgae to the combination of increased pCO2 and nutrients’

Microbiome dynamics in early life stages of the scleractinian coral Acropora gemmifera in response to elevated pCO2

Reef-building corals are complex holobionts, harbouring diverse microorganisms that play essential roles in maintaining coral health. However, microbiome development in early life stages of corals remains poorly understood. Here, microbiomes of Acropora gemmifera were analysed during spawning and early developmental stages, and also under different seawater partial pressure of CO2 (pCO2) conditions, using amplicon sequencing of 16S rRNA gene for bacteria and archaea and of ITS2 for Symbiodinium. No remarkable microbiome shift was observed in adults before and after spawning. Moreover, microbiomes in eggs were highly similar to those in spawned adults, possibly suggesting a vertical transmission from parents to offspring. However, significant stage-specific changes were found in coral microbiome during development, indicating that host development played a dominant role in shaping coral microbiome. Specifically, Cyanobacteria were particularly abundant in 6-day-old juveniles, but decreased largely in 31-day-old juveniles with a possible subclade shift in Symbiodinium dominance from C2r to D17. Larval microbiome showed changes in elevated pCO2, while juvenile microbiomes remained rather stable in response to higher pCO2. This study provides novel insights into the microbiome development during the critical life stages of coral.

Continue reading ‘Microbiome dynamics in early life stages of the scleractinian coral Acropora gemmifera in response to elevated pCO2’

Very large release of mostly volcanic carbon during the Palaeocene–Eocene Thermal Maximum

The Palaeocene–Eocene Thermal Maximum1, 2 (PETM) was a global warming event that occurred about 56 million years ago, and is commonly thought to have been driven primarily by the destabilization of carbon from surface sedimentary reservoirs such as methane hydrates3. However, it remains controversial whether such reservoirs were indeed the source of the carbon that drove the warming1, 3, 4, 5. Resolving this issue is key to understanding the proximal cause of the warming, and to quantifying the roles of triggers versus feedbacks. Here we present boron isotope data—a proxy for seawater pH—that show that the ocean surface pH was persistently low during the PETM. We combine our pH data with a paired carbon isotope record in an Earth system model in order to reconstruct the unfolding carbon-cycle dynamics during the event6, 7. We find strong evidence for a much larger (more than 10,000 petagrams)—and, on average, isotopically heavier—carbon source than considered previously8, 9. This leads us to identify volcanism associated with the North Atlantic Igneous Province10, 11, rather than carbon from a surface reservoir, as the main driver of the PETM. This finding implies that climate-driven amplification of organic carbon feedbacks probably played only a minor part in driving the event. However, we find that enhanced burial of organic matter seems to have been important in eventually sequestering the released carbon and accelerating the recovery of the Earth system

Continue reading ‘Very large release of mostly volcanic carbon during the Palaeocene–Eocene Thermal Maximum’


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Ocean acidification in the IPCC AR5 WG II

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