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’Posts Tagged 'South Pacific'
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
Nutritional status and shell properties of the scallop Argopecten purpuratus are sensitive to intense upwelling events
Published 8 July 2025 Science ClosedTags: adaptation, biological response, field, mollusks, morphology, multiple factors, otherprocess, oxygen, physiology, South Pacific, temperature
Highlights
- The scallop Argopecten purpuratus cope with permanent environmental fluctuations.
- Upwelling intensity and duration affect its physiological perfomance.
- Shell organic matrix was adversely affected by intense upwelling events.
- The nutritional status of the A. purpuratus is modulated by upwelling intensity.
- A. purpuratus seems to be partially adapted to colder, low pH and hypoxic conditions.
Abstract
Changes in environmental conditions can be particularly stressful for marine biota. However, marine organisms possess a variety of biological mechanisms (e.g., expression of stress proteins, down or up metabolic regulation, among others) that enable them to adapt to such conditions. This will ultimately determine their resilience and adaptive capacity to the natural environmental fluctuations occurring in their habitats, but also to future climate-driven shifts. In Chile, the scallop Argopecten purpuratus inhabits regions under permanent upwelling conditions causing, at different temporal and spatial scales, cooling, low pH and hypoxic conditions of diverse magnitude. In one-year field experiment, we observed that A. purpuratus was, in some occasions, adversely affected by intense upwelling events during the spring season, when the most intense upwelling events were observed, and thus the lowest temperatures, pH and oxygen levels were registered. These effects were more evident in some shell properties, such as the shell organic matrix, a key component of the biomineralization process. Also, no impacts or positive responses (i.e., up-regulation) were observed on parameters associated to their nutritional status (i.e., carbohydrate and protein muscle content), and periostracum thickness suggesting the presence of physiological trade-offs, but also adaptive mechanisms serving to cope with stressful environmental conditions. Ultimately, our findings also raise concerns about the potential consequences of intensified upwelling due to climate change, particularly for the aquaculture sector that relies on this species, since the majority of impacts were observed in individuals of sizes considered attractive to the market.
Continue reading ‘Nutritional status and shell properties of the scallop Argopecten purpuratus are sensitive to intense upwelling events’Variability of marine carbonate systems in seagrass and coral reef ecosystems of Pari and Lombok Islands, Indonesia
Published 2 July 2025 Science ClosedTags: chemistry, field, South Pacific
The increase in anthropogenic CO2 emissions has induced significant physical and biogeochemical alterations in oceans worldwide, including warming, acidification, and oxygen depletion. Coastal areas are particularly vulnerable due to intensified human activities and terrestrial influences, resulting in increased coastal ocean acidification driven by atmospheric CO2 absorption and regional biological and anthropogenic processes. However, research on the collective impact of land-sea interaction and air-sea CO2 exchange on coastal ocean acidification in severely disturbed areas, such as the small islands of Lombok and Pari in Indonesia, remains limited. This study aims to investigate the daily fluctuations in marine carbonate systems and aragonite saturation (Ωarag) levels in the vicinity of seagrass and coral reef habitats in Pari Island and Sire Bay, Lombok. Seawater samples were collected from Sire Bay, Lombok, and the coastal waters of Pari Island to analyze the carbonate systems, CO₂ flux, and metabolic processes. The findings indicate that Pari Island’s coastal waters are more susceptible to ocean acidification than Sire Bay, Lombok, showing significantly lower pH values and Ωarag (P<0.05), ranging from 7.60 to 8.00 and 1.04 to 2.54, respectively. This disparity arises from the decreased temperature and salinity in Pari Island’s coastal waters during the northwest monsoon, coupled with the deteriorated state of the seagrass and coral reef ecosystems, altering the equilibrium of ecosystem productivity and calcification. The study underscores the necessity of adopting specific coastal management tactics to lessen the effects on fragile ecosystems, highlighting the urgency for additional studies to evaluate adaptive and conservation strategies to preserve coastal biodiversity and ecosystem services.
Continue reading ‘Variability of marine carbonate systems in seagrass and coral reef ecosystems of Pari and Lombok Islands, Indonesia’The seven sins of climate change: a review of rates of change, and quantitative impacts on ecosystems and water quality in the Great Barrier Reef
Published 1 July 2025 Science ClosedTags: biological response, BRcommunity, chemistry, corals, review, South Pacific
Highlights
- Reviewed rates of change for 7 climate change factors, quantifying impacts
- Climate change affects water quality, emphasising local management needs
- Extreme weather events are still the most destructive climate change factors
- Progressive climate factors will increase in importance, altering ecosystems.
- Ocean acidification may reach critical thresholds within decades.
Abstract
The term climate change encompasses many types of impacts and threats to the long-term outlook of coastal marine ecosystems. Based on a structured Evidence Summary methodology, this review synthesises the peer-reviewed knowledge on climate change impacts on the Great Barrier Reef (GBR). We summarise the observed and predicted region-specific rates of change for seven climate change factors; three representing episodic extreme weather events (heatwaves, tropical storms, and extreme rainfall events), and four chronic progressive climate change factors (rising temperatures, ocean acidification and sea level, and altered cloudiness/windiness). We extract key quantitative findings on their impacts on GBR ecosystems and associated organisms, especially coral reefs, seagrasses, mangroves and wetlands, and on GBR water quality. Quantifying GBR-wide effects requires data on their four dimensions: intensity, duration, spatial extent, and frequency. The review shows that to date, most damage to GBR ecosystems is inflicted by extreme weather events. Of the progressive climate change factors, ocean acidification is already altering some GBR ecosystem functions, potentially reaching a critical threshold within decades. The progressive climate change factors are already causing selective mortality and changes in communities. We document regional differences, and we outline the evidence of climate change impacts on GBR water quality, suggesting further cumulative effects. This review provides an overview of empirical data for modellers and ecologists, and for experimentalists to choose environmentally relevant treatment levels. Intensifying climate change disturbances increase the urgency of climate change mitigation, as well as effective local management to accelerate ecosystem recovery.
Continue reading ‘The seven sins of climate change: a review of rates of change, and quantitative impacts on ecosystems and water quality in the Great Barrier Reef’Infaunal bivalves exhibit resilience to ocean acidification but remain sensitive to food supply
Published 26 June 2025 Science ClosedTags: biological response, chemistry, dissolution, laboratory, mesocosms, mollusks, morphology, multiple factors, physiology, South Pacific
Soft-sediment habitats are crucial for marine coastal ecosystems, supporting diverse biodiversity both above and below the sediment. Ocean acidification, driven by rising CO2 and nutrient influx, enhances heterotrophic metabolism, raising CO2 levels and lowering pH. These alterations complicate the dynamics of tidal flat, emphasizing the need for further research into their impact on biodiversity. Within these ecosystems, deposit- and suspension-feeding bivalves play crucial roles. Tagelus dombeii, a bivalve mollusc found in soft sediments, exhibits burrowing behavior linked to food supply and is of significant commercial value in southern Chile. This study assessed the response capacity of T. dombeii to key stressors associated with global ocean change, such as ocean acidification and food availability. Our results revealed significant differences in pH levels between the water column and pore water from the sediment in experimental mesocosms. T. dombeii was affected by ocean acidification and food availability in terms of its morphological traits (i.e. length, width, height and growth rate), while oxygen consumption was influenced only by the interaction between acidification and food supply. Notably, heart rate remained constant but increased when food supply was low. Our study suggests that T. dombeii exhibits partial tolerance to variations in seawater pH and carbonate chemistry, possibly due to its natural exposure to acidic pore water, but it is sensitive to food availability. These plastic physiological responses suggest that T. dombeii may be less vulnerable to future global change scenarios, demonstrating potential resilience and ecological success in its natural habitat.
Continue reading ‘Infaunal bivalves exhibit resilience to ocean acidification but remain sensitive to food supply’Modeling terrestrial dissolved organic carbon and its effect on the carbonate system in the Sunda Shelf seas, Southeast Asia
Published 17 April 2025 Science ClosedTags: biogeochemistry, chemistry, modeling, North Pacific, regionalmodeling, South Pacific
Abstract
The flux of dissolved organic carbon (DOC) from land to sea is an important transfer within the global carbon cycle. The biogeochemical fate of this terrestrial DOC (tDOC) remains poorly understood and is usually neglected in ocean models. Southeast Asia accounts for around 10% of global tDOC flux, mostly from tropical peatland-draining rivers discharging onto the Sunda Shelf. We developed a new light-driven parameterization of tDOC remineralization that accounts for photochemical, microbial, and interactive photochemical–microbial degradation, and simulated the transport and remineralization of tDOC through the Sunda Shelf seas using the regional 3D hydrodynamical HAMSOM and biogeochemical ECOHAM models (only for the carbonate system). Our realistic hindcast simulations for 1958–2022 show that about 50% of riverine tDOC is remineralized before leaving the shelf. This lowers seawater pH across the entire inner Sunda Shelf by an average of 0.005 (by up to 0.05 in the Malacca Strait). Correspondingly, seawater pCO2 is raised, increasing yearly CO2 outgassing from the shelf by 19% (3.1 Tg C yr−1, 0.14 mol m−2 yr−1) during 2013–2022. Even regional ocean acidification trends increase, because river discharge and tDOC flux increase. Our model reveals large spatial variability with greatest inputs and remineralization of tDOC close to major peatlands, especially off Sumatra and Borneo. The interannual variability in tDOC input and the monsoonal current reversal lead to strong temporal variability in carbonate system parameters in these areas. Our results highlight the importance of representing tDOC in ocean models, and reveal the fate of tropical peatland tDOC.
Key Points
- We modeled terrestrial dissolved organic carbon (tDOC) using a new scheme for photo-, bio-, and interactive photo-bio-degradation
- TDOC input to the Sunda Shelf in 2013–2022 is 15.9 Tg C yr−1. 50% is remineralized on the shelf, 28% directly exported to Indian Ocean
- This drives shelf-wide outgassing of 3.1 Tg C yr−1 in 2013–2022, lowers pH and aragonite saturation, increases ocean acidification trends
Plain Language Summary
The transport of terrestrial dissolved organic carbon (tDOC) from land to sea via rivers is an important part within the global carbon cycle. The majority of this tDOC is remineralized by sunlight and marine bacteria, which produces CO2 leading to ocean acidification and CO2 outgassing into the atmosphere. The degradation process is poorly understood, usually neglected in ocean models. Southeast Asia accounts for around 10% of global tDOC flux, mostly from rivers with peatland areas in their catchment. We developed an equation of tDOC remineralization that depends on sunlight and accounts for photochemical, microbial, and interactive photochemical–microbial degradation. With this, we simulated the fate of tDOC using a 3D computer model system for the Southeast Asian region. Our realistic results for 1958–2022 show: 50% of the tDOC is remineralized before leaving the Sunda Shelf. As a result, the shelf water acidifies and emits more CO2 to the atmosphere. Because of increasing river freshwater runoff (from climate change), more tDOC is transported in time into the sea and more is remineralized, increasing the ocean acidification. This happens mostly in coastal seas close to rivers with much peatland in their catchment. This is harmful for calcifying marine organisms like corals.
Continue reading ‘Modeling terrestrial dissolved organic carbon and its effect on the carbonate system in the Sunda Shelf seas, Southeast Asia’Building ocean science capacity in the Solomon Islands: an ocean acidification training to empower local experts
Published 15 April 2025 Web sites and blogs ClosedTags: South Pacific
The Solomon Islands, consisting of more than 900 islands, are already suffering from the effects of climate change. The country faces rising sea levels (projected to increase by up to 89 cm by 2090 under high-emission scenarios) along with intensifying storms and coastal erosion. Between 1999 and 2018, the Solomon Islands ranked as the 65th most affected country by extreme weather events.
In addition to these threats, there is a hidden danger: the ocean is slowly becoming more acidic. This puts coral reefs and marine ecosystems at risk, vital for the local economy and providing food. Recent global models estimate that the pH in the southwest Pacific has decreased by 0.06 since preindustrial times. Leisz’s (2009) projections showed that by 2040, ocean acidification will begin to impact the areas around the Solomon Islands.
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In response to these growing threats, efforts are intensifying in the country to equip local scientists and institutions with the tools they need to monitor and adapt to ocean acidification. A recent five-day training held at the Solomon Islands National University (SINU) in Honiara marked a milestone in this journey.
Delivered by the Pacific Community, in partnership with The Ocean Foundation, the training brought together ocean experts from government, agencies and SINU. The training was led by Kim Currie and Miriama Vuiyasawa, experts in Ocean acidification at the Pacific Islands Ocean Acidification Centre (PIOAC), which SPC hosts.
The workshop aimed to improve participants’ skills and provide them with the latest tools to support ocean acidification research. They received practical training on how to use the “Global Ocean Acidification Observing Network in a Box kit,” a key toolkit that helps researchers and coastal communities collect and analyse ocean water samples for pH and total alkalinity, and to determine aragonite saturation.
Continue reading ‘Building ocean science capacity in the Solomon Islands: an ocean acidification training to empower local experts’Skeletal morphometrics suggests high fitness of hybrid coral recruits under ocean warming and acidification
Published 10 April 2025 Science ClosedTags: biological response, BRcommunity, corals, laboratory, morphology, multiple factors, South Pacific, temperature
Anthropogenic greenhouse gas emissions increase sea surface temperature and acidification, inhibiting calcification of reef-building corals. While ocean acidification is known to hinder skeletal development of newly settled coral recruits, little is known of its effects on older purebred or interspecific hybrid recruits, or its combined effects with temperature. Using 3D X-ray microscopy, we found that predicted mid-century ocean warming and acidification conditions (28 °C, 685 ppm pCO2) negatively affected the skeletal development of 7-month-old Acropora purebreds and hybrids in one direction (Acropora cf. kenti mother x Acropora loripes father). Conversely, the skeletal parameters of reciprocal hybrids (A. loripes mother x A. cf. kenti father) remained unaffected. Skeletal measurements taken from 3D data revealed patterns overlooked by previous 2D measurements, leading support to the likelihood of hybrid vigour in hybrids of A. loripes (mother) and A. cf. kenti (father) and the potential of interspecific hybridization as a reef restoration tool to enhance coral resilience.
Continue reading ‘Skeletal morphometrics suggests high fitness of hybrid coral recruits under ocean warming and acidification’Safeguarding South-East Asia’s marine ecosystems from ocean acidification threats
Published 28 March 2025 Newsletters and reports ClosedTags: Indian, policy, South Pacific
The increasing carbon dioxide emissions from human activities are being absorbed by the oceans, leading to a decrease in seawater pH levels worldwide. South-East Asia is particularly vulnerable to this problem, as the projected trend of ocean acidification severely threatens marine life in the region, as well as marine industry productivity and food safety. Urgent action must be taken by the Association of Southeast Asian Nations (ASEAN) Secretariat and its Member States to sustain coastal populations’ livelihoods and economic prosperity.
Recommendations:
- Improve marine protected areas (MPAs) by applying science-based design and grass-roots community participation
- Establish a regional task force and collaborative funding
- Increase public awareness and implement marine educational programmes through curriculum integration
Detrital source diversity moderates decomposition and nutrient release in current and future ocean conditions
Published 25 March 2025 Science ClosedTags: algae, biological response, BRcommunity, laboratory, multiple factors, South Pacific, temperature
Highlights
- The decomposition of mixed and single detrital sources was assessed in current and future ocean conditions.
- The identity of detrital sources significantly influenced decomposition rates, and carbon and nutrient release.
- Detrital mixing significantly decreased variation in mass loss and nitrogen release.
- Ocean warming sometimes increased rates of decomposition of macrophyte detritus.
- Ocean acidification did not significantly influence detrital mass loss or nutrient release.
Abstract
The complex interactions between detrital diversity and ocean climate change are not well understood. Here, we used sixteen outdoor raceways to test the hypothesis that ocean warming, and acidification would increase rates of decomposition and nutrient release from detritus of common macroalgae, but the magnitude of change would vary for single detrital sources compared to mixed sources. Our litter-bag experiment to test this hypothesis had six types of macroalgal detritus: (i) Ecklonia radiata, (ii) Sargassum vestitum, (iii) Caulerpa filiformis, (iv) Ecklonia and Sargassum mix, (v) Ecklonia and Caulerpa mix, and (vi) Sargassum and Caulerpa mix. The experimental design also had an orthogonal set of treatments testing effects of ocean warming and acidification, individually and combined, based on the RCP 8.5 climate model for 2081–2100. The identity of detrital sources significantly influenced decomposition rates, carbon liberation and nutrient release. The treatments with two detrital sources did not have increased rates of decomposition and nutrient release compared to single sources. However, detrital source mixing significantly moderated variation in decomposition and nutrient release rates. While ocean acidification had little effect on the decomposition of macroalgal detritus, ocean warming tended to increase rates of decomposition. Given that excessive decomposition can lead to severe anoxia, the results suggest the risk of this occurring will be greater in the warmer oceans of coming decades. In such circumstances, the moderating force of detrital diversity may become increasingly important in maintaining benthic oxygen concentrations and detritus-based production.
Continue reading ‘Detrital source diversity moderates decomposition and nutrient release in current and future ocean conditions’On the measurement of ocean acidity with ambient sound
Published 12 March 2025 Science ClosedTags: chemistry, field, methods, North Pacific, South Pacific
The volume-integrated pH of seawater can be determined from the frequency and depth dependence of wind-generated ambient noise in the ocean. Over the 1 − 10 kHz frequency band, three main processes contribute to the acoustic attenuation in seawater: the chemical relaxation of boric acid and magnesium carbonate (< 3 kHz, related to pH), and magnesium sulfate (> 3 kHz, unrelated to pH). When local winds are strong (> 10 m/s), the ambient noise is dominated by locally generated surface noise, which exhibits a depth-independent directionality, and weak frequency and depth-dependent intensity. By measuring the depth-dependence of the spectral slope, the pH may be estimated from a comparison of the experimental data with an analytical model of ambient noise. Measurements of the depth-dependent ambient noise field were carried out in the Philippine Sea, Mariana Trench, and Tonga Trench from 2009 to 2021. The wideband (5 Hz – 30 kHz) acoustic data were recorded with untethered, free-falling, autonomous instrument platforms known as Deep Sound, equipped with two or four hydrophones. In all the data collected, the power spectral slopes became steeper with depth due to the stronger attenuation of high frequencies compared to low frequencies. Depth-averaged pH values, ranging from 7.68 to 8.35, were obtained from eight instrument drops. The noise spectral method, which has the potential for determining the depth-averaged value of pH, with the averaging depth being adjustable, could be suitable for the long-term passive acoustic monitoring of ocean acidity.
Continue reading ‘On the measurement of ocean acidity with ambient sound’Spatiotemporal variability of seawater carbonate chemistry in diverse coral reef environments in South East Asia and Australia
Published 26 February 2025 Science ClosedTags: biogeochemistry, chemistry, field, modeling, regionalmodeling, South Pacific
Coral reefs are under threat from global environmental perturbations including ocean warming, acidification, and deoxygenation. The degree to which these perturbations will affect coral reefs is dependent on a range of factors including the local hydrodynamics and biogeochemical processes, both which vary widely across space and time. Consequently, not all coral reefs will be affected equally due to differences in local properties and processes. To develop predictive capacity for how coral reefs will be affected by ocean acidification (OA) it is necessary to first understand the current seawater CO2 chemistry variability and drivers. In this dissertation, autonomous sensors and discrete seawater samples were used to characterize the natural spatial and temporal variability of seawater CO2 chemistry across different reef scales and habitats in Australia and South East Asia (i.e., Heron Island, Great Barrier Reef; Dongsha Atoll and Taiping Island, South China Sea; and Onna-son Reef, Okinawa). In Heron Island, the largest spatial and temporal variability in seawater chemistry was associated with the most shallow, western region of the platform that also had the longest residence time. Interactions between reef geomorphology and timing of the tidal cycle greatly influenced chemical gradients and variability leading to some unexpected trends and patterns. On Dongsha, elevated pH and aragonite saturation state (ΩAr) were observed inside a semi-enclosed lagoon during both day and night. Future projections showed that this environment will not cross, detrimental aragonite thresholds (e.g., ΩAr < 2.92) as frequently as patch reefs and the large-scale lagoon of Dongsha. However, concurrent high water temperature and hypoxia indicated that this environment will not offer respite to taxa sensitive to OA. In Onna-son, the influence of seaweed cultivation on seawater chemistry during spring was compared to times of no cultivation during fall and winter. pH elevation was observed during both spring (+0.13 units) and fall (+0.10 units), but it was not possible to separate the role of cultivated seaweed from natural taxa. This dissertation demonstrates current coral reef seawater CO2 chemistry conditions and biochemical function, information that will be critical for making rigorous projections for the future.
Continue reading ‘Spatiotemporal variability of seawater carbonate chemistry in diverse coral reef environments in South East Asia and Australia’Conspecific interactions between corals mediate the effect of submarine groundwater discharge on coral physiology
Published 30 January 2025 Science ClosedTags: biological response, BRcommunity, chemistry, corals, field, photosynthesis, physiology, respiration, South Pacific
Land-based inputs, such as runoff, rivers, and submarine groundwater, can alter biologic processes on coral reefs. While the abiotic factors associated with land-based inputs have strong effects on corals, corals are also affected by biotic interactions, including other neighboring corals. The biologic responses of corals to changing environmental conditions and their neighbors are likely interactive; however, few studies address both biotic and abiotic interactions in concert. In a manipulative field experiment, we tested how the natural environmental gradient created by submarine groundwater discharge (SGD) affected holobiont and symbiont metabolic rates and endosymbiont physiology of Porites rus. We further tested how the effect of SGD on the coral was mediated by intra and interspecific interactions. SGD is a natural land-sea connection that delivers nutrients, inorganic carbon, and other solutes to coastal ecosystems worldwide. Our results show that a natural gradient of nutrient enrichment and pH variability as a result of acute SGD exposure generally benefited P. rus, increasing gross photosynthesis, respiration, endosymbiont densities, and chlorophyll a content. Conspecifics in direct contact with the a neighboring coral, however, altered the relationship between coral physiology and SGD, lowering the photosynthetic and respiration rates from expected values when the coral had no neighbor. We show that the response of corals to environmental change is dependent on the types of nearby neighbor corals and how neighbors alter the chemical or physical environment around the coral. Our study underscores the importance of considering biotic interactions when predicting the physiologic responses of corals to the environment.
Continue reading ‘Conspecific interactions between corals mediate the effect of submarine groundwater discharge on coral physiology’Uncertainties about the role of river and mangrove dissolved inorganic carbon and alkalinity loads in buffering the Great Barrier Reef lagoon
Published 13 January 2025 Science ClosedTags: chemistry, field, South Pacific
Terrestrial dissolved inorganic carbon (DIC) and total alkalinity (TAlk) loads have contrasting effects on the pH and carbonate chemistry of the coastal ocean. While TAlk can buffer against ocean acidification, elevated exports of free CO2 can further exacerbate ocean acidification. In this study, we quantify terrestrial DIC and TAlk loads from rivers and mangrove floodplains across six bioregions and varying flow conditions to assess their impact on the buffering capacity of the Great Barrier Reef (GBR) lagoon in Australia. For a mid-flow year, median terrestrial DIC and TAlk loads ranged from 0.72 to 0.89 Tg C yr−1 and 0.26 to 1.03 Tg C yr−1, respectively. We find that mangrove-dominated terrestrial inputs only have a small influence on the whole GBR but contribute 12.5% (range: 1.9%–45.7%) of the DIC and 18.7% (range: 2.8%–68.2%) of the TAlk inner shelf inventory. Depending on the approach used to estimate TAlk loads, mangroves have a potential short-term buffering effect on near-shore coastal waters due to higher TAlk loads. However, long-term mangrove TAlk production via pyrite formation complicates this interpretation, highlighting the need for ongoing monitoring to understand the complex interplay between terrestrial inputs and their effect on the GBR carbonate chemistry.
Key Points
- Current measurement uncertainties hinder our ability to accurately predict the effects of terrestrial inputs on the GBR coastal waters
- Mangrove floodplains dominate terrestrial dissolved inorganic carbon (DIC) and total alkalinity (TAlk) loads to the Great Barrier Reef (GBR) lagoon
- Terrestrial loads of DIC and TAlk are higher in high flow years and in tropical wet bioregions with localized effects on the GBR lagoon
Multi-variate hybrid modeling for pacific ocean acidification: predicting future pH trends and analyzing key biogeochemical drivers
Published 7 January 2025 Science ClosedTags: chemistry, modeling, North Pacific, regionalmodeling, South Pacific
Ocean acidification, driven by rising atmospheric carbon dioxide levels, poses a significant threat to the health of marine ecosystems, particularly in the Pacific Ocean. This study employs a multi-variate hybrid machine learning approach to predict future pH trends within the Pacific and to analyze the influence of key biogeochemical drivers on these trends. Hybrid models, strategically combining the strengths of individual algorithms, were developed for predicting several ocean acidification parameters. A performance analysis demonstrated the superior accuracy of hybrid models compared to their counterparts. The predicted pH trends reveal a concerning shift towards increased acidity within the Pacific Ocean, highlighting the urgency of understanding and mitigating its impacts. In-depth analysis was conducted to identify the relative influence of key biogeochemical factors on the changing pH dynamics. This research aims to provide crucial insights for developing targeted mitigation strategies and protecting the vulnerable ecosystems of the Pacific Ocean from the escalating consequences of ocean acidification.
Continue reading ‘Multi-variate hybrid modeling for pacific ocean acidification: predicting future pH trends and analyzing key biogeochemical drivers’Effects of pH, temperature, and light on the inorganic carbon uptake strategies in early life stages of Macrocystis pyrifera (Ochrophyta, Laminariales)
Published 1 January 2025 Science ClosedTags: algae, biological response, laboratory, light, multiple factors, physiology, South Pacific, temperature
The responses of seaweed species to increased CO2 and lowered pH (Ocean Acidification: OA) depend on their carbon concentrating mechanisms (CCMs) and inorganic carbon (Ci) preferences. However, few studies have described these mechanisms in the early life stages of seaweeds or assessed the effects of OA and its interactions with other environmental drivers on their functionality and photophysiology. Our study evaluated the effects of pH, light (PAR), temperature, and their interactions on the Ci uptake strategies and photophysiology in the early stages of Macrocystis pyrifera. Gametophytes were cultivated under varying pH (7.80 and 8.20), light (20 and 50 µmol photons m−2s−1), and temperature (12 and 16 °C) conditions for 25 days. We assessed photophysiological responses and CCMs (in particular, the extracellular dehydration of HCO3− to CO2 mediated by the enzyme carbonic anhydrase (CA) and direct HCO3− uptake via an anion exchange port). This study is the first to describe the Ci uptake strategies in gametophytes of M. pyrifera, demonstrating that their primary CCM is the extracellular conversion of HCO3− to CO2 mediated by CA. Additionally, our results indicate that decreased pH can positively affect their photosynthetic efficiency and maximum quantum yield; however, this response is dependent on the light and temperature conditions.
Continue reading ‘Effects of pH, temperature, and light on the inorganic carbon uptake strategies in early life stages of Macrocystis pyrifera (Ochrophyta, Laminariales)’Coexisting mangrove-coral habitats: trends in seawater chemistry and coral diversity
Published 20 December 2024 Science ClosedTags: biological response, BRcommunity, chemistry, corals, field, morphology, phanerogams, South Pacific
Coral reefs face unprecedented threats from climate change, with rising temperatures, ocean acidification, and other stressors endangering their survival. Coexisting mangrove-coral (CMC) habitats provide a natural laboratory to study coral resilience under extreme conditions. However, these habitats are rare and understudied, leaving gaps in understanding their biogeochemical and ecological dynamics. This thesis examines how mangrove proximity influences seawater chemistry, coral diversity, and morphology. A global review identified differences in seawater chemistry between habitat types and regions, driven by biogeochemical processes and freshwater inputs. Edge habitats, particularly in the Great Barrier Reef (GBR), were identified as understudied. An empirical study at Pioneer Bay, GBR, revealed significant spatial and temporal variations in seawater chemistry along a gradient from mangroves to open reefs. Corals near mangroves experienced greater fluctuations in pH, temperature, and oxygen, stabilizing with distance. Tidal flushing mitigated extremes, fostering coral resilience. Mangrove proximity significantly influenced benthic communities, coral morphology, and biodiversity. Extreme conditions near mangroves favored resilient corals like *Porites*, while intermediate sites supported the highest diversity due to nutrient influx and moderate disturbances. Farther sites were dominated by complex coral communities. Edge CMC habitats play a vital role in supporting coral adaptation to climate change. However, intensifying stressors threaten even resilient systems, underscoring the need for long-term monitoring and adaptive management to protect these critical biodiversity hotspots.
Continue reading ‘Coexisting mangrove-coral habitats: trends in seawater chemistry and coral diversity’Particulate inorganic carbon quotas by coccolithophores in low oxygen/low pH waters off the Southeast Pacific margin
Published 12 December 2024 Science ClosedTags: biogeochemistry, biological response, chemistry, community composition, field, otherprocess, phytoplankton, South Pacific
A predicted consequence of ocean acidification is its negative effect on the pools of Particulate Inorganic Carbon (PIC) that are essential for ‘ballasting’ the sinking of organic carbon, potentially leading to decreased subsurface oxygen. To explore such possible feedbacks, we investigated the relationships between PIC, coccolithophores, carbonate chemistry, and dissolved oxygen in the Southeast Pacific open ocean oxygen minimum zone, which naturally exhibits extremely low dissolved oxygen, low pH, and high pCO2 levels. Measurements of PIC and coccolithophore counts during late-spring 2015 and mid-summer 2018 revealed that coccolithophores, particularly Gephyrocapsa (Emiliania) huxleyi, significantly contributed to PIC through the shedding of coccoliths in the upper waters. On average, about a half of the PIC was attributed to countable coccoliths, with significantly diminished quotas observed below the euphotic depth. Temperature, oxygen, and pH were identified as key variables influencing PIC variation. PIC quotas were similar to those reported in other upwelling zones. However, PIC:POC ratios were substantially lower than what has been reported both in other open ocean and coastal margin areas, an effect that was more pronounced within the vertically defined oxygen minimum zone core. This study contributes to understanding the role of coccolithophores in PIC pools and suggests that the presence of low O2/low pH subsurface waters does not inhibit coccolithophore PIC quotas but may decrease the role of PIC in ballasting the export of organic carbon.
Continue reading ‘Particulate inorganic carbon quotas by coccolithophores in low oxygen/low pH waters off the Southeast Pacific margin’Extreme environmental variability induces frontloading of coral biomineralisation genes to maintain calcification under pCO2 variability
Published 6 December 2024 Science ClosedTags: adaptation, biological response, calcification, corals, field, laboratory, mesocosms, molecular biology, otherprocess, photosynthesis, physiology, South Pacific
Corals residing in habitats that experience high-frequency seawater pCO2 variability may possess an enhanced capacity to cope with ocean acidification, yet we lack a clear understanding of the molecular toolkit enabling acclimatisation to environmental extremes or how life-long exposure to pCO2 variability influences biomineralisation. Here, we examined the gene expression responses and micro-skeletal characteristics of Pocillopora damicornis originating from the reef flat and reef slope of Heron Island, southern Great Barrier Reef. The reef flat and reef slope had similar mean seawater pCO2, but the reef flat experienced twice the mean daily pCO2 amplitude (range of 797 v. 399 μatm day−1, respectively). A controlled mesocosm experiment was conducted over 8 weeks, exposing P. damicornis from the reef slope and reef flat to stable (218 ± 9) or variable (911 ± 31) diel pCO2 fluctuations (μatm; mean ± SE). At the end of the exposure, P. damicornis originating from the reef flat demonstrated frontloading of 25% of the expressed genes regardless of treatment conditions, suggesting constitutive upregulation. This included higher expression of critical biomineralisation-related genes such as carbonic anhydrases, skeletal organic matrix proteins, and bicarbonate transporters. The observed frontloading corresponded with a 40% increase of the fastest deposited areas of the skeleton in reef flat corals grown under non-native, stable pCO2 conditions compared to reef slope conspecifics, suggesting a compensatory response that stems from acclimatisation to environmental extremes and/or relief from stressful pCO2 fluctuations. Under escalating ocean warming and acidification, corals acclimated to environmental variability warrant focused investigation and represent ideal candidates for active interventions to build reef resilience while societies adopt strict policies to limit climate change.
Continue reading ‘Extreme environmental variability induces frontloading of coral biomineralisation genes to maintain calcification under pCO2 variability’
