Anthropogenic CO2 emissions and their continuous dissolution into seawater lead to seawater pCO2 rise and ocean acidification (OA). Phytoplankton groups are known to be differentially affected by carbonate chemistry changes associated with OA in different regions of contrasting physical and chemical features. To explore responses of phytoplankton to OA in the Chinese coastal waters, we conducted a mesocosm experiment in a eutrophic bay of the southern East China Sea under ambient (410 μatm, AC) and elevated (1000 μatm, HC) pCO2 levels. The HC stimulated phytoplankton growth and primary production during the initial nutrient-replete stage, while the community diversity and evenness were reduced during this stage due to the rapid nutrient consumption and diatom blooms, and the subsequent shift from diatoms to hetero-dinoflagellates led to a decline in primary production during the mid and later phases under nutrient depletion. Such suppression of diatom-to-dinoflagellate succession occurred with enhanced remineralization of organic matter under the HC conditions, with smaller phytoplankton becoming dominant for the sustained primary production. Our findings indicate that, the impacts of OA on phytoplankton diversity in the coastal water of the southern East China Sea depend on availability of nutrients, with primary productivity and biodiversity of phytoplankton reduced in the eutrophicated coastal water.
Continue reading ‘Ocean acidification alters phytoplankton diversity and community structure in the coastal water of the East China Sea’Posts Tagged 'biogeochemistry'
Ocean acidification alters phytoplankton diversity and community structure in the coastal water of the East China Sea
Published 5 December 2025 Science ClosedTags: biogeochemistry, biological response, community composition, laboratory, mesocosms, North Pacific, otherprocess, phytoplankton, primary production, respiration
Resilience of pH to seasonal change in a large subtropical lagoonal estuary
Published 5 December 2025 Science ClosedTags: biogeochemistry, chemistry, field, South Atlantic
Highlights
- The lower Patos Lagoon Estuary displays a broad range of alkalinity and pH values, with riverine inputs marked by low buffering capacity.
- A critical period of corrosive conditions occurs from winter to mid-spring, likely driven by enhanced respiration and/or external CO₂ inputs.
- The estuary operates as a moderate to weakly buffered system, exhibiting aragonite undersaturation even under medium to high salinity conditions.
- pH sensitivity to environmental drivers is highest in summer and winter, whereas autumn presents the most uniform seasonal response.
Abstract
Coastal ecosystems exhibit a wide range of pH trends, from −0.023 to 0.023 pH units yr−1, making them particularly susceptible to acidification or basification. These variations are primarily driven by ecosystem metabolism and the influence of oceanic and riverine endmembers, as observed in the subtropical system of the Patos Lagoon Estuary (PLE, southern Brazil), where biogeochemical variability is largely governed by mixing of water masses with different properties. This study provides the first quantification of the seasonal variability of pH buffering capacity in the inner and outer zones of PLE. From May 2017 to September 2023, we assessed temporal variability using multiple approaches: (i) carbonate system parameters, (ii) sensitivity factors, (iii) buffering capacity of pH to fractional change of dissolved inorganic carbon (βDIC), (iv) metabolic effects on pH, and (v) environmental drivers of pH. The results revealed a distinct seasonal pH pattern, especially between summer with winter and spring, with consistently higher values at the outer station compared to the inner station, though spatial differences were not statistically significant. In winter and particularly in early spring, calcium carbonate (CaCO3) dissolution prevailed due to riverine input characterized by low buffering capacity. Along the salinity gradient, pH exhibited a pronounced difference, particularly between low and high salinity conditions. However, the persistent negative deviation of the metabolic effect on pH throughout the year and in salinity ranges, even under seawater conditions, supports the characterization of this coastal ecosystem as a net CO2 source, with especially high variability at mid-salinity conditions. Although the salinity gradient was comparable between stations, they exhibited differences in the magnitude of pH sensitivity to seasonal biogeochemical changes. These findings indicate that PLE functions as a system with moderate to low buffering capacity, with the outer zone showing greater resilience to pH fluctuations.
Continue reading ‘Resilience of pH to seasonal change in a large subtropical lagoonal estuary’A global perspective on river alkalinity: drivers and implications for coastal ocean carbonate chemistry
Published 4 December 2025 Science ClosedTags: biogeochemistry, chemistry, globalmodeling, modeling
Abstract
The chemical nature of river water significantly influences the coastal carbonate system, contributing to coastal acidification and creating suboptimal conditions for marine calcifiers. While several regional efforts have assessed observationally based riverine concentrations and fluxes of total alkalinity (TA) and dissolved inorganic carbon (DIC), these values in global ocean biogeochemical models have generally been simplified, often set to zero or balanced against global sediment calcium carbonate burial. To enhance our understanding of rivers’ role in the coastal carbonate system, we applied multiple linear regression (MLR) to develop global empirical relationships for estimating river TA and DIC from watershed properties. We find that river TA values are primarily controlled by forest, carbonate rock coverage, and annual mean precipitation, explaining 74% of the spatial variability in TA. The variability explained improves to 77% with the inclusion of permafrost and glacial coverage, especially in high latitude and altitude regions. Additionally, nearly 30% of the spatial variability in the river DIC-to-TA ratio can be explained by terrestrial gross primary production and carbonate rock coverage. Applying these MLR-derived TA and DIC concentrations to a 1/4° resolution global ocean model reduces the high bias in model estimates of global coastal CO2 uptake by 69% (equivalent to 0.11 Pg C yr−1 less CO2 uptake) compared to the case with zero river TA and DIC. This study elucidates key drivers of the river carbonate system and underscores the importance of accurately representing riverine inputs to improve predictions of global coastal carbon dynamics and ecosystem responses to environmental changes.
Plain Language Summary
Rivers play a critical role in shaping the chemistry of coastal waters, influencing how much carbon dioxide (CO2) the ocean absorbs and creating conditions that affect marine life, such as shellfish and corals. Global models are essential for predicting carbon dynamics at large scales, offering insights into the interactions between rivers, coastal systems, and the global ocean. However, global models often simplify or partially overlook key chemical contributions from rivers, leading to biases in predictions. In this study, we analyzed how river chemistry, particularly river carbon inputs, is influenced by factors such as forest cover, carbonate rocks, rainfall, permafrost, and glaciers on land. We developed statistical models to estimate two key properties: total alkalinity and dissolved inorganic carbon. Incorporating these improved river chemistry estimates into a global ocean model markedly reduced the overestimation of coastal CO2 absorption. This research underscores the importance of accurately including riverine inputs in global models to enhance predictions of coastal carbon dynamics and ecosystem responses to climate change.
Key Points
- Global empirical relationships are developed using multiple linear regression (MLR) to estimate river TA and DIC concentrations from watershed properties
- Forest and carbonate rock coverage, and annual mean precipitation explain 74% of the spatial variability in global river TA values
- Applying MLR-derived river TA and DIC concentrations to a global ocean model substantially reduces biases in coastal CO2 uptake estimates
Typhoon-induced cascade effects on hydrological and biogeochemical dynamics in estuary-coast continuum: insights from multidisciplinary observations and model forecasting in Zhanjiang Bay, China
Published 28 November 2025 Science ClosedTags: biogeochemistry, chemistry, field, North Pacific
Highlights
- Typhoon-induced nutrient surge triggered cascade effects in Zhanjiang Bay.
- Skeletonema costatum proliferated and decayed rapidly in eutrophic waters.
- Bloom collapse caused water acidification and oxygen depletion.
- A CNN-LSTM model achieved 73% relative accuracy in 6 h Chl-a rolling forecast.
Abstract
Typhoons can trigger biogeochemical cascade effects, including eutrophication, algal blooms, acidification, and dissolved oxygen (DO) depletion in the estuary-coast continuum, yet the underlying mechanisms remain poorly understood. This study employed a multidisciplinary observation approach, combining high-frequency in situ monitoring with field surveys, to capture the dynamics of the cascade during Typhoon “Yagi” (Sep 2024) in Zhanjiang Bay (ZJB). The analysis incorporated multivariate hydrological, meteorological, and physicochemical parameters, stable isotopes (δ15N-NO3−, δ18O-NO3−, δ18O-H2O, δD-H2O), and phytoplankton community characterization. Results showed that during the pre-algal bloom period, freshwater discharge, fluxes of dissolved inorganic nitrogen (DIN), and dissolved inorganic phosphorus (DIP) increased by factors of 8.7, 43.4, and 3.0, respectively, relative to the pre-typhoon stage, while salinity decreased by 9.7%. This nutrient surge exacerbated eutrophication, leading to a serious algal bloom eight days after the typhoon. Subsequent bloom decay triggered acidification and DO decline. Field investigations confirmed typhoon-driven freshwater input and algal blooms. Moreover, a deep learning model was developed for Chlorophyll-a forecasts, achieving 73% relative accuracy (RA) in rolling 6-hour forecasting. Typhoon-driven nutrient surge triggered the cascade: Skeletonema costatum bloomed under extreme thermohaline perturbation and decayed rapidly, leading to acidification and DO depletion. This study advances mechanistic understanding of typhoon-driven cascading effects in tropical coastal ecosystems, providing a scientific basis for the assessment of their ecological consequences and predictive coastal management strategies.
Continue reading ‘Typhoon-induced cascade effects on hydrological and biogeochemical dynamics in estuary-coast continuum: insights from multidisciplinary observations and model forecasting in Zhanjiang Bay, China’Monsoon-driven biogeochemical shifts and acidification risk in tropical estuarine ecosystems: a case study from the Indian coast
Published 17 November 2025 Science ClosedTags: biogeochemistry, chemistry, field, Indian
Tropical estuaries serve as biogeochemical hotspots where the interactions between monsoon hydrology and human activities significantly impact ecosystem health. However, limited information exists on their carbonate chemistry, which is crucial for assessing climate vulnerability. This study provides the first seasonal assessment of hydrography, nutrients, and carbonate system dynamics in the Haripur estuary, Bay of Bengal. Seasonal evaluation revealed significant variations in pH, carbonate system indicators, and nutrients (p < 0.001). During the monsoon, pH declined to 7.12 ± 0.17, dissolved oxygen dropped to near-hypoxic levels (2.95 ± 0.35 mg L−1), and nutrient enrichment was observed with elevated dissolved inorganic nitrogen (6.07 ± 0.74 μM) and phosphate (1.61 ± 0.39 μM). Carbonate saturation states remained persistently corrosive, reaching minima of ΩAr (0.03 ± 0.01) and ΩCa = 0.04 ± 0.01) among the lowest reported for Indian estuaries. Multivariate analysis identified nutrient enrichment and carbonate imbalance as the dominant stressors, explaining 32.4 % of the total variance. These findings clearly indicate that the Haripur estuary functions as a regional hotspot of monsoon-driven acidification and a global outlier exhibiting year-round carbonate undersaturation. Urgent management interventions are recommended to mitigate hypoxia and acidification risks in this vulnerable tropical estuary through nutrient load reduction, enhanced tidal flushing, and ecosystem-based adaptation. The results further provide a valuable basis for developing best management practices in the context of regional and global climate change, thereby supporting the objectives of Sustainable Development Goal 14 (Life Below Water).
Continue reading ‘Monsoon-driven biogeochemical shifts and acidification risk in tropical estuarine ecosystems: a case study from the Indian coast’Biogeochemical controls on the co-occurrence of mid-depth pH and DO minima in the inner shelf of the East China Sea
Published 12 November 2025 Science ClosedTags: biogeochemistry, chemistry, field, North Pacific
Highlights
- Mid-depth pH minima co-occur with DO minima and nitrate maxima near the thermocline.
- Mid-depth pH minima are driven by both organic matter respiration and upwelling.
- Low carbonate buffering capacity amplifies mid-depth pH and pCO2 signals.
Abstract
While ocean acidification in coastal oceans is well documented, mid-depth pH dynamics remains largely understudied. In August 2017, we conducted high-resolution vertical profiling of temperature, salinity, pH, dissolved oxygen (DO), and nitrate using in situ biogeochemical sensors in the inner East China Sea shelf. Additionally, vertical distributions of dissolved inorganic carbon (DIC), total alkalinity (TA), partial pressure of CO2 (pCO2), and aragonite saturation state (Ωa) were also calculated. Our observations revealed that mid-depth pH minima (<7.85) co-occurred with DO minima (<60 μmol L−1) and nitrate maxima within or just below the seasonal thermocline. The DO–pH relationships at these stations followed Redfield stoichiometry, indicating organic matter respiration as a primary driver of mid-depth pH minima. High chlorophyll a concentrations (>5.0 μg L−1) at these sites suggested recent phytoplankton blooms fueling the mid-depth oxygen and pH decrease. Although temperature-salinity relationships indicated upwelled water masses contribute to mid-depth pH minima at some stations, their low-pH signature is fundamentally caused by aerobic respiration. A synthesis of five years of cruise data showed that mid-depth pH and DO minima, as well as nitrate maxima, were consistently located along the margins of upwelling zones or salinity fronts—regions of high biological productivity. These patterns underscore the coupled effects of physical transport and biogeochemical processes on mid-depth pH dynamics. Additionally, waters at mid-depth exhibited the lowest carbonate buffer capacity and highest DIC/TA ratios in vertical profiles, amplifying pH declines and pCO2 elevations. Such mid-depth pH minima may negatively affect upper-layer coastal ecosystems, including shellfish aquaculture.
Continue reading ‘Biogeochemical controls on the co-occurrence of mid-depth pH and DO minima in the inner shelf of the East China Sea’From global emissions to local impacts: spatially explicit modeling of ocean acidification in life cycle assessment
Published 22 October 2025 Science ClosedTags: biogeochemistry, biological response, chemistry, globalmodeling, modeling
Ocean acidification poses a critical threat to marine ecosystems. While life cycle assessment frameworks provide a method for assessing and combatting many anthropogenic impacts, marine impact models remain underdeveloped compared to their terrestrial counterparts. This study presents the first spatially explicit characterization model for quantifying the impacts of ocean acidification that includes both midpoint and endpoint characterization factors (CFs). Midpoint CFs were spatially delineated by using marine ecoregions and Food and Agriculture Organization fishing areas, leveraging spatially explicit fate and fate sensitivity factors. Endpoint CFs were calculated using species sensitivity distributions that include species across a range of calcification levels, climate zones, and trophic levels. Results demonstrate significant geographic variability in ocean acidification impacts, with polar regions showing heightened vulnerability. Our findings emphasize the need for spatially explicit modeling to account for the diverse biogeochemical and ecological responses to ocean acidification. This work advances marine impact assessment by integrating spatial and biological complexity, providing critical tools for quantifying ocean acidification’s global ecological and economic consequences.
Continue reading ‘From global emissions to local impacts: spatially explicit modeling of ocean acidification in life cycle assessment’Coupled acidification-nitrification dynamics in eutrophic estuarine waters
Published 20 October 2025 Science ClosedTags: biogeochemistry, biological response, chemistry, community composition, field, molecular biology, North Pacific, otherprocess, prokaryotes
Highlights
- Mid-estuary emerges as a hotspot for coupled acidification-nitrification, intensified by hydrology.
- Nitrifier community structure adapts to acidification stress, while responds differently.
- AOB is more sensitive to acidification in estuarine water compared to AOA.
- Future climate change scenarios project intensified acidification and nitrification coupling in mid-estuary.
Abstract
The interplay between acidification and nitrification in estuarine systems could have profound effects on coastal biogeochemistry and ecosystem health. However, the lack of integrated field research risks oversimplifying their relationships in complex ecosystem dynamics. This study investigates the spatiotemporal covariations of acidification sensitivity and nitrification rates derived from observed inorganic carbon and nutrients data along a land-sea continuum. In the middle estuary, estuarine pH exhibited the highest sensitivity to ammonium concentration, coinciding with maximum nitrification rates. The coupling effect intensified by 40% during the transition from dry to wet hydrological conditions. Despite that microbial network complexity generally decreased with increased acidification sensitivity, ammonia-oxidizing bacterial communities are more sensitive to acidification in estuarine water compared to ammonia-oxidizing archaea. Conversely, in the lower estuary, acidification was associated with a decline in nitrification activities. Machine learning-based models suggest that climate change scenarios could exacerbate acidification and nitrification in the Pearl River Estuary, potentially amplifying their coupling effect in the middle estuary. This holistic approach not only advances our fundamental understanding of estuarine processes, also provides critical insights for policymakers and coastal managers striving to maintain the ecological integrity of these vital ecosystems in an era of rapid global change.
Continue reading ‘Coupled acidification-nitrification dynamics in eutrophic estuarine waters’Macroalgae farming increases DO and pH, reduces pCO2 and nutrients, and enhances blue carbon potential
Published 17 October 2025 Science ClosedTags: algae, biogeochemistry, biological response, chemistry, field, fisheries, mitigation, North Pacific
Edible macroalgal cultivation is increasingly promoted as a nature-based solution to mitigate coastal eutrophication and improve seawater quality. However, the species-specific impacts and spatial extent of these ecological effects remain poorly understood, particularly in semi-enclosed bays with complex hydrodynamics. This study aims to quantify the biogeochemical influence of two widely cultivated species—Porphyra haitanensis and Hizikia fusiformis—on seawater carbonate chemistry and nutrient levels in Yueqing Bay, eastern China. High-resolution field surveys were conducted at 52 stations, enabling direct comparisons between cultivated and non-cultivated waters. Geostatistical modeling, including spherical semivariograms and Empirical Bayesian Kriging, was applied to delineate species-specific influence zones and quantify changes in key water quality parameters. P. haitanensis farming induced broad, kilometer-scale improvements in seawater chemistry, including elevated dissolved oxygen (DO) (+ 2.72%) and pH (+ 0.09 units), and significantly lower partial pressure of CO2 (pCO2) (− 118 µatm), relative to distant reference sites (all p < 0.05). A slight increase in total phosphorus (TP) (+ 0.007 mg L− 1) was also observed, likely reflecting nearby riverine inputs. In contrast, H. fusiformis cultivation produced more localized (< 100 m) but significant changes, including reductions in dissolved inorganic carbon (DIC) (− 1.84 mg L− 1) and pCO2 (− 82.6 µatm), alongside increases in DO (+ 1.72%), pH (+ 0.02 units), and chlorophyll-a (Chl-a) (+ 0.72 µg L− 1) (all p < 0.05). These results provide the first fine-scale, species-resolved spatial assessment of macroalgal farming effects on water quality in a semi-enclosed bay. By quantifying distance-dependent ecological responses, this study offers science-based guidance for spatial planning, nutrient management, and blue carbon integration—particularly as the routine harvest of biomass facilitates net carbon export from coastal waters. These findings highlight the potential of macroalgal farming as a scalable, multifunctional nature-based solution for sustainable aquaculture and climate mitigation.
Continue reading ‘Macroalgae farming increases DO and pH, reduces pCO2 and nutrients, and enhances blue carbon potential’Insights from a changing ocean: evolving biogeochemistry and its impacts on marine ecosystems and climate
Published 13 October 2025 Science ClosedTags: biogeochemistry, chemistry, communitymodeling, field, modeling, paleo, regionalmodeling
Marine biogeochemistry integrates chemical, biological, geological, and physical processes that are fundamental to Earth’s climate and ecosystems. As elements cycle through the ocean, atmosphere, and biosphere, they leave behind biogeochemical fingerprints that serve as proxies to track environmental change. Over the industrial era, anthropogenic CO2 emissions and other human activities have caused the oceans to change rapidly, perturbing this biogeochemical landscape. Characterizing biogeochemical shifts is critical to advance our understanding of climate-driven impacts, assess marine ecosystem health, and evaluate climate solutions. Recent advancements in biogeochemical tools and technologies have deepened our insights into oceanic change. The development of high-precision paleoproxies has extended records of ocean conditions into the pre-industrial era, while the Argo float array has enabled four-dimensional monitoring of biogeochemistry globally. High-resolution numerical modeling has also improved our ability to capture complex interactions at fine spatial and temporal scales, offering a holistic framework to understand anthropogenic impacts from past to future. Together, these technologies provide a comprehensive toolkit to characterize shifts in ocean biogeochemistry in unprecedented detail and advance our understanding of global environmental change. This thesis weaves together applications of novel biogeochemical tools to examine the drivers, impacts, and mitigation strategies of a rapidly changing ocean. Each chapter leverages diverse datasets and multiple tools to provide new insights on ocean change based on marine biogeochemistry. In Chapter 2, I combine boron-isotope measurements from cold-water corals with a biogeochemical model to reconstruct and investigate subsurface acidification trends over the industrial era in the California Current System. In Chapter 3, I combine Argo-based biogeochemical data products, archival tagging records, and machine learning methods to develop a four-dimensional species distribution model for an economically important fishery species, revealing biogeochemical constraints on its migration. In Chapter 4, I employ a high-resolution biogeochemical model of the Salish Sea to evaluate the detectability of ocean alkalinity enhancement, a marine carbon dioxide removal strategy for climate mitigation. These studies provide new frameworks and tools to investigate, monitor, and respond to a changing ocean.
Continue reading ‘Insights from a changing ocean: evolving biogeochemistry and its impacts on marine ecosystems and climate’Research progress on responses of upper-ocean nitrogen uptake and nitrification to ocean acidification and warming (in Chinese)
Published 10 October 2025 Science ClosedTags: biogeochemistry, biological response, multiple factors, otherprocess, phytoplankton, prokaryotes, review, temperature
Nitrogen uptake by phytoplankton and nitrification mediated by nitrifying microorganisms in the upper ocean are key processes affecting marine productivity and carbon sequestration. How these two critical nitrogen cycle processes respond to the dual stressors of ocean acidification and warming represents a pressing research frontier in marine biogeochemical cycles and global change. Elucidating this issue will provide a theoretical foundation for accurately assessing future changes in ocean productivity and the efficiency of the biological pump. However, most existing studies rely on laboratory pure culture experiments, which may fail to adequately reflect the complex interactions between phytoplankton and nitrifying microorganisms in natural marine ecosystems and their responses to changes in environmental factors. The impacts and mechanisms of ocean acidification and warming on nitrogen uptake and nitrification are systematically summarized. In addition, more attention needs to be paid to other factors, such as strengthened ocean stratification and decreased dissolved oxygen contents, induced by ocean acidification and warming, which could indirectly affect nitrogen uptake and nitrification. Existing problems, such as insufficient in-situ monitoring of ecosystems, limited synergistic studies on multiple processes and stresses, and inadequate understanding of long-term adaptation processes, are highlighted. Finally, three key areas of research that need to be focused on in the future were prospected: ① to conduct the synchronous coupling analysis of nitrogen uptake and nitrification processes and clarify the interactive effects of acidification and warming, ② to explore the vertical differentiation response mechanisms of the above processes in the upper ocean, particularly in oligotrophic oceans, where critical knowledge gaps exist, and ③ to elucidate the long-term adaptation processes and nonlinear response laws of phytoplankton and nitrifying microorganisms. A three-in-one research framework is constructed in the spatial dimension, temporal scale and the experimental system to provide a scientific basis for evaluating the evolution of key nitrogen processes and marine productivity under global change.
Continue reading ‘Research progress on responses of upper-ocean nitrogen uptake and nitrification to ocean acidification and warming (in Chinese)’Environmental conditions and carbonate chemistry variability influencing coral reef composition along the Pacific coast of Costa Rica
Published 10 October 2025 Science ClosedTags: biogeochemistry, BRcommunity, chemistry, community composition, corals, field, North Pacific, otherprocess
Coral reef development is influenced by a wide variety of factors, including temperature, salinity, nutrient concentrations, and carbonate chemistry. Studies focusing on physicochemical drivers of coral reef distribution and composition in the Eastern Tropical Pacific (ETP) are scarce, and carbonate chemistry and nutrient data for this region are limited. This study measured coral reef composition and physicochemical parameters along the Pacific coast of Costa Rica, over a one-year period at three locations: Santa Elena and Matapalo in the north, and Parque Nacional Marino Ballena in the south. Our results show high seasonal and spatial variability of physicochemical conditions with significant differences mainly explained by inorganic nutrient concentrations, with driving processes also having a strong influence on the variability of carbonate chemistry parameters. Coastal upwelling is the main driver of the seasonal variability in Santa Elena. Comparison of seasonal dissimilarity within locations confirms the presence of a geographical gradient, with stronger influence of the upwelling in Santa Elena relative to Matapalo, where several parameters displayed a lower seasonality and a carbonate system that supports reef development throughout the year. Conversely, in Marino Ballena the river discharges during rainy season exerted a strong control on the seasonal variability. The integrated analysis of coral reef composition and physicochemical parameters suggests that in addition to inorganic nutrients carbonate chemistry also plays a key role in coral distribution. Analyzing the spatial distribution of the main reef builders provides insights into the species-specific tolerance to varying conditions. Pavona clavus is widely distributed in both the northern and southern locations, suggesting that this massive coral is very tolerant to the high variability of physicochemical conditions. The dominant corals in the north (Pavona gigantea and Pocillopora spp.) are highly tolerant to nutrient-enriched cold waters with low aragonite saturation, while one of the main reef-builders in southern locations (Porites cf. lobata) cope better with low salinity, low aragonite saturation and low light intensity caused by river discharges. Understanding the preferences of individual coral species at our study locations can shed light on the environmental factors driving coral reef distribution in other locations of the ETP.
Continue reading ‘Environmental conditions and carbonate chemistry variability influencing coral reef composition along the Pacific coast of Costa Rica’Relative enrichment of ammonium and its impacts on open-ocean phytoplankton community composition under a high-emissions scenario
Published 7 October 2025 Science ClosedTags: biogeochemistry, biological response, community composition, field, globalmodeling, modeling, otherprocess, phytoplankton
Ammonium (NH4+) is an important component of the ocean’s dissolved inorganic nitrogen (DIN) pool, especially in stratified marine environments where intense recycling of organic matter elevates its supply over other forms. Using a global-ocean biogeochemical model with good fidelity to the sparse NH4+ data that are available, we project increases in the NH4+: DIN ratio in over 98 % of the ocean by the end of the 21st century under a high-emission scenario. This relative enrichment of NH4+ is driven largely by circulation changes and secondarily by warming-induced increases in microbial metabolism, as well as reduced nitrification rates due to pH decreases. Supplementing our model projections with geochemical measurements and phytoplankton abundance data from Tara Oceans, we demonstrate that shifts in the form of DIN to NH4+ may impact phytoplankton communities by disadvantaging nitrate-dependent taxa like diatoms while promoting taxa better adapted to NH4+. This could have cascading effects on marine food webs, carbon cycling and fishery productivity. Overall, the form of bioavailable nitrogen emerges as a potentially underappreciated driver of ecosystem structure and function in the changing ocean.
Continue reading ‘Relative enrichment of ammonium and its impacts on open-ocean phytoplankton community composition under a high-emissions scenario’Remote sensing of coastal acidification: UAS and satellite-based estimation in the Mississippi Sound and landscape change impact assessment
Published 7 October 2025 Science ClosedTags: biogeochemistry, chemistry, field, modeling, North Atlantic, regionalmodeling
Ocean acidification results from atmospheric CO₂ absorption, while coastal acidification is more localized, influenced by nutrient runoff, freshwater input, and organic matter decomposition. Due to its complexity, specialized monitoring is essential. The present research estimated two key carbonate system parameters total alkalinity (TA) and partial pressure of carbon dioxide (pCO₂) using uncrewed aircraft systems (UAS) imagery and autonomous surface vessel (ASV) observations over an oyster reef in the Western Mississippi Sound (WMS). Field campaigns were conducted from 2018 to 2022 to collect high resolution aerial imagery over the largest oyster reef in WMS, utilizing a multispectral sensor mounted on a drone. An ASV was deployed during June, July, and September 2021 UAS missions over the same sites to collect in situ data, including pH, partial pressure of carbon dioxide (pCO2), sea surface temperature (SST), sea surface salinity (SSS), colored dissolved organic matter (CDOM), and chlorophyll-a (Chl-a). Random forest models developed and accurately estimated TA and pCO₂ (R² > 0.91). Time-series maps were generated using Chl-a images derived from UAS imagery and SSS images derived from CDOM maps, employing salinity-CDOM linear regression model developed in this study. Results demonstrate UAS effectiveness in small-scale coastal monitoring due to its high spatial resolution. However, UAS lacks spatial coverage needed for broader regions like Mississippi Sound. To address this, MODIS imagery and HYCOM model outputs were integrated with ASV data collected in June and August 2023 in this research. Random forest models using SST, SSS, and Chl-a performed well (R² = 0.81 for TA, 0.87 for pCO₂). By incorporating MODIS Level 3 SST and Chl-a (1 km) and HYCOM SSS (downscaled 4 km to 1 km), this research generated annual and monthly time-series maps of mean TA and pCO₂ over the entire Mississippi Sound for the period 2002–2020. These maps reveal spatial seasonal dynamics and long-term trends. This research also investigated how land use and land cover (LULC) changes influenced TA and pCO₂ across the entire Mississippi Sound from 2002 to 2020. Spatial correlation and trend maps revealed associations between eight LULC class type changes and TA and pCO₂ patterns. The findings suggest connections between environmental changes and carbonate system responses but do not confirm causation, instead providing a basis for hypothesis generation and further study of biogeochemical processes. Overall, this dissertation highlights how combining remote sensing, in situ measurements, machine learning technique, and LULC analysis improves coastal acidification assessment in the Mississippi Sound.
Continue reading ‘Remote sensing of coastal acidification: UAS and satellite-based estimation in the Mississippi Sound and landscape change impact assessment’The evolution of ocean carbon cycle feedbacks in observations and models
Published 7 October 2025 Science ClosedTags: biogeochemistry, chemistry, field, globalmodeling, modeling, North Pacific
Since the Industrial Revolution, the ocean has absorbed a cumulative ~40% of the anthropogenic carbon (Cant) released into the atmosphere by fossil fuel emissions. Cant accumulation in the upper ocean has driven an increase in the partial pressure of carbon dioxide gas (pCO2) and associated declines in pH and carbonate ion concentration. These chemical changes, collectively referred to as ocean acidification (OA), progressively weaken the ocean’s buffer capacity and reflect the evolution of a positive marine carbon cycle feedback that reduces the efficiency of future Cant uptake and amplifies the influence of natural variability on the carbonate system. This dissertation investigates the spatial and temporal changes in the ocean carbon cycle caused by Cant using a combination of in situ observations, data synthesis products, and output from regional and global ocean models to improve our understanding of the processes governing the ocean carbon sink and its evolving feedbacks. Chapter 1 evaluates the impact of Cant accumulation on multiple OA metrics throughout the water column in the North Pacific Ocean and California Current Large Marine Ecosystem using ship-based observations. Results indicate that the greatest increases in pCO2 occur subsurface, where Cant content is moderate and pCO2 change can exceed overlying surface change by ≥100%. Amplified pCO2 responses in the interior ocean are related to background ocean carbonate chemistry, with the greatest subsurface changes associated with poorly buffered waters that have experienced substantial organic matter remineralization. Chapter 2 evaluates the impact of Cant on the seasonal variability of pCO2 in the surface ocean using output from global ocean biogeochemical models (GOBMs) used by global carbon budgeting efforts to estimate the historical ocean carbon sink strength. Results indicate that dissimilar model representations of surface ocean pCO2 seasonality, particularly during winter, lead to increasing disagreement in annual ocean carbon sink strength estimates over time. Chapter 3 examines how differences in representations of interior ocean Cant and natural carbon influence patterns of amplified subsurface pCO2 change using the same set of GOBMs, in addition to observation-based data products. Results indicate that GOBMs dissimilarly simulate subsurface Cant-induced pCO2 changes, particularly at the depth of maximum winter mixing, when these signals can re-emerge at the surface and bias estimates of the annual ocean carbon sink strength. This research contributes to ongoing international efforts to better constrain the global ocean carbon sink. Discrepancies between observation- and model-based estimates of the modern ocean carbon sink have grown over time, with across-model disagreements compounding in future climate projections. This points to an outstanding need to constrain sources of model discrepancies. This work helps to address this by clarifying: (1) a model’s projected end-of-century ocean carbon sink magnitude is highly dependent on its post-spin-up seasonal and annual mean-state; (2) a more realistic representation of interior ocean carbon distributions and ecosystem processes is needed to achieve a more realistic representation of ocean carbon cycle change and the evolution of its feedbacks.
Continue reading ‘The evolution of ocean carbon cycle feedbacks in observations and models’Ocean acidification, iodine bioavailability, and cardiovascular health: a review of possible emerging risks
Published 16 September 2025 Science ClosedTags: biogeochemistry, review, socio-economy
Anthropogenic climate change drives ocean acidification, which alters marine iodine cycling and increases bioaccumulation in marine ecosystems. This environmental shift elevates dietary and atmospheric iodine exposure, particularly in coastal populations, posing risks for thyroid dysfunction and downstream cardiovascular complications. Acidification enhances iodine uptake in marine species, such as kelp and seafood, thereby amplifying human intake. Chronic iodine excess can induce hypothyroidism or hyperthyroidism, both linked to cardiovascular diseases, including heart failure, atrial fibrillation, and atherosclerosis. This narrative review synthesizes the mechanistic pathways connecting ocean acidification, iodine bioavailability, thyroid dysfunction, and cardiovascular health. We emphasize the need for proactive clinical screening, dietary interventions, environmental monitoring, international collaboration, and inter-disciplinary research to address this climate-sensitive public health challenge. Coastal communities, reliant on marine diets, require targeted strategies to mitigate these emerging risks.
Continue reading ‘Ocean acidification, iodine bioavailability, and cardiovascular health: a review of possible emerging risks’Particulate inorganic carbon pools by coccolithophores in low-oxygen–low-pH waters off the Southeast Pacific margin
Published 10 September 2025 Science ClosedTags: biogeochemistry, biological response, chemistry, field, phytoplankton, South Pacific
A predicted consequence of ocean acidification is the decrease in coccolithophore-produced particulate inorganic carbon (PIC) pools. PIC is thought to enhance the sinking of particulate organic carbon (POC) to deeper waters, potentially influencing the depth of organic matter remineralization and subsurface O2 levels. To explore these potential feedbacks, we examined the relationships between PIC, coccolithophores, carbonate chemistry, and dissolved O2 in the Southeast Pacific open-ocean oxygen minimum zone – a region characterized by naturally low dissolved O2, low pH, and high pCO2 levels. Measurements of PIC and coccolithophore abundance from late spring 2015 and mid-summer 2018 revealed that coccolithophores, particularly Gephyrocapsa (Emiliania) huxleyi, were major contributors to PIC through the shedding of coccoliths. On average, about half of the PIC was attributed to reliably enumerated coccospheres and detached coccoliths, with significantly diminished pools below the euphotic zone. Temperature, O2, and pH emerged as key factors associated with PIC variability. PIC pools and PIC : POC ratios in both surface and subsurface waters in this naturally low-pH–low-O2 zone are lower than available data from most oceanic regions, with the exception of the Western Arctic. Our findings support the prediction that in upwelling regions with a shallow oxygen minimum zone, POC production is promoted by phytoplankton other than PIC-producing coccolithophores due to the injection of nutrient rich but low-pH water. This process decreases PIC : POC ratios, suggesting that the role of PIC in POC sedimentation might be decreased under such conditions. We emphasize that comparing PIC dynamics across diverse upwelling systems will be valuable for understanding how low-pH and low-O2 conditions influence POC fluxes mediated by coccolithophores.
Continue reading ‘Particulate inorganic carbon pools by coccolithophores in low-oxygen–low-pH waters off the Southeast Pacific margin’Ocean acidification: impacts on marine ecosystems and deep-sea carbon sequestration
Published 10 September 2025 Science ClosedTags: biogeochemistry, biological response, fisheries, mitigation, review
Carbon dioxide (CO₂) is a major greenhouse gas that plays an essential role in Earth’s climate system. Oceans help climate stability by absorbing about 30% of the anthropogenic CO₂ emissions. However, this process leads to ocean acidification (OA) and reduces the availability of carbonate ions, which are necessary for organisms that build shells and skeletons, such as corals, mollusks, and certain plankton. Since the Industrial Revolution, ocean pH has dropped by approximately 0.1 units, a significant shift that threatens marine ecosystems. OA affects marine organisms in multiple ways. Calcifying species struggle to form shells, leading to reduced survival and disrupted food webs. Coral reefs, often called the “rainforests of the sea” due to their exceptional biodiversity, are particularly vulnerable, and their decline results in biodiversity and habitat loss. Phytoplankton, the foundation of the marine food web and the ocean’s biological carbon pump, also respond in mixed ways; some benefit from higher CO₂, while others are negatively affected, reducing ocean productivity and carbon cycling. OA weakens the ocean’s biological carbon pump, reducing long-term carbon storage in the deep sea. It also contributes to harmful algal blooms, which can contaminate seafood and pose human health risks. Economically, OA threatens global seafood production, especially shellfish and crustaceans, jeopardizing food security and coastal livelihoods. This paper explores the biological, ecological, and economic impacts of OA and discusses mitigation strategies such as reducing CO₂ emissions, protecting blue carbon ecosystems, controlling coastal pollution, and supporting adaptive aquaculture. Addressing OA is essential to protect marine biodiversity, sustain seafood resources, and maintain climate stability.
Continue reading ‘Ocean acidification: impacts on marine ecosystems and deep-sea carbon sequestration’A regional physical–biogeochemical ocean model for marine resource applications in the Northeast Pacific (MOM6-COBALT-NEP10k v1.0)
Published 5 September 2025 Science ClosedTags: biogeochemistry, modeling, North Pacific, regionalmodeling
Regional ocean models enable the generation of computationally affordable and regionally tailored ensembles of near-term forecasts and long-term projections of sufficient resolution to serve marine resource management. Climate change, however, has created marine resource challenges, such as shifting stock distributions, that cut across domestic and international management boundaries and have pushed regional modeling efforts toward “coastwide” approaches. Here, we present and evaluate a multidecadal hindcast with a Northeast Pacific regional implementation of the Modular Ocean Model, version 6, with sea ice and biogeochemistry that extends from the Chukchi Sea to the Baja California Peninsula at 10 km horizontal resolution (MOM6-COBALT-NEP10k, or NEP10k). This domain includes an Arctic-adjacent system with a broad, shallow shelf seasonally covered by sea ice (the eastern Bering Sea), a sub-Arctic system with upwelling in the Alaska Gyre and predominant downwelling winds and large freshwater forcing along the coast (the Gulf of Alaska), and a temperate, eastern boundary upwelling ecosystem (the California Current Ecosystem). The coastwide model was able to recreate seasonal and cross-ecosystem contrasts in numerous ecosystem-critical properties including temperature, salinity, inorganic nutrients, oxygen, carbonate saturation states, and chlorophyll. Spatial consistency between modeled quantities and observations generally extended to plankton ecosystems, though small to moderate biases were also apparent. Fidelity with observed zooplankton biomass, for example, was limited to first-order seasonal and cross-system contrasts. Temporally, simulated monthly surface and bottom temperature anomalies in coastal regions (<500 m deep) closely matched estimates from data-assimilative ocean reanalyses. Performance, however, was reduced in some nearshore regions coarsely resolved by the model’s 10 km resolution grid and for point measurements. The time series of satellite-based chlorophyll anomaly estimates proved more difficult to match than temperature. System-specific ecosystem indicators were also assessed. In the eastern Bering Sea, NEP10k robustly matched observed variations, including recent large declines, in the area of the summer bottom water “cold pool” (<2 °C), which exerts a profound influence on eastern Bering Sea fisheries. In the Gulf of Alaska, the simulation captured patterns of sea surface height variability and variations in thermal, oxygen, and acidification risk associated with local modes of interannual to decadal climate variability. In the California Current Ecosystem, the simulation robustly captured variations in upwelling indices and coastal water masses, though discrepancies in the latter were evident in the Southern California Bight. Enhanced model resolution may reduce such discrepancies, but any benefits must be carefully weighed against computational costs given the intended use of this system for ensemble predictions and projections. Meanwhile, the demonstrated NEP10k skill level herein, particularly in recreating cross-ecosystem contrasts and the time variation of ecosystem indicators over multiple decades, suggests considerable immediate utility for coastwide retrospective and predictive applications.
Continue reading ‘A regional physical–biogeochemical ocean model for marine resource applications in the Northeast Pacific (MOM6-COBALT-NEP10k v1.0)’Model based analysis of the methane seeping influence on the acidification in the East Siberian Arctic Shelf waters
Published 4 September 2025 Science ClosedTags: Arctic, biogeochemistry, chemistry, modeling, regionalmodeling
A giant Arctic subsea permafrost reservoir of methane (CH4) in different forms (hydrates, free gas) is leaking, likely at an increasing rate under climate warming. This is causing a massive CH4 release from sediments into the water column and atmosphere. A part of the released CH4 is oxidized in the water column to CO2. In this work we applied a model for analyzing of consequences for the water column carbonate system of excessive production of CO2 during the aerobic oxidation of CH4 in an area of its intensive seeping in the East Siberian Arctic Shelf (ESAS). The model system comprised a 2-Dimensional vertical Benthic Pelagic transport Model 2DBP, principal biogeochemistry and carbonate system modules from the biogeochemical model BROM (Bottom RedOx Model), and a gas bubble fate module that parameterizes bubbles rising and dissolution. The simulations showed that consumption of oxygen and production of carbon dioxide via aerobic oxidation of methane results in spatial anomalies of pH and dissolved oxygen concentration that are consistent with the field observations. We hypothesize that aerobic oxidation of methane in the regions of intensive seeping leads to production of CO2, with associated decrease of pH and lowering of aragonite saturation to less than 1, therefore contributing to the extreme acidification states that are observed on the East Siberian Arctic Shelf.
Continue reading ‘Model based analysis of the methane seeping influence on the acidification in the East Siberian Arctic Shelf waters’
