Archive for March, 2012

Detection and projection of carbonate dissolution in the water column and deep-sea sediments due to ocean acidification

Dissolution of fossil fuel CO2 in seawater results in decreasing carbonate ion concentration and lowering of seawater pH with likely negative impacts for many marine organisms. We project detectable changes in carbonate dissolution and evaluate their potential to mitigate atmospheric CO2 and ocean acidification with a global biogeochemistry model HAMOCC forced by different CO2 emission scenarios. Our results suggest that as the anthropogenic CO2 signal penetrates into ocean interior, the saturation state of carbonate minerals will drop drastically – with undersaturation extending from the ocean floor up to 100–150 m depth in the next century. This will induce massive dissolution of CaCO3 in the water column as well as the sediment, increasing the Total Alkalinity (TA) by up to 180 μmol kg−1 at the surface and in the ocean interior over the next 2500 years. Model results indicate an inhomogeneous response among different ocean basins: Atlantic carbonate chemistry responds faster and starts recovering two millennia after CO2 emissions cease, which is not the case in the Pacific. CaCO3 rain stops in the Pacific Ocean around 2230. Using an observation-derived detection threshold for TA, we project detectable dissolution-driven changes only by the year 2070 in the surface ocean and after 2230 and 2500 in the deep Atlantic and Pacific respectively. We show that different model assumptions regarding dissolution and calcification rates have little impact on future projections. Instead, anthropogenic CO2 emissions overwhelmingly control the degree of perturbation in ocean chemistry. In conclusion, ocean carbonate dissolution has insignificant potential in mitigating atmospheric CO2 and ocean acidification in the next millennia.

Continue reading ‘Detection and projection of carbonate dissolution in the water column and deep-sea sediments due to ocean acidification’

Long-term and trans-life-cycle effects of exposure to ocean acidification in the green sea urchin Strongylocentrotus droebachiensis

Anthropogenic CO2 emissions are acidifying the world’s oceans. A growing body of evidence demonstrates that ocean acidification can impact survival, growth, development and physiology of marine invertebrates. Here, we tested the impact of long-term (up to 16 months) and trans-life-cycle (adult, embryo/larvae and juvenile) exposure to elevated pCO2 (1,200 μatm, compared to control 400 μatm) on the green sea urchin Strongylocentrotus droebachiensis. Female fecundity was decreased 4.5-fold when acclimated to elevated pCO2 for 4 months during reproductive conditioning, while no difference was observed in females acclimated for 16 months. Moreover, adult pre-exposure for 4 months to elevated pCO2 had a direct negative impact on subsequent larval settlement success. Five to nine times fewer offspring reached the juvenile stage in cultures using gametes collected from adults previously acclimated to high pCO2 for 4 months. However, no difference in larval survival was observed when adults were pre-exposed for 16 months to elevated pCO2pCO2 had no direct negative impact on juvenile survival except when both larvae and juveniles were raised in elevated pCO2. These negative effects on settlement success and juvenile survival can be attributed to carry-over effects from adults to larvae and from larvae to juveniles. Our results support the contention that adult sea urchins can acclimate to moderately elevated pCO2 in a matter of a few months and that carry-over effects can exacerbate the negative impact of ocean acidification on larvae and juveniles.

Continue reading ‘Long-term and trans-life-cycle effects of exposure to ocean acidification in the green sea urchin Strongylocentrotus droebachiensis’

High temporal and spatial variability of dissolved oxygen and pH in a nearshore California kelp forest

Predicting consequences of ocean deoxygenation and ocean acidification for nearshore marine ecosystems requires baseline dissolved oxygen (DO) and carbonate chemistry data that are both high-frequency and high-quality. Such data allow accurate assessment of environmental variability and present-day organism exposure regimes. In this study, scales of DO and pH variability were characterized over one year in a nearshore, kelp forest ecosystem in the Southern California Bight. DO and pH were strongly, positively correlated revealing that organisms on this upwelling shelf are not only exposed to low pH but also low DO. The dominant temporal scale of DO and pH variability occurred on semidiurnal, diurnal and event (days–weeks) time scales. Daily ranges in DO and pH at 7 m water depth (13 mab) could be as large as 220 μmol kg−1 and 0.36 units, respectively. This range is much greater than the expected decreases in pH in the open ocean by the year 2100. Sources of pH and DO variation include photosynthesis within the kelp forest ecosystem, which can elevate DO and pH by up to 60 μmol kg−1 and 0.1 units over one week following the intrusion of high-density, nutrient-rich water. Accordingly, highly productive macrophyte-based ecosystems could serve as deoxygenation and acidification refugia by acting to elevate DO and pH relative to surrounding waters. DO and pH exhibited greater spatial variation over a 10 m increase in water depth (from 7 to 17 m) than along a 5-km stretch of shelf in a cross-shore or alongshore direction. Over a three-month time period mean DO and pH at 17-m water depth were 168 μmol kg−1 and 7.87, respectively. These values represent a 35% decrease in mean DO and 37% increase in [H+] relative to surface waters. High-frequency variation was also reduced at depth. The mean daily range in DO and pH was 39% and 37% less, respectively, at 17-m water depth relative to the surface. As a consequence, the exposure history of an organism is largely a function of its depth of occurrence within the kelp forest. These findings raise the possibility that the benthic communities along eastern boundary current systems are currently acclimatized and adapted to natural, variable, and low DO and pH. Future exposure of coastal California populations to low DO and pH may increase as upwelling intensifies and hypoxic boundaries shoal, compressing habitats and challenging the physiological capacity of intolerant species.

Continue reading ‘High temporal and spatial variability of dissolved oxygen and pH in a nearshore California kelp forest’

Spoiling our marine soup

I have always heard that the waters of Kachemak Bay, Cook Inlet, and the Gulf of Alaska boast some the richest marine “soup” in the world. This accounts for the diverse and deluxe assortment of fish and shellfish that we are able to harvest from these waters. Many in the region enjoy a good living because of it. There is a threat that I have become familiar with in the last five years that worries me more than the threat of another major oil spill.

Ocean acidification is the result of the ocean acting like a giant sponge, soaking up carbon dioxide from the atmosphere. We all like to be warm in winter, travel the world, navigate our boats, and enjoy the convenience of driving our vehicles just about anywhere we want to go. The very act of harvesting contributes to this threat.

I like to eat oysters and have enjoyed them ever since I was a youngster growing up in Puget Sound and Willipa Bay. These days, I enjoy fresh oysters from Kachemak Bay. I have been told that the reason the supply is sometimes inadequate to satisfy demand is that there is a shortage of seed.

Continue reading ‘Spoiling our marine soup’

Resilience of cold-water scleractinian corals to ocean acidification: Boron isotopic systematics of pH and saturation state up-regulation

The boron isotope systematics has been determined for azooxanthellate scleractinian corals from a wide range of both deep-sea and shallow-water environments. The aragonitic coral species, Caryophyllia smithii, Desmophyllum dianthus, Enallopsammia rostrata, Lophelia pertusa, and Madrepora oculata, are all found to have relatively high δ11B compositions ranging from 23.2 to 28.7‰. These values lie substantially above the pH-dependent inorganic seawater borate equilibrium curve, indicative of strong up-regulation of pH of the internal calcifying fluid (pHcf), being elevated by ∼0.6 to 0.8 units (ΔpH) relative to ambient seawater. In contrast, the deep-sea calcitic coral Corallium sp. has a significantly lower δ11B composition of 15.5‰, with a corresponding lower δpH value of ∼0.3 units, reflecting the importance of mineralogical control on biological pH up-regulation.

The solitary coral D. dianthus was sampled over a wide range of seawater pHT and shows an approximate linear correlation with δpHDesmo = 6.43 – 0.71pHT (r2 = 0.79). An improved correlation is however found with the closely related parameter of seawater aragonite saturation state, where δpHDesmo = 1.09 − 0.14δarag (r2 = 0.95), indicating the important control that carbonate saturation state has on calcification. The ability to up-regulate internal pHcf, and consequently δcf, of the calcifying fluid is therefore a process present in both azooxanthellate and zooxanthellate aragonitic corals, and is attributed to the action of Ca2+-ATPase in modulating the proton gradient between seawater and the site of calcification. These findings also show that the boron isotopic compositions (δ11Bcarb) of aragonitic corals are highly systematic and consistent with direct uptake of the borate species within the biologically-controlled extracellular calcifying medium.

We also show that the relatively strong up-regulation of pH and consequent elevation of the internal carbonate saturation state (Ωcf ∼8.5 to ∼13) at the site of calcification by cold-water corals, facilitates calcification at or in some cases below the aragonite saturation horizon, providing a greater ability to adapt to the already low and now decreasing carbonate ion concentrations. Although providing greater resilience to the effects of ocean acidification and enhancing rates of calcification with increasing temperature, the process of internal pHcf up-regulation has an associated energetic cost, and therefore growth-rate cost, of ∼10% per 0.1 pH unit decrease in seawater pHT. Furthermore, as the aragonite saturation horizon shoals with rapidly increasing pCO2 and δarag < 1, increased dissolution of the exposed skeleton will ultimately limit their survival in the deep oceans.

Continue reading ‘Resilience of cold-water scleractinian corals to ocean acidification: Boron isotopic systematics of pH and saturation state up-regulation’

Ocean Acidification: Invisible now, but not for long

As I look out on Kachemak Bay, I know that the waters of the Bay, Cook Inlet, and the Gulf of Alaska are teeming with organisms that nourish the fish that I depend on to make a living and to fill my freezer. Some days, the water is too rough to go fishing, but still, I know the fish are there waiting when I can go. For over 30 years, my family and I have enjoyed some of the most sought-after and prized foods in the world, harvested right at our doorsteps. It is only in the last five years that I have learned that the very food web that supports this luxury and sustenance is under attack from a silent killer.

Ocean acidification is the result of the ocean absorbing carbon dioxide from the atmosphere. As the world population has increased, so has the use and demand of energy that is produced by many different methods and fuels. Most of these methods result in the emission of carbon in the atmosphere. As the ocean absorbs this carbon dioxide, the acidity in seawater is increased and this reduces the availability of calcium carbonate minerals, which are the building blocks of shells and skeletons for many marine organisms.

Continue reading ‘Ocean Acidification: Invisible now, but not for long’

Smith appointed to panel on ocean acidification

Dist. 10 Rep. Norma Smith has been appointed by Gov. Chris Gregoire to Washington state’s Ocean Acidification Blue Ribbon Panel.

According to a press release from the Washington House Republicans, Smith is interested in protecting Washington’s marine waters and improving the state’s business climate. This appointment will give her the opportunity to do both.

“There is concern that the acidity of the Pacific Ocean could be a threat to our shellfish industry, leading to significant negative impacts in many communities along the coast,” said Smith, R-Clinton, in the release. “We need to make sure we are doing what we can to protect our marine waterways and our shellfish habitat. These are important issues to the 10th District, so I am pleased the governor’s office has asked me to be part of this panel.”

Continue reading ‘Smith appointed to panel on ocean acidification’

Acidification conference

The state has organized a news conference for tomorrow for the co-chairs of the Washington Shellfish Initiative Blue Ribbon Panel on Ocean Acidification. Reporters can then see some of the science that is happening at a Seattle-based laboratory that is studying the problem that threatens the Northwest shellfish industry. The blue ribbon panel of science and policy experts is the first of its kind in the nation. It convenes for its first meeting this Friday in Seattle.
Continue reading ‘Acidification conference’

Coupled CO2 and O2-driven compromises to marine life in summer along the Chilean sector of the Humboldt Current System (update)

Carbon dioxide and coupled CO2 and O2-driven compromises to marine life were examined along the Chilean sector of the Humboldt Current System, a particularly vulnerable hypoxic and upwelling area, applying the Respiration index (RI = log10 pO2pCO2) and the pH-dependent aragonite saturation (Ω) to delineate the water masses where aerobic and calcifying organisms are stressed. As expected, there was a strong negative relationship between oxygen concentration and pH or pCO2 in the studied area, with the subsurface hypoxic Equatorial Subsurface Waters extending from 100 m to about 300 m depth and supporting elevated pCO2 values. The lowest RI values, associated to aerobic stress, were found at about 200 m depth and decreased towards the Equator. Increased pCO2 in the hypoxic water layer reduced the RI values by as much as 0.59 RI units, with the thickness of the upper water layer that presents conditions suitable for aerobic life (RI>0.7) declining by half between 42° S and 28° S. The intermediate waters hardly reached those stations closer to the equator so that the increased pCO2 lowered pH and the saturation of aragonite. A significant fraction of the water column along the Chilean sector of the Humboldt Current System suffers from CO2–driven compromises to biota, including waters corrosive to calcifying organisms, stress to aerobic organisms or both. The habitat free of CO2-driven stresses was restricted to the upper mixed layer and to small water parcels at about 1000 m depth. Overall pCO2 acts as a hinge connecting respiratory and calcification challenges expected to increase in the future, resulting in a spread of the challenges to aerobic organisms.

Continue reading ‘Coupled CO2 and O2-driven compromises to marine life in summer along the Chilean sector of the Humboldt Current System (update)’

High nitrate to phosphorus regime attenuates negative effects of rising pCO2 on total population carbon accumulation (update)

The ongoing rise in atmospheric pCO2 and consequent increase in ocean acidification have direct effects on marine calcifying phytoplankton, which potentially alters carbon export. To date it remains unclear, firstly, how nutrient regime, in particular by coccolithophores preferred phosphate limitation, interacts with pCO2 on particulate carbon accumulation; secondly, how direct physiological responses on the cellular level translate into total population response. In this study, cultures of Emiliania huxleyi were full-factorially exposed to two different N:P regimes and three different pCO2 levels. Cellular biovolume and PIC and POC content significantly declined in response to pCO2 in both nutrient regimes. Cellular PON content significantly increased in the Redfield treatment and decreased in the high N:P regime. Cell abundance significantly declined in the Redfield and remained constant in the high N:P regime. We hypothesise that in the high N:P regime severe phosphorous limitation could be compensated either by reduced inorganic phosphorous demand and/or by enzymatic uptake of organic phosphorous. In the Redfield regime we suggest that enzymatic phosphorous uptake to supplement enhanced phosphorous demand with pCO2 was not possible and thus cell abundance declined. These hypothesised different physiological responses of E. huxleyi among the nutrient regimes significantly altered population carrying capacities along the pCO2 gradient. This ultimately led to the attenuated total population response in POC and PIC content and biovolume to increased pCO2 in the high N:P regime. Our results point to the fact that the physiological (i.e. cellular) PIC and POC response to ocean acidification cannot be linearly extrapolated to total population response and thus carbon export. It is therefore necessary to consider both effects of nutrient limitation on cell physiology and their consequences for population size when predicting the influence of coccolithophores on atmospheric pCO2 feedback and their function in carbon export mechanisms.

Continue reading ‘High nitrate to phosphorus regime attenuates negative effects of rising pCO2 on total population carbon accumulation (update)’

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Ocean acidification in the IPCC AR5 WG II

OUP book