Anthropogenic CO2 Concentrations Research Articles

Low Potential Electrochemical CO2 Reduction to Methanol over Nickel‐Based Hollow 0D Carbon Superstructure

AbstractElectrochemical carbon dioxide reduction reaction (CO2RR) to valuable fuels and chemical feedstock is a sustainable strategy to lower the anthropogenic CO2 concentration, thereby dynamising the carbon cycle in the environment. CH3OH on the other hand is undoubtedly the most desirable C1 product of CO2RR. However, selective electroreduction of CO2‐to‐CH3OH is very challenging and only limited catalysts are reported in literature. Pyrolyzing metal‐organic frameworks (MOFs) to generate carbon matrix impregnated with metal nanoparticles, heralds exciting electrocatalytic properties. This study unveiled the morphological evolution of a mixed‐ligand Ni‐MOF (Ni‐OBBA‐Bpy) during pyrolysis, to generate Ni nanoparticles anchored 0D porous hollow carbon superstructures (Pyr‐CP‐800 and Pyr‐CP‐600). This unique morphology invokes high specific surface area and surface roughness to the materials, which synergistically facilitates the selective electroreduction of CO2‐to‐CH3OH. In comparison to most of the previously reported Ni electrocatalysts that mainly produced CO, Pyr‐CP‐800 selectively yielded CH3OH with Faradaic efficiency (FE) of 32.46% at −0.60 V versus RHE (reversible hydrogen electrode) in 1.0 M KOH solution, which is highest among other reported Ni‐based electrocatalysts in the literature, to best of our knowledge. Additionally, insights from density functional theory (DFT) calculations revealed that Ni (111) plane to be the active site toward the electrochemical. CO2‐to‐CH3OH formation.

Development of an autonomous on-site dissolved inorganic carbon analyzer using conductometric detection

BackgroundThe increase in anthropogenic CO2 concentrations in the Earth's atmosphere since the industrial revolution has resulted in an increased uptake of CO2 by the oceans, leading to ocean acidification. Dissolved Inorganic Carbon (DIC) is one of the key variables to characterize the seawater carbonate system. High quality DIC observations at a high spatial-temporal resolution is required to improve our understanding of the marine carbonate system. To meet the requirements, autonomous DIC analyzers are needed which offer a high sampling frequency, are cost-effective and have a low reagent and power consumption. ResultsWe present the development and validation of a novel analyzer for autonomous measurements of DIC in seawater using conductometric detection. The analyzer employs a gas diffusion sequential injection approach in a “Tube In A Tube” configuration that facilitates diffusion of gaseous CO2 from an acidified sample through a gas permeable membrane into a stream of an alkaline solution. The change in conductivity in the alkaline medium is proportional to the DIC concentration of the sample and is measured using a detection cell constructed of 4 hollow brass electrodes. Physical and chemical optimizations of the analyzer yielded a sampling frequency of 4 samples h−1 using sub mL reagent volumes for each measurement. Temperature and salinity effects on DIC measurements were mathematically corrected to increase accuracy. Analytical precision of ±4.9 μmol kg−1 and ±9.7 μmol kg−1 were achieved from measurements of a DIC reference material in the laboratory and during a field deployment in the southwest Baltic Sea, respectively. SignificanceThis study describes a simple, cost-effective, autonomous, on-site benchtop DIC analyzer capable of measuring DIC in seawater at a high temporal resolution as a step towards an underwater DIC sensor. The analyzer is able to measure a wide range of DIC concentrations in both fresh and marine waters. The achieved accuracy and precision offer an excellent opportunity to employ the analyzer for ocean acidification studies and CO2 leakage detection in the context of Carbon Capture and Storage operations.

Direct, carryover, and maternal effects of ocean acidification on snow crab embryos and larvae.

Ocean acidification, a decrease in ocean pH with increasing anthropogenic CO2 concentrations, is expected to affect many marine animals. To examine the effects of decreased pH on snow crab (Chionoecetes opilio), a commercial species in Alaska, we reared ovigerous females in one of three treatments: Ambient pH (~8.1), pH 7.8, and pH 7.5, through two annual reproductive cycles. Morphometric changes during development and hatching success were measured for embryos both years and calcification was measured for the adult females at the end of the 2-year experiment. Embryos and larvae analyzed in year one were from oocytes developed, fertilized, and extruded in situ, whereas embryos and larvae in year two were from oocytes developed, fertilized, and extruded under acidified conditions in the laboratory. In both years, larvae were exposed to the same pH treatments in a fully crossed experimental design. Starvation-survival, morphology, condition, and calcium/magnesium content were assessed for larvae. Embryo morphology during development, hatching success, and fecundity were unaffected by pH during both years. Percent calcium in adult females' carapaces did not differ among treatments at the end of the experiment. In the first year, starvation-survival of larvae reared at Ambient pH but hatched from embryos reared at reduced pH was lowered; however, the negative effect was eliminated when the larvae were reared at reduced pH. In the second year, there was no direct effect of either embryo or larval pH treatment, but larvae reared as embryos at reduced pH survived longer if reared at reduced pH. Treatment either did not affect other measured larval parameters, or effect sizes were small. The results from this two-year study suggest that snow crabs are well adapted to projected ocean pH levels within the next two centuries, although other life-history stages still need to be examined for sensitivity and potential interactive effects with increasing temperatures should be investigated.

Homogeneous Metal-Catalyzed Hydrogenation of CO2 Derivatives: Towards Indirect Conversion of CO2 to Methanol

The increase in anthropogenic CO2 concentrations and associated environmental issues have demanded the development of technologies for CO2 utilization. Among various potential solutions to decrease CO2 emissions and achieve carbon neutrality, the recycling of post-combustion CO2 into value-added chemicals and fuels is considered one of the most economically attractive processes. In this regard, due to its large global demand and versatile applications in the chemical and energy sectors, methanol serves as the most appealing target for the chemical utilization of CO2. However, direct hydrogenation of CO2 to MeOH has proved challenging due to selectivity issues and high energy input, mainly dependent on CO2-emitting fossil energy sources. To address these challenges, an alternative indirect CO2-to-MeOH methodology has been proposed, which involves the hydrogenation of CO2 via the intermediate formation of well-known CO2 derivatives, such as formates, carbonates, formamides, carbamates, and urea derivatives. Homogeneous transition metal catalysts have been at the center of this research avenue, potentially allowing for more selective and low-temperature alternative routes from CO2 to MeOH. This review aims to highlight the advances and challenges in homogeneous transition metal-catalyzed hydrogenation of major CO2 derivatives to MeOH. Special attention is paid to the mechanisms of such transformations.

Greenhouse warming and internal variability increase extreme and central Pacific El Niño frequency since 1980

El Niño has been recorded to change its properties since the 1980s, characterized by more common extreme El Niño and Central Pacific (CP) El Niño events. However, it is still unclear whether such change is externally forced or part of the natural variability. Here, we find that the frequency of the extreme and CP El Niño events also increased during the period 1875–1905, when the anthropogenic CO2 concentration was relatively lower, but with a positive phase of the Atlantic Multidecadal Oscillation (AMO). Models and palaeoclimate proxies reveal that a positive AMO enhances the zonal sea surface temperature gradient in the CP, which strengthens zonal advective feedback, favoring extreme and CP El Niño development. Moreover, we estimate that internal variability contributed to ~65% of the increasingly extreme and CP El Niño events, while anthropogenic forcing has made our globe experience ~1 more extreme and ~2 more CP events over the past four decades.

World Atmospheric CO2, Its 14C Specific Activity, Non-fossil Component, Anthropogenic Fossil Component, and Emissions (1750-2018).

After 1750 and the onset of the industrial revolution, the anthropogenic fossil component and the non-fossil component in the total atmospheric CO2 concentration, C(t), began to increase. Despite the lack of knowledge of these two components, claims that all or most of the increase in C(t) since 1800 has been due to the anthropogenic fossil component have continued since they began in 1960 with "Keeling Curve: Increase in CO2 from burning fossil fuel." Data and plots of annual anthropogenic fossil CO2 emissions and concentrations, C(t), published by the Energy Information Administration, are expanded in this paper. Additions include annual mean values in 1750 through 2018 of the 14C specific activity, concentrations of the two components, and their changes from values in 1750. The specific activity of 14C in the atmosphere gets reduced by a dilution effect when fossil CO2, which is devoid of 14C, enters the atmosphere. We have used the results of this effect to quantify the two components. All results covering the period from 1750 through 2018 are listed in a table and plotted in figures. These results negate claims that the increase in C(t) since 1800 has been dominated by the increase of the anthropogenic fossil component. We determined that in 2018, atmospheric anthropogenic fossil CO2 represented 23% of the total emissions since 1750 with the remaining 77% in the exchange reservoirs. Our results show that the percentage of the total CO2 due to the use of fossil fuels from 1750 to 2018 increased from 0% in 1750 to 12% in 2018, much too low to be the cause of global warming.

Acidification Analysis of Black Sea

Increasing anthropogenic CO2 concentration in the troposphere results in ocean acidification. Albeit, food web in the ocean, marine animals and calcifying bioata are affected negatively. Some marine species might have the possibility of extinction and some may have evolve eventually due to ocean acidification. In this study, the acidification of Black Sea is analyzed based on the pH observations made between 1990 and 2014. Sea surface pH value is found to be decreased by 0,07 and increased by 0,104 between 1990-2004 and 2005-2014 respectively. The pH annual variations also compared analytically to the annual averages of air temperature and CO2 emissions of Turkey. Both the air temperature and CO2 emission are increasing either in 1990-2004 or 2005-2014, while the rate of increase in 2005-2014 is greater than in 1990-2004. The decreasing pH (which means acidification) in 1990-2004 is found to be the reason of this difference, because some CO2 is considered to be emitted by Black Sea. In terms of climate change, it shows that this acidification is a little bit slowing down the temperature increase over the Black Sea region while CO2 and air temperature increasing rate more between 2005-2014 where there is no acidification in the Black Sea.

Ventilation in the Arctic Ocean and the Role of Pacific Inflow Deduced From Transient Tracer Measurements

AbstractDuring the seventh Chinese National Arctic Research Expedition, measurements of CFC‐12 and SF6 were used to estimate ventilation time scales and anthropogenic CO2 (Cant) concentrations in the Arctic Ocean and Bering Sea based on the transit time distribution (TTD) method. The profile distribution showed that there was a high CFC tongue entering through the Canada Basin in the intermediate layer (27.6 kg m−3 < σθ < 28 kg m−3), at latitudes between 75 and 85°N, related to the inflow of Atlantic water. The result shows that both intermediate and deep/bottom waters are better ventilated in the Arctic Ocean than in the Bering Sea. The mean age gradient of the Bering Sea Surface Water and Pacific water core of the southwest Canada Basin (24.7 < σθ < 26.2) could be a consequence of intensive mixing and entrainment of the inflow water from the Bering Sea. An expected difference in age between these areas was interpreted to reflect the transit time for the given water layers. Thus, a mean transit time from the Bering Sea (175.2–179.9°E, 59.7–61.6°N) to the western Arctic Ocean (151.6–158°W, 73.1–74.8°N) of 14.6 ± 4.6 years was estimated. The mean Cant column inventory in the upper 2,000 m was higher (~45 mol m−2) in the Arctic Ocean than in the Bering Sea (~25 mol m−2).

Control of gas permeability by transforming the molecular structure of silk fibroin in multilayered nanocoatings for CO2 adsorptive separation

Carbon dioxide (CO2) is considered one of the causes of global warming because anthropogenic CO2 concentration in the atmosphere has greatly increased. The objective of this work was to design silk fibroin (SF) and graphene oxide (GO) membranes with very high CO2 gas capture characteristics and high gas selectivity toward nitrogen rather than CO2 gas, and to demonstrate the effect on transforming the SF secondary structure at the molecular level. GO-NH3+/SF multilayer nanocoatings were fabricated by automatic spray-assisted layer-by-layer (LbL) assembly with physical molecular interaction between GO-NH3+ and SF. We demonstrated transformation of the SF secondary structures in GO-NH3+/SF LbL-assembled nanocoatings with MeOH solvent treatment. After MeOH treatment, the SF secondary structures in the GO-NH3+/SF LbL-assembled nanocoatings preferred β-sheets to random coils. This phenomenon affects the internal amine groups and CO2 transport. The MeOH-treated GO-NH3+/SF LbL-assembled nanocoatings have high β-sheet content, and the gas permeability of the nanocoatings was quite different. Before the predominance of the β-sheet, CO2 gas permeated twice as fast as nitrogen (N2) gas in the GO-NH3+/SF LbL-assembled nanocoatings. On the other hand, CO2 gas was transmitted 10-times slower than N2 gas in MeOH-treated GO-NH3+/SF LbL-assembled nanocoatings. In other words, we successfully fabricated a CO2 adsorptive separation membrane with GO-NH3+ and SF.

Ventilation time and anthropogenic CO2 in the Bering Sea and the Arctic Ocean based on carbon tetrachloride measurements

The Arctic Ocean is connected to the Pacific by the Bering Sea and the Bering Strait. During the 4th Chinese National Arctic Research Expedition, measurements of carbon tetrachloride (CCl4) were used to estimate ventilation time-scales and anthropogenic CO2 (Cant) concentrations in the Arctic Ocean and Bering Sea based on the transit time distribution method. The profile distribution showed that there was a high-CCl4 tongue entering through the Canada Basin in the intermediate layer (27.6 < σθ < 28), at latitudes between 78 and 85°N, which may be related to the inflow of Atlantic water. Between stations B09 and B10, upwelling appeared to occur near the continental slope in the Bering Sea. The ventilation time scales (mean ages) for deep and bottom water in the Arctic Ocean (~ 230–380 years) were shorter than in the Bering Sea (~ 430–970 years). Higher mean ages show that ventilation processes are weaker in the intermediate water of the Bering Sea than in the Arctic Ocean. The mean Cant column inventory in the upper 4000 m was higher (60–82 mol m−2) in the Arctic Ocean compared to the Bering Sea (35–48 mol m−2).

The combined effects of acidification and hypoxia on pH and aragonite saturation in the coastal waters of the California current ecosystem and the northern Gulf of Mexico

Inorganic carbon chemistry data from the surface and subsurface waters of the West Coast of North America have been compared with similar data from the northern Gulf of Mexico to demonstrate how future changes in CO2 emissions will affect chemical changes in coastal waters affected by respiration-induced hypoxia ([O2] ≤ ~ 60µmolkg−1). In surface waters, the percentage change in the carbon parameters due to increasing CO2 emissions are very similar for both regions even though the absolute decrease in aragonite saturation is much higher in the warmer waters of the Gulf of Mexico. However, in subsurface waters the changes are enhanced due to differences in the initial oxygen concentration and the changes in the buffer capacity (i.e., increasing Revelle Factor) with increasing respiration from the oxidation of organic matter, with the largest impacts on pH and CO2 partial pressure (pCO2) occurring in the colder West Coast waters. As anthropogenic CO2 concentrations begin to build up in subsurface waters, increased atmospheric CO2 will expose organisms to hypercapnic conditions (pCO2 >1000 µatm) within subsurface depths. Since the maintenance of the extracellular pH appears as the first line of defense against external stresses, many biological response studies have been focused on pCO2-induced hypercapnia. The extent of subsurface exposure will occur sooner and be more widespread in colder waters due to their capacity to hold more dissolved oxygen and the accompanying weaker acid-base buffer capacity. Under present conditions, organisms in the West Coast are exposed to hypercapnic conditions when oxygen concentrations are near 100µmolkg−1 but will experience hypercapnia at oxygen concentrations of 260µmolkg−1 by year 2100 under the highest elevated-CO2 conditions. Hypercapnia does not occur at present in the Gulf of Mexico but will occur at oxygen concentrations of 170µmolkg−1 by the end of the century under similar conditions. The aragonite saturation horizon is currently above the hypoxic zone in the West Coast. With increasing atmospheric CO2, it is expected to shoal up close to surface waters under the IPCC Representative Concentration Pathway (RCP) 8.5 in West Coast waters, while aragonite saturation state will exhibit steeper gradients in the Gulf of Mexico. This study demonstrates how different biological thresholds (e.g., hypoxia, CaCO3 undersaturation, hypercapnia) will vary asymmetrically because of local initial conditions that are affected differently with increasing atmospheric CO2. The direction of change in amplitude of hypercapnia will be similar in both ecosystems, exposing both biological communities from the West Coast and Gulf of Mexico to intensification of stressful conditions. However, the region of lower Revelle factors (i.e., the Gulf of Mexico), currently provides an adequate refuge habitat that might no longer be the case under the most severe RCP scenarios.

Variability of soil carbon stocks in a mixed deciduous forest on hydromorphic soils

Forests play an important role for carbon (C) storage and a large part of C in forest ecosystems is stored in the soil. Although large-scale inventories of soil C stocks have been published recently, detailed site-specific studies are still needed because C storage depends on various site specific soil, ecological and management factors. Quantification of soil C stocks is hampered by spatial and temporal variability. Here, we assess C stocks in an ancient forest site at a stand which has not been managed for >60years and analyse the spatial variability of C concentrations and stocks to evaluate inter-annual variability and elucidate possible causes. Samples were taken down to 1m depth by auger cores in May of three consecutive years (2013, 2014, 2015) on regular hexagonal grids covering an area of 0.25ha and 19 sampling spots. In addition, to address small scale variability, 36 auger cores were taken in November 2014 using a nested sampling design.C stocks were on average 34kgCm−2 (0–1m depth). This is distinctly higher than soil C stocks reported for most other forest sites in similar climatic conditions, and is likely caused by the interplay of several parameters, i.e., hydromorphic soil conditions, high biomass production due to high soil fertility, stand structure (tree age, species and density), and the management history of the site. The coefficients of variation for C concentrations (>50%) and for C stocks (30–50%) show that spatial variability is high. Geostatistical analysis revealed a larger scale component with ranges of 5–20m and a small scale component represented by high nugget effects in the semivariograms (>50%).As hydromorphic soil types are widespread in NE Germany, large amounts of organic C could be sequestered into soil under unmanaged old forests, thus contributing to alleviating the rise in anthropogenic CO2 concentrations in the atmosphere.

Fabrication of Visible‐Light‐Responsive InVO4 for Photoreduction of CO2

AbstractThe gradual rise in anthropogenic CO2 concentration in the atmosphere leads to global warming, and hence draws attention to develop different catalysts for CO2 reduction to fuel. Indium vanadate has attractive photocatalytic properties under visible light. InVO4 was synthesized by a hydrothermal method without using any organic precursor. Catalyst was well characterized with different techniques involving X‐ray diffraction, UV‐Vis diffuse reflectance spectroscopy, scanning electron microscopy, transmission electron microscopy, X‐ray photoelectron microscopy and thermal gravimetric analysis. Its catalytic performance was evaluated for photoreduction of CO2 in a batch reactor under visible light irradiation. 520 ppm of CO was obtained in presence of triethanolamine (TEOA) as an electron donor.

Changes in microbial communities, photosynthesis and calcification of the coral Acropora gemmifera in response to ocean acidification.

With the increasing anthropogenic CO2 concentration, ocean acidification (OA) can have dramatic effects on coral reefs. However, the effects of OA on coral physiology and the associated microbes remain largely unknown. In the present study, reef-building coral Acropora gemmifera collected from a reef flat with highly fluctuating environmental condition in the South China Sea were exposed to three levels of partial pressure of carbon dioxide (pCO2) (i.e., 421, 923, and 2070 μatm) for four weeks. The microbial community structures associated with A. gemmifera under these treatments were analyzed using 16S rRNA gene barcode sequencing. The results revealed that the microbial community associated with A. gemmifera was highly diverse at the genus level and dominated by Alphaproteobacteria. More importantly, the microbial community structure remained rather stable under different pCO2 treatments. Photosynthesis and calcification in A. gemmifera, as indicated by enrichment of δ18O and increased depletion of δ13C in the coral skeleton, were significantly impaired only at the high pCO2 (2070 μatm). These results suggest that A. gemmifera can maintain a high degree of stable microbial communities despite of significant physiological changes in response to extremely high pCO2.

Antarctic crustacean grazer assemblages exhibit resistance following exposure to decreased pH

Anthropogenic atmospheric CO2 concentrations are increasing rapidly, resulting in declining seawater pH (ocean acidification). The majority of ocean acidification research to date has focused on the effects of decreased pH in single-species experiments. To assess how decreased pH may influence natural macroalgal-grazer assemblages, we conducted a mesocosm experiment with the common, chemically defended Antarctic brown macroalga Desmarestia menziesii and natural densities of its associated grazer assemblage, predominantly amphipods. Grazer assemblages were collected from the immediate vicinity of Palmer Station (64°46′S, 64°03′W) in March 2013. Assemblages were exposed for 30 days to three levels of pH representing present-day mean summer ambient conditions (pH 8.0), predicted near-future conditions (2100, pH 7.7), and distant-future conditions (pH 7.3). A significant difference was observed in the composition of mesograzer assemblages in the lowest pH treatment (pH 7.3). The differences between assemblages exposed to pH 7.3 and those maintained in the other two treatments were driven primarily by decreases in the abundance of the amphipod Metaleptamphopus pectinatus with decreasing pH, reduced copepod abundance at pH 7.7, and elevated ostracod abundance at pH 7.7. Generally, the assemblages maintained at pH 7.7 were not significantly different from those at ambient pH, demonstrating resistance to short-term decreased pH. The relatively high prevalence of generalist amphipods may have contributed to a net stabilizing effect on the assemblages exposed to decreased pH. Overall, our results suggest that crustacean grazer assemblages associated with D. menziesii, the dominant brown macroalgal species of the western Antarctic Peninsula, may be resistant to short-term near-future decreases in seawater pH.

Acidifying intermediate water accelerates the acidification of seawater on shelves: An example of the East China Sea

This study is the first to present observed acidification rates at the shelf break of the East China Sea (ECS) and in the Okinawa Trough between 1982 and 2007. The use of apparent oxygen utilization (AOU) data to quantify the change in pH due to physical changes and changes in biological activities is demonstrated. The results thus obtained reveal that the drop in pH of the Kuroshio Intermediate Water (KIW) in the ECS is a result of not only the intrusion of atmospheric CO2, but also an increase in AOU concentration. The acidification rates caused by the increasing AOU concentration could contribute up to −0.00086±0.00017pH unityr-1 at 900m in the Okinawa Trough and −0.00082±0.00057 pH unityr-1 on the shelf break of the ECS. These values are equivalent to 54% and 51%, respectively, of the acidification rate of −0.0016pH unityr-1 based on an assumption of the air–sea CO2 equilibrium. When the effects of changing AOU and θ are eliminated, the acidification rate in the basin of the ECS captures the rate of change that is caused by an increase in anthropogenic CO2 concentration. In contrast, when the effects of changing AOU and θ are eliminated, the acidification rate at the shelf break is 69% higher than the rate based on an assumption of the air–sea CO2 equilibrium. Since the seawater on the shelf contains a higher proportion of the South China Sea (SCS) seawater and coastal water than does that in the Okinawa Trough, the result herein may imply that the SCS seawater, coastal water, or a combination of them suffered a higher acidification rate during the studied period. This study, to the best of the authors’ knowledge, is the first to demonstrate that changing the carbonate chemistry of both incoming offshore intermediate seawater and coastal water results in the acidification of seawater on a continental shelf. The results herein reveal a situation in which the acidification of coastal seawater may be faster than expected when the reduction of pH of the incoming offshore seawater is considered along with the increasing atmospheric CO2 and terrestrial nutrient fluxes.

Acidification of the Mediterranean Sea from anthropogenic carbon penetration

This study presents an estimation of the anthropogenic CO2 (CANT) concentrations and acidification (ΔpH=pH2013–pHpre-industrial) in the Mediterranean Sea, based upon hydrographic and carbonate chemistry data collected during the May 2013 MedSeA cruise. The concentrations of CANT were calculated using the composite tracer TrOCA. The CANT distribution shows that the most invaded waters (>60µmolkg−1) are those of the intermediate and deep layers in the Alboran, Liguro- and Algero-Provencal Sub-basins in the Western basin, and in the Adriatic Sub-basin in the Eastern basin. Whereas the areas containing the lowest CANT concentrations are the deep layers of the Eastern basin, especially those of the Ionian Sub-basin, and those of the northern Tyrrhenian Sub-basin in the Western basin. The acidification level in the Mediterranean Sea reflects the excessive increase of atmospheric CO2 and therefore the invasion of the sea by CANT. This acidification varies between −0.055 and −0.156 pH unit and it indicates that all Mediterranean Sea waters are already acidified, especially those of the Western basin where ΔpH is rarely less than −0.1 pH unit. Both CANT concentrations and acidification levels are closely linked to the presence and history of the different water masses in the intermediate and deep layers of the Mediterranean basins. Despite the high acidification levels, both Mediterranean basins are still highly supersaturated in calcium carbonate minerals.

Effects of food and CO2 on growth dynamics of polyps of two scyphozoan species (Cyanea capillata and Chrysaora hysoscella)

Increasing anthropogenic CO2 concentration in the atmosphere is altering sea water carbonate chemistry with unknown biological and ecological consequences. Whereas some reports are beginning to emerge on the effects of ocean acidification (OA) on fish, very little is known about the impact of OA on jellyfish. In particular, the benthic stages of metagenetic species are virtually unstudied in this context despite their obvious importance for bloom dynamics. Hence, we conducted tri-trophic food chain experiments using the algae Rhodomonas salina as the primary producer, the copepod Acartia tonsa as the primary consumer and the benthic life stage of the scyphozoans Cyanea capillata and Chrysaora hysoscella as secondary consumers. Two experiments were conducted examining the effects of different levels of CO2 and food quality (experiment 1) and the effect of food quality and quantity (experiment 2) on the growth and respiration of scyphozoan polyps. Polyp growth and carbon content (µg polyp−1) were not affected by the CO2 treatments, but were significantly negatively affected by P limitation of the food in C. capillata but not in Ch. hysoscella. Growth and carbon content were reduced in low-food treatments, but increased with decreasing P limitation in high- and low-food treatments in C. capillata. Respiration was not significantly influenced by food quality and quantity in C. capillata. We conclude that phosphorus can be a limiting factor affecting the fitness of scyphopolyps and that P-limited food is of poor nutritional quality. Furthermore, OA, at least using realistic end-of-century scenarios, will have no direct effect on the growth of scyphistomae

Anthropogenic CO2 changes in the Equatorial Atlantic Ocean

Methods based on CO2 and chlorofluorocarbon (CFC) data are used to describe and evaluate the anthropogenic CO2 (Cant) concentrations, Cant specific inventories, and Cant storage rates in the Equatorial Atlantic Ocean. The Cant variability in the water masses is evaluated from the comparison of two hydrographic sections along 7.5°N carried out in 1993 and 2010. During both cruises, high Cant concentrations are detected in the upper layers, with values decreasing progressively towards the deep layers. Overall, the Cant concentrations increase from 1993 to 2010, with a large increment in the upper North Atlantic Deep Water layer of about 0.18±0.03μmolkg−1y−1. In 2010, the Cant inventory along the whole section amounts to 58.9±2.2 and 45.1±2.0molm−2 using CO2 and CFC based methods, respectively, with most Cant accumulating in the western basin. Considering the time elapsed between the two cruises, Cant storage rates of 1.01±0.18 and 0.75±0.17molm−2y−1 (CO2 and CFC based methods, respectively) are obtained. Below ∼1000m, these rates follow the pace expected from a progressive increase of Cant at steady state; above ∼1000m, Cant increases faster, mainly due to the retreat of the Antarctic Intermediate Waters.

Evidence of prolonged aragonite undersaturations in the bottom waters of the southern Bering Sea shelf from autonomous sensors

The southeastern shelf of the Bering Sea is a dynamic area that experiences seasonal variability in primary production and remineralization of organic matter, both of which control the carbon biogeochemistry of the water column. Surface-water partial pressure of carbon dioxide (pCO2) is greatly reduced in summer by biological production, which increases carbonate mineral saturation states (Ω). In contrast, the export of large quantities of organic matter from surface blooms drives an active remineralization loop that sharply increases pCO2 near the bottom, lowering pH and suppressing Ω. New observations from moored biogeochemical sensors in 2011 showed that seasonal net community production lowers surface-water pCO2, causing large gradients between the ocean and atmosphere that are sustained throughout the summer, confirming that these waters likely remain supersaturated with respect to aragonite throughout the open water season. On the other hand, moored sensors deployed near the bottom showed that pCO2 levels exceed 500μatm by early June and remain at these high levels well into the autumn months, indicating that the bottom waters are likely continuously undersaturated in aragonite for at least several months during each year. Only a small fraction of the increased pCO2 can currently be attributed to the intrusion of anthropogenic CO2 from the atmosphere, while the majority is due to natural respiration processes. The biological impacts, along with the timing and duration of these undersaturation events, could play a role in the development of larval and juvenile calcifiers in the region and will change as anthropogenic CO2 concentrations continue to rise.