The Gulf and Lower St. Lawrence Estuary have experienced major environmental change over the past century, including the development of hypoxic bottom waters and their simultaneous warming and acidification. Here, we use biogeochemical observations collected during the 2021–2023 TReX project as well as historical data, combined with a tracer-calibrated 1D Advection-Diffusion model with variable boundary conditions to represent dissolved oxygen (DO) and dissolved inorganic carbon (DIC) dynamics within the core of the oxygen minimum zone (27.15–27.3 kg m-3 isopycnals) of the Laurentian Channel. The rate of in-channel oxygen utilization in the deep layer was nearly invariant from 2003 to 2023 at 21.1 ± 2.5 µmol kg-1 yr-1 and the DIC accumulation rate was estimated to be 18.3 ± 2.5 μmol kg-1 yr-1. Using δ13CDIC data, we assess the effect of microbial organic matter remineralization processes and dilution of the 13CDIC pool (−6.6×10-3 ‰ per μmol of added metabolic DIC). These data and the use of a tracer-calibrated model to resolve advection and mixing dynamics reconcile differences in prior estimates of biogeochemical transformation rates. Finally, we apply the model to the mitigation scenario proposed by Wallace et al. (2023) for artificial re-oxygenation of the Laurentian Channel bottom waters using pure oxygen. We estimate that the injection of ~8.3 × 105 tonnes yr-1 of oxygen, equivalent to an additional 55 μmol kg-1 relative to the 2023 boundary concentration proximal to the Cabot Strait, would be required to achieve and maintain above hypoxic levels (>62.5 μmol kg-1) at the head of the Laurentian Channel. Using the model, we estimate the time required to re-establish steady-state along-channel distributions of DO and DIC following a change in offshore boundary conditions to be about 10 years, or twice the along-channel transit time.
Continue reading ‘The coupled oxygen and carbon dynamics in the subsurface waters of the Gulf and Lower St. Lawrence Estuary and implications for artificial oxygenation’Posts Tagged 'North Atlantic'
The coupled oxygen and carbon dynamics in the subsurface waters of the Gulf and Lower St. Lawrence Estuary and implications for artificial oxygenation
Published 7 July 2025 Science ClosedTags: biogeochemistry, chemistry, mitigation, modeling, North Atlantic, regionalmodeling
Data-driven modeling of 4D ocean and coastal acidification in the Massachusetts and Cape Cod Bays from surface measurements
Published 7 July 2025 Science ClosedTags: chemistry, modeling, North Atlantic, regionalmodeling
Abstract
A significant portion of atmospheric emissions is absorbed by the ocean, resulting in acidified seawater and altered carbonate composition that is harmful to marine life. Despite detrimental effects, assessing ocean and coastal acidification (OCA) is difficult due to the scarcity of in situ measurements and the high costs of computational modeling. We develop a parsimonious data-driven framework to model indicators of OCA and test it in the Massachusetts Bay and Stellwagen Bank, a region with fishing and tourism industries affected by OCA. First, we trained a neural network to predict in-depth fields for temperature and salinity using surface quantities from satellites and in situ measurements . The relationship between 2D surface and 3D properties is captured through the in-depth modes and coefficients obtained from principal component analysis applied to a high-resolution historical reanalysis data set. Next, we used Bayesian regression methods to estimate region-specific relationships for in-depth total alkalinity (TA), dissolved inorganic carbon (DIC), and aragonite saturation state as functions of temperature, salinity, and chlorophyll. Lastly, 4D daily field predictions are generated from surface measurements with a spatial resolution of 4 km horizontally and 45 sigma levels vertically. The model’s performance is evaluated using withheld measurements across depths, locations, and seasons with RMSEs of 1.59°C, 0.31 PSU, 37.54 mol, 39.40 mol, and 0.42 for temperature, salinity, TA, DIC, and , respectively, at one withheld location. The framework is useful for understanding OCA and includes uncertainty quantification for future planning and optimal sensor placement.
Plain Language Summary
About a quarter of carbon dioxide emissions in the atmosphere is absorbed by the oceans. When this carbon dioxide dissolves in seawater, it results in ocean acidification (OA). A useful indicator of OA is the saturation state of aragonite, a type of calcium carbonate used by organisms that form shells. However, understanding the effects of OA is difficult due to the lack of observations and the high cost and complexity of modeling. We present a data-driven approach to model carbonate chemistry using readily available observations from satellites and low-cost sensors. Given surface measurements of temperature, salinity, and chlorophyll, our machine learning model produces temperature, salinity, total alkalinity, dissolved inorganic carbon, and aragonite saturation state covering spatial (latitude, longitude, and depth) and temporal domains for these variables. Compared to withheld observations, our model achieved reasonable accuracy across many seasons and depths, a level of resolution not matched by other models for the same set of inputs. Our model is useful for monitoring, decision-making, and future planning.
Key Points
- We present a data-driven approach to rapidly model 4D carbonate chemistry fields given readily available surface observations
- By using training data from both physics simulations and field observations, the model achieves very high resolution with minimal inputs
- The step-by-step method can be reproduced in other regions or for new data, and includes uncertainty quantification for decision-making
Increased temperature and acidification elevate the risk of starvation in American lobster larvae
Published 4 July 2025 Science ClosedTags: biological response, crustaceans, laboratory, morphology, multiple factors, North Atlantic, physiology, reproduction, temperature
The geographic range of the American lobster, Homarus americanus, spans a steep thermal gradient along the coastal Northwest Atlantic. As CO2 emissions increase globally, this range is rapidly warming and acidifying. Larval H. americanus hatch with a finite amount of maternally sourced lipid stores in their yolk sac, which provide an energetic buffer during the intermediate period between hatch and first feed. This study examines the response of newly-hatched, unfed H. americanus larvae to the combined effects of elevated pCO2 and temperature. Using a space-for-time approach, we compared larvae of two distinct sub-populations from thermally contrasting regions: Rhode Island, at the warmer, southern limit of the species range, and Midcoast, Maine, a cooler northern region. Average larval initial post-hatch weight was similar across regions and variability therein could be explained by maternal effects. Under 6 days of starvation, larvae from the two regions lost ∼14% of their initial dry weight and 25% of their Carbon weight. Still, end-century elevated temperature or acidification did not substantially alter those rates for larvae from either region. However, under an identical range of conditions over the 6-day experiment, larvae from the warmer regime maintained relatively stable oxygen consumption rates, while those from the cooler regime started 50% higher, then dropped by 80% within 2 days. If depressed metabolic functioning translates to reduced feeding efficiency for cool regime larvae, our findings suggest that subpopulations in the southern edge of the species range have a relative advantage in food-scarce environments under these conditions, adding to previous evidence for countergradient variation in this species. Further analysis of total fatty acid losses conducted on Midcoast larvae suggested starved larvae exposed to elevated temperature (19°C) experienced considerably greater losses of key lipid groups than larvae under ambient conditions (16°C, 400 ppm), particularly within the first 2 days of exposure. Our results highlight the short time frames over which ocean warming can accelerate the depletion of energy stores and make larvae more vulnerable to starvation.
Continue reading ‘Increased temperature and acidification elevate the risk of starvation in American lobster larvae ‘First study of seawater carbonate chemistry variability in a portion of the southern Atlantic coast of Cameroon: impact of organic pollution
Published 2 July 2025 Science ClosedTags: biogeochemistry, chemistry, field, North Atlantic
The carbonate system variability and acidification process remain little understood in the coastal ocean of Cameroon. The aim of this study was to assess the variability of the carbonate system in a portion of the southern coast of Cameroon, and the influence of local seawater physicochemical and biological properties on keys parameters of this system. The study was carried out at three fixed sampling stations (Bp, Kb, and Eb), from September 2021 to August 2022 involving all the seasons encountered in the study area. The carbonate system was determined from Total alkalinity (TA), pH, temperature and salinity, using the CO2SYS_xls program. In addition, nutrients (nitrate, nitrite, phosphate and nitrogen ammonia) and chlorophyll-a data were collected simultaneously at each station. The results showed a high variability of the carbonate system parameters on both temporal and spatial scale. TA and bicarbonate ions (HCO3− ) were significantly different between the large rainy season (LRS) and small rainy season (SRS), while CO2 and CO2 partial pressure (pCO2) were significantly different between Kb and Eb sampling stations (p-value < 0.05). The critical thresholds for ocean acidification (OA) seems to not been reached in the southern coastal ocean of Cameroon, given the means values of pH (8.14 ± 0.17), aragonite (3.31 ± 1.3 Ω) and calcite (5.3 ± 2.05 Ω) saturation states obtained. Salinity appears as the main driver of the variability of TA in the study area, while, nitrogen ammonia and the dissolved carbon dioxide from the degradation of organic matter, respiration and atmospheric absorption, appears as the drivers of pH variation. The large rainy season (LRS) seems to be the most critical period for OA sensitive organisms, while the Bp station looks most vulnerable.
Continue reading ‘First study of seawater carbonate chemistry variability in a portion of the southern Atlantic coast of Cameroon: impact of organic pollution’Non-additive phospholipidomic responses to ocean warming and acidification drive intraspecific variation in cell membrane vulnerability in a marine ectotherm
Published 1 July 2025 Science ClosedTags: adaptation, biological response, crustaceans, laboratory, multiple factors, North Atlantic, otherprocess, physiology, temperature
Highlights
- Shrimp show non-additive phospholipidome responses to combined OW and OA.
- Synergistic and antagonistic responses are origin- and scenario-dependent.
- Physiological shifts emerge when OA occurs near shrimp’s thermal limits.
- Shrimp show potential local adaptation/acclimatisation of cell membrane phenotypes.
- Shrimp cell membrane vulnerability to combined OW and OA is origin-dependent.
Abstract
The lipidome is fundamental to the good functioning of cells and organisms. However, its role in species acclimatisation and adaptation to global changes remains overlooked. Investigating intraspecific variation in lipidome responses to combined global change drivers is therefore paramount to predict species’ vulnerability in future oceans. Here, we profiled the phospholipidome of the Northern shrimp, Pandalus borealis, from four different origins in the Northwest Atlantic, within an orthogonal design of ocean warming (OW) and acidification (OA) scenarios. We report complex origin-dependent non-additive responses under combined global changes. Shrimp display a high degree of intraspecific variation with distinct profiles of synergism, antagonism or temperature-driven phospholipidome responses when OA is superimposed on OW. Shrimp from the southernmost origin are only sensitive to OW, whilst those from the other three origins respond to combined OW and OA. These patterns involve changes in cellular membranes’ unsaturation, fluidity, curvature and thickness, underlying differential intraspecific cellular vulnerability to global changes. The isolated effects of OA are subtler, visible only in shrimp from the St. Lawrence Estuary (SLE). Shrimp from SLE also show the most pronounced phospholipidome remodelling, allowing them to acclimate to combined OW and OA. Whilst SLE shrimp seem most sensitive to global changes, those from the northernmost origins (Newfoundland and Esquiman Channel) display the greatest cellular vulnerability under combined OW and OA. Our findings evidence the highly complex interplay of OW and OA in remodelling marine ectotherms’ phospholipidomes, with direct implications for prioritising conservation efforts on populations most vulnerable to global changes.
Continue reading ‘Non-additive phospholipidomic responses to ocean warming and acidification drive intraspecific variation in cell membrane vulnerability in a marine ectotherm’Effects of acidification and habitat loss on coastal nitrogen cycling dynamics
Published 29 May 2025 Science ClosedTags: biogeochemistry, chemistry, field, North Atlantic
Excess nitrogen (N) in urbanized coastal waterways from wastewater or agricultural inputs causes widespread habitat decline due to harmful algal blooms, poor water quality, and changes to seawater chemistry. For example, during an algal bloom, nocturnal respiration and seasonal decomposition of algal biomass release carbon dioxide (CO2) into the water column, which lowers seawater pH in a process known as coastal acidification. Additionally, high N loading leads to the death of salt marsh vegetation communities, in turn leading to salt marsh erosion and loss, with implications for coastal stability. Estuarine habitats such as seagrass beds and salt marshes are known as hotspots of microbially-mediated nutrient cycling, but it has been unclear how stressors caused by N loading (i.e., coastal acidification, macroalgal blooms, and salt marsh erosion/loss) impact vital biogeochemical processes in these habitats. This dissertation explored the effects of acidification on nutrient cycling in eelgrass beds and salt marshes (in Shinnecock Bay, Long Island and Jamaica Bay, New York City, respectively), as well as the impacts of salt marsh loss on N dynamics in eutrophic urban estuaries. Results show that lower seawater pH shifted sediments in eelgrass beds from net sources of reactive N to net N sinks, with implications for water quality mitigation. In salt marshes, acidification appeared to have no effect on nutrient cycles. Instead, N cycling in salt marshes is likely to respond to erosion and increasing inundation. De-vegetated marsh sediments showed net N release compared to still-intact vegetated marsh areas, suggesting that losses in salt marsh habitat may contribute to water quality decline and algal bloom conditions, as well as perpetuate further habitat loss. This body of research addressed critical gaps in understanding the processes that underpin coastal habitat function under various N loading-related stressors, such as acidification-induced impacts on nitrification and denitrification in eelgrass beds and changes to sediment N cycling as marshes erode. The former finding may suggest that N loading may be at least partially mitigated during a coastal acidification event, while the latter finding suggests that marsh restoration may prevent loss of N removal services. The applications of this research are likely to become increasingly critical, as these habitats serve as vital natural infrastructure against sea level rise, storm surges, and coastal change.
Continue reading ‘Effects of acidification and habitat loss on coastal nitrogen cycling dynamics’Exploring the land-ocean biogeochemical and microbial connectivity in the Ría de Vigo (NW Iberian Peninsula) through submarine groundwater discharge
Published 20 May 2025 Science ClosedTags: biogeochemistry, BRcommunity, chemistry, community composition, field, molecular biology, North Atlantic, otherprocess, prokaryotes
Highlights
- SGD affects the carbonate system, methane and nitrous oxide content of the embayment
- Solute composition of SGD largely impacted by subterranean estuary reactivity
- Contrasting poor microbial connectivity across the different aquatic environments
- Subterranean estuaries may act as microbial boundaries in the aquatic continuum
Abstract
Increasing evidence demonstrates the widespread occurrence of submarine groundwater discharge (SGD) in coastal zones, where it may influence biogeochemistry and microbial ecology. Here, we analyze the biogeochemical composition and microbial communities across diverse aquatic environments in a highly productive coastal system (Ría de Vigo, NW Iberian Peninsula), influenced by significant fresh SGD, to assess the extent of microbial and biogeochemical connectivity—i.e., mass transfer—among them. Samples were collected from surface and deep porewaters from two subterranean estuaries (STEs), surface seawater, riverine water, and continental groundwater. These samples were analyzed for a comprehensive set of microbial and biogeochemical variables, including radioisotopes used as SGD tracers. A significant correlation between SGD tracers and carbonate system parameters, N2O, and CH4 concentrations in surface seawater indicates SGD influences biogeochemistry of the embayment. However, some of these solutes do not originate from continental groundwater but are produced in the local STEs, which act as biogeochemical reactors modifying fresh SGD. The findings also reveal highly diverse microbial communities, with higher diversity in STEs due to the variety of niches present. Indicator taxa included the phyla Euryarchaeota, Chloroflexi, Omnitrophicaeota, and the family Nitrosopumilaceae in STEs; the phylum Cyanobacteria and the family Burkholderiaceae in freshwater endmembers; and the Flavobacteriaceae and Cryomorphaceae families in seawater. Most operational taxonomic units (∼87%) were unique to a single environment (river, continental groundwater, coastal water, or STE), showing STEs limit subterranean microbial transfer between groundwater and marine ecosystems. Our results highlight STEs as reservoirs of diversity and zones of intense biogeochemical reactivity.
Continue reading ‘Exploring the land-ocean biogeochemical and microbial connectivity in the Ría de Vigo (NW Iberian Peninsula) through submarine groundwater discharge’A widely distributed clam, Chama macerophylla, exhibits mixed responses to single and combined warming and acidification stress
Published 7 May 2025 Science ClosedTags: biological response, laboratory, mollusks, morphology, multiple factors, North Atlantic, physiology, temperature
Bivalves enhance microhabitat complexity and improve water clarity in coastal ecosystems. Ocean warming (OW) and acidification (OA), pose a significant threat to bivalves in shallow continental shelf environments where stressors can be amplified and uncoupled. This study investigated global change effects on Chama macerophylla, a widespread clam in the Gulf of Mexico. Laboratory experiments assessed physiology and shell mineralogy of C. macerophylla exposed to different levels of OW, OA, and combined stressors (OWA). Temperature and carbonate chemistry from collection sites confirm ambient (control) treatments used in experiments were commonly observed in the field. Clam oxygen consumption increased with OW and, initially, with OA. After 30 days, clams within moderate and extreme OA lowered consumption. In contrast, clam oxygen consumption declined in OWA treatments. Net calcification was only affected by OA with higher calcification in the extreme treatment than in moderate. Meat weight relative to shell weight (condition) was negatively affected by OW in the extreme treatment. Shell accretion, clearance rates, and mineralogy were unaffected by OW, OA, and OWA. This is the first report of a bimineralic shell for this species. Results highlight resilience of clam survivorship to stressors. OW appears to increase metabolism and drive declines in clam condition (meat: shell weight). OWA may have a greater impact on C. macerophylla than single stressors, particularly if reduced oxygen consumption is sustained. This research underscores the need to understand long-term stress on bivalves. Future research should examine both size-age relationships with global stressors and the role of acclimation to prolonged stress.
Continue reading ‘A widely distributed clam, Chama macerophylla, exhibits mixed responses to single and combined warming and acidification stress’Aragonite saturation state as an indicator for oyster habitat health in the Delaware Inland Bays
Published 28 April 2025 Science ClosedTags: chemistry, field, North Atlantic
Aragonite and calcite are important nutrients for bivalves who biomineralize calcium carbonate in the water to form their outer shells. Ocean acidification can lead to a decrease in carbonate ions making forming these shells difficult. When the saturation state falls below a certain threshold (Ω < 1), it can cause oyster shells to dissolve. Therefore, measuring the Aragonite Saturation State yields crucial insight into the suitability of habitats to support oyster growth and productivity. Physiochemical water quality parameters were monitored from May to October 2020-2023. Using Seacarb, the aragonite-calcite saturation state was calculated using the following water quality parameters: temperature, salinity, alkalinity, and pH as inputs. Calcium hardness and dissolved oxygen was also measured to determine whether values were at a recommended threshold for shellfish hatcheries. There were fluctuations in the saturation states at each site, and oftentimes the values were undersaturated, especially during the cooling months. Spearman heatmaps demonstrate significant positive correlations between temperature and salinity (p = 0.46); pH and aragonite (p = 0.72); and alkalinity and aragonite (p = 0.51). This project aimed to determine the feasibility of different sites in supporting the establishment of oyster farms and oyster restoration efforts based on water quality conditions.
Continue reading ‘Aragonite saturation state as an indicator for oyster habitat health in the Delaware Inland Bays’Cold spells, fresh waves, and the biogeochemical response in the North Atlantic cold anomaly region
Published 22 April 2025 Science ClosedTags: biogeochemistry, chemistry, field, North Atlantic
Regional effects of marine cold spells (MCS, periods of anomalous cooling), their impact on ecosystem biogeochemistry, and link to salinity extremes remain underexplored. A case in point is North Atlantic’s Cold Anomaly (CA) region (known as the “cold blob”), which hits record low temperatures during 2014–16 while most of the global ocean warmed. Using up to 42 years of observations, we characterize the CA as a manifestation of both MCS and Fresh Waves (FW, low salinity extremes) and analyze the surface biogeochemical response. We observe a quasiperiodic pattern of MCS from the 1980s and FW (at least) from the 1990s to early 2020s in the CA region with alternations from cool and freshwater to warm and saline conditions. Since 1990s, the CA region appears to be potentially undergoing MCS and FW compound events that are more frequent and prolonged but less intense than other North Atlantic areas. The 2014‐16 CA was among the most widespread and prolonged MCS and FW events associated with a deeper mixed layer and distinct biogeochemical signature, including elevated nutrients and oxygen, an overall increased chlorophyll‐a and intensified ocean acidification. These resultssuggest that MCS could mitigate certain climate change effects through cooling and enhanced productivity, while exacerbating others such as ocean acidification. We compare 2014–16 CA region effects with those of Pacific’s warm blob, identifying contrasting behaviors from physical processes to biogeochemical impacts and discussing a common atmospheric driver. Our findings emphasize the need to further study ecological responses to MCS in the North Atlantic.
Continue reading ‘Cold spells, fresh waves, and the biogeochemical response in the North Atlantic cold anomaly region’The Piver’s Island coastal observatory – a decade of weekly+ observations reveal the press and pulse of a changing temperate coastal marine system
Published 16 April 2025 Science ClosedTags: chemistry, field, North Atlantic
Historically, oceanographic time-series have focused on long-term measurements of large open ocean gyres; yet, the coastal oceans, with their high productivity, tidal impacts, human feedbacks, and land-sea coupling, represent critical regions for predicting ocean dynamics and biogeochemistry under global change. The Piver’s Island Coastal Observatory (PICO) time-series, located in the second largest estuarine system on the US East Coast (Albemarle-Pamlico Sound), comprises more than a decade of weekly (or more frequent) measurements of core physical, chemical, and biological oceanographic variables. PICO provides insight into a coastal, mesotrophic ecosystem in an ecologically-diverse and biochemically-active region impacted by global change. Here, we report on a decade of observations focusing on pulse and press ecosystem changes. We observe strong mean annual cycles in environmental variables including temperature (10.1-28.9°C), pH (7.89-8.12), dissolved inorganic carbon (DIC: 1965 – 2088 µM), chlorophyll (2.54-5.77 mg Chl m-3), upon which are layered episodic disturbances (e.g., tropical cyclones) that dramatically and persistently (>1 month) impact this ecosystem. Among other variables, long term trends in pH (-0.004 ± 0.001 y-1; p<0.01), DIC (-9.8 ± 1.5 µM y -1; p<0.01) and chlorophyll (-0.17 ± 0.02 µg L-1 y-1; p<0.01) are exceeding those observed in the open ocean, suggesting an ecosystem in flux. These analyses provide a benchmark for future studies of the impact of changing climate and oceanographic climatology; further research will use this long-term research to developed targeted sampling and experimental manipulations to better understand ecosystem structure and function.
Continue reading ‘The Piver’s Island coastal observatory – a decade of weekly+ observations reveal the press and pulse of a changing temperate coastal marine system’Benthic biogeochemical processes and fluxes in the hypoxic and acidified northern Gulf of Mexico (nGoM), part I: carbonate dissolution from in situ microprofiles
Published 14 April 2025 Science ClosedTags: biogeochemistry, chemistry, field, North Atlantic
Highlights
- High resolution in situ pH and O₂ microprofiles at the sediment-water interface.
- Benthic measurements of carbonate system parameters, including pH, DIC, TA, Ca2+.
- Large decrease in oxygen concentrations in overlying water, accompanied by DIC accumulation and a pH drop.
- Undersaturation with respect to aragonite and occasionally calcite.
- No significant dissolution of calcium carbonate minerals detected.
Abstract
The northern Gulf of Mexico (nGoM) experiences seasonal coastal hypoxia due to nutrient enrichment from the Mississippi-Atchafalaya River basin, leading to one of the world’s largest hypoxic zones. In these shallow zones, benthic processes play an essential role in driving/maintaining deoxygenation and acidification of bottom waters. In this regard, this paper investigates carbonate dissolution processes in surface sediment of the nGoM during hypoxic conditions in summer 2022, as the main acidification feedback mechanism, with a specific focus on the effects of bottom water acidification. A strong linear relationship is observed between oxygen and pH, with a pH difference of 0.37 between the most oxygenated and the nearly anoxic station, reaching a value of 7.63. Using high-resolution techniques, this study combines pH and O₂ microprofiling (200 μm) with benthic measurements of carbonate system parameters (pH, DIC, TA, Ca2+) to assess carbonate dissolution at millimeter-scale resolution. The pH microprofiles reveal a significant decrease in the first 3 cm, with pore water pH reaching values of 6.90 at the most hypoxic station. Despite undersaturation with respect to aragonite and occasionally calcite, Ca2+ profiles indicate no significant carbonate dissolution, suggesting stability of calcium carbonate in these sediments during the summer. This lack of dissolution, likely influenced by the absence of aragonite, and possible inhibitory effects of dissolved organic carbon and orthophosphate, points to a limited buffering capacity in these sediments. These insights are essential for refining models predicting coastal acidification and hypoxia responses to environmental stressors in the nGoM and similar eutrophic systems.
Continue reading ‘Benthic biogeochemical processes and fluxes in the hypoxic and acidified northern Gulf of Mexico (nGoM), part I: carbonate dissolution from in situ microprofiles’New capability in autonomous ocean carbon observations using the autosub long-range AUV equipped with novel pH and total alkalinity sensors
Published 11 April 2025 Science ClosedTags: chemistry, methods, North Atlantic
The development of marine autonomous platforms has improved our capability to gather ocean observations at fine spatial scales and high temporal frequency, which can be used to better measure, characterize, and model ocean carbon. As part of the OCEANIDS program, novel carbonate sensors were integrated into the Autosub Long-Range (ALR) autonomous underwater vehicle (AUV) and deployed in the Celtic Sea. Autonomous Lab-On-Chip (LOC) sensors measured pH and total alkalinity (TA) while onboard the ALR. Using interpolation, the ALR-sensor data set is compared against CTD co-samples. The average differences between the LOC sensor and co-sample pH range from −0.011 to −0.015. The TA sensor data agrees with co-samples within 1–2 μmol kg–1 on average. Biogeochemical water properties differing between CTD and ALR observations reveal correlations to carbonate parameter variations. The LOC sensors enabled the characterization of the marine carbonate system from autonomous subsurface measurements for the first time. Sensor pH and TA data were used to calculate dissolved inorganic carbon (DIC), partial pressure of CO2 (pCO2), and aragonite saturation state (ΩAr) and are compared with CTD co-samples with mean residuals of 4–7 μmol kg–1, 10–17 μatm, and −0.03 to −0.06, respectively. Future perspectives on sensor deployment and analysis are discussed.
Continue reading ‘New capability in autonomous ocean carbon observations using the autosub long-range AUV equipped with novel pH and total alkalinity sensors’Long-term monitoring of hydrological dynamics and phytoplankton biomass indicator in three shellfish ecosystems of the English Channel (2000-2024)
Published 11 April 2025 Science ClosedTags: biogeochemistry, chemistry, field, North Atlantic
This study investigates the long-term monitoring of physico-chemical parameters and biogeochemical cycles in coastal ecosystems, focusing on three stations in Normandy: Blainville-sur-Mer, Saint-Vaast-la Hougue, and Utah Beach. Over a 24-year period, we analyzed trends in temperature, pH, chlorophyll a concentrations, and nutrient levels, aiming to assess the impacts of climate change and human activities on marine ecosystems. Results show a consistent rise in winter temperatures, particularly since 2013, alongside increasing ocean acidification, especially at Blainville-sur-Mer. These trends suggest potential consequences for planktonic communities and mollusk health. Nutrient analysis revealed significant variations, including high ammonium concentrations on the East coast and a gradual decline in phosphates over the last 15 years, highlighting the influence of anthropogenic activities. The study also identified nutrient limitations, with phosphorus dominating the East coast and nitrogen on the West coast. Our findings emphasize the need for effective nutrient management strategies to mitigate the effects of climate change and human impact, ensuring the sustainability of coastal ecosystems and aquaculture practices. This long-term monitoring is crucial for understanding ecological dynamics and guiding future coastal zone management in the face of global environmental changes.
Continue reading ‘Long-term monitoring of hydrological dynamics and phytoplankton biomass indicator in three shellfish ecosystems of the English Channel (2000-2024)’Cold seeps and coral reefs in northern Norway: carbon cycling in marine ecosystems with coexisting features
Published 31 March 2025 Science ClosedTags: biogeochemistry, biological response, chemistry, corals, field, North Atlantic
Abstract
Cold seeps and cold-water corals (CWCs) coexist on Northern Norway’s continental shelf at the Hola trough between Lofoten and Vesterålen. Here, cold seeps release methane from the seabed, yet none reaches the sea surface. Instead, the methane dissolves and disperses in the ocean where it is ultimately consumed by methane-oxidizing microorganisms. These microorganisms metabolize methane and release carbon dioxide and dissolved organic matter (DOM), which may impact the biogeochemical habitat of CWCs in close vicinity of cold seeps. We investigated the biogeochemistry of carbon, carbon isotopes, nutrients, DOM compositions, and microbial diversity in the water column. Our results indicated that dissolved inorganic carbon concentrations were 29% higher near cold seeps with modified carbon’s isotopic compositions. The hydrophysical parameters and surface-to-bottom control of sinking particles mainly govern water column productivity and nutrient cycle. DOM compositions implied that the seep-associated microbiomes modify DOM’s chemical diversity and isotopic composition at CWCs and the entire water column near cold seeps. Cold seeps and CWCs coexist in Northern Norway’s continental shelves; however, enhanced water temperatures and consequent increase in methane release at cold seeps may modify the carbon cycling in the area, which could mitigate the ecological role and functioning of CWC reefs in the future.
Plain Language Summary
Cold seeps are geological features that release methane from the seabed to the water column. In oxygenated sea water column, seeping methane is consumed by specialized microbes that convert it into carbon dioxide. Although the increase in carbon dioxide can lead to ocean acidification, cold seeps are often found in the Hola trough of Northern Norway near cold-water corals (CWCs), which are vulnerable to changes in ocean acidity. This raises questions about how these features coexist in the same marine ecosystem and how they impact each other. We investigated the carbon exchange between cold seeps and CWCs by analyzing seawater samples. Our data on nutrients, organic matter, and microbial compositions implied cooccurring carbon processes such as methane oxidation and organic matter synthesis. Notably, cold seeps might support CWCs by producing dissolved organic matter that corals feed on. However, this relationship may be valid for a moderate amount of methane release. If methane release increases, consequent acidification may influence the CWC reefs in the future.
Key Points
- Hola trough of Northern Norway is a natural system offering insights into carbon cycling within coexisting marine ecosystems
- Despite their proximity, cold seeps and coral reefs reveal distinct biogeochemical characteristics in the Hola trough
- Cold seeps and methane oxidation impact the inorganic carbon cycle, yet the exchange of organic carbon might be just as significant
Multi-endmember mixing and primary productivity drive carbonate system variability on a highly heterogeneous, shallow productive bank
Published 27 March 2025 Science ClosedTags: chemistry, field, North Atlantic
This study presents the first high-resolution spatial analysis of carbonate chemistry on Georges Bank, a highly productive shallow bank located at the southeastern edge of the Gulf of Maine. Despite numerous studies on the hydrography, nutrient chemistry, and biology, regional carbonate chemistry remains unexplored, in particular for near-bottom conditions. Observations from cruises in May and October 2021 were used to identify multi-endmember mixing, and a Bayesian mixing model was applied to temperature and salinity to separate water mass mixing from non-conservative drivers such as net community production, air–sea exchange, and other biogeochemical processes/errors. Major findings from this study indicate that carbonate chemistry is highly heterogeneous and driven by multi-endmember mixing, although biological production and respiration were notable while air–sea CO2 exchange was minimal. Five water masses with unique carbonate chemistry were observed that varied by season and with depth, showing complexity that is uncommon in other regions along the US Atlantic coast. In both cruises, a Warm Slope Water intrusion was identified at depth that contained a strong signal of CaCO3 dissolution during the October cruise, observed in situ for the first time in this region. Under a high emissions scenario, our results suggest that much of the bank’s bottom waters may become undersaturated with respect to aragonite by 2100. Together, these findings suggest that the in situ dissolution observed may only worsen with future ocean acidification, with potentially significant implications for ecologically and economically important shellfish species on Georges Bank.
Continue reading ‘Multi-endmember mixing and primary productivity drive carbonate system variability on a highly heterogeneous, shallow productive bank’Molecular evidence for the intermediate disturbance hypothesis in an acidified marine system
Published 25 March 2025 Science ClosedTags: biological response, echinoderms, field, molecular biology, North Atlantic, vents
The Intermediate Disturbance Hypothesis (IDH), postulated by Connell (1978), suggests that ecosystems exhibit higher species diversity when disturbances occur at intermediate scales. In this study, the applicability of the IDH at the intraspecific scales (organismal) was investigated using molecular data. As an experimental perturbation framework, a naturally acidified system located in La Palma Island, Canary Island (Spain) with a sharp fluctuating pH gradient was sampled. Molecular data were obtained from sequences of a fragment of the mitochondrial Cytochrome C Oxidase subunit I gene in two sea urchin species (Arbacia lixula and Paracentrotus lividus) to explore genetic diversity at the organism level. These data were compared with previous metabarcoding results of taxonomic benthic diversity at the community level. Both sea urchin species showed the highest levels of haplotype and nucleotide diversity at the intermediate pH fluctuation zone, mirroring metabarcoding data that revealed the highest levels of taxonomic diversity at the same zone. The results support the validity of the IDH in marine ecosystems affected by strong pH fluctuations and across different levels of biological organization (from organisms to communities).
Continue reading ‘Molecular evidence for the intermediate disturbance hypothesis in an acidified marine system’Food availability, but not tidal emersion, influences the combined effects of ocean acidification and warming on oyster physiological performance
Published 25 March 2025 Science ClosedTags: biological response, growth, laboratory, mollusks, multiple factors, North Atlantic, physiology, reproduction, respiration, temperature
Highlights
- Effects of pH/temperature conditions, tidal treatments, and food levels are studied.
- Ocean acidification and warming enhance the physiological performance of oysters.
- Food level impacts responses to future conditions and disease susceptibility.
- Intertidal oysters increase food intake to compensate for limits during emersion.
Abstract
Many studies on the effects of ocean acidification and warming (OAW) in intertidal mollusks overlook critical factors like tidal emersion and food availability, both of which can shape organisms’ responses. Experiments on intertidal bivalves often use constant immersion and abundant food, which likely underestimate global change impacts and underscore the need for more realistic experiments mimicking natural ecosystems. This study investigated the physiological responses of juvenile Pacific oyster Crassostrea gigas exposed for 81 days to current and OAW conditions (+3 °C, −0.3 pH units) under two tidal treatments (0 vs. 30 % emersion) and two food levels (ad libitum vs. limited). We measured growth, reproduction, food ingestion, respiration, and biochemical traits like energy reserves and membrane fatty acids. At the experiment’s end, oysters were challenged with a viral disease to assess the physiological cost of acclimation and potential trade-offs. Results showed improved oyster physiological performance under OAW with high food level. Nevertheless, food availability emerged as the predominant factor in oyster performance, limiting growth, reproduction, and energy reserves, while increasing oxygen consumption and disease susceptibility. Food deprivation attenuated the beneficial effects of OAW through antagonistic interaction, suggesting physiologically weakened oysters may struggle to adapt to environmental hazards. Finally, tidal treatment had no significant effect, implying that oysters possess physiological compensatory mechanisms, particularly in food acquisition, enabling them to meet nutritional needs during immersion periods. This study provides valuable insights for designing global climate change experiments that align with ecological realism and improves our understanding of the acclimation potential in bivalves facing rapid ocean changes.
Continue reading ‘Food availability, but not tidal emersion, influences the combined effects of ocean acidification and warming on oyster physiological performance’Physical and biogeochemical controls of sea surface pCO2 along the North American Atlantic coastal ocean margins on different time scales
Published 24 March 2025 Science ClosedTags: biogeochemistry, chemistry, modeling, North Atlantic, regionalmodeling
Coastal ocean margins play a crucial role in the global carbon cycle, acting as significant carbon sinks and highly productive ecosystems while being particularly vulnerable to climate change and ocean acidification. Despite their importance, there remains a critical knowledge gap in understanding the complex carbon dynamics and acidification processes in these regions, especially in the North American Atlantic Coastal Ocean Margin (NAACOM), which encompasses diverse and economically vital coastal ecosystems. This dissertation aims to investigate the complex physical and biogeochemical processes controlling inorganic carbon chemistry and ocean acidification processes along the NAACOM on different spatial and temporal scales. Through a series of studies, I address critical gaps in understanding the spatial and temporal variability of surface ocean partial pressure of CO2 (pCO2) and air-sea CO2 fluxes in these regions.
I first evaluate the reliability of multiple pCO2 products in the Gulf of Mexico (GoMx). Our analysis reveals significant spatial and seasonal variations in pCO2 due to complex local non-thermal dynamics, particularly in the Louisiana Shelf and Western Florida Shelf. I find that the GoMx is CO2-neutral overall, but with notable spatial differences in pCO2 trends. However, despite the fact that all the reconstructed data products are capable of providing a reasonable estimated annual mean pCO2 climatology for the GoMx, they are unable to simulate the long-term trend of pCO2 within the GoMx.
To address the limitations in existing pCO2 products, I develop a new regional reconstructed pCO2 product (ReCAD-NAACOM-pCO2) for the entire NAACOM. This product uses a novel two-step approach combining random forest and linear regression. Trained on Surface Ocean CO2 Atlas (SOCAT) observations and various environmental variables, ReCAD-NAACOM-pCO2 demonstrates high accuracy and robustness in capturing regional-scale variations, seasonal cycles, and decadal trends of pCO2 from 1993 to 2021.
Utilizing this new product, I investigate the spatial and seasonal variability of pCO2 and air-sea fluxes across the NAACOM. I reveal a south-to-north decreasing gradient in pCO2, primarily driven by the meridional temperature gradient and modulated by regional processes. In southern areas, seasonal thermal cycles dominate pCO2 seasonality, while in northern areas, biological processes play a more significant role. Our analysis identifies the NAACOM as a CO2 sink, with a mean flux of -0.63 ± 0.19 mol C m-2 yr-1 (-10.14 ± 3.00 Tg C yr-1) in the narrow margin (depth < 200m) and -0.60 ± 0.21 mol C m-2 yr-1 (-24.24 ± 8.31 Tg C yr-1) in the wide margin (distance from coast < 400km). This wide-margin CO2 uptake is around 60% lower than previously reported values, emphasizing the importance of accurate regional assessments.
Finally, I explore the impact of Gulf Stream variability on coastal acidification along the U.S. East Coast. Our findings show unexpectedly rapid acidification, with pCO2 increasing faster than atmospheric CO2 in both the Mid and South Atlantic Bights (MAB and SAB) during 2002-2021, accompanied by a rapid decline in the dissolution saturation of pH and calcium carbonate saturation state (Ω). Specifically, during this period, the sea surface pCO2 of the SAB shelf grew 60% faster than the atmosphere pCO2 and 28% faster than the MAB. I attribute this acceleration to an overall extraordinary regional warming background, and additionally to reduced biological carbon removal and decreased buffer capacity on the SAB shelf — all linked to Gulf Stream dynamics. By incorporating Gulf Stream dynamic parameters into a multiple linear regression model and Earth System Models, I provide revised estimates for past and future pCO2 levels in these regions. I show that the rapid pCO2 contrast between SAB and MAB can be traced back to the 1990s and will continue to be larger in the future due to a weakening Gulf Stream.
This dissertation significantly advances our understanding of carbon dynamics in the NAACOM, providing crucial insights for improved coastal carbon cycle modeling. Our findings highlight the complex interplay of physical, biological, and chemical processes in shaping coastal carbon dynamics and acidification patterns. The development of the ReCAD-NAACOM-pCO2 product offers a valuable tool for future research in this area.
Furthermore, our research underscores the urgent need for enhanced ocean acidification monitoring in Gulf Stream-influenced areas and other Western Boundary Current regions. The rapid coastal acidification observed along the U.S. East Coast has important implications for marine ecosystem management and policy-making. As coastal regions face increasing pressures from climate change, our work provides critical information to support informed decision-making and adaptation strategies.
Continue reading ‘Physical and biogeochemical controls of sea surface pCO2 along the North American Atlantic coastal ocean margins on different time scales’Physiological effects of acute exposure to acidification conditions in embryos of the American lobster (Homarus americanus)
Published 12 March 2025 Science ClosedTags: biological response, crustaceans, laboratory, North Atlantic, physiology, reproduction
Highlights
- Protein carbonyl concentration increased, and Na+/K+-ATPase activity decreased with decreasing acute pH in American lobster embryos.
- Oxygen consumption rate and antioxidant content of embryos increased significantly over development.
- American lobster embryos were sensitive to acute pH reductions representative of future ocean and coastal acidification.
Abstract
Ocean and coastal acidification are altering carbonate chemistry conditions and inducing physiological stress in marine organisms. Early life history stages of marine invertebrates, including commercially important species like the American lobster (Homarus americanus) may have limited physiological capacity to tolerate changes in carbonate chemistry. Using American lobster embryos, we quantified physiological disturbances caused by acute changes in carbonate chemistry. We exposed freshly isolated lobster embryos to conditions ranging from 6.94 to 8.07 pH for 24 h at three points during embryo development. With more extreme conditions of acidification, protein carbonyl concentration (indicative of cellular damage from oxidative stress) increased, and Na+/K+-ATPase activity (associated with acid-base regulation) decreased at all stages of development examined. Although oxygen consumption rate and ferric-reducing antioxidant potential both increased over the course of embryogenesis, we found no evidence that the relationship between pH and these physiological metrics varied during ontogeny. Our results indicate that acid-base regulation and oxidative stress in American lobster embryos may be sensitive to acidification-induced hypercapnia within a 24-h period across a large portion of embryo development.
Continue reading ‘Physiological effects of acute exposure to acidification conditions in embryos of the American lobster (Homarus americanus)’
