The accelerating melt of the Greenland Ice Sheet is releasing large volumes of freshwater into the coastal ocean, diluting seawater alkalinity. Biogeochemical processes such as photosynthesis, respiration, and sediment mineral dissolution also shape carbon dynamics in these freshened waters, but their combined influence on the ocean’s carbon pump remains unresolved. Here we isolate the chemical effects of meltwater dilution through a controlled seawater-freshwater mixing experiment, providing empirical evidence for nonlinear reduction in the partial pressure of carbon dioxide (pCO2). Carbonate system modeling revealed the mechanisms behind this nonlinearity, helping to explain 17 years of low pCO2 in a Greenlandic fjord. Sensitivity analysis shows that the influence of biogeochemical processes is fundamentally shaped by the chemical environment in which they operate. Freshwater input reduces buffering capacity and therefore amplifies the system’s sensitivity to biological activity and acidification. Our findings highlight how meltwater amplifies biogeochemical control of pCO2 in Arctic coastal systems.
Continue reading ‘Glacial meltwater increases coastal carbon dioxide uptake and sensitivity to biogeochemical change’Posts Tagged 'biogeochemistry'
Glacial meltwater increases coastal carbon dioxide uptake and sensitivity to biogeochemical change
Published 28 August 2025 Science ClosedTags: Arctic, biogeochemistry, chemistry, field, modeling, regionalmodeling
Unraveling ocean pCO2 dynamics in northwest Greenland fjords
Published 19 August 2025 Science ClosedTags: Arctic, biogeochemistry, chemistry, field
We investigated the relative contributions of various factors that influence seasonal changes in sea surface partial pressure of CO2 (pCO2, calculated from the measured pH and total alkalinity) in four regions of northwestern Greenland: Nares Strait, Lincoln Sea, Sherard Osborn and Petermann fjords. Using the temperature minimum layer as a proxy for winter conditions, we examined pCO2 dynamics from the onset of sea-ice melt to summer. Our findings revealed significant spatial variability in pCO2, driven by differences in temperature, freshwater inputs, and biological activity. In particular, in Sherard Osborn Fjord substantial freshwater inputs and strong stratification were found to enhance pCO2 accumulation, while in Petermann Fjord biological CO2 uptake was the main driver. This study, conducted in summer 2019, underscores the critical role of northwest Greenland’s coastal waters as a summer CO2 sink. It highlights the complex interplay of physical and biogeochemical processes in modulating pCO2, suggesting significant regional differences in CO2 dynamics between two neighboring fjords.
Continue reading ‘Unraveling ocean pCO2 dynamics in northwest Greenland fjords’Impact of water mass dynamical and property variability on the inflow of a semi-enclosed sea
Published 18 August 2025 Science ClosedTags: biogeochemistry, chemistry, modeling, North Pacific, regionalmodeling
The biogeochemistry of the Salish Sea is strongly connected to its Pacific Ocean inflow through Juan de Fuca Strait (JdF), which varies seasonally and interannually in both volume and property flux. Long-term trends in warming, acidification, and deoxygenation are a concern in the region, and inflow variability influences the flux of tracers potentially contributing to these threats in the Salish Sea. Using ten years (2014-2023, inclusive) of Lagrangian particle tracking from JdF, we quantified the contributions of distinct Pacific water masses to interannual variability in JdF inflow and its biogeochemical properties. We decompose variability in salinity, temperature, dissolved oxygen, nitrate, and carbonate system tracers into components arising from changes in water mass transport (dynamical variability) and changes in source properties (property variability). Observations in the region provide insight into water mass processes not resolved by the model, including denitrification and trace metal supply. Deep water masses dominate total inflow volume and drive variability in nitrate flux through changes in transport. Shallow water masses, particularly south shelf water, exhibit greater interannual variability and disproportionately affect temperature, oxygen, and [TA–DIC], driving change through both dynamical and property variability. This study highlights the combined roles of circulation and source water properties in shaping biogeochemical variability in a semi-enclosed sea, and how these roles differ between biogeochemical tracers. It provides a framework for attributing flux changes to specific source waters and physical and biogeochemical drivers, with implications for forecasting coastal ocean change under future climate scenarios.
Continue reading ‘Impact of water mass dynamical and property variability on the inflow of a semi-enclosed sea’Detangling the elevated sea-surface pCO2 trend in a river-dominated continental shelf using a high-resolution regional ocean model
Published 8 August 2025 Science ClosedTags: biogeochemistry, chemistry, modeling, regionalmodeling
River-dominated continental shelves significantly influence coastal carbon cycling and ocean acidification due to substantial freshwater river discharge. Despite this importance, the contributions of riverine dissolved inorganic carbon (DIC), total alkalinity (TA), and nutrient loads to surface pCO2 trends remain inadequately quantified. This study employs the Regional Ocean Modelling System (ROMS) to evaluate the effects of riverine DIC, TA, and nutrient fluxes on surface pCO2 trends in the northern Gulf of Mexico/America from 2001 to 2019. A control simulation (CTR) representing historical river inputs was compared to three scenarios: no historical riverine DIC and TA flux (NRC), no historical nutrient flux (NRN), and high freshwater discharge (60% of historical levels, HRD60). Results indicated positive pCO2 trends in most nGoM regions, except for HRD60, which exhibited some negative trends. First-order Taylor series decomposition revealed that DIC is the primary contributor to increasing pCO2 trends, accounting for 50%, while TA offsets this by 31%. Sea surface temperature (SST) contributes 13%, and sea surface salinity (SSS) contributes 6%. Under the HRD60 simulation, increased freshwater discharge enhances both DIC and TA delivery, leading to spatially heterogeneous yet dampened pCO2 trends due to stronger buffering. These findings emphasize that coastal pCO2 trajectories depend on the magnitude and composition of riverine fluxes. Carbonate supplies account for 59% of total river-driven modulation of surface pCO2, with biological uptake offsetting the remaining 41%. Future climate projections must consider these nonlinear interactions to effectively assess acidification risks in river-influenced coastal regions.
Continue reading ‘Detangling the elevated sea-surface pCO2 trend in a river-dominated continental shelf using a high-resolution regional ocean model’Biogeochemical effects of Golden Gate Strait exchange and other land-base inputs to the San Francisco and Monterey Bay coasts
Published 8 August 2025 Science ClosedTags: biogeochemistry, chemistry, modeling, North Pacific, regionalmodeling
The central California coast between San Francisco Bay (SFB) and Monterey Bay (MB) is an upwelling-dominated marine ecosystem with a coastal population of 8.5 million. Anthropogenically enhanced terrestrial nutrients enter the ocean via three primary pathways: (1) SFB exchanges across the Golden Gate Strait, (2) coastal rivers, and (3) municipal wastewater discharged to ocean outfalls. The consequences of these inputs on primary production, acidification and hypoxia remain poorly understood. Here, we investigate these effects with a submesoscale-resolving ocean biogeochemical model. Simulations show that while terrestrial nutrient inputs collectively affect a broad region, the stronger impacts are found in nearshore waters, increasing dissolved inorganic nitrogen by 11.4%, primary production by 6.5%, and chlorophyll concentration by 4.5% along a 15-km coastal band. While exchanges from the SFB dominate these effects, all sources, including coastal rivers and ocean outfalls, produce distinct, localized footprints. Subsurface oxygen and pH decline due to terrestrial nutrient loading, but vigorous upwelling and circulation limit the intensity of these changes. Enhanced nutrient inputs are predicted to promote conditions favorable for diatom growth, potentially including Pseudo-nitzschia spp., creating an environment more conducive to domoic acid (DA) production. Model results show that chlorophyll concentrations exceed the threshold associated with elevated DA risk on 10-45% more days under nutrient-enriched conditions, compared to a scenario without terrestrial inputs. These findings highlight the need for expanded observational and modeling efforts to better understand the ecological consequences of anthropogenic nutrient inputs along the central California coast.
Continue reading ‘Biogeochemical effects of Golden Gate Strait exchange and other land-base inputs to the San Francisco and Monterey Bay coasts’Potential for regional resilience to ocean warming and acidification extremes: projected vulnerability under contrasting pathways and thresholds
Published 30 July 2025 Science ClosedTags: adaptation, biogeochemistry, chemistry, globalmodeling, mitigation, modeling, otherprocess
We analyze the frequency and amplitude of projected warming and ocean acidification extremes under high CO2 and strongly mitigating scenarios. We find interpretational differences in projections arising from methodological choices associated with specification of stressor thresholds. Use of absolute versus distribution-based thresholds, and, in the distribution-based case, the inclusion or exclusion of seasonal variability, can lead to very different regional patterns in projected stress. The choice of fixed versus adaptive baseline, for example, determines whether future stress frequency in the low-CO2 scenario most closely resembles that in the high-emissions scenario or historical period. We find that mitigation through emissions reductions, in combination with representation of rates of adaptation that are realistic for some marine organisms, has the potential to dampen end of century threshold exceedance to frequencies of occurrence closer to the recent historical period than to the high-emissions scenario.
Continue reading ‘Potential for regional resilience to ocean warming and acidification extremes: projected vulnerability under contrasting pathways and thresholds’Seasonal upwelling drives surface water biogeochemistry with implication for ocean acidification along the Northwest African coast
Published 25 July 2025 Science ClosedTags: biogeochemistry, chemistry, field, North Atlantic
This study assesses the impact of intensified upwelling on the marine carbonate system along the Northwest African coast, from Cape Blanc (21°N) to Cape Cantin (33°N), a region where ocean acidification observations remain limited. We analyze surface water variability using data from two oceanographic surveys conducted aboard the R/V Dr. Fridtjof Nansen in spring and autumn 2022. The analysis is based on observational data of temperature, salinity, dissolved oxygen, chlorophyll a, pH, total alkalinity, and derived carbonate system variables. In spring, upwelling was widespread across the study area, while in autumn it was more localized near Cape Draa (28°30’N), between Cape Boujdour and Dakhla (25°30N–23°30N), and at Cape Blanc (21°N). Both spring and autumn were influenced by low-oxygenated South Atlantic Central Water (SACW), which is rich in DIC (2160–2250 µmol/kg), and upwelled to the surface, lowering pH (~7.85–7.95) and aragonite saturation state (ΩAr ~1.5–2.5). The strongest acidification signals were observed in autumn at Cape Draa (28°30N) and Cape Blanc (21°N), where the lowest pH (7.8) and ΩAr (1.5), along with the highest DIC (2250 µmol/kg), were recorded. The study clearly shows that the lowest pH values and highest DIC concentrations were related to the influence of SACW upwelling at Cape Blanc. It was also evident that areas with high chlorophyll a coincided with higher ΩAr and pH in spring. This suggests that primary production (PP) during spring counteracts the effect of upwelled low-pH water along the coast. Areas of high PP, such as at Cape Draa (28°30N), experienced increased DIC levels and enhanced acidification after the bloom season, potentially influenced by organic matter remineralization. Our findings highlight the influence of upwelling and biological processes on surface carbonate chemistry along the Northwest African coast. This study emphasizes the necessity of long-term monitoring to assess ocean acidification trends and their ecological implications in this vulnerable region.
Continue reading ‘Seasonal upwelling drives surface water biogeochemistry with implication for ocean acidification along the Northwest African coast’Future biogeochemical changes in southern South China Sea from CMIP6 model projection
Published 24 July 2025 Science ClosedTags: biogeochemistry, chemistry, modeling, North Pacific, regionalmodeling
The ongoing climate change has significant impacts on global ocean biogeochemistry. This study employs Coupled Model Intercomparison Project Phase 6 Earth System Models under Shared Socioeconomic Pathways (SSPs) scenarios SSP2-4.5, SSP3-7.0, and SSP5-8.5 to investigate the future projection of biogeochemical changes in the southern South China Sea (SCS) from 2015 to 2100. The focus is on projected changes in Sea Surface Temperature (SST) and seven important biogeochemical variables, including Chlorophyll, Phytoplankton, integrated Primary Production, Oxygen, Nitrate, Phosphate, and pH. The results consistently indicate significant warming of 1 to 3 °C at the end of 21st century across all scenarios in southern SCS region, potentially leading to cascading consequences for marine ecosystems and fisheries. The projected increases in SST induce declines in dissolved Oxygen levels about − 3 to -8 mmol m-3 and ocean acidification about − 0.1 to -0.4 units, posing a multifaceted threat to this crucial fishing ground. This intensified warming is driven by the weakening of surface wind speeds and the strengthening of upper-ocean stratification, which simultaneously contribute to reductions in nutrient availability and productivity in the southern SCS. This projection assessment provides valuable insights into the anticipated biogeochemical shifts in the southern SCS under various climate scenarios, offering a vital foundation for understanding the adverse effects of climate change on the southern SCS ecosystems and ensuring its long-term sustainability.
Continue reading ‘Future biogeochemical changes in southern South China Sea from CMIP6 model projection’Observations of Sargassum carbon influx and biogeochemical impact in La Parguera Marine Reserve
Published 15 July 2025 Science ClosedTags: algae, biogeochemistry, biological response, chemistry, field, North Atlantic
The massive influx of pelagic Sargassum spp. species, also known as Sargassum inundation events (SIEs), first arrived at the Caribbean’s coastal waters in 2011. These events have been linked to hypoxia, among other ecological disturbances. Here, we report data from 2022 on (1) an assessment of the relative magnitude of particulate organic carbon (POC) load arising from SIEs into the La Parguera Marine Reserve (LPMR) basin off the southwest coast of Puerto Rico and (2) the biogeochemical impact of SIE in a nearshore mangrove key within the reserve, Monsio Jose Key Bay (MJKB). Our analysis yields that the carbon influx increased by 20% in the LPMR basin and by 103% in MJKB. Weekly observations of Sargassum input, along with the collection and analysis of water samples in MJKB, evidenced a cause-effect relation between Sargassum carbon loading and frequency of hypoxic (DO < 2 mg·L-1) and critically acidic conditions (Aragonite saturation, Ω < 2.0). During the 2022 Sargassum season, hypoxic conditions were detected in 43% of samples collected in MJKB. Considering the modulation of biogeochemical parameters by changes in tide height (Δh) and wind speed (m·s-1), stepwise multiple regression analyses (RDA-AIC model selection) showed that significant parameters influencing DO, pH, and Ω include the Sargassum carbon influx and Δh (p < 0.05). These findings strongly support the hypothesis that the additional input of POC influx enhances microbial mineralization rates responsible for depressed oxygen concentrations and acidic conditions, which could be detrimental to coastal ecosystems. This is particularly concerning in areas prone to SIEs where geomorphological features facilitate the entrainment of floating materials. Proper management requires the identification of vulnerable sites and Sargassum removal. Ongoing efforts towards that goal are underway for LPMR.
Continue reading ‘Observations of Sargassum carbon influx and biogeochemical impact in La Parguera Marine Reserve’Terrestrial nutrient inputs restructure coral reef dissolved carbon fluxes via direct and indirect effects
Published 11 July 2025 Science ClosedTags: biogeochemistry, BRcommunity, calcification, chemistry, corals, field, South Pacific
The addition of terrestrial inputs to the ocean can have cascading impacts on coastal biogeochemistry by directly altering the water chemistry and indirectly changing ecosystem metabolism, which also influences water chemistry. Here, we use submarine groundwater discharge (SGD) as a model system to examine the direct geochemical and indirect biologically mediated effects of terrestrial nutrient subsidies on a fringing coral reef. We hypothesize that the addition of new solutes from SGD alters ecosystem metabolic processes including net ecosystem production and calcification, thereby changing the patterns of uptake and release of carbon by benthic organisms. SGD is a common land–sea connection that delivers terrestrially sourced nutrients, carbon dioxide, and organic matter to coastal ecosystems. Our research was conducted at two distinct coral reefs in Moʻorea, French Polynesia, characterized by contrasting flow regimes and SGD biogeochemistry. Using a Bayesian structural equation model, our research elucidates the direct geochemical and indirect biologically mediated effects of SGD on both dissolved organic and inorganic carbon pools. We reveal that SGD-derived nutrients enhance both net ecosystem production and respiration. Furthermore, the study demonstrates that SGD-induced alterations in net ecosystem production significantly influence pH dynamics, ultimately impacting net ecosystem calcification. Notably, the study underscores the context-dependent nature of these cascading direct and indirect effects resulting from SGD, with flow conditions and the composition of the terrestrial inputs playing pivotal roles. Our research provides valuable insights into the interplay between terrestrial inputs and coral reef ecosystems, advancing our understanding of coastal carbon cycling and the broader implications of allochthonous inputs on ecosystem functioning.
Continue reading ‘Terrestrial nutrient inputs restructure coral reef dissolved carbon fluxes via direct and indirect effects’Spatiotemporal analysis of sea-surface pH in the Pacific Ocean based on interpretable machine learning
Published 9 July 2025 Science ClosedTags: biogeochemistry, chemistry, modeling, North Pacific, regionalmodeling, South Pacific
Increasingly severe ocean acidification (OA) disrupts the balance of marine ecosystems. Seawater pH is a key indicator of OA but remains challenging to characterize due to sparse and limited in situ observations. In this study, we propose a spatiotemporal inversion method for surface pH based on interpretable machine learning. By applying carbonate system calculations, we construct an expanded pH observational dataset and obtain spatiotemporal distributions of pH and its influencing factors across the Pacific Ocean from 2003 to 2021. The interpretability analysis reveals that physical, biological, and optical factors contribute 53.9%, 23.9%, and 22.2%, respectively, to pH variability. Sea-surface temperature is the dominant driver, contributing 15.9% of all factors by regulating CO2 solubility and biological activity. Particulate inorganic carbon (PIC) and particulate organic carbon (POC) show relative contributions of 12.6% and 9.4%, respectively, quantitatively reflecting the important roles of biogenic calcification and the biological carbon pump. Furthermore, the analysis focusing on the Niño 3.4 region reveals a potential pathway through which the ENSO disturbances may affect pH by influencing PIC and POC. Therefore, this study provides a data-driven approach to gain deeper insights into the spatiotemporal patterns of pH and its influencing factors.
Continue reading ‘Spatiotemporal analysis of sea-surface pH in the Pacific Ocean based on interpretable machine learning’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
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’Magnesium (Mg∕Ca, δ26Mg), boron (B∕Ca, δ11B), and calcium (Ca2+) geochemistry of Arctica islandica and Crassostrea virginica extrapallial fluid and shell under ocean acidification
Published 4 July 2025 Science ClosedTags: biogeochemistry, biological response, calcification, chemistry, laboratory, mollusks, physiology
The geochemistry of biogenic carbonates has long been used as proxies to record changing seawater parameters. However, the effect of ocean acidification (OA) on seawater chemistry and organism physiology could impact isotopic signatures and how elements are incorporated into the shell. In this study, we investigated the geochemistry of three reservoirs important for biomineralization – seawater, the extrapallial fluid (EPF), and the shell – in two bivalve species: Crassostrea virginica and Arctica islandica. Additionally, we examined the effects of three ocean acidification conditions (ambient: 500 ppm CO2, moderate: 900 ppm CO2, and high: 2800 ppm CO2) on the geochemistry of the same three reservoirs for C. virginica. We present data on calcification rates, EPF pH, measured elemental ratios (Mg/Ca, B/Ca), and isotopic signatures (δ26Mg, δ11B). In both species, comparisons of seawater and EPF Mg/Ca and B/Ca, Ca2+, and δ26Mg indicate that the EPF has a distinct composition that differs from seawater. Shell δ11B did not faithfully record seawater pH, and δ11B-calculated pH values were consistently higher than pH measurements of the EPF with microelectrodes, indicating that the shell δ11B may reflect a localized environment within the entire EPF reservoir. In C. virginica, EPF Mg/Ca and B/Ca, as well as absolute concentrations of Mg2+, B, and Ca2+, were all significantly affected by ocean acidification, indicating that OA affects the physiological pathways regulating or storing these ions, an observation that complicates their use as proxies. Reduction in EPF Ca2+ may represent an additional mechanism underlying reduction in calcification in C. virginica in response to seawater acidification. The complexity of dynamics of EPF chemistry suggests boron proxies in these two mollusk species are not straightforwardly related to seawater pH, but ocean acidification does lead to both a decrease in microelectrode pH and boron-isotope-based pH, potentially showing applicability of boron isotopes in recording physiological changes. Collectively, our findings show that bivalves have high physiological control over the internal calcifying fluid, which presents a challenge in using boron isotopes for reconstructing seawater pH.
Continue reading ‘Magnesium (Mg∕Ca, δ26Mg), boron (B∕Ca, δ11B), and calcium (Ca2+) geochemistry of Arctica islandica and Crassostrea virginica extrapallial fluid and shell under ocean acidification’CO2 enrichment enhances biomass density and C:N:P ratios in phytoplankton assemblage in the coastal water of the Taiwan Strait
Published 3 July 2025 Science ClosedTags: abundance, biogeochemistry, biological response, community composition, laboratory, North Pacific, otherprocess, phytoplankton
Seawater CO2 concentrations are steadily increasing in the Taiwan Strait of the Southeast China, while the effects of rising CO2 on carbon fixation and elemental composition of phytoplankton assemblages in this area are still poorly understood. Here, we enriched the seawater CO2 concentrations to 808 μatm and above to simulate the CO2–induced ocean acidification, and investigated the effects of CO2 enrichment on concentrations of chlorophyll (Chl) a, particulate organic carbon (POC), nitrogen (PON) and phosphorus (POP), the C:N:P ratio, and phytoplankton community composition in the coastal surface seawaters of the northwest Taiwan Strait in autumn 2023 and spring 2024 through an outdoor incubation experiment. After three days of incubation, CO2 enrichment increased the concentrations of Chl a by 1–14%, POC by 21–32% and PON by 21–56%, whereas reduced the POP concentrations by 1–37%, leading to elevated ratios of POC:POP and PON:POP. Furthermore, elevated CO2 level enhanced cell abundances of the dominant diatom genera at three stations. These results suggest that phytoplankton has the potential to buffer against rising atmospheric CO2 level and can help us to understand the elemental biogeochemistry in the Taiwan Strait under future ocean acidification scenarios.
Continue reading ‘CO2 enrichment enhances biomass density and C:N:P ratios in phytoplankton assemblage in the coastal water of the Taiwan Strait’Decreased dimethylsulfide and increased polybrominated methanes: potential climate effects of microplastic pollution in acidified ocean
Published 3 July 2025 Science ClosedTags: biogeochemistry, biological response, community composition, laboratory, multiple factors, otherprocess, phytoplankton, plastics
Microplastic (MP) pollution and ocean acidification (OA) are pressing marine environmental concerns, but their combined impacts on short-lived biogenic climate-active gases and the resulting climate effects remain unclear. To address this gap, a ship-based microcosm experiment was conducted, where OA and MP pollution were simulated under in situ conditions to explore their effects on the production of dimethylsulfide (DMS), bromoform (CHBr3), and dibromomethane (CH2Br2). The results indicated that both MP and OA inhibited phytoplankton growth and DMS concentration, with OA inducing further reductions in the production rate and yield of DMS. MP addition led to extra dissolved organic matter, and the acidified condition enhanced bromoperoxidase activity, both of which promoted the production of CHBr3 and CH2Br2. When OA and MP addition were combined, DMS concentrations decreased by 61%, whereas CHBr3 and CH2Br2 concentrations increased by 132% and 45%, respectively. Based on the results, MP pollution under OA conditions might directly reduce DMS accumulation or decrease the formation of DMS-derived sulfate aerosols by increasing CHBr3 and CH2Br2 levels, which finally weaken DMS’s climate-cooling capabilities. This study underscores the potential for MP pollution in future acidified oceans to exacerbate global warming by disrupting the cycle of marine biogenic climate-active gases.
Continue reading ‘Decreased dimethylsulfide and increased polybrominated methanes: potential climate effects of microplastic pollution in acidified ocean’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’Effects of different environmental stressors on marine biogenic sulfur compounds in the Northwest Pacific and Eastern Indian Oceans
Published 2 July 2025 Science ClosedTags: abundance, biogeochemistry, biological response, community composition, growth, Indian, laboratory, multiple factors, North Pacific, otherprocess, physiology, phytoplankton
Abstract
Key roles of marine dimethyl sulfoniopropionate (DMSP), dimethyl sulfide (DMS), methyl mercaptan (MeSH), and carbon disulfide (CS2) in the sulfur cycle and/or atmospheric chemistry, alongside the rapid environmental changes in marine ecosystems, underscore the need to understand their responses to dynamic ecosystem shifts. We conducted two ship-based incubation experiments in the Northwest Pacific and Eastern Indian Oceans to explore how dust deposition, ocean acidification, and microplastic exposure impact these compounds. Our results demonstrate that these stressors not only alter phytoplankton community but also modify per-cell DMSP production capacity and DMSP degradation pathways, subsequently influencing DMSP, DMS, and MeSH concentrations. CS2‘s response closely mirrors phytoplankton abundance and species. Initial physical-chemical conditions, such as carbonate system and nutrient availability, may mediate the sensitivity of phytoplankton and sulfur compounds to environmental shifts. This study enhances our understanding of biogenic sulfur responses in dynamic marine ecosystems and provides essential basis for future climate modeling.
Key Points
- External stressors alter algal communities and production and degradation of dimethyl sulfoniopropionate, thus affecting biogenic sulfides
- Response of carbon disulfide to different environmental stressors is closely linked to algal abundance
- Initial physical-chemical conditions of seawater mediate algae and biogenic sulfides’ sensitivity to environmental stressors
Plain Language Summary
Biogenic sulfur-containing compounds in the ocean, such as dimethyl sulfoniopropionate (DMSP), dimethyl sulfide (DMS), methyl mercaptan (MeSH), and carbon disulfide (CS2), play critical roles in the global sulfur cycle and have the potential to influence the Earth’s climate. For instance, DMS released from the ocean into the atmosphere contributes to cloud formation, which in turn affects weather patterns. Over recent decades, rapid environmental changes in marine ecosystems may have significantly impacted marine biogeochemical processes. To investigate how these compounds respond to such changes, we conducted two ship-based incubation experiments in the Northwest Pacific and Eastern Indian Oceans. We assessed the effects of dust deposition, ocean acidification (due to increased carbon dioxide), and microplastic pollution on the production of DMSP, DMS, MeSH, and CS2 by marine organisms. Our results demonstrate that these stressors alter phytoplankton growth and community composition and impact the pathways through which DMSP is degraded. Consequently, the concentrations of sulfur compounds in seawater are affected. Notably, changes in CS2 levels were more closely related to shifts in phytoplankton abundance. These findings enhance our understanding of how marine sulfur compounds may respond to future oceanic changes and offer valuable data for improving climate models.
Continue reading ‘Effects of different environmental stressors on marine biogenic sulfur compounds in the Northwest Pacific and Eastern Indian Oceans’Biogeochemical parameters collected and analysed during the French cruises of the PIRATA programme in the Guinea Gulf, 1997–2024
Published 23 June 2025 Science ClosedTags: biogeochemistry, chemistry, field, South Atlantic
This paper presents a biogeochemistry dataset derived from the French component of the PIRATA (Prediction and Research Moored Array in the Tropical Atlantic) program in the Gulf of Guinea. This program, which started in 1997 with the deployment of a buoy network, has offered the opportunity to collect seawater biogeochemistry parameters since 2004. The measured parameters include salinity, dissolved oxygen, nutrients (since 2004), phytoplankton pigments (since 2011), marine pH (since 2021) and total alkalinity (since 2023). Following rigorous procedures, we provide high-quality data for studying the spatial and temporal variability of these parameters, with the aim of gaining a better understanding of the underlying processes that drive the ocean’s biogeochemical cycles in the Tropical Atlantic. The data are available in the SEANOE repository, which is accessible for scientific data in the marine sciences.
Continue reading ‘Biogeochemical parameters collected and analysed during the French cruises of the PIRATA programme in the Guinea Gulf, 1997–2024’Regionally distinct drivers of the carbonate system dynamics in the Drake Passage and northern Antarctic Peninsula
Published 4 June 2025 Science ClosedTags: Antarctic, biogeochemistry, chemistry
Highlights
- AT and CT in the DP and NAP were influenced by salinity, terrestrial inputs, and coastal upwelling.
- Oceanic regions of the DP were significantly influenced by phosphate levels and high eddy kinetic energy.
- AT and CT in the DP and NAP exhibited both conservative (coastal regions) and non-conservative (oceanic regions) behaviors.
- The highest risk for carbonate undersaturation was observed in the NAP.
Abstract
The Drake Passage (DP) and the adjacent northern Antarctic Peninsula (NAP) are highly dynamic regions within the Southern Ocean where physical and biogeochemical processes simultaneously influence the CO2 system. Ocean total alkalinity (AT) and total dissolved inorganic carbon (CT) serve as valuable early indicators of calcium carbonate undersaturation and help evaluate the buffering capacity of the ocean. However, significant uncertainty remains in predicting carbonate system dynamics in the DP and NAP due to a lack of seasonal representation and the spatial variability. To address this uncertainty, we identified factors affecting the carbonate system at a regional level using unprecedented surface data from two consecutive austral summer and early fall periods (February–April 2003 and 2004). The data revealed that the dynamics of AT and CT in the DP and NAP exhibited both conservative and non-conservative behaviors influenced by the position of the Polar Front (PF), and the proximity to land. In coastal regions, salinity and terrestrial influence were major determinants, while in oceanic regions, nutrients and phytoplankton productivity played a more prominent role. The position of the PF creates a latitudinal edge in nutrient ratios, establishing a new hierarchy of carbonate chemistry drivers where silicate gains prevalence toward the southern DP and NAP. The results highlight significant regional variability in the carbonate system, with increasing AT and CT from north to south, making NAP the most vulnerable region due to accelerated acidification and ice melt-growth. Susceptibility to ocean acidification and seasonal fluctuations in the carbonate system indicate a higher risk to calcareous structures in the southernmost region.
Continue reading ‘Regionally distinct drivers of the carbonate system dynamics in the Drake Passage and northern Antarctic Peninsula’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’
