Seawater Alkalinity Research Articles

Increasing seawater alkalinity using fly ash to restore the pH and the effect of temperature on seawater flue gas desulfurization

Wet type flue gas desulfurization (FGD) using lime or limestone is popular because of its operational simplicity and the availability of lime and limestone. Seawater FGD (SWFGD) utilizes the alkalinity of seawater, and its efficiency varies depending on the seawater alkalinity. This study examined the effects of temperature, gas/water ratio, and total alkalinity of the absorbing solution on the removal efficiency of SO2 from flue gas by seawater. In addition, this study showed the possibility of increasing the total alkalinity of seawater using fly ash from coal power plants. The experimental results showed a 8% increase in removal efficiency, while temperature decreased by 10 °C from 25 °C under the conditions of a gas/water ratio of 100 and a resultant pH of 3. The increase in removal efficiency with increasing alkalinity was measured as 0.27%/ppm of bicarbonate alkalinity. This study showed that fly ash has the ability to increase the total alkalinity of seawater. The pH restoration experiment was conducted using fly ash and limestone. The conceptual design processes of SWFGD using NaOH, fly ash, and limestone for a 400 MW coal power plant were developed, and the material balance was calculated using ASPEN Plus software.

Drivers of pH Variability in Coastal Ecosystems.

A synthesis of long-term changes in pH of coastal ecosystems shows that, in contrast to the uniform trends of open-ocean acidification (-0.0004 to -0.0026 pH units yr-1) driven by increased atmospheric CO2, coastal ecosystems display a much broader range of trends (-0.023 to 0.023 pH units yr-1) and are as likely to show long-term increase as decline in pH. The majority of the 83 investigated coastal ecosystems displayed nonlinear trends, with seasonal and interannual variations exceeding 1 pH unit for some sites. The high pH variability of coastal ecosystems is primarily driven by inputs from land. These include freshwater inputs that typically dilute the alkalinity of seawater thereby resulting in reduced buffering, nutrients enhancing productivity and pH, as well as organic matter supporting excess respiration driving acidification. For some coastal ecosystems, upwelling of nutrient-rich and corrosive water may also contribute to variability in pH. Metabolic control of pH was the main factor governing variability for the majority of coastal sites, displaying larger variations in coastal ecosystems with low alkalinity buffering. pH variability was particularly pronounced in coastal ecosystems with strong decoupling of production and respiration processes, seasonally or through stratification. Our analysis demonstrate that coastal pH can be managed by controlling inputs of nutrients, organic matter, and alkalinity. In well-mixed coastal waters, increasing productivity can improve resistance to ocean acidification, whereas increasing productivity enhances acidification in bottom waters of stratified coastal ecosystems. Environmental management should consider the balance between the negative consequences of eutrophication versus those of acidification, to maintain biodiversity and ecosystem services of our coastal ecosystems.

Carbonate dissolution by reef microbial borers: a biogeological process producing alkalinity under different pCO2 conditions

Rising atmospheric CO2 is acidifying the world’s oceans, affecting both calcification and dissolution processes in coral reefs. Among processes, carbonate dissolution by bioeroding microflora has been overlooked, and especially its impact on seawater alkalinity. To date, this biogeological process has only been studied using microscopy or buoyant weight techniques. To better understand its possible effect on seawater alkalinity, and thus on reef carbonate budget, an experiment was conducted under various seawater chemistry conditions (2 ≤ Ωarag ≤ 3.5 corresponding to 440 ≤ pCO2 (µatm) ≤ 940) at 25 °C under night and daylight (200 µmol photons m−2 s−1) with natural microboring communities colonizing dead coral blocks (New Caledonia). Both the alkalinity anomaly technique and microscopy methods were used to study the activity of those communities dominated by the chlorophyte Ostreobium sp. Results show that (1) the amount of alkalinity released in seawater by such communities is significant and varies between 12.8 ± 0.7 at ΩArag ~ 2 and 5.6 ± 0.4 mmol CaCO3 m−2 day−1 at ΩArag ~ 3–3.5 considering a 12:12 photoperiod; (2) although dissolution is higher at night (~ 80 vs. 20% during daylight), the process can occur under significant photosynthetic activity; and (3) the process is greatly stimulated when an acidity threshold is reached (pCO2 ≥ 920 µatm vs. current conditions at constant light intensity). We show that carbonate dissolution by microborers is a major biogeochemical process that could dissolve a large part of the carbonates deposited by calcifying organisms under ocean acidification.

Winter iron supply processes fueling spring phytoplankton growth in a sub-polar marginal sea, the Sea of Okhotsk: Importance of sea ice and the East Sakhalin Current

To evaluate the winter iron (Fe) supply processes fueling spring phytoplankton growth in the southern Sea of Okhotsk, the distributions of the Fe concentrations in seawater were investigated using hydrographic observations in late November (in the absence of sea ice) and mid-February (in the presence of sea ice). The results obtained from the hydrographic observations indicated a temporal increase in the Fe concentration in the surface mixed layer from November to February, which coincided with a decrease in seawater salinity. Changes in the alkalinity and oxygen isotopic composition of seawater indicated that the mixed layer in February was affected by sea ice meltwater as well as the less saline East Sakhalin Current (ESC) water, with a significant Fe supply originating from these waters. The magnitude of the Fe supply from these waters is greater than the upward Fe supply from deep water. The sea ice meltwater enriches the Fe in the near-surface water of the mixed layer, whereas the ESC water enriches the Fe at the depth of the mixed layer by the entrainment of sedimentary Fe associated with deep mixing due to Ekman transport. Additionally, the Fe nutritional status of the phytoplankton in the surface water of the ice-covered area was investigated by a shipboard incubation experiment. The results showed that bio-available Fe existed in the surface water and that large (>10 μm) phytoplankton were not stressed by low Fe availability. The Fe supply processes related to sea ice melting and the ESC water inflow play important roles in sustaining the suitable Fe nutritional status of phytoplankton in the southern Sea of Okhotsk in early spring.

Mass and Fine‐Scale Morphological Changes Induced by Changing Seawater pH in the Coccolith Gephyrocapsa oceanica

AbstractCoccolithophores have been extensively studied to understand the environmental control on calcification in a key biological group influencing the alkalinity of seawater. Previous studies have established that bulk calcification scales with cell division rates under a wide range of pH conditions. Yet the fine‐scale ultrastructural changes of the coccoliths and therefore the pH‐sensitive underlying mechanisms altering biomineralization of the coccoliths remain largely underconstrained. Using circularly polarized light and high‐resolution microscopy, we have generated mass estimates of cultured Gephyrocapsa oceanica coccoliths grown in media with pH values ranging from 7.4 to 9.0. These mass estimates representing a bulk calcification response were related to the morphological changes within the coccoliths. From optimal (pH 8.6) down to pH 7.4 conditions, we have observed that impaired cell growth and lower calcite quota are accompanied by a 35% decrease in mean coccolith mass. The data further show that seawater acidification does not homogenously affect calcification of the coccoliths, as a clear decrease of the breadth of the tube (a structure surrounding the central area of the coccoliths) was detected, whereas all other ultrastructural components were far less impacted. We discuss this specific sensitivity to acidification as the possible consequence of the altered interaction of the acidic polysaccharides used for biomineralization and ambient concentration of protons released by calcification that substantially modify the growth patterns, the morphology, and ultimately the mass of the coccoliths.

Uncertainty evaluation of alkalinity measurements on seawater samples

Alkalinity and pH are chemical parameters that, once measured in seawater, allow the calculation of the concentration of the carbonate system species CO32−, HCO3−, H2CO3 and CO2 which tend to be in equilibrium. Hence, these are key parameters used in oceanic carbon cycle models. The interpretation of the measured values depends on their respective uncertainties.This work presents a bottom-up evaluation of the uncertainty associated with measurements of total alkalinity, carbonate and bicarbonate concentrations in seawater samples by acid-base titration, with potentiometric detection, using as titrant a hydrochloric acid solution, 0.01 mol L−1 HCl in 0.67 mol L−1 NaCl, in order to approach working conditions to those of real seawater, with average ionic strength I = 0.67 mol L−1. The precision of the endpoint identification is estimated by the difference between the standard deviation of measurements repeatability and the combination of the repeatability of volumetric operations. Endpoint identification is the major uncertainty component that can be reduced by estimating alkalinity and concentration of the titrant solution, using a larger number of replicates. Total alkalinity was evaluated with a relative standard uncertainty of 1.5 % from triplicate measurements enabling distinction of relative differences larger than 6.3 % on a pair of seawater samples.A validated spreadsheet for estimating seawater alkalinity, carbonate and bicarbonate equivalent concentrations with respective uncertainty is made available as Electronic Supplementary Material.

Acidified seawater increases accumulation of cobalt but not cesium in manila clam Ruditapes philippinarum

The pH of seawater around the world is expected to continue its decline in the near future in response to ocean acidification that is driven by heightened atmospheric CO2 emissions. Concomitantly, economically-important molluscs that live in coastal waters including estuaries and embayments, may be exposed to a wide assortment of contaminants, including trace metals and radionuclides. Seawater acidification may alter both the chemical speciation of select elements as well as the physiology of organisms, and may thus pose at risk to many shellfish species, including the manila clam Ruditapes philippinarum. The bioconcentration efficiency of two common radionuclides associated with the nuclear fuel cycle, 134Cs and 57Co, were investigated by exposing live clams to dissolved 134Cs and 57Co at control (pH = 8.1) and two lowered pH (pH = 7.8 and 7.5) levels using controlled aquaria. The uptake and depuration kinetics of the two radionuclides in the whole-body clam were followed for 21 and 35 days, respectively. At steady-state equilibrium, the concentration factor (CFss) for 57Co increased as the pH decreased (i.e. 130 ± 5, 194 ± 6, and 258 ± 10 at pH levels 8.1, 7.8 and 7.5, respectively), whereas the 134Cs uptake was not influenced by a change in pH conditions. During depuration, the lowest depuration rate constant of 57Co by the manila clam was observed at the intermediate pH of 7.8. An increase in the accumulation of 57Co at the intermediate pH value was thought to be caused mainly by the aragonitic shell of the clam, as well as the low salinity and alkalinity of seawater used in the experiment. Considering that accumulation consists of uptake and depuration, among the three pH conditions moderately acidified seawater enhanced most the accumulation of 57Co. Accumulation of 134Cs was not strongly influenced by a reduced pH condition, as represented by an analogous uptake constant rate and CFss in each treatment. Such results suggest that future seawater pH values that are projected to be lower in the next decades, may pose a risk for calcium-bearing organisms such as shellfish.

Design and experimental study on desulphurization process of ship exhaust

This desulfurization process involves removing sulfur oxides with seawater or alkaline aqueous solutions and then treating the effluent by aeration and pH adjustment before discharging it into the ocean. In the desulfurization system, the spray tower is the key equipment and the venturi tubes are the pretreatment device. The two stages of plates are designed to fully absorb sulfur oxides in exhaust gases. The spiral nozzles atomize and evenly spray the desulfurizers into the tower. This study experimentally investigated the effectiveness of this desulfurization process and the factors influencing it under laboratory conditions, with a diesel engine exhaust used to represent ship exhaust. The experimental results show that this process can effectively absorb the SO2 in the exhaust. When the exhaust flow rate was 25 m3/h and the desulfurizer flow rate was 4 L/min, the sulfur removal efficiency (SRE) reached 99.7%. The flow rate, alkalinity, and temperature of seawater were found to have significant effects on the SRE. Adjusting seawater flow rate (SWR) and alkalinity within certain ranges can substantially improve the SRE.

Updated methods for global locally interpolated estimation of alkalinity, pH, and nitrate

AbstractWe have taken advantage of the release of version 2 of the Global Data Analysis Project data product (Olsen et al. ) to refine the locally interpolated alkalinity regression (LIAR) code for global estimation of total titration alkalinity of seawater (AT), and to extend the method to also produce estimates of nitrate (N) and in situ pH (total scale). The updated MATLAB software and methods are distributed as Supporting Information for this article and referred to as LIAR version 2 (LIARv2), locally interpolated nitrate regression (LINR), and locally interpolated pH regression (LIPHR). Collectively they are referred to as locally interpolated regressions (LIRs). Relative to LIARv1, LIARv2 has an 18% lower average AT estimate root mean squared error (RMSE), improved uncertainty estimates, and fewer regions in which the method has little or no available training data. LIARv2, LINR, and LIPHR produce estimates globally with skill that is comparable to or better than regional alternatives used in their respective regions. LIPHR pH estimates have an optional adjustment to account for ongoing ocean acidification. We have used the improved uncertainty estimates to develop LIR functionality that selects the lowest‐uncertainty estimate from among possible estimates. Current and future versions of LIR software will be available on GitHub at https://github.com/BRCScienceProducts/LIRs.

Assessment of Responses of Tropical Pacific Air–Sea CO2 Flux to ENSO in 14 CMIP5 Models

Responses of tropical Pacific air–sea CO2 flux (fCO2) to El Niño–Southern Oscillation (ENSO) events in 14 models from phase 5 of the Coupled Model Intercomparison Project (CMIP5) are examined. The contributions of sea surface temperature (SST), dissolved inorganic carbon in surface seawater (DIC), and total alkalinity of surface seawater (TALK) to interannual variation of ln(pCO2sea) (instead of partial pressure of CO2 in surface seawater pCO2sea) are quantified based on standardized empirical orthogonal function (EOF) results. Results show that six of the models have poor responses because they fail to reproduce observed interannual variation of pCO2sea in the central-eastern tropical Pacific. These six models underestimate the contribution of DIC interannual variation to interannual variation of pCO2sea in the central-eastern tropical Pacific due to a weak relation between interannual variation of upwelling and ENSO events or a weak relation (including no relation) between interannual variation of upwelling and that of DIC. Furthermore, some models have biases in interannual variation of DIC, in terms of both location and period, that are associated with interannual variation of modeled precipitation. It is also found that two models produce unreasonable interannual variation of bioproductivity, which enlarges interannual variation of DIC in the central-eastern tropical Pacific; this may partly explain why the influence of upwelling on interannual variation of DIC is weak in these models, even when the relationship between interannual variation of DIC and ENSO index is reasonable.

Solid State Sensor for Simultaneous Measurement of Total Alkalinity and pH of Seawater.

A novel design is demonstrated for a solid state, reagent-less sensor capable of rapid and simultaneous measurement of pH and Total Alkalinity (AT) using ion sensitive field effect transistor (ISFET) technology to provide a simplified means of characterization of the aqueous carbon dioxide system through measurement of two "master variables": pH and AT. ISFET-based pH sensors that achieve 0.001 precision are widely used in various oceanographic applications. A modified ISFET is demonstrated to perform a nanoliter-scale acid-base titration of AT in under 40 s. This method of measuring AT, a Coulometric Diffusion Titration, involves electrolytic generation of titrant, H+, through the electrolysis of water on the surface of the chip via a microfabricated electrode eliminating the requirement of external reagents. Characterization has been performed in seawater as well as titrating individual components (i.e., OH-, HCO3-, CO32-, B(OH)4-, PO43-) of seawater AT. The seawater measurements are consistent with the design in reaching the benchmark goal of 0.5% precision in AT over the range of seawater AT of ∼2200-2500 μmol kg-1 which demonstrates great potential for autonomous sensing.

Ba incorporation in benthic foraminifera

Abstract. Barium (Ba) incorporated in the calcite of many foraminiferal species is proportional to the concentration of Ba in seawater. Since the open ocean concentration of Ba closely follows seawater alkalinity, foraminiferal Ba ∕ Ca can be used to reconstruct the latter. Alternatively, Ba ∕ Ca from foraminiferal shells can also be used to reconstruct salinity in coastal settings in which seawater Ba concentration corresponds to salinity as rivers contain much more Ba than seawater. Incorporation of a number of minor and trace elements is known to vary (greatly) between foraminiferal species, and application of element ∕ Ca ratios thus requires the use of species-specific calibrations. Here we show that calcite Ba ∕ Ca correlates positively and linearly with seawater Ba ∕ Ca in cultured specimens of two species of benthic foraminifera: Heterostegina depressa and Amphistegina lessonii. The slopes of the regression, however, vary two- to threefold between these two species (0.33 and 0.78, respectively). This difference in Ba partitioning resembles the difference in partitioning of other elements (Mg, Sr, B, Li and Na) in these foraminiferal taxa. A general trend across element partitioning for different species is described, which may help develop new applications of trace elements in foraminiferal calcite in reconstructing past seawater chemistry.

Effectiveness of N,O-carboxymethyl chitosan on destabilization of Marine Diesel, Diesel and Marine-2T oil for oil spill treatment

Oil spills are the significant sources of hydrocarbons entering in the receiving aquatic environment. An efficient method to remove hydrocarbons from water resources is adsorption. In this study, water soluble N,O-carboxymethyl chitosan (NO-CS) was synthesized by carboxymethylation of chitosan in a hydro-alcoholic medium at 50°C by chloroacetic acid. The polymer was characterized through degree of deacetylation, degree of substitution, FTIR and 1H NMR. Effectiveness of NO-CS as an adsorbent was studied as a function of dosage, salinity and pH to destabilize the Marine diesel (Oil-1), Diesel (Oil-2) and Marine-2T oil (Oil-3) into small oil droplets of less than 100μm. Optical microscope was used for studying the size of oil droplets and adsorption effect of the oils on this polymer. The destabilization of marine diesel was the most effective among the studied three oils, which showed excellent adsorption at sea water alkalinity and salinity.

Olivine Dissolution in Seawater: Implications for CO2 Sequestration through Enhanced Weathering in Coastal Environments.

Enhanced weathering of (ultra)basic silicate rocks such as olivine-rich dunite has been proposed as a large-scale climate engineering approach. When implemented in coastal environments, olivine weathering is expected to increase seawater alkalinity, thus resulting in additional CO2 uptake from the atmosphere. However, the mechanisms of marine olivine weathering and its effect on seawater–carbonate chemistry remain poorly understood. Here, we present results from batch reaction experiments, in which forsteritic olivine was subjected to rotational agitation in different seawater media for periods of days to months. Olivine dissolution caused a significant increase in alkalinity of the seawater with a consequent DIC increase due to CO2 invasion, thus confirming viability of the basic concept of enhanced silicate weathering. However, our experiments also identified several important challenges with respect to the detailed quantification of the CO2 sequestration efficiency under field conditions, which include nonstoichiometric dissolution, potential pore water saturation in the seabed, and the potential occurrence of secondary reactions. Before enhanced weathering of olivine in coastal environments can be considered an option for realizing negative CO2 emissions for climate mitigation purposes, these aspects need further experimental assessment.

Paleo-climatic and paleo-environmental evolution of the Neoproterozoic basal sedimentary cover on the Río de La Plata Craton, Argentina: Insights from the δ13C chemostratigraphy

The Sierras Bayas Group of the Tandilia System constitutes the Neoproterozoic sedimentary cover of the Río de La Plata Craton in Argentina that accumulated amid the breakup of the Rodinia supercontinent and subsequent assembly of Gondwanaland. Evidence for glaciation in the Villa Mónica Formation (VMF) at the base of the succession comes in the form of iron-rich laminated sediments containing dropstones composed predominantly of basement crystalline rocks and quartzites that, are sequentially overlain by a phosphatic mudstone and a ~40m thick stromatolitic dolomite. Subtidal facies preserve columnar forms similar to post-glacial tubestone stromatolites seen in the Neoproterozoic records. These morphologies suggest rapid growth associated with elevated seawater alkalinity and high rates of carbonate accumulation records. The VMF dolomites in our four studied sections near Olavarría-Sierras Bayas area reveal a pronounced negative-to-positive δ13C up section that is similarly to these cap carbonates and others worldwide. Our sedimentological and geochemical study of the VMF sections reveal consistent carbon and oxygen isotope trends that may be useful for detailed intra-basinal correlations. Samples of the VMF fabric-retentive dolomite preserve an unusually narrow range of non-radiogenic strontium isotopic compositions (0.7068 to 0.7070) that are consistent with Cryogenian limestone facies in the potential Namibian and Brazilian equivalents. Exceptional preservation of 87Sr/86Sr compositions suggest the possibility of primary dolomite precipitation in post-glacial seawater, and furthermore that REE patterns and distributions may yield similar insights to redox conditions in the depositional basin. In particular, the VMF dolomites reveal depleted LREE abundances, a negative Ce anomaly, positive La and Gd anomalies, and low Y/Ho values. As a whole, these observations suggest oxidizing post-glacial seawater conditions associated with significant freshwater inputs into the basin. Global warming and increases in primary productivity and organic carbon burial linked to the buildup of oxygen, the positive δ13C trend and the increase in stromatolite biodiversity in the VMF.

Global sources, emissions, transport and deposition of dust and sand and their effects on the climate and environment: a review

Dust and Sand Storms (DSS) originating in deserts in arid and semi-arid regions are events raising global public concern. An important component of atmospheric aerosols, dust aerosols play a key role in climatic and environmental changes at the regional and the global scale. Deserts and semi-deserts are the main source of dust and sand, but regions that undergo vegetation deterioration and desertification due to climate change and human activities also contribute significantly to DSS. Dust aerosols are mainly composed of dust particles with an average diameter of 2 mm, which can be transported over thousands of kilometers. Dust aerosols influence the radiation budget of the earthatmosphere system by scattering solar short-wave radiation and absorbing surface long-wave radiation. They can also change albedo and rainfall patterns because they can act as cloud condensation nuclei (CCN) or ice nuclei (IN). Dust deposition is an important source of both marine nutrients and contaminants. Dust aerosols that enter marine ecosystems after long-distance transport influence phytoplankton biomass in the oceans, and thus global climate by altering the amount of CO2 absorbed by phytoplankton. In addition, the carbonates carried by dust aerosols are an important source of carbon for the alkaline carbon pool, which can buffer atmospheric acidity and increase the alkalinity of seawater. DSS have both positive and negative impacts on human society: they can exert adverse impacts on human’s living environment, but can also contribute to the mitigation of global warming and the reduction of atmospheric acidity. Open image in new window

Ecological Roles of Exploited Sea Cucumbers

Sea cucumbers (Echinodermata: Holothuroidea) are large and abundant members of marine benthic communities. Overexploitation worldwide has raised concern because they have important functions within ecosystems. The ecological roles of commercially exploited sea cucumbers (Aspidochirotida and Dendrochirotida) are reviewed here, focusing on recent literature. Of the more than 70 species commercially exploited, at least 12 regularly bury into sand and mud, playing major roles in bioturbation. Most aspidochirotids are deposit-feeders, reducing the organic load and redistributing surface sediments, making them bioremediators for coastal mariculture. Sea cucumbers excrete inorganic nitrogen and phosphorus, enhancing the productivity of benthic biota. This form of nutrient recycling is crucial in ecosystems in oligotrophic waters such as coral reefs. Feeding and excretion by sea cucumbers also act to increase seawater alkalinity which contributes to local buffering of ocean acidification. Sea cucumbers host more than 200 species of parasitic and commensal symbionts from seven phyla, thereby enhancing ecosystem biodiversity. They are preyed on by many taxa, thereby transferring animal tissue and nutrients (derived from detritus and microalgae) to higher trophic levels. Overexploitation of sea cucumbers is likely to decrease sediment health, reduce nutrient recycling and potential benefits of deposit-feeding to seawater chemistry, diminish biodiversity of associated symbionts, and reduce the transfer of organic matter from detritus to higher trophic levels. Ecosystem-based fisheries management needs to consider the importance of sea cucumbers in marine ecosystems and implement regulatory measures to safeguard their ecological roles.

INTERACTIONS BETWEEN HYDROLOGY AND BENTHIC COVERAGE AT ROCAS ATOLL

Abiotic parameters and benthic coverage were determined in shallow habitats at Rocas Atoll. It was found daily and seasonal variations on seawater characteristics related to tides, pluviometry, daily solar cycle, and organisms’ metabolism. Habitats with high coverage of carbonatic organisms were associated with the alkalinity of seawater, whereas habitats with elevated abundance of turf and macro algae were correlated to dissolved inorganic nutrients. Therefore, it is suggested that the availability of nutrients and carbonates in seawater are important for the organism’s distribution in the atoll. Only seven corals settled on the plates during the experiment (Porites spp. and Siderastrea spp.). In order to better constrain the causes of the low coral recruitment in the atoll and predicted the effects of climate changes and ocean acidification over this important reef ecosystem, it is necessary to assess, in high resolution (i.e. week to monthly), the environmental variables that overlaps a short-term period. Keywords: macroalgae; coral reefs; dissolved inorganic nutrients; environment variables.

Behavioural response of bivalve molluscs to calcium hydroxide

Blue mussels (Mytilus edulis) that are cultivated in the marine area around Prince Edward Island, Eastern Canada, are susceptible to the heavy biofouling of their shells by an invasive solitary tunicate, Styela clava, which rapidly proliferates. To mitigate this issue, mussel farmers periodically lift the longlines on which the mussels are suspended out of the water to spray a highly alkaline (~12.7pH units) calcium hydroxide solution onto fouled individuals. Here, we tested the hypothesis that calcium hydroxide exerts behavioural stress on mussels and other bivalves. Field surveys revealed that the alkalinity of the seawater in the vicinity of longlines increased (9.3–11.7pH units) immediately after treated mussel sleeves were returned into the water column. Thereafter, pH values declined rapidly, and met federal water quality guidelines (7.0–8.7pH units) within 3.1±0.5min (range 0.3–10.5min, n=31 sleeves). Cultivated mussels challenged to both emersion and calcium hydroxide closed their valves for 14.0±3.3min (n=18) compared to 6.5±1.6min (n=17) by control mussels (emersion only). We subsequently assessed how three benthic bivalve species (M. edulis, Crassostrea virginica (eastern oyster) and Argopecten irradians (bay scallop)) respond to weak (pH≤9.2) but sustained (3-h daily for 3days) alkalinity conditions. All three species consistently responded by completely or partially closing their valves. However, all behavioural responses were short-lived (0.2–4.7h), and were generally confined to the treatment period. In conclusion, spraying calcium hydroxide onto cultivated mussels has limited impact on seawater alkalinity and the behaviour of nearby bivalves.

Enhanced weathering of olivine in seawater: The efficiency as revealed by thermodynamic scenario analysis

Enhanced weathering of olivine has been suggested as a measure to lower the atmospheric CO2 level and it might also mitigate ocean acidification. This study aimed to characterise how olivine can weather in seawater, to elucidate the role of secondary precipitation and to ascertain the efficiency in terms of molar CO2 removal per mole of olivine dissolution. Geochemical thermodynamic equilibrium modelling was used, which considered both the variable mineralogical composition of olivine and the kinds of secondary precipitates that may be formed. The advantage is that such an approach is independent from local or regional factors as temperature, related kinetics, mineralogy, etc. The results show that the efficiency falls when secondary precipitates are formed. When Fe-bearing olivine undergoes weathering in an oxic environment, Fe(III) hydroxides will inevitably be formed, and as a result of this acidifying process, CO2 could be released to the atmosphere. This might also enhance ocean acidification when Fe-rich olivine becomes used. Ocean alkalinisation only happens when more than 1mol/kgH2O Mg-rich olivine weathers. Maintenance of supersaturation for calcite or aragonite as holds in seawater reduces the efficiency by about a factor of two compared to the efficiency without secondary precipitation. Precipitation of sepiolite as Mg silicate reduces the efficiency even more. Magnesite precipitation has a similar effect to Ca carbonate precipitation, but according to the literature magnesite precipitation is improbable at ambient conditions and relatively low supersaturation. When less than 0.05mmololivine/kg(seawater) weathers the efficiency is slightly different than at higher intensities, due to strong buffering by seawater alkalinity.