Archive for November, 2013

Environmental considerations for subseabed geological storage of CO2

Many countries are now using or investigating offshore geological storage of CO2 as a means to reduce atmospheric CO2 emissions. Although associated research often focuses on deep-basin geology (e.g. seismic, geomagnetics), environmental data on the seabed and shallow subseabed is also crucial to 1) detect and characterise potential indicators of fluid seeps and their potential connectivity to targeted storage reserves, 2) obtain baseline environmental data for use in future monitoring, and 3) acquire information to facilitate an improved understanding of ecosystem processes for use in impact prediction. This study reviews the environmental considerations, including potential ecological impacts, associated with subseabed geological storage of CO2. Due to natural variations in CO2 levels in seafloor sediments, baseline CO2 measurements and knowledge of physical-chemical processes affecting the regional distribution of CO2 and pH are critical for the design of appropriate monitoring strategies to assess potential impacts of CO2 seepage from subseabed storage reservoirs. Surficial geological and geophysical information, such as that acquired from multibeam sonar and sub-bottom profiling, can be used to investigate the connectivity between the deep reservoirs and the surface, which is essential in establishing the reservoir containment properties. CO2 leakage can have a pronounced effect on sediments and rocks which in turn can have carryover effects to biogeochemical cycles. The effects of elevated CO2 on marine organisms are variable and species-specific but can also have cascading effects on communities and ecosystems, with marine benthic communities at natural analogues (e.g. volcanic vents) showing decreased diversity, biomass, and trophic complexity. Despite their potential applications, environmental surveys and data are still not a standard and integral part of subseabed CO2 storage projects. However, the habitat mapping and seabed characterisation methodology that underpins such surveys is well developed and has a strong record of providing information to industry and decision makers. This review provides recommendations for an integrated and interdisciplinary approach to offshore geological storage of CO2, which will benefit national programs and industry and will be valuable to researchers in a broad range of disciplines.

Continue reading ‘Environmental considerations for subseabed geological storage of CO2’

Embryonic response to long-term exposure of the marine crustacean Nephrops norvegicus to ocean acidification and elevated temperature

Due to anthropogenic CO2 emissions, our oceans have gradually become warmer and more acidic. To better understand the consequences of this, there is a need for long-term (months) and multistressor experiments. Earlier research demonstrates that the effects of global climate change are specific to species and life stages. We exposed berried Norway lobsters (Nephrops norvegicus), during 4 months to the combination of six ecologically relevant temperatures (5–18°C) and reduced pH (by 0.4 units). Embryonic responses were investigated by quantifying proxies for development rate and fitness including: % yolk consumption, mean heart rate, rate of oxygen consumption, and oxidative stress. We found no interactions between temperature and pH, and reduced pH only affected the level of oxidative stress significantly, with a higher level of oxidative stress in the controls. Increased temperature and % yolk consumed had positive effects on all parameters except on oxidative stress, which did not change in response to temperature. There was a difference in development rate between the ranges of 5–10°C (Q10: 5.4) and 10–18°C (Q10: 2.9), implicating a thermal break point at 10°C or below. No thermal limit to a further increased development rate was found. The insensitivity of N. norvegicus embryos to low pH might be explained by adaptation to a pH-reduced external habitat and/or internal hypercapnia during incubation. Our results thus indicate that this species would benefit from global warming and be able to withstand the predicted decrease in ocean pH in the next century during their earliest life stages. However, future studies need to combine low pH and elevated temperature treatments with hypoxia as hypoxic events are frequently and increasingly occurring in the habitat of benthic species.

Continue reading ‘Embryonic response to long-term exposure of the marine crustacean Nephrops norvegicus to ocean acidification and elevated temperature’

Ocean acidification: the climate change buffer, but another environmental disaster in the making

After attending the talk “Ocean Acidification – The Other CO2 Problem” here at COP19 in Warsaw, it is quite clear that there is another significant issue concerning climate change. About one-quarter of the human-made CO2 emissions have been absorbed by oceans creating yet another environmental problem of global concern. We are changing seawater chemistry through a type of carbon sequestration. This creates a potential environmental disaster in the ocean and delays the inevitable temperature rise associated with our CO2 emissions. Starting with the impact from the ocean’s perspective — CO2 is absorbed and dissolved in water which forms carbonic acid.

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Research cruise to explore ocean acidification; film to document the rising problem (text and video)

Erik Cordes, marine biologist and assistant professor of biology at Temple, will lead an NSF-funded, three-week research cruise in the Gulf of Mexico to explore the effects of rising ocean acidification in the deep sea and on deepwater corals specifically.

The cruise will take place next spring aboard the state-of-the-art research vessel Atlantis, operated by the Woods Hole Oceanographic Institute. The researchers on the cruise will make  a series of dives from the ship in the newly refurbished submersible Alvin.

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The future of the oceans: acid test

The world’s seas are becoming more acidic. How much that matters is not yet clear. But it might matter a lot.

HUMANS, being a terrestrial species, are pleased to call their home “Earth”. A more honest name might be “Sea”, as more than seven-tenths of the planet’s surface is covered with salt water. Moreover, this water houses algae, bacteria (known as cyanobacteria) and plants that generate about half the oxygen in the atmosphere. And it also provides seafood—at least 15% of the protein eaten by 60% of the planet’s human population, an industry worth $218 billion a year. Its well-being is therefore of direct concern even to landlubbers.

That well-being, some fear, is under threat from the increasing amount of carbon dioxide in the atmosphere, a consequence of industrialisation. This concern is separate from anything caused by the role of CO2 as a climate-changing greenhouse gas. It is a result of the fact that CO2, when dissolved in water, creates an acid.

That matters, because many creatures which live in the ocean have shells or skeletons made of stuff that dissolves in acid. The more acidic the sea, the harder they have to work to keep their shells and skeletons intact. On the other hand, oceanic plants, cyanobacteria and algae, which use CO2 for photosynthesis, might rather like a world where more of that gas is dissolved in the water they live in—a gain, rather than a loss, to ocean productivity.

Two reports attempting to summarise the world’s rather patchy knowledge about what is going on have recently been published. Both are the products of meetings held last year (the wheels grind slowly in environmental bureaucracy). One, in Monterey, California, looked at the science. The other, in Monaco, looked at possible economic consequences. Together, the documents suggest this is an issue that needs to be taken seriously, though worryingly little is known about it.

Omega point

Regular, direct measures of the amount of CO2 in the air date to the 1950s. Those of the oceans’ acidity began only in the late 1980s (see chart). Since it started, that acidity has risen from pH 8.11 to pH 8.06 (on the pH scale, lower numbers mean more acid). This may not sound much, but pH is a logarithmic scale. A fall of one pH point is thus a tenfold rise in acidity, and this fall of 0.05 points in just over three decades is a rise in acidity of 12%.

Patchier data that go back further suggest there has been a 26% rise in oceanic acidity since the beginning of the industrial revolution, 250 years ago. Projections made by assuming that carbon-dioxide emissions will continue to increase in line with expected economic growth indicate this figure will be 170% by 2100.

Worrying about what the world may be like in nine decades might sound unnecessary, given more immediate problems, but another prediction is that once the seas have become more acidic, they will not quickly recover their alkalinity. Ocean life, in other words, will have to get used to it. So does this actually matter?

The variable people most worry about is called omega. This is a number that describes how threatening acidification is to seashells and skeletons. Lots of these are made of calcium carbonate, which comes in two crystalline forms: calcite and aragonite. Many critters, especially reef-forming corals and free-swimming molluscs (and most molluscs are free-swimming as larvae), prefer aragonite for their shells and skeletons. Unfortunately, this is more sensitive to acidity than calcite is.

An omega value for aragonite of one is the level of acidity where calcium carbonate dissolves out of the mineral as easily as it precipitates into it. In other words, the system is in equilibrium and shells made of aragonite will not tend to dissolve. Merely creeping above that value does not, however, get you out of the woods. Shell formation is an active process, and low omega values even above one make it hard. Corals, for example, require an omega value as high as three to grow their stony skeletons prolifically.

As the map above shows, that could be a problem by 2100. Low omega values are spreading from the poles (whose colder waters dissolve carbon dioxide more easily) towards the tropics. The Monterey report suggests that the rate of erosion of reefs could outpace reef building by the middle of the century, and that all reef formation will cease by the end of it.

Other species will suffer, too. A study published in Nature last year, for example, looked at the shells of planktonic snails called pteropods. In Antarctic waters, which already have an omega value of one, their shells were weak and badly formed when compared with those of similar species found in warmer, more northerly waters. Earlier work on other molluscs has come to similar conclusions.

Not everything suffers from more dissolved CO2, though. The Monterey report cites studies which support the idea that algae, cyanobacteria and sea grasses will indeed benefit. One investigation also suggests acidification may help cyanobacteria fix nitrogen and turn it into protein. Since a lack of accessible nitrogen keeps large areas of the ocean relatively sterile, this, too could be good for productivity.

The Monaco report attempts to identify fisheries that will be particularly affected by these changes. These include the Southern Ocean (one of the few areas not already heavily fished) and the productive fishery off the coast of Peru and northern Chile, where upwelling from the deep brings nutrients to the surface, but which is already quite acidic. The principal threat here, and to similar fisheries, such as that off the west coast of North America, is to planktonic larvae that fish eat. Oyster and clam beds around the world are also likely to be affected—again, the larvae of these animals are at risk. The report does not, though, investigate the possibility of increases in algal plankton raising the oceans’ overall productivity.

At the back of everyone’s mind (as in wider discussions of climate change) are events 56m years ago. At that time, the boundary between the Palaeocene and Eocene geological epochs, carbon-dioxide levels rose sharply, the climate suddenly warmed (by about 6°C) and the seas became a lot more acidic. Many marine species, notably coccolithophores (a group of shelled single-celled algae) and deep-dwelling foraminifera (a group of shelled protozoa), became extinct in mere centuries, and some students of the transition think the increased acidity was more to blame for this than the rise in temperature. Surface-dwelling foraminifera, however, thrived, and new coccolithophore species rapidly evolved to replace those that had died out.

On land, too, some groups of animals did well. Though the rise of the mammals is often dated from 66m years ago, when a mass extinction of the dinosaurs left the planet open for colonisation by other groups, it is actually the beginning of the Eocene, 10m years later, which marks the ascendancy of modern mammal groups.

Oceanic acidity levels appear now to be rising ten times as fast as they did at the end of the Palaeocene. Some Earth scientists think the planet is entering, as it did 56m years ago, a new epoch—the Anthropocene. Though the end of the Palaeocene was an extreme example, it is characteristic of such transitions for the pattern of life to change quickly. Which species will suffer and which will benefit in this particular transition remains to be seen.

Continue reading ‘The future of the oceans: acid test’

Enhancement of photosynthetic carbon assimilation efficiency by phytoplankton in the future coastal ocean (update)

A mesocosm experiment was conducted to evaluate the influence of photosynthetic performance on the energetic balance of coastal phytoplankton, in relation to community production and autotrophic phytoplankton biomass in future coastal oceans. Natural phytoplankton assemblages were incubated in field mesocosms under ambient condition (control: ca. 400 μatm CO2 and ambient temperature), and two sets of potential future ocean conditions (acidification: ca. 900 μatm CO2 and ambient temperature; greenhouse: ca. 900 μatm CO2 and 3 °C warmer). The photosynthetic performances were estimated by in vivo fluorometry (effective quantum yield (ΦPSII), steady-state light response curves (LCs)) and in situ incorporation of 14C (photosynthesis-irradiance curves). The ΦPSII and rETRm,LC (relative maximum electron transport rate) clearly reduced under acidification, in particular, when phytoplankton were exposed to high light levels. However, PBmax (maximum photosynthetic rate) was the same in the ambient and acidification conditions. Thus, phytoplankton utilized less light under acidification condition, but could still assimilate a similar amount of carbon compared to the ambient condition. The PBmax and α (photosynthetic efficiency) under greenhouse condition were significantly higher than those under ambient condition without any difference in ΦPSII, rETRm,LC and α,LC (electron transport efficiency) between the treatments. Therefore, phytoplankton utilized the same amount of light under greenhouse condition, but could assimilate more carbon than under ambient condition. As a result, Chl a normalized primary production was higher in greenhouse than in other conditions. Nevertheless, the community production did not change between the experimental treatments. The main reason for the lack of a change in primary production under future climate conditions is the control of autotrophic phytoplankton biomass by grazing. Consequently, acidification and greenhouse environments have a potential to increase growth and primary production of phytoplankton by enhancing inorganic carbon assimilation efficiency when top-down regulation is negligible.

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Medium-term exposure of the North Atlantic copepod Calanus finmarchicus (Gunnerus, 1770) to CO2-acidified seawater: effects on survival and development (update)

The impact of medium-term exposure to CO2-acidified seawater on survival, growth and development was investigated in the North Atlantic copepod Calanus finmarchicus. Using a custom developed experimental system, fertilized eggs and subsequent development stages were exposed to normal seawater (390 ppm CO2) or one of three different levels of CO2-induced acidification (3300, 7300, 9700 ppm CO2). Following the 28-day exposure period, survival was found to be unaffected by exposure to 3300 ppm CO2, but significantly reduced at 7300 and 9700 ppm CO2. Also, the proportion of copepodite stages IV to VI observed in the different treatments was significantly affected in a manner that may indicate a CO2-induced retardation of the rate of ontogenetic development. Morphometric analysis revealed a significant increase in size (prosome length) and lipid storage volume in stage IV copepodites exposed to 3300 ppm CO2 and reduced size in stage III copepodites exposed to 7300 ppm CO2. Together, the findings indicate that a pCO2 level ≤2000 ppm (the highest CO2 level expected by the year 2300) will probably not directly affect survival in C. finmarchicus. Longer term experiments at more moderate CO2 levels are, however, necessary before the possibility that growth and development may be affected below 2000 ppm CO2 can be ruled out.

Continue reading ‘Medium-term exposure of the North Atlantic copepod Calanus finmarchicus (Gunnerus, 1770) to CO2-acidified seawater: effects on survival and development (update)’

Time of Emergence of trends in ocean biogeochemistry

For the detection of climate change, not only the magnitude of a trend signal is of significance. An essential issue is the time period required by the trend to be detectable in the first place. An illustrative measure for this is Time of Emergence (ToE), i.e., the point in time when a signal finally emerges from the background noise of natural variability. We investigate the ToE of trend signals in different biogeochemical and physical surface variables utilizing a multi-model ensemble comprising simulations of 17 ESMs. We find that signals in ocean biogeochemical variables emerge on much shorter timescales than the physical variable sea surface temperature (SST). The ToE patterns of pCO2 and pH are spatially very similar to DIC, yet the trends emerge much faster – after roughly 12 yr for the majority of the global ocean area, compared to between 10–30 yr for DIC and 45–90 yr for SST. In general, the background noise is of higher importance in determining ToE than the strength of the trend signal. In areas with high natural variability, even strong trends both in the physical climate and carbon cycle system are masked by variability over decadal timescales. In contrast to the trend, natural variability is affected by the seasonal cycle. This has important implications for observations, since it implies that intra-annual variability could question the representativeness of irregularly seasonal sampled measurements for the entire year and, thus, the interpretation of observed trends.

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Regulation of intracellular pH in cnidarians: response to acidosis in Anemonia viridis

The regulation of intracellular pH is a fundamental aspect of cell physiology that has received little attention in studies of the phylum Cnidaria, which includes ecologically important sea anemones and reef building corals. Like all organisms, cnidarians must maintain pH homeostasis to counterbalance reduction in intracellular pH, which can arise due to changes in either intrinsic or extrinsic parameters. Corals and sea anemones face natural daily changes in internal fluids where extracellular pH can range from 8.9 during the day to 7.4 at night. Furthermore, cnidarians are likely to experience future CO2-driven declines in seawater pH, a process known as ocean acidification. Here, we carried out the first mechanistic investigation to determine how cnidarian pHi responds to decreases in extracellular and intracellular pH. Using the anemone Anemonia viridis, we employed confocal live cell imaging and a pH-sensitive dye to track the dynamics of pHi after intracellular acidosis induced by acute exposure to decreases in seawater pH and NH4Cl prepulses. The investigation was conducted on cells that contained intracellular symbiotic algae (Symbiodinium sp.) and on symbiont-free endoderm cells. Experiments using inhibitors and sodium-free seawater indicate a potential role of Na+/H+ plasma membrane exchangers (NHE) in mediating pHi recovery following intracellular acidosis in both cell types. We also measured the buffering capacity of cells and obtained values between 20.8 and 43.8 mM/pH unit, comparable with other invertebrates. Our findings provide the first steps towards a better comprehension of acid-base regulation in these basal metazoans, for which information on cell physiology is extremely limited.

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Partial offsets in ocean acidification from changing coral reef biogeochemistry

Concerns have been raised about how coral reefs will be affected by ocean acidification1, 2, but projections of future seawater CO2 chemistry have focused solely on changes in the pH and aragonite saturation state (Ωa) of open-ocean surface seawater conditions surrounding coral reefs1, 2, 3, 4 rather than the reef systems themselves. The seawater CO2 chemistry within heterogeneous reef systems can be significantly different from that of the open ocean depending on the residence time, community composition and the main biogeochemical processes occurring on the reef, that is, net ecosystem production (NEP=gross primary productionautotrophic and heterotrophic respiration) and net ecosystem calcification (NEC=gross calcificationgross CaCO3 dissolution), which combined act to modify seawater chemistry5, 6, 7. On the basis of observations from the Bermuda coral reef, we show that a range of projected biogeochemical responses of coral reef communities to ocean acidification by the end of this century could partially offset changes in seawater pH and Ωa by an average of 12–24% and 15–31%, respectively.

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Ocean acidification in the IPCC AR5 WG II

OUP book