Climatic modulation of surface acidification rates through summertime wind forcing in the Southern Ocean

While the effects of the Southern Annular Mode (SAM), a dominant climate variability mode in the Southern Ocean, on ocean acidification have been examined using models, no consensus has been reached. Using observational data from south of Tasmania, we show that during a period with positive SAM trends, surface water pH and aragonite saturation state at 60°–55° S (Antarctic Zone) decrease in austral summer at rates faster than those predicted from atmospheric CO2 increase alone, whereas an opposite pattern is observed at 50°–45° S (Subantarctic Zone). Together with other processes, the enhanced acidification at 60°–55° S may be attributed to increased westerly winds that bring in more “acidified” waters from the higher latitudes via enhanced meridional Ekman transport and from the subsurface via increased vertical mixing. Our observations support climatic modulation of ocean acidification superimposed on the effect of increasing atmospheric CO2.

Continue reading ‘Climatic modulation of surface acidification rates through summertime wind forcing in the Southern Ocean’

Ocean acidification may affect lobster molt, reproduction

Stage IV lobster. Increased ocean acidity may affect reproductive rates in adult lobster. Photo by J. Waller.

The fact that the Gulf of Maine is warming more quickly than the majority of the world’s ocean regions is alarming enough. But with that warming comes an equally threatening change to the Gulf’s waters, increasing acidity. The effect of a more acidic Gulf on lobsters was the subject of a conference at Bowdoin College in June, organized by the Friends of Casco Bay and the University of Maine.
The cause of increased acidity is increased carbon dioxide (CO2) in the atmosphere. The world’s oceans naturally absorb atmospheric carbon dioxide; in fact, oceans have absorbed between one third and one half of the carbon dioxide emitted by human activities since the start of the Industrial Age in the mid-1800s. In seawater, CO2 reacts with H20 to form carbonic acid. Carbonic acid then breaks down into hydrogen ions and bicarbonate ions. Those hydrogen ions reduce seawater’s pH, thus making the water more acidic. The chemical process also reduces the amount of calcium carbonate available in seawater, a factor that has affected the shell-building abilities of shellfish.
But what effect does all this chemistry have on Maine lobster?

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Elevated pCO2 affects feeding behaviour and acute physiological response of the brown crab Cancer pagurus

Anthropogenic climate change exposes marine organisms to CO2 induced ocean acidification (OA). Marine animals may make physiological and behavioral adaptations to cope with OA. Elevated pCO2 may affect metabolism, feeding and energy partition of marine crabs, and thereby affect their predator-prey dynamics with mussels. Therefore, we examined the effects of simulated future elevated pCO2 on feeding behavior and energy metabolism of the brown crab Cancer pagurus. Following 54 days of pre-acclimation to control CO2 levels (360 μatm) at 11 °C, crabs were exposed to consecutively increased oceanic CO2 levels (two weeks for 1200 and 2300 μatm, respectively) and subsequently returned to control CO2 level (390 μatm) for two weeks in order to study their potential to acclimate elevated pCO2 and recovery performance. Standard metabolic rate (SMR), specific dynamic action (SDA) and feeding behaviour of the crabs were investigated during each experimental period. Compared to the initial control CO2 conditions, the SMRs of CO2 exposed crabs were not significantly increased, but increased significantly when the crabs were returned to normal CO2 levels. Conversely, SDA was significantly reduced under high CO2 and did not return to control levels during recovery. Under high CO2, crabs fed on smaller sized mussels than under control CO2; food consumption rates were reduced; foraging parameters such as searching time, time to break the prey, eating time and handling time were all significantly longer than under control CO2, and prey profitability was significantly lower than that under control conditions. Again, a two-week recovery period was not sufficient for feeding behavior to return to control values. PCA results revealed a positive relationship between feeding/SDA and pH, but negative relationships between the length of foraging periods and pH. In conclusion, elevated pCO2 caused crab metabolic rate to increase at the expense of SDA. Elevated pCO2 affected feeding performance negatively and prolonged foraging periods. These results are discussed in the context of how elevated pCO2 may impair the competitiveness of brown crabs in benthic communities.

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Getting warmer: understanding threats to ocean health

The global ocean covers 70 percent of our planet, makes Earth habitable, and contributes to economies, food supplies, and our health. Yet the ocean is increasingly threatened by the growing amount of carbon dioxide in the atmosphere.

Two Lamont-Doherty Earth Observatory scientists affiliated with the Center for Climate and Life are leading research projects that examine a few of the ways climate change affects the health of the ocean. Both researchers use the fossil remains of sea creatures as natural recorders of past climate and marine ecosystem changes. The information they obtain from these provides clues about how the future ocean and its inhabitants might be shaped by climate change.

Their studies are funded in part by the Center’s partnership with the World Surf League PURE, which enables Lamont-Doherty scientists to pursue critical research that advances understanding of climate impacts on the ocean.

Ocean acidification: The other carbon dioxide problem

Bärbel Hönisch, a marine geochemist, studies how seawater chemistry changed through time. Today, the ocean is becoming more acidic due to the rising concentration of carbon dioxide in Earth’s atmosphere, about 30 percent of which is absorbed by the ocean. While this process helps to minimize global warming, the dissolution of carbon dioxide in the ocean leads to the formation of carbonic acid. As the name implies, the addition of carbonic acid makes seawater more acidic and this ‘ocean acidification’ makes it harder for calcifying organisms such as corals, mollusks, and some plankton to build their shells and skeletons.

The current pH of the ocean is around 8.1, representing a 25 percent increase in acidity over the past 200 years. As the amount of carbon dioxide in the atmosphere continues to rise, scientists expect seawater acidity to increase another 25 percent by the end of the 21st century. This level of acidification is similar to that of the Paleocene-Eocene Thermal Maximum (PETM), which occurred around 56 million years ago. During the PETM, a sudden rise in atmospheric carbon dioxide coincided with rapid warming and seawater acidification — conditions that lasted for 70,000 years or more.

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Trading reproductive potential for survival? How acidification could affect a key crustacean in the future ocean

Credit: Pixabay

The climate is changing. This dire scenario is slowly starting to be felt all around the world, with global temperature averages increasing and climate patterns becoming disrupted. The problem begins with the continuous injection of carbon dioxide (CO2) into the atmosphere. As concentrations of this greenhouse gas increase, its dissolution into surface waters is favoured, and thus oceanic-CO2 increases as well. This gives rise to the phenomenon of Ocean Acidification (OA), which effectively creates a harsh environment for most marine species, and that has been the source of growing interest and concern not only in the scientific community but also in the general public.

Despite extensive research being conducted on the immediate effects of increased CO2 – i.e. the exposure of a single generation – a relatively new approach in experimental ecology aims to assess the short- to long-term effects of this stressor across several generations. As acclimation occurs in one generation, individuals experience different physiological and behaviour changes that emerge as a response to a stressful environment, and which aim at maximizing the individual’s ability to endure or move away from these conditions. Organisms may also effectively influence the following generations through parental conditioning, which includes the inheritance of non-genetic traits from adults to their offspring. This is something that has been shown to lead to largely positive effects in the offspring’s response, but that can also render the next generations more vulnerable to these environmental stressors.

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Oysters and eelgrass: potential partners in a high pCO2 ocean

Climate change is affecting the health and physiology of marine organisms and altering species interactions. Ocean acidification (OA) threatens calcifying organisms such as the Pacific oyster, Crassostrea gigas. In contrast, seagrasses, such as the eelgrass Zostera marina, can benefit from the increase in available carbon for photosynthesis found at a lower seawater pH. Seagrasses can remove dissolved inorganic carbon from OA environments, creating local daytime pH refugia. Pacific oysters may improve the health of eelgrass by filtering out pathogens such as Labyrinthula zosterae (LZ), which causes eelgrass wasting disease (EWD). We examined how co-culture of eelgrass ramets and juvenile oysters affected the health and growth of eelgrass and the mass of oysters under different pCO(2) exposures. In Phase I, each species was cultured alone or in co-culture at 12 degrees C across ambient, medium, and high pCO(2) conditions, (656, 1,158 and 1,606 mu atm pCO(2), respectively). Under high pCO(2), eelgrass grew faster and had less severe EWD (contracted in the field prior to the experiment). Co-culture with oysters also reduced the severity of EWD. While the presence of eelgrass decreased daytime pCO(2), this reduction was not substantial enough to ameliorate the negative impact of high pCO(2) on oyster mass. In Phase II, eelgrass alone or oysters and eelgrass in co-culture were held at 15 degrees C under ambient and high pCO(2) conditions, (488 and 2,013atm pCO(2), respectively). Half of the replicates were challenged with cultured LZ. Concentrations of defensive compounds in eelgrass (total phenolics and tannins), were altered by LZ exposure and pCO(2) treatments. Greater pathogen loads and increased EWD severity were detected in LZ exposed eelgrass ramets; EWD severity was reduced at high relative to low pCO(2). Oyster presence did not influence pathogen load or EWD severity; high LZ concentrations in experimental treatments may have masked the effect of this treatment. Collectively, these results indicate that, when exposed to natural concentrations of LZ under high pCO(2) conditions, eelgrass can benefit from co-culture with oysters. Further experimentation is necessary to quantify how oysters may benefit from co-culture with eelgrass, examine these interactions in the field and quantify context-dependency.

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Simulation of coastal processes affecting pH with impacts on carbon and nutrient biogeochemistry

Naturally occurring microbial decomposition of organic matter (OM) in coastal marine environments cause increased acidity in deeper layers similar or even exceeding the future predictions for global ocean acidification (OA). Experimental studies in coastal areas characterized by increased inputs of OM and nutrients, coping with intermittent hypoxic/anoxic conditions, provide decrease. Laboratory CO2-manipulated microcosm experiments were conducted using seawater and surface sediment collected from thdecrease. Labouratory CO2-manipulated microcosm experiments were conducted using seawater and surface sediment collected form the deepest part of Elefsis Bay (Saronikos Gulf, Eastern Mediterranean) focusing to study the co-evolution of processes affected by the decline of dissolved oxygen and pH induced by (a) OM remineralization and (b) the future anthropogenic increase of atmospheric CO2. Under more acidified conditions, a significant increase of total alkalinity was observed partially attributed to the sedimentary carbonate dissolution and the reactive nitrogen species shift towards ammonium. Nitrate and nitrite decline, in parallel with ammonium increase, demonstrated a deceleration of ammonium oxidation processes along with decrease in nitrate production. The decreased DIN:DIP ratio, the prevalence of organic nutrient species against the inorganic ones, the observations of constrained DON degradation and nitrate production decline and the higher DOC concentrations revealed the possible inhibition of OM decomposition under lower pH values. Finally, our results highlight the need for detailed studies of the carbonate system in coastal areas dominated by hypoxic/anoxic conditions, accompanied by other biogeochemical parameters and properly designed experiments to elucidate the processes sequence or alterations due to pH reduction.

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Ocean acidification in the IPCC AR5 WG II

OUP book