Ocean alkalinity enhancement (OAE) is an emerging carbon dioxide removal (CDR) strategy that leverages the natural processes of weathering and acid neutralisation to durably store atmospheric CO2 in seawater. OAE can be achieved with a variety of methods, all of which have different environmental implications. One widely considered method utilizes electrochemistry to remove strong acid from seawater, leaving sodium hydroxide (NaOH) behind. This study evaluates the impacts of OAE via NaOH (NaOH-OAE) on a coastal plankton bloom, with particular focus on how macronutrient regeneration in the aftermath of the bloom responds to the perturbation. To investigate this, we enclosed a natural coastal phytoplankton community, including coccolithophores, in nine microcosms. The microcosms were divided into three groups: control, unequilibrated (512.1 ± 2.5 µmol kg-1 alkalinity increase) and equilibrated (499.3 ±5.65 µmol kg-1 alkalinity increase). Light was provided for 11 days to stimulate a bloom (light phase) and lights were turned off thereafter to investigate alkalinity and nutrient changes for 21 days (dark phase). We found no detectable effect of equilibrated NaOH-OAE on phytoplankton community and bacteria abundances determined with flow cytometry but observed a small yet detectable restructuring of phytoplankton communities under unequilibrated conditions. NaOH-OAE had no significant effect on alkalinity, NOx- and phosphate regeneration, but increased silicate regeneration by 64% over 21 days under darkness in the unequilibrated treatments where seawater pH was highest (8.65 relative to 7.92 in the control). Additional dissolution experiments with two diatom species supported this outcome on silicate regeneration for one of the two species, thereby suggesting that the effect is species specific. Our results point towards the potential of NaOH-OAE to influence regeneration of silicate in the surface ocean and thus the growth of diatoms, at least under the very extreme NaOH-OAE conditions simulated here.

Ocean alkalinity enhancement (OAE) is an emerging carbon dioxide removal (CDR) strategy that leverages the natural processes of weathering and acid neutralisation to durably store atmospheric CO2 in seawater. OAE can be achieved with a variety of methods, all of which have different environmental implications. One widely considered method utilizes electrochemistry to remove strong acid from seawater, leaving sodium hydroxide (NaOH) behind. This study evaluates the impacts of OAE via NaOH (NaOH-OAE) on a coastal plankton bloom, with particular focus on how macronutrient regeneration in the aftermath of the bloom responds to the perturbation. To investigate this, we enclosed a natural coastal phytoplankton community, including coccolithophores, in nine microcosms. The microcosms were divided into three groups: control, unequilibrated (512.1 ± 2.5 µmol kg-1 alkalinity increase) and equilibrated (499.3 ±5.65 µmol kg-1 alkalinity increase). Light was provided for 11 days to stimulate a bloom (light phase) and lights were turned off thereafter to investigate alkalinity and nutrient changes for 21 days (dark phase). We found no detectable effect of equilibrated NaOH-OAE on phytoplankton community and bacteria abundances determined with flow cytometry but observed a small yet detectable restructuring of phytoplankton communities under unequilibrated conditions. NaOH-OAE had no significant effect on alkalinity, NOx- and phosphate regeneration, but increased silicate regeneration by 64% over 21 days under darkness in the unequilibrated treatments where seawater pH was highest (8.65 relative to 7.92 in the control). Additional dissolution experiments with two diatom species supported this outcome on silicate regeneration for one of the two species, thereby suggesting that the effect is species specific. Our results point towards the potential of NaOH-OAE to influence regeneration of silicate in the surface ocean and thus the growth of diatoms, at least under the very extreme NaOH-OAE conditions simulated here.

The effect of ocean alkalinity enhancement on a coastal phytoplankton community was assessed via a microcosm experiment. The effect of alkalinity enhancement in two scenarios (i) when enclosed seawater was in equilibrium with atmospheric CO2 and (ii) when enclosed seawater was not in equilibrium with atmospheric CO2 were explored. Alkalinity was increased by ~497 umol/kg in these two treatments and plankton communities, carbonate chemistry, dissolved inorganic nutrients, particulate matter and chlorophyll a dynamics monitored over a 22 day period where a spring bloom occurred.

Ocean alkalinity enhancement is a proposed method of marine carbon dioxide removal that enhances the ocean’s uptake of atmospheric carbon dioxide (CO2) and converts it to dissolved bicarbonate for long-term ocean storage. This method of marine carbon dioxide removal has been gaining attention for its potential to durably (10,000+ years) store large amounts of CO2 (Gt+ where 1 Gt = 1 x 10^9 tons), while potentially ameliorating acidification in the vicinity of the alkalinity release. This study focuses on a novel release of electrochemically derived aqueous alkalinity into Sequim Bay, WA, through a previously established wastewater treatment plant (WWTP). This research was made possible through the collaboration of industry, academic, and federal partners, which enabled the establishment of an Ebb Carbon electrochemical mCDR system at the Pacific Northwest National Laboratory in Sequim, WA, for ocean alkalinity enhancement field trials. During these field trials, pH was measured across the WWTP system from the initial alkalinity dosing, throughout the WWTP, and at the outfall. We use the NBS scale for pH throughout this study as it is the scale used in discharge permit limits specified for WWTP and NPDES regulation and compliance monitoring. The background pHNBS of Sequim Bay seawater was between 7.5 to 7.7 for the November and February field tests. The mixing tank's pHNBS was raised to the maximum value permitted for the WWTP (9.0) and maintained across the system (±0.2) during the outfall releases. At the outfall, the elevated pH and alkalinity was quickly diluted, such that the region with a measurable signal was limited to within ~2.5 m of the discharge pipe. We were able to successfully monitor an increase in pHNBS across all four pulses of alkalinity-enhanced seawater discharge during the February 2025 field trial, with peak pHNBS values of 8.3 or 8.1, as recorded by outfall-adjacent YSI Exo 2 sonde and SAMI-pH sensors, respectively. The alkalinity-enhanced seawater did not measurably alter the surrounding waters' temperature, salinity, turbidity, or oxygen. This study provides proof-of-concept for a conservative small-scale release of electrochemically generated alkalinity-enhanced seawater from a coastal outfall.

This dataset contains laboratory experimental data that were collected to examine the effects of elevated levels of carbon dioxide on the growth of Atlantic surfclam (Spisula solidissima), a species that supports both commercial and recreational fisheries in the Northeast United States. Three levels of carbon dioxide enrichment (low, medium, and high) were delivered to surfclams in a 12-week exposure experiment. All treatments were done in 3 replicates (A, B, C). Approximately every 2 to 3 weeks, 12 individuals were removed from each treatment and measurements of length, width, height, dry tissue, and dry shell were recorded. Length was measured across the longest part of the shell, parallel to the hinge. Width was the thickness of the shell, and height was measured form the hinge to the outer edge of the shell. Dry tissue and dry shell samples were dried at 60°C until constant weight was achieved (~5 days). DIC measurements of carbon dioxide enrichment were taken and analyzed on an Apollo SciTech, while pH was measured weekly with a spectrophotometer. Values reported for DIC, pH, temperature, and salinity are the mean of each treatment during the 12-week experiment. The data indicated that increased carbon dioxide affected growth, tissue mass, and shell weight for Atlantic surfclam.

These data characterize treatments and outcomes in laboratory-based ocean acidification experiments conducted that the NOAA NEFSC Howard Laboratory. Experiments vary by species used, scope of study (experiment duration and species’ life-stages examined), and experimental design including number of treatments, levels, and replicates, and the suite of response variables. This experiment used summer flounder (Paralichthys dentatus) as subjects, one treatment (concentration of aqueous pCO2), three treatment levels (775, 1808, and 4714 uatm pCO2, pHs of 7.8, 7.5, and 7.1, respectively), three replicates (replicated downstream from each unique CO2 source), and the following response variables: survival of embryos to hatching and of larvae to age 28 d post-hatching; size, shape, and image-based developmental features of larvae; and histopathologically determined status of key organs (eye, heart, liver, gall bladder, gastro-intestinal tract, epidermis, kidney, spinal cord, and muscles) and cranio-facial and skeletal elements.

To study the effects of ocean acidification we conducted laboratory experiments with adult ovigerous females of the economically important southern Tanner crab, Chionoecetes bairdi. Ovigerous females were reared in one of 3 treatments: control (ambient pH ~8.1), pH 7.8, and pH 7.5 for 2 years. The adult female sizes used for the experiments ranged from 87 to 112 mm among the three treatments. Throughout the experiment , pH and temperature were measured daily in each of the 3 treatments. The mean daily temperature was 5.0 C, varied seasonally from a low of ~1 C in January 2012 to a high of ~ 9C in August 2011, and did not vary between treatments. pH remained significantly different among the treatments. Brooding duration for each female was defined as beginning the day of egg extrusion in 2012 and ended when larval hatching began in 2013. Mean brood duration ranged from 340 to 366 days. Magnesium and calcium content were determined at the end of the experiment from a portion of exoskeleton. Magnesium did not differ with pH treatment but the ratio of magnesium to calcium did differ among treatments.

Marine carbon dioxide removal (mCDR) approaches are under development to mitigate the effects of climate change by sequestering carbon in stable reservoirs, with potential co-benefits of local reduction of coastal acidification impacts. One such method is ocean alkalinity enhancement (OAE). A specific OAE method is the generation of aqueous alkalinity via electrochemistry to enhance the alkalinity of the receiving water by the extraction of acid from seawater, thereby avoiding issues of solid dissolution kinetics and the release of impurities into the ocean from alkaline minerals. While electrochemical acid extraction is a promising method for increasing the carbon dioxide sequestration potential of the ocean, the biological effects of increasing seawater alkalinity and pH within an OAE project site are relatively unknown. This study aims to address this knowledge gap by testing the effects of increased pH and alkalinity, delivered in the form of aqueous NaOH, on two eelgrass epifauna in the U.S. Pacific Northwest, Taylor’s sea hare (Phyllaplysia taylori) and eelgrass isopod (Idotea resecata), chosen for their ecological importance as salmon prey and for their roles in eelgrass ecosystems. Four-day experiments were conducted in closed bottles to allow measurements of the evolution of carbonate species throughout the experiment with water refreshed twice daily to maintain elevated pH, across pHNBS treatments ranging from 7.8 to 9.3. Sea hares experienced mortality in all pH treatments, ranging from 37% mortality at pHNBS 7.8 to 100% mortality at pHNBS 9.3. Isopods experienced lower mortality rates in all treatment groups, ranging from 13% at pHNBS 7.8 to 21% at pHNBS 9.3, which did not significantly increase with higher pH treatments. These experiments represent an extreme of constant exposure to elevated pH and alkalinity, which should be considered in the context of both the natural variation and the dilution of alkalinity experienced by marine communities across an OAE project site. Different invertebrate species will likely have different responses to increased pH and alkalinity, depending on their physiological vulnerabilities. Investigation of the potential vulnerabilities of local marine species will help inform the decision-making process regarding mCDR planning and permitting.

This dataset contains laboratory experiment data that were collected to examine the effects of elevated levels of CO2 on the growth, survival, otolith (ear bone) condition and the skeleton of juvenile scup, Stenotomus chrysops, a species that supports both commercial and recreational fisheries. Increasing amounts of atmospheric carbon dioxide from human industrial activities are causing changes in global ocean carbon chemistry resulting in a reduction in pH, a process termed ocean acidification. Studies have demonstrated adverse effects on calcifying organisms, particularly some invertebrates, corals, sea urchins, pteropods, and coccolithophores. It is important to determine which species are sensitive to elevated levels of CO2 because of the potential impacts to ecosystems, marine resources, biodiversity, food webs, populations and effects on human communities and economies. There have been few studies examining the effects of ocean acidification on marine fish, particularly the juvenile stages of species that support important fisheries. These data demonstrated that elevated levels of pCO2 (>1300 micro-atm) had no statistically significant effect on growth, survival, or otolith condition after 8 weeks of rearing. There was a trend towards a greater gain in weight and length in scup exposed to the mid-level (1726 micro-atm) and the high level (2614 micro-atm) treatments of pCO2 when compared to the fish in the control (1205 micro-atm) treatments, but these differences were not statistically significant. X-ray analysis of the fish revealed a slightly higher incidence of hyper-ossification in the vertebrae of a few scup from the highest treatments compared to fish from the control treatments. The study's results show that juvenile scup are tolerant to increases in levels of environmental pCO2, possibly due to conditions this species encounters in their naturally variable environment.

Black sea bass (Centropristis striata) and scup (Stenotomus chrysops) compose important recreational and commercial fisheries along the United States Atlantic coast. Black sea bass is a temperate species, associated with reef habitat. Wild stocks and landings have been decreasong in recent decades. The demand for black sea bass exceeds supply, and the high market value has prompted research to evaluate their potential for commercial aquaculture. Recent studies conducted at the National Marine Fisheries Service, Milford, CT laboratory examined growth rates of juvenile scup fed commercial diets. This and other on-going studies at Milford have shown scup to acclimate quickly to tank conditions in the laboratory, and to exhibit rapid growth rates. These studies indicate the possibility that scup have potential as a candidiate species for commercial aquaculture. Studies with both fish species suggest they are interesting species for studies of the effects of ocean acidification because of their economic importance as fisheries species. These studies focused on laboratory-based experiments to measure the biological effects of elevated levels of CO2 on embryos of these important marine finfish. Adult black sea bass were naturally conditioned and spawned in the laboratory by photo-thermal manipulation. Adult scup were strip-spawned at sea and their eggs were fertilized at sea. The fertilized eggs of both species of fish were exposed to two treatment levels of pCO2 and one control level, with three replicates per treatment and the controls. Measurements of biological effects included percent hatch, viable embryos, abnormal embryos, and dead embryos. Measurements of dissolved oxygen concentration, percent oxygen saturation, temperature, salinity and pH were taken daily in each treatment container and the controls. Samples of seawater were taken at the time of intial experimental setup and at the time of hatching from each container for analyses of dissolved inorganic carbon (DIC), and analyses of pH by spectrometry.