UK Parliamentary Office of Science and Technology on ocean acidification

The increasing amount of carbon dioxide (CO2) in the atmosphere is acidifying the oceans. The resulting changes to ecosystems and marine biodiversity may have negative impacts on fisheries and food security and reduce the coastal protection provided by coral reefs. This POSTnote outlines the science behind ocean acidification and summarises the threats to the marine environment. A global reduction of carbon emissions is the only certain way to minimise these risks.

Dissolute behavior up North

Credit: Steeve Comeau, CNRS-UPMC

Some species of sea butterfly have shells composed of aragonite, a metastable form of calcium carbonate. These pelagic mollusks are considered sentinels for environmental change; even though they can survive for a couple of days in water depleted of calcium carbonate, their shells already begin to show dissolution marks.

Announcement of Opportunity for a carbonate chemistry facility

Closing date: 16:00 on 10 December 2009

Proposals are invited for a service of carbonate chemistry measurements as part of the UK Ocean Acidification Research Programme. This £12m collaborative programme is a Living With Environmental Change (LWEC) accredited programme and is co-funded by NERC, the Department for Environment, Food & Rural Affairs (Defra) and the Department of Energy & Climate Change (DECC).

Impact of anthropogenic ocean acidification on thermal tolerance of the spider crab Hyas araneus (update)

Future scenarios for the oceans project combined developments of CO₂ accumulation and global warming and their impact on marine ecosystems. The synergistic impact of both factors was addressed by studying the effect of elevated CO₂ concentrations on thermal tolerance of the cold-eurythermal spider crab Hyas araneus from the population around Helgoland. Here ambient temperatures characterize the southernmost distribution limit of this species. Animals were exposed to present day normocapnia (380 ppm CO₂), CO₂ levels expected towards 2100 (710 ppm) and beyond (3000 ppm). Heart rate and haemolymph PO₂ (P_eO₂) were measured during progressive short term cooling from 10 to 0°C and during warming from 10 to 25°C. An increase of P_eO₂ occurred during cooling, the highest values being reached at 0°C under all three CO₂ levels. Heart rate increased during warming until a critical temperature (T_c) was reached. The putative T_c under normocapnia was presumably >25°C, from where it fell to 23.5°C under 710 ppm and then 21.1°C under 3000 ppm. At the same time, thermal sensitivity, as seen in the Q₁₀ values of heart rate, rose with increasing CO₂ concentration in the warmth. Our results suggest a narrowing of the thermal window of Hyas araneus under moderate increases in CO₂ levels by exacerbation of the heat or cold induced oxygen and capacity limitation of thermal tolerance.

Effect of CO2 on the properties and sinking velocity of aggregates of the coccolithophore Emiliania huxleyi

Coccolithophores play an important role in organic matter export due to their production of the mineral calcite that can act as ballast. Recent studies indicated that calcification in coccolithophores may be affected by changes in seawater carbonate chemistry. We investigated the influence of CO₂ on the aggregation and sinking behaviour of the coccolithophore Emiliania huxleyi (PML B92/11) during a laboratory experiment. The coccolithophores were grown under low (~180 μatm), medium (~380 μatm), and high (~750 μatm) CO₂ conditions. Aggregation of the cells was promoted using roller tables. Size and settling velocity of aggregates were determined during the incubation using video image analysis. The results show that CO₂ induced changes in the inorganic carbon to organic carbon ratio (PIC/POC) influence the porosity and hence the sinking velocity of aggregates of Emiliania huxleyi. Average sinking velocity was highest for low CO₂ aggregates (~1292 m d⁻¹) that also had the highest PIC/POC ratio. Lowest PIC/POC ratios and lowest sinking velocity (~366 m d⁻¹) at comparable sizes were observed for aggregates of the high CO₂ treatment. Aggregates of the high CO₂ treatment showed an excess density about one order of magnitude lower (~4.2×10⁻⁴ g cm⁻³) when compared to aggregates from the medium and low CO₂ treatments (~1.7×10⁻³ g cm⁻³). Thus, the amount of calcite in aggregates is crucial for the degree of ballasting effect. In the high CO₂ treatment, aggregates with lower calcite content had higher bacterial abundance, suggesting enhanced bacterial degradation. Thus, our findings indicate that a CO₂ induced reduction of calcite content aggregates could affect the vertical export of organic matter in the ocean, particularly in areas dominated by coccolithophores blooms.

A blueprint for restoring the world’s oceans to health

In her long career as an oceanographer, Sylvia Earle has witnessed the damage that humanity has done to the Earth’s oceans. But in an interview with Yale Environment 360, she says there’s still time to pull the seas back from the brink.

For nearly half a century, Sylvia Earle has been exploring the world’s oceans, taking part in more than 400 expeditions and spending thousands of hours under the sea. An explorer-in-residence at the National Geographic Society and former chief scientist at the National Oceanic and Atmospheric Administration, Earle has broken many barriers in the world of deep-sea exploration.

Coupling of CO2 and ice sheet stability over major climate transitions of the last 20 million years

The CO₂ content of the atmosphere has varied cyclically between ~180 and ~280 ppmv over the last 800,000 years, closely coupled with temperature and sea level. For earlier periods in Earth’s history, pCO₂ is much less certain and the relationship between pCO₂ and climate remains poorly constrained. We use boron/calcium ratios in foraminifera to estimate pCO₂ during major climate transitions of the last 20 million years (myr). During the Middle Miocene, when temperatures were ~3 to 6°C warmer and sea level 25 to 40 meters higher than present, pCO₂ was similar to modern levels. Decreases in pCO₂ were synchronous with major episodes of glacial expansion during the Middle Miocene (~14 to 10 million years ago; Ma) and Late Pliocene (~3.3 to -2.4 Ma).

CO2 perturbation experiments: similarities and differences between dissolved inorganic carbon and total alkalinity manipulations (update)

Increasing atmospheric carbon dioxide (CO₂) through human activities and invasion of anthropogenic CO₂ into the surface ocean alters the seawater carbonate chemistry, increasing CO₂ and bicarbonate (HCO₃⁻) at the expense of carbonate ion (CO₃²⁻) concentrations. This redistribution in the dissolved inorganic carbon (DIC) pool decreases pH and carbonate saturation state (Ω). Several components of the carbonate system are considered potential key variables influencing for instance calcium carbonate precipitation in marine calcifiers such as coccolithophores, foraminifera, corals, mollusks and echinoderms. Unravelling the sensitivities of marine organisms and ecosystems to CO₂ induced ocean acidification (OA) requires well-controlled experimental setups and accurate carbonate system manipulations. Here we describe and analyse the chemical changes involved in the two basic approaches for carbonate chemistry manipulation, i.e. changing DIC at constant total alkalinity (TA) and changing TA at constant DIC. Furthermore, we briefly introduce several methods to experimentally manipulate DIC and TA. Finally, we examine responses obtained with both approaches using published results for the coccolithophore Emiliania huxleyi. We conclude that under most experimental conditions in the context of ocean acidification DIC and TA manipulations yield similar changes in all parameters of the carbonate system, which implies direct comparability of data obtained with the two basic approaches for CO₂ perturbation.

Benefits, risks, and costs of stratospheric geoengineering

Injecting sulfate aerosol precursors into the stratosphere has been suggested as a means of geoengineering to cool the planet and reduce global warming. The decision to implement such a scheme would require a comparison of its benefits, dangers, and costs to those of other responses to global warming, including doing nothing. Here we evaluate those factors for stratospheric geoengineering with sulfate aerosols. Using existing U.S. military fighter and tanker planes, the annual costs of injecting aerosol precursors into the lower stratosphere would be several billion dollars. Using artillery or balloons to loft the gas would be much more expensive. We do not have enough information to evaluate more exotic techniques, such as pumping the gas up through a hose attached to a tower or balloon system. Anthropogenic stratospheric aerosol injection would cool the planet, stop the melting of sea ice and land-based glaciers, slow sea level rise, and increase the terrestrial carbon sink, but produce regional drought, ozone depletion, less sunlight for solar power, and make skies less blue. Furthermore it would hamper Earth-based optical astronomy, do nothing to stop ocean acidification, and present many ethical and moral issues. Further work is needed to quantify many of these factors to allow informed decision-making.

Tropics face fish famine due to climate change, report warns

The first study to look at how climate change will affect food supplies offshore warns of severe declines in fish stocks in some of the world’s poorest regions.

Fish populations in the tropics could fall by as much as 40% over the next half century because of global warming, jeopardising a vital food source for the developing world, a new study published today has found.

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It did not take into account the effects of ocean acidification – caused by more carbon dioxide dissolving in seawater and which scientists expect will reinforce the effects of warming on the oceans. “We think that our estimates should be considered conservative because adding ocean acidification into the equation would further decrease future fishery potential,” said Cheung. He said a follow-up study would look at the effects of acidification.