Regional variability of acidification in the Arctic: a sea of contrasts

The Arctic Ocean is a region that is particularly vulnerable to the impact of ocean acidification driven by rising atmospheric CO₂, negatively impacting calcifying organisms such as coccolithophorids and foraminiferans. In this study, we use an ocean general circulation model, with embedded biogeochemistry and a full description of the carbon cycle, to study the response of pH and saturation states of calcite and aragonite to changing climate in the Arctic Ocean. Particular attention is paid to the strong regional variability within the Arctic and, for comparison, simulation results are contrasted with those for the global ocean. Simulations were run to year 2099 using the RCP 8.5 (the highest IPCC AR5 CO₂ emission scenario). The separate impacts of the direct increase in atmospheric CO₂ and indirect effects via climate feedbacks (changing temperature, stratification, primary production and fresh water fluxes) were examined by undertaking two simulations, one with the full system and the other in which ocean-atmosphera exchange of CO₂ was prevented from increasing beyond the flux calculated for year 2000. Results indicate that climate feedbacks, and spatial heterogeneity thereof, play a strong role in the declines in pH and carbonate saturation (Ω) seen in the Arctic. The central Arctic, Canadian Arctic Archipelago and Baffin Bay show greatest rates of acidification and Ω decline as a result of melting sea ice. In contrast, areas affected by Atlantic inflow including the Greenland Sea and outer shelves of the Barents, Kara and Laptev seas, had minimal decreases in pH and Ω because weakening stratification associated with diminishing ice cover led to greater mixing and primary production. As a consequence, the predicted onset of undersaturation is highly variable regionally within the Arctic, occurring during the decade of 2000–2010 in the Siberian shelves and Canadian Arctic Archipelago, but as late as the 2080s in the Barents and Norwegian Seas. We conclude that, in order to make future projections of acidification and carbon saturation state in the Arctic, regional variability needs to be adequately resolved, with particular emphasis on reliable predictions of the rates of retreat of the sea-ice which are a major source of uncertainty.

Ocean acidification seminar scheduled for Friday Harbor Labs

San Juan County residents wanting to learn more about ocean acidification are invited to a free seminar at the University of Washington’s Friday Harbor Labs on February 27.

Ocean acidification results from carbon dioxide emissions being absorbed from the atmosphere into seawater, forming carbonic acid. This radically alters ocean chemistry and endangers sea life. Between 2005 and 2009, up to 80 percent of the oyster larvae in in some Washington hatcheries were killed by acidification before the problem was identified and temporary counter-measures were taken.

The seminar, hosted by the San Juan County Marine Resources Committee (MRC), will feature Shallin Busch, a National Oceanic and Atmospheric Administration research ecologist, speaking on “The Science and Food Web Implications of Ocean Acidification.” Busch was a member of the Washington State Panel on Ocean Acidification.

Evaluation of reagentless pH modification for in situ ocean analysis: determination of dissolved inorganic carbon using mass spectrometry

RATIONALE

In situ analytical techniques that require the storage and delivery of reagents (e.g., acidic or basic solutions) have inherent durability limitations. The reagentless electrolytic technique for pH modification presented here was developed primarily to ease and to extend the longevity of dissolved inorganic carbon (DIC) determinations in seawater, but can also be used for other analytical methods. DIC, a primary carbon dioxide (CO₂) system variable along with alkalinity, controls seawater pH, carbonate saturation state, and CO₂ fugacity. Determinations of these parameters are central to an understanding of ocean acidification and global climate change.

METHODS

Electrodes fabricated with electroactive materials, including manganese(III) oxide (Mn₂O₃) and palladium (Pd), were examined for potential use in electrolytic acidification. In-line acidification techniques were evaluated using a bench-top membrane introduction mass spectrometry (MIMS) setup to determine the DIC content of artificial seawater. Linear least-squares (LLSQ) calibrations for DIC concentration determinations over a range between 1650 and 2400 µmol kg^–1 were obtained, using both the novel electrolytic and conventional acid addition techniques.

RESULTS

At sample rates of 4.5 mL min^–1, electrodes clad with Mn₂O₃ and Pd were able to change seawater pH from 7.6 to 2.8 with a power consumption of less than 3 W. Although calibration curves were influenced by sampling rates at a flow of 4.5 mL min^–1, the 1σ measurement precision for DIC was of the order of ±20 µmol kg^–1.

CONCLUSIONS

Calibrations obtained with the novel reagentless technique and the in-line addition of strong acid showed similar capabilities for DIC quantification. However, calculations of power savings for the reagentless technique relative to the mechanical delivery of stored acid demonstrated substantial advantages of the electrolytic technique for long-term deployments (>1 year).

Detrimental effects of ocean acidification on the economically important Mediterranean red coral (Corallium rubrum)

The mean predicted decrease of 0.3 to 0.4 pH units in the global surface ocean by the end of the century has prompted urgent research to assess the potential effects of ocean acidification on the marine environment, with strong emphasis on calcifying organisms. Among them, the Mediterranean red coral (Corallium rubrum) is expected to be particularly susceptible to acidification effects, due to the elevated solubility of its Mg-calcite skeleton. This, together with the large overexploitation of this species, depicts a bleak future for this organism over the next decades. In this study, we evaluated the effects of low pH on this species from aquaria experiments. Several colonies of C. rubrum were long-term maintained for 314 days in aquaria at two different pH levels (8.10 and 7.81, pH_T). Calcification rate, spicule morphology, major biochemical constituents (protein, carbohydrates and lipids) and fatty acids composition were measured periodically. Exposure to lower pH conditions caused a significant decrease in the skeletal growth rate in comparison to the control treatment. Similarly, the spicule morphology clearly differed between both treatments at the end of the experiment, with aberrant shapes being observed only under the acidified conditions. On the other hand, while total organic matter was significantly higher under low pH conditions, no significant differences were detected between treatments regarding total carbohydrate, lipid, protein and fatty acid composition. However, the lower variability found among samples maintained in acidified conditions relative to controls, suggests a possible effect of pH decrease on the metabolism of the colonies. Our results show, for the first time, evidence of detrimental ocean acidification effects on this valuable and endangered coral species.