Impacts of shellfish and macroalgae mariculture on the seawater carbonate system and air-sea CO2 flux in Haizhou Bay, China.

China is the largest mariculture country, and shellfish and algae output ranks first, showing high carbon sink capacity. In recent years, the single cultivation of macroalgae (Pyropia yezoensis) has been changed to macroalgae-shellfish mariculture in Haizhou Bay to increase the yield of P. yezoensis and improve the water environment quality. In this study, four surveys were carried out in July 2022 during the monoculture period of oyster (Magallana gigas), as well as at different stages of P. yezoensis culture (head-crop period, November 2022, peak growing season, January 2023, and end of harvesting, March 2023) in the mariculture and the surrounding waters of Haizhou Bay. The effects of different stages of culture on the seawater environment and seasonal and spatial variations in the carbonate system were analyzed, and the carbon sink capacity was preliminarily estimated. The results showed that in summer, the calcification of M. gigas and the primary production process of phytoplankton effectively reduced the dissolved inorganic carbon (DIC) level in the culture area. The culture area acts as a CO2 sink, with an average air-sea CO2 flux of -4.5 mmol m-2 d-1. During the polyculture period, the P. yezoensis culture activities maintained the stability of the seawater carbonate system, and the culture area shows strong CO2 sinks, with the average air-sea CO2 flux of -24.10 mmol m-2 d-1, -37.68 mmol m-2 d-1, and -38.99 mmol m-2 d-1, respectively. The absorption of CO2 by large-scale cultured P. yezoensis through the "biological pump" effect is the main factor affecting the CO2 exchange process at the air-sea interface, and the absorption rate of CO2 by P. yezoensis at the mature stage is higher than that at the growth stage before harvesting. The study revealed that macroalgae-shellfish mariculture could promote mutual growth, alleviate environmental pressure, and enhance the carbon sink of the culture area. The relationship between mariculture and the carbon cycle of a mariculture ecosystem is very complicated, and its biochemical process should be given great attention for further study.

Assessing the Limit of CO2 Storage in Seawater as Bicarbonate-Enriched Solutions.

The dissolution of CO2 in seawater in the form of bicarbonate ions is an attractive alternative to storage in geological formations, on the condition that the storage is stable over long periods and does not harm the marine environment. In this work, we focus on the long-term chemical stability of CO2 absorbed in seawater as bicarbonate by monitoring the physico-chemical properties of the solutions (pH, dissolved inorganic carbon and alkalinity) in six different sets of experiments on both natural and artificial seawater lasting up to three months. The bicarbonate treatment of natural seawater consists of mixing it with pre-equilibrated solutions obtained from the reaction of CO2 and Ca(OH)2, with the same pH as natural seawater. This was achieved with a pilot plant working with tons of seawater, while small-scale laboratory experiments were carried out by adding sodium bicarbonate to artificial seawater solutions. If the increase in the overall carbon concentration in the final mixture does not exceed a critical threshold (about 1000-1500 µmol/L), the resulting bicarbonate-rich solutions are found to be stable for over three months.

In Situ Quantification of Carbonate Species Concentrations, pH, and pCO2 in Calcite Fluid Inclusions Using Confocal Raman Spectroscopy.

Carbonate minerals are globally distributed on the modern and ancient Earth and are abundant in terrestrial and marine depositional environments. Fluid inclusions hosted by calcite retain primary signatures of the source fluid geochemistry at the time of mineral formation (i.e., pCO2) and can be used to reconstruct paleoenvironments. Confocal laser Raman spectroscopy provides a quick, nondestructive approach to measuring the constituents of fluid inclusions in carbonates and is a reliable method for qualitatively determining composition in both the aqueous and gas phases. Here, we demonstrate a method for accurately quantifying bicarbonate and carbonate ion concentrations (down to 20 mM) and pH (7-11) from calcite fluid inclusions using confocal Raman spectroscopy. Instrument calibrations for carbonate (CO32-) and bicarbonate (HCO3-) concentrations and pH were performed using stock solutions. We show that the calcite host mineral does not affect the accurate quantification of carbonate solution concentrations and that these parameters can be used to estimate the pH and pCO2 of a solution entrapped within a fluid inclusion. We apply the technique to Icelandic spar calcite and find a [CO32-] = 0.11, [HCO3-] = 0.17, pH = 10.1, and CO2 parts per million = 2217. The presence of gaseous Raman bands for CO2, CH4, and H2S suggests that the mineral precipitated in a reducing environment.

Emission of CO2 and its related carbonate system dynamics in a hotspot area during winter and summer: The Changjiang River estuary.

The carbonate chemistry in river-dominated marginal seas is highly heterogeneous, and there is ongoing debate regarding the definition of atmospheric CO2 source or sink. On this basis, we investigated the carbonate chemistry and air-sea CO2 fluxes in a hotspot estuarine area: the Changjiang Estuary during winter and summer. The spatial characteristics of the carbonate system were influenced by water mixing of three end-members in winter, including the Changjiang freshwater with low total alkalinity (TA) concentration, the less saline Yellow Sea Surface Water with high TA, and the saline East China Sea (ECS) offshore water with moderate TA. While in summer with increased river discharge, the carbonate system was regulated by simplified two end-member mixing between the Changjiang freshwater and the ECS offshore water. By performing the end-member mixing model on DIC variations in the river plume region, significant biological addition of DIC was found in winter with an estimation of -120 ± 113 µmol kg-1 caused by wintertime organic matter remineralization from terrestrial source. While this biological addition of DIC shifted to DIC removal due to biological production in summer supported by the increased nutrient loading from Changjiang River. The pCO2 dynamics in the river plume and the ECS offshore were both subjected to physical mixing of freshwater and seawater, whether in winter and summer. In the inner estuary without horizontal mixing, the pCO2 dynamics were mainly influenced by biological uptake in winter and temperature in summer. The inner estuary, the river plume, and the ECS offshore were sources of atmospheric CO2, with their contributions varying seasonally. The Changjiang runoff enhanced the inner estuary's role as a CO2 source in summer, while intensive biological uptake reduced the river plume's contribution.

Effects of HCO3- and CO2 conversion rates on carbon assimilation strategies in marine microalgae: Implication by stable carbon isotope analysis of fatty acids.

Marine microalgae are an essential component of marine plankton and critical primary producers, playing a vital role in marine ecosystems. The seawater carbonate system is a dynamic equilibrium system, and changes in any component can alter the carbonate balance. In CO2-concentrating mechanisms (CCMs), carbonic anhydrase (CA) regulates CO2 concentration by catalyzing the interconversion between CO2 and HCO3-. Therefore, limiting the activity of extracellular carbonic anhydrase (exCA) alters the rate at which carbonate equilibrium is reached and further affects the carbon assimilation process in microalgae. In this study, two different microalgae, Phaeodactylum tricornutum and Nannochloropsis oceanica, were selected to investigate the effects of changes in the carbonate system on photosynthetic carbon assimilation in microalgae by inhibiting exCA activity with acetazolamide (AZ). Inhibition of exCA activity reduces specific growth rates and photosynthetic efficiency of microalgae. The total alkalinity, HCO3- concentration, and CO2 concentration of the cultures increased with the decrease of pH, but the changes of the ribulose 1,5- bisphosphate carboxylase/oxygenase (Rubisco) activities of the two microalgae were different. In addition, the two microalgae possessed different lipid and carbohydrate synthesis strategies, but both restricted triacylglycerol (TAG) synthesis. Meanwhile, the microalgal cells had to utilize more 13CO2 when HCO3- and CO2 conversion rates were limited and restricted. This led to the continuous accumulation of 13C in fatty acids and the elevation of δ13CFAs. In conclusion, our study provides a new perspective on the role of microalgae in correlating carbonate changes with photosynthetic carbon assimilation strategies under mechanistic constraints on inorganic carbon utilization.

Geographical and seasonal patterns in the carbonate chemistry of Narragansett Bay, RI.

This study examined geographical and seasonal patterns in carbonate chemistry and will facilitate assessment of acidification conditions and the current state of the seawater carbonate chemistry system in Narragansett Bay. Direct measurements of total alkalinity, dissolved inorganic carbon, dissolved oxygen percent saturation, water temperature, salinity and pressure were performed during monthly sampling cruises carried out over three years. These measurements were used to calculate the following biologically relevant carbonate system parameters: total pH (pHT), the partial pressure of carbon dioxide in the gas phase pCO2, and the aragonite saturation state ΩA. The information provided by carbonate chemistry analysis allowed for the characterization of acidification events which have the potential to disrupt the species composition and ecological functioning of coastal biological communities and threaten commercially important aquatic life. We found very robust relationships between salinity and total alkalinity Radjusted2=0.82 and between salinity and dissolved inorganic carbon Radjusted2=0.81 that persisted through all regions, seasons, and depth-layers with mixing of coastal waters with freshwater entering in the upper bay being an important driver on alkalinity and dissolved inorganic carbon distributions. We compared the metabolically linked calculated carbonate system parameters with dissolved oxygen (DO) saturation and found high correlation, with DO percent saturation exhibiting robust correlation with the calculated carbonate system parameters total pH (r=0.70) and with partial pressure of carbon dioxide in the gas phase (r=-0.71). Using a statistical model to correct for the confounded effects of time and space that are a common challenge in marine survey design, we found that acidification events occurred in the Northern Region of the bay, primarily during the Summer and Fall, and likely due to a combination of microbial respiration and stratification. These acidification events, especially in the Northern Region, have the potential to adversely impact aquatic life.

Daily variability of pH and temperature in seawater from a near-pristine oceanic atoll, Southwest Atlantic.

The study of pH and temperature variability in reef environments, and the underlying processes that control this variability, is of great importance for ocean acidification research. Therefore, in the reef environment of Rocas Atoll, we conducted continuous monitoring of pH and temperature and periodic sampling of carbonate chemistry, and we hypothesize that seawater temperature is not the determining factor in the daily variability of pH at this atoll. Our results showed that the seawater of the atoll presented a high daily variability in pH, [H+], and temperature. The cycles of variations occurred primarily with a periodicity of ∼24 h, related to the daily light cycle, and secondarily with a periodicity of ∼12 h, associated with the semi-diurnal tidal cycles of the atoll. The results indicate that the relative balance of net organic carbon metabolism is the main process modulating carbonate chemistry on the atoll throughout the day.

Haemolymph pH of two important mollusc species is susceptible to seawater buffering capacity instead of pH or pCO2.

The acid-base status and balance of molluscs are considered to be susceptible to environmental changes, especially in the context of ocean acidification (OA). Here, we studied the effects of manipulated seawater carbonate chemistry on the acid-base status of scallop Chlamys farreri and abalone Haliotis discus hannai. The haemolymph pH of the tested individuals showed a fast response to acidified seawater incubation, and the pH level was restored to a normal value within 1 h of recovery in control seawater. However, no significant correlation (P > 0.05) was found between haemolymph pH and seawater pCO2 or pH, while the squared Pearson correlation coefficient (R2) ranged from close to zero to 0.41. In addition, although the pCO2 level of total alkalinity (TA)-lowered seawater was lower than half of that in the control, molluscs eliminated less CO2 (less than 80%) to TA lowered waters than to the control waters. These findings seem to disagree with the crucial role of seawater pCO2 in influencing the acid-base balance of molluscs. CO2 elimination occurs in the microenvironment, and CO2 first diffuses to limited amounts of seawater that tightly surround the gills, causing dissolved inorganic carbon (DIC) accumulation in the ventilation sites, which leads to a sharp increase in the pCO2 of the surrounding seawater. Moreover, in this microenvironment, the pCO2 level increases much faster and more greatly if the environmental seawater is acidified or contains a lower level of TA. Therefore, mollusc acid-base status is influenced by rapidly varying pCO2 levels at the ventilation site, which is largely independent of that of the rest of the incubating seawater. In summary, CO2 elimination by molluscs relies heavily on the carbonate chemistry of environmental seawater, and seawater buffering capacity should be taken into consideration instead of considering only pCO2 or pH in studying the acid-base balance of marine molluscs.

Variations in aragonite saturation state and its controlling factors in the South Yellow Sea in spring and autumn.

To assess the progression of ocean acidification in the South Yellow Sea (SYS), the aragonite saturation state (Ωarag) was determined from dissolved inorganic carbon (DIC) and total alkalinity (TA) in the surface and bottom waters of the SYS in spring and autumn. The Ωarag exhibited large spatiotemporal variations in the SYS; DIC was a major factor controlling the Ωarag variations, whereas temperature, salinity, and TA were minor factors. Surface DIC concentrations were mainly influenced by the lateral transport of the DIC-enriched Yellow River waters and DIC-depleted East China Sea Surface Water; bottom DIC concentrations were affected by aerobic remineralization in spring and autumn. Ocean acidification is now seriously progressing in the SYS, particularly in the Yellow Sea Bottom Cold Water (YSBCW) where the mean value of Ωarag substantially decreased from 1.55 in spring to 1.22 in autumn. All Ωarag values measured in the YSBCW in autumn were lower than the critical threshold value of 1.5 necessary for the survival of calcareous organisms.

Assessment on seasonal acidification and its controls in the Muping Marine Ranch, Yantai, China.

Ocean acidification has emerged as a major challenge affecting the development of the marine aquaculture. Seasonal variations of seawater pH and aragonite saturation (Ωarag) were investigated in the Muping Marine Ranch, Yantai. The results showed that the seasonal variations of pH and Ωarag were distinct. The temperature exerted opposite effects on pH and Ωarag and played a dominant role in pH variation, while limited role in Ωarag. The air-sea exchange had a syntropic effect on pH and Ωarag but less impact on their seasonal variations. Biological activities affected seasonal variations of surface seawater pH and Ωarag, but they largely canceled each other out with other non-temperature effects; while bottom seawater Ωarag was mainly controlled by biological respiration in summer. This study demonstrates that pH is primarily controlled by seasonal temperature changes, whereas Ωarag would be a better indicator for ocean acidification caused by non-temperature processes.

The carbon sink of the Coral Sea, the world's second largest marginal sea, weakened during 2006-2018.

The latest reports show that the ocean absorbs approximately 26 % of anthropogenic CO2 and that the carbon sink of the global ocean (air-sea CO2 flux) is continually increasing, while variations in different marginal seas are complicated. The Coral Sea, the second largest marginal sea in the world, is characterized by a generally oligotrophic basin and borders the biodiversity hotspot of Great Barrier Reef. In this study, we proposed a semianalytical method and reconstructed the first high-resolution satellite-based pCO2 and air-sea CO2 flux dataset from 2006 to 2018 for the Coral Sea. This dataset performed well in the basin (RMSE<10 µatm, R2 > 0.72) and coral reef areas (RMSE<12 µatm, R2 > 0.8) based on validation by a massive independent dataset. We found that sea surface pCO2 is increasing (1.8 to 2.7 µatm/year) under the forcing of increasing atmospheric CO2, and the pCO2 growth rate in water is faster than that in the atmosphere. The combination of increasing sea surface pCO2, high pCO2 seawater from coral reef areas, and the low depletion capacity of the oligotrophic basin led to a gradual weakening of the carbon sink in the Coral Sea, with the 2016 carbon sink being 52 % of that in 2006. This weakening was more pronounced after strong El Niño events (e.g., 2007, 2010, and 2016), with the corresponding high SST and low wind speed further weakening the carbon sink. This understanding of the long-term change in the Coral Sea provides new insight on the carbonate system variation and carbon sink capacity evolution in seawater under increasing atmospheric CO2.

Evidence for enhanced primary production driving significant CO2 drawdown associated with the Atlantic ITCZ.

The intense rainfall associated with the Intertropical Convergence Zone (ITCZ), a narrow zone of confluence of the northeast and southeast trades, can significantly alter sea surface salinity, the chemistry of inorganic C and the resulting sea-air CO2 exchange in the tropics. We have analyzed extensive underway data collected from 2008 until 2014 and recorded by an autonomous CO2 system installed on a commercial ship that crosses the central tropical Atlantic (5°S to 15°N, 18°W to 36°W) to disentangle the effects of the ITCZ over the carbonate system there. Based on statistically significant linear co-variance of sea surface fugacity of CO2 (fCO2sw) and sea surface salinity in the areas affected by the ITCZ, we calculated CO2 drawdown rates associated with the impact of the ITCZ in the central tropical Atlantic ranging from 0.11 ± 0.02 to 2.35 ± 0.08 mmol m-2 d-1. These were calculated by comparing the observed fCO2sw with that expected without surface seawater carbonate system dilution and increase in gas transfer caused by the ITCZ. The observed decrease in fCO2sw associated with the freshening caused by the ITCZ is much larger than expected from thermodynamics alone. 59.1 ± 4.1 % of the total observed CO2 drawdown associated with the ITCZ cannot be explained by abiotic processes. Instead, we found significant negative correlations between underway sea surface salinity and remote-sensed chlorophyll a in the areas affected by the ITCZ. Different to other tropical oceanic basins, the tropical Atlantic receives large amounts of continental dust originated from Africa. Wet dust deposition driven by the ITCZ appears associated with the interannual variability of the CO2 drawdown associated with the ITCZ. Fertilization driven by the ITCZ seems to enhance primary production in the otherwise oligotrophic tropical Atlantic, thus significantly lowering CO2 emissions to the atmosphere.

Forensic carbon accounting: Assessing the role of seaweeds for carbon sequestration.

Carbon sequestration is defined as the secure storage of carbon-containing molecules for >100 years, and in the context of carbon dioxide removal for climate mitigation, the origin of this CO2 is from the atmosphere. On land, trees globally sequester substantial amounts of carbon in woody biomass, and an analogous role for seaweeds in ocean carbon sequestration has been suggested. The purposeful expansion of natural seaweed beds and aquaculture systems, including into the open ocean (ocean afforestation), has been proposed as a method of increasing carbon sequestration and use in carbon trading and offset schemes. However, to verify whether CO2 fixed by seaweeds through photosynthesis leads to carbon sequestration is extremely complex in the marine environment compared to terrestrial systems, because of the need to jointly consider: the comparatively rapid turnover of seaweed biomass, tracing the fate of carbon via particulate and dissolved organic carbon pathways in dynamic coastal waters, and the key role of atmosphere-ocean CO2 exchange. We propose a Forensic Carbon Accounting approach, in which a thorough analysis of carbon flows between the atmosphere and ocean, and into and out of seaweeds would be undertaken, for assessing the magnitude of CO2 removal and robust attribution of carbon sequestration to seaweeds.

Responses of the marine carbonate system to a green tide: A case study of an Ulva prolifera bloom in Qingdao coastal waters.

As an environmental nuisance, Ulva prolifera green tides have occurred annually in the southern Yellow Sea since 2007. While it is expected that high levels of biological activity during these blooms can alter seawater carbonate chemistry, there has been little research on the responses of marine carbonate system to green tides. Here, the effects of the bloom on the carbonate system were examined on three cruises in June, July, and September, corresponding to the early-, late-, and after-bloom periods of the U. prolifera bloom in Qingdao coastal waters in 2018. Among these three stages, the pH (National Bureau of Standards scale), dissolved inorganic carbon (DIC), total alkalinity (TA), and partial pressure of CO2 (pCO2) were all affected by bloom, with the highest pH and lowest DIC and TA concentrations of the surface seawater occurring at the late-bloom stage. While pCO2 continuously increased from the beginning to the end of the bloom. TA increased by ∼40 µmol kg-1 between the early- and after-bloom periods likely due to the shifts in the carbonate system equilibrium caused by increased CO32- concentrations and the organic matter released by U. prolifera during decomposition. Compared to nearby areas with no U. prolifera bloom, the green tide, along with increasing temperature, reduced the pH and DIC but increased the TA and pCO2. This large-scale bloom also turned the coastal waters from being an atmospheric CO2 sink to a strong source, with the estimation of air-sea CO2 fluxes about 1.69 ± 1.70, 2.28 ± 1.16, and 7.44 ± 5.84 mmol m-2 d-1 during the early-, late-, and after-bloom periods, respectively. This bloom event also promoted the formation of CaCO3 and was an important source of low molecular weight organic acids. These new findings provide nuances for the current conversations on the role of biological processes in modulating marine carbonate system and the contribution of organic matter to alkalinity.

Massive shellfish farming might accelerate coastal acidification: A case study on carbonate system dynamics in a bay scallop (Argopecten irradians) farming area, North Yellow Sea.

Seven cruises were carried out in a bay scallop (Argopecten irradians) farming area and its surrounding waters, North Yellow Sea, from March to November 2017 to study the dynamics of the carbonate system and its controlling factors. Results indicated that the studied parameters were highly variability over a range of spatiotemporal scales, comprehensively forced by various physical and biological processes. Mixing effect and scallop calcification played the most important role in the seasonal variation of total alkalinity (TAlk). For dissolved inorganic carbon (DIC), in addition to mixing, air-sea exchange and microbial activity, e.g. photosynthesis and microbial respiration processes, had more important effects on its dynamics. Different from the former, the changes of water pHT, partial pressure of CO2 (pCO2) and aragonite saturation state (ΩA) were mainly controlled by the combining of the temperature, air-sea exchange, microbial activity and scallop metabolic activities. In addition, the results indicated that massive scallop farming can significantly increase the DIC/TAlk ratio by reducing the TAlk concentration in seawater, thereby reducing the buffering capacity of the carbonate system in seawater especially for ΩA. Preliminary calculated, ~75.7 and ~45.5 µmol kg-1 of TAlk were removed from the surface and bottom waters respectively in one scallop cultivating cycle. If these carbonates cannot be replenished in time, it is likely to accelerate the acidification process of coastal waters. This study highlighted the control mechanism of the carbonate system under the influence of bay scallop farming, and provided useful information for revealing the potential link between human activities (shelled-mollusc mariculture) and coastal acidification.

Carbonate chemistry variability in the southern Yellow Sea and East China Sea during spring of 2017 and summer of 2018.

Marginal seas are highly productive and disproportionately large contributors to global air-sea CO2 fluxes. Due to complex physical and biogeochemical conditions, the southern Yellow-East China Sea is an ideal site for studying carbonate chemistry variability. The carbonate system was investigated in the area in spring of 2017 and summer of 2018. Dissolved inorganic carbon (DIC) and total alkalinity (TA) concentrations were higher in the SYS than the ECS due to material from carbonate weathering and erosion carried by the Yellow River. High pH and low DIC and TA were observed in the Zhe-Min Coastal Current in spring due to high primary productivity caused by Changjiang River input and the Taiwan Warm Current. Temperature and biological activity were the primary drivers controlling the partial pressure of CO2 (pCO2) in the SYS, pCO2 was controlled by primary productivity related to nutrients carried by the Changjiang River and physical mixing in the Changjiang River plume and inner/middle shelves of the ECS, whereas temperature was the dominant factor determining pCO2 distributions in the ECS outer shelf waters influenced by the Kuroshio Current. Overall, the entire study area shifted from a CO2 sink (-4.18 ± 5.60 mmol m-2 d-1) to a weak source (1.02 ± 4.87 mmol m-2 d-1) from spring to summer. Specifically, the SYS and ECS offshore waters changed from CO2 sinks in spring to sources in summer, while the Changjiang River plume was always a CO2 sink.

Effect of large-scale kelp and bivalve farming on seawater carbonate system variations in the semi-enclosed Sanggou Bay.

Although cultured algae and shellfish can be the dominant species in some localized coastal waters, research on the effect of large-scale mariculture on the carbonate system variations in these local waters is still lacking. We conducted five cruises from May to September and studied spatiotemporal variations in the seawater carbonate system in the semi-closed Sanggou Bay, which is famous for its large-scale mariculture. Our results showed that both kelp and bivalve farming induced significant spatiotemporal variations in the carbonate system within the bay. When cultured kelp reached its highest biomass in May, the maximum ΔDIC, ΔpCO2 and ΔpHT between the seawater from the kelp farming area and the non-farming outer bay area was -156 µmol kg-1, -102 µatm and 0.15 pH units, respectively. However, no significant effect of kelp farming on seawater total alkalinity (TA) was observed. Kelp farming also caused the carbonate system variations of seawater from the bivalve farming area. Assuming no kelp was farmed in May, the average pH and pCO2 would reduce by 0.12 pH units and increase by 179 µatm, respectively, in the bivalve farming area. Bivalve farming significantly reduced seawater TA, indicating that fast deposition of calcium carbonate occurred in the bivalve farming area. Although bivalve respiration released CO2 into seawater and elevated seawater pCO2 level and reduced seawater pHT, surprisingly, seawater dissolved inorganic carbon (DIC) reduced significantly in the bivalve farming area. These results indicated that bivalves fixed a larger amount of inorganic carbon by calcification than that released into seawater by respiration. Overall, large-scale kelp and bivalve farming are important biological drivers of variations in the carbonate system within the semi-enclosed Sanggou Bay. Altered carbonate systems by kelp farming may favour calcification of farmed bivalves and provide an essential refuge for these species during the future ocean acidification.

Nickel(II) complexes based on L-amino-acid-derived ligands: synthesis, characterization and study of the role of the supramolecular structure in carbon dioxide capture.

The formation of the symmetrical µ3-carbonate-bridged self-assembled trinuclear NiII complex Na2{[Ni(LO)2(H2O)]3(µ3-CO3)} (LO is the carboxylate anion of a L-tyrosine derivative), involves atmospheric CO2 uptake. The asymmetric unit of the complex comprises an octahedral coordination for the NiII with two L-tyrosine-based ligands, a water molecule and one O atom of the carbonate bridge. The Ni3-µ3-CO3 core in this compound is the first reported of this kind according to the Cambridge Structural Database (CSD). The supramolecular structure is mainly sustained by hydrogen bonds developed by the phenolic functionality of the L-tyrosine moiety of one ligand and the carboxylate group of a neighbouring ligand. The crystal packing is then characterized by three interpenetrated supramolecular helices associated with a diastereoisomer of the type R-supP, which is essential for the assembly process. Magnetic susceptibility and magnetization data support weak ferromagnetic exchange interactions within the novel Ni3-µ3-CO3 core. The NiII complex obtained under the same synthetic conditions but using the analogous ligand derived from the amino acid L-phenylalanine instead of L-tyrosine gives rise to to a mononuclear octahedral system. The results obtained for the different complexes demonstrate the role of the supramolecular structure regarding the CO2 uptake property for these NiII-amino-acid-based systems.

Transgenerational acclimation to changes in ocean acidification in marine invertebrates.

The rapid pace of increasing oceanic acidity poses a major threat to the fitness of the marine ecosystem, as well as the buffering capacity of the oceans. Disruption in chemical equilibrium in the ocean leads to decreased carbonate ion precipitation, resulting in calcium carbonate saturation. If these trends continue, calcifying invertebrates will experience difficultly maintaining their calcium carbonate exoskeleton and shells. Because malfunction of exoskeleton formation by calcifiers in response to ocean acidification (OA) will have non-canonical biological cascading results in the marine ecosystem, many studies have investigated the direct and indirect consequences of OA on ecosystem- and physiology-related traits of marine invertebrates. Considering that evolutionary adaptation to OA depends on the duration of OA effects, long-term exposure to OA stress over multi-generations may result in adaptive mechanisms that increase the potential fitness of marine invertebrates in response to OA. Transgenerational studies have the potential to elucidate the roles of acclimation, carryover effects, and evolutionary adaptation within and over generations in response to OA. In particular, understanding mechanisms of transgenerational responses (e.g., antioxidant responses, metabolic changes, epigenetic reprogramming) to changes in OA will enhance our understanding of marine invertebrate in response to rapid climate change.

Constraining the carbonate system in soils via testing the internal consistency of pH, pCO2 and alkalinity measurements.

Inorganic carbon exists in various dissolved, gaseous and solid phase forms in natural waters and soils. It is important to accurately measure and model these forms to understand system responses to global climate change. The carbonate system can, in theory, be fully constrained and modelled by measuring at least two of out of the following four parameters: partial pressure (pCO2), total alkalinity (TA), pH and dissolved inorganic carbon (DIC) but this has not been demonstrated in soils. In this study, this "internal consistency" of the soil carbonate system was examined by predicting pH of soil extracts from laboratory measurement of TA through alkalinity titration for solutions in which pCO2 was fixed through equilibrating the soil solution with air with a known pCO2. This predicted pH (pHCO2) was compared with pH measured on the same soil extracts using spectrophotometric and glass electrode methods (pHspec and pHelec). Discrepancy between measured and calculated pH was within 0.00-0.1 pH unit for most samples. However, more deviation was observed for those sample with low alkalinity (≤ 0.5 meq L-1). This is likely attributable to an effect of dissolved organic matter, which can contribute alkalinity not considered in the thermodynamic carbonate model calculations; further research is required to resolve this problem. The effects of increasing soil pCO2 was modelled to illustrate how internally consistent models can be used to predict risks of pH declines and carbonate mineral dissolution in some soils.