Hurricane Harvey more than doubled the acidity of Texas’ Galveston Bay, threatening oyster reefs

Most people associate hurricanes with high winds, intense rain and rapid flooding on land. But these storms can also change the chemistry of coastal waters. Such shifts are less visible than damage on land, but they can have dire consequences for marine life and coastal ocean ecosystems.

We are oceanographers who study the effects of ocean acidification, including on organisms like oysters and corals. In a recent study, we examined how stormwater runoff from Hurricane Harvey in 2017 affected the water chemistry of Galveston Bay and the health of the bay’s oyster reefs. We wanted to understand how extreme rainfall and runoff from hurricanes influenced acidification of bay waters, and how long these changes could last.

Our findings were startling. Hurricane Harvey, which generated massive rainfall in the Houston metropolitan area, delivered a huge pulse of fresh water into Galveston Bay. As a result, the bay was two to four times more acidic than normal for at least three weeks after the storm.

This made bay water corrosive enough to damage oyster shells in the estuary. Because oyster growth and recovery rely on many factors, it is hard to tie specific changes to acidification. However, increased acidification certainly would have made it harder for oyster reefs damaged by Hurricane Harvey to recover. And while our study focused on Galveston Bay, we suspect that similar processes may be occurring in other coastal areas.

Continue reading Hurricane Harvey more than doubled the acidity of Texas’ Galveston Bay, threatening oyster reefs

Impacts of rising temperatures and water acidification on the oxidative status and immune system of aquatic ectothermic vertebrates: a meta-analysis


  • CO2 emissions are driving increase in temperature and water acidification.
  • Meta-analysis implemented to assess impacts of CO2-stressors on ectotherms physiology.
  • High temperature and water acidification induce higher oxidative damage in ectotherms.
  • Early life stages are more capable than adults to upregulate antioxidant enzymes.
  • Oxidative status regulation underlies thermal acclimation.


Species persistence in the Anthropocene is dramatically threatened by global climate change. Large emissions of carbon dioxide (CO2) from human activities are driving increases in mean temperature, intensity of heatwaves, and acidification of oceans and freshwater bodies. Ectotherms are particularly sensitive to CO2-induced stressors, because the rate of their metabolic reactions, as well as their immunological performance, are affected by environmental temperatures and water pH. We reviewed and performed a meta-analysis of 56 studies, involving 1259 effect sizes, that compared oxidative status or immune function metrics between 42 species of ectothermic vertebrates exposed to long-term increased temperatures or water acidification (≥48 h), and those exposed to control parameters resembling natural conditions. We found that CO2-induced stressors enhance levels of molecular oxidative damages in ectotherms, while the activity of antioxidant enzymes was upregulated only at higher temperatures, possibly due to an increased rate of biochemical reactions dependent on the higher ambient temperature. Differently, both temperature and water acidification showed weak impacts on immune function, indicating different direction (increase or decrease) of responses among immune traits. Further, we found that the intensity of temperature treatments (Δ°C) and their duration, enhance the physiological response of ectotherms, pointing to stronger effects of prolonged extreme warming events (i.e., heatwaves) on the oxidative status. Finally, adult individuals showed weaker antioxidant enzymatic responses to an increase in water temperature compared to early life stages, suggesting lower acclimation capacity. Antarctic species showed weaker antioxidant response compared to temperate and tropical species, but level of uncertainty in the antioxidant enzymatic response of Antarctic species was high, thus pairwise comparisons were statistically non-significant. Overall, the results of this meta-analysis indicate that the regulation of oxidative status might be one key mechanism underlying thermal plasticity in aquatic ectothermic vertebrates.

Continue reading ‘Impacts of rising temperatures and water acidification on the oxidative status and immune system of aquatic ectothermic vertebrates: a meta-analysis’

Multi-stress interplay: time and duration of ocean acidification modulate the toxicity of mercury and other metals

The current understanding of multi-stress interplay assumes stresses occur in perfect synchrony, but this assumption is rarely met in the natural marine ecosystem. To understand the interplay between non-perfectly overlapped stresses in the ocean, we manipulated different temporal scenarios of acidification and assessed their effect on mercury toxicity in a marine copepod. We found that the scenario of past acidification aggravated mercury toxicity, but personal and persistent acidification mitigated the toxicity. This is because personal and persistent acidification initiated the energy compensation to enhance growth and mercury efflux. To explore how general temporal scenarios of acidification affected multi-stress interplay, we conducted a meta-analysis on marine animals and found that scenarios significantly changed the toxicity of several other metals. Our study thus demonstrates that time and duration of stresses modulate multi-stress interplay in the marine ecosystem, and suggests that future studies should move beyond the scenario of perfect synchrony.

Continue reading ‘Multi-stress interplay: time and duration of ocean acidification modulate the toxicity of mercury and other metals’

Common sea star (Asterias rubens) coelomic fluid changes in response to short-term exposure to environmental stressors

Common sea stars (Asterias rubens) are at risk of physiological stress and decline with projected shifts in oceanic conditions. This study assessed changes in coelomic fluid (CF) blood gases, electrolytes, osmolality, and coelomocyte counts in adult common sea stars after exposure to stressors mimicking effects from climate change for 14 days, including decreased pH (−0.4 units, mean: 7.37), hypoxia (target dissolved oxygen ~1.75 mg O2/L, mean: 1.80 mg O2/L), or increased temperature (+10 °C, mean: 17.2 °C) and compared sea star CF electrolytes and osmolality to tank water. Changes in CF blood gases, electrolytes, and/or coelomocyte counts occurred in all treatment groups after stressor exposures, indicating adverse systemic effects with evidence of increased energy expenditure, respiratory or metabolic derangements, and immunosuppression or inflammation. At baseline, CF potassium and osmolality of all groups combined were significantly higher than tank water, and, after exposures, CF potassium was significantly higher in the hypoxia group as compared to tank water. These findings indicate physiological challenges for A. rubens after stressor exposures and, given increased observations of sea star wasting events globally, this provides evidence that sea stars as a broad group are particularly vulnerable to changing oceans.

Continue reading ‘Common sea star (Asterias rubens) coelomic fluid changes in response to short-term exposure to environmental stressors’

Tidal restrictions in a central Californian estuarine system are associated with higher mean pH, but increased low-pH exposure

Coastal acidification is an emerging concern in estuaries impaired by nutrient pollution. In addition to rising levels of atmospheric CO2 which drives ocean acidification, high nutrient inputs to coastal areas can amplify heterotrophic metabolism, raise water column CO2 levels, and exacerbate pH declines. This study focuses on how a third anthropogenic stressor, tidal restriction, shapes effects of coastal acidification. Tidal restrictions associated with installation of gates that reduce tidal flow to a portion of an estuary are a common impact to coastal landscapes and can negatively affect water quality. This study examined pH in locations subject to varying levels of tidal restriction across a series of interconnected central California estuaries, whose waters are nutrient-impaired due to surrounding agriculture, and where 50% of the system is affected by tidal restrictions. Mean and variance of pH differed based on the level of tidal restriction. Sites lacking tidal restrictions had the lowest mean pH (7.98) but the least pH variance (0.07), and the most infrequent exposure to low pH (<7.0) conditions. In contrast, sites with minimal tidal exchange had the most exposure to low pH conditions, although mean pH levels were greater (8.08), because they also saw greater pH variance (0.46). Our results suggest that tidal restrictions alter pH levels and affect the resilience of estuaries to coastal acidification.

Continue reading ‘Tidal restrictions in a central Californian estuarine system are associated with higher mean pH, but increased low-pH exposure’

Fresh and saline submarine groundwater discharge as sources of carbon and nutrients to the Japan Sea


  • Fresh groundwater was comparable to the discharge from rivers and the main source of carbon, phosphate, and nitrate to coastal waters.
  • Groundwater-derived alkalinity fluxes were 7 times greater than river inputs, buffering the coastal ocean.
  • Nutrient and chlorophyll observations revealed the strong influence of groundwater discharge on primary productivity.


Submarine groundwater discharge (SGD) is an important pathway for carbon and nutrients to the coastal ocean, sometimes exceeding river inputs. SGD fluxes can have implications for long-term carbon storage, ocean acidification and nutrient dynamics. Here, we used radium (223Ra and 226Ra) isotopes to quantify SGD-derived fluxes of dissolved inorganic (DIC) and organic (DOC) carbon, nitrate (NO3), nitrite (NO2), ammonium (NH4+) and phosphate (PO43−) in a spring-fed coastal bay in the Japan Sea. The average coastal water residence times using 223Ra/226Ra ratios was 32.5 ± 17.9 days. Fresh and saline SGD were estimated using a radium mixing model with short- and long-lived isotopes. The volume of fresh SGD entering the bay (4.6 ± 4.6 cm day−1) was more than twice that of the volume of saline SGD (1.9 ± 2.1 cm day−1). Fresh SGD (mmol m2 day−1) was the main source of DOC (2.7 ± 2.6), DIC (13.9 ± 13.7), PO43− (0.3 ± 0.3) and NO3 (6.6 ± 6.5) to the coastal ocean, whereas saline SGD was the main source of NH4+ (0.2 ± 0.2). Total SGD-derived carbon and nutrient fluxes were 4 – 7 and 2–16 times greater than local river inputs. Positive correlations between chlorophyll-a, 226Ra and δ13C-DIC indicate that SGD significantly (p < 0.05) enhances primary productivity nearshore. Overall, fresh SGD of nitrogen and carbon to seawater drove chlorophyll-a, decreased DIC/Alkalinity ratios, and modified the carbonate biogeochemistry of the coastal ocean.

Continue reading ‘Fresh and saline submarine groundwater discharge as sources of carbon and nutrients to the Japan Sea’

Effect of seagrass cover loss on seawater carbonate chemistry: implications for the potential of seagrass meadows to mitigate ocean acidification

Seagrass meadows are important marine ecosystems for mitigating ocean acidification because of their ability to raise the pH of seawater during the day. This ability may decrease as a result of the loss of these meadows, which is primarily caused by human activities and climate change. Here, we test the effect of seagrass cover loss on seawater carbonate chemistry to understand how the loss of seagrass meadows affects their ability to mitigate ocean acidification. pH, dissolved inorganic carbon (DIC), partial pressure of carbon dioxide (pCO2), and aragonite saturation state (ΩAr) were measured in experimental tidal pools with varying proportions of seagrass coverage: 0% (mimicking a complete loss of seagrass meadows); 1%–29% (mimicking the greatest loss of seagrass meadows); 30%–59% (mimicking a moderate loss of seagrass meadows); and 60%–100% (mimicking the lowest loss of seagrass meadows). It was found that as seagrass cover decreased, pH and ΩAr levels in seawater decreased proportionally during the day, while pCO2 and DIC increased. Additionally, correlation analysis showed a strong significant positive correlation between the seagrass cover and pH (rs = 0.9096, p < 0.0001) and ΩAr (rs = 0.9031, p < 0.0001), as well as a strong significant negative correlation between the seagrass cover and pCO2 (rs = −0.9068, p < 0.0001) and DIC (rs = −0.8947, p < 0.0001). These results imply that the 7% annual global loss in seagrass meadows may limit seagrass meadows’ ability to raise the pH of their surrounding seawater during the day, reducing their potential to mitigate ocean acidification. The study recommends that management strategies that minimize anthropogenic activities that cause seagrass loss be implemented in order for seagrass meadows to continue mitigating ocean acidification within their ecosystem and nearby ecosystems.

Continue reading ‘Effect of seagrass cover loss on seawater carbonate chemistry: implications for the potential of seagrass meadows to mitigate ocean acidification’

Breaking boundaries – ocean acidification

Date: 23 February 2023

Time: 15:00


Since pre-industrial times, surface ocean acidity has already risen by 30%. Beyond a certain concentration, this increasing acidity hinders the growth and survival of organisms like corals, some shellfish, and plankton species. The loss of these species would alter the dynamics and organization of ocean ecosystems and might even result in a sharp decline in fish stocks. A rich ocean is crucial, as billions of humans depend on it for daily life. What are the possibilities for change? 


  • Get to know how ocean acidification is induced by humans 
  • Find out what the tipping points are for this boundary 
  • Learn about the impact of ocean acidification for different regions 

The oceans eventually dissolve about a quarter of the CO2 that humans release into the atmosphere. Here, it turns into carbonic acid, changing the chemistry of the ocean and bringing the pH of the surface water down. Ocean acidification has implications for the entire planet, in contrast to the majority of other human impacts on the marine environment, which are frequently local in scope. Since atmospheric CO2 concentration is the fundamental controlling factor for both the climate and ocean acidification boundaries, it is also an illustration of how connected the boundaries are. 

Continue reading ‘Breaking boundaries – ocean acidification’

Climate change: what is ocean acidification? (text & video)

As carbon emissions change the chemistry of the seas, ocean acidification threatens marine life and human livelihoods. How worried should you be about climate change’s so-called “evil twin”?

The threat of ocean acidification | The Economist

Another consequence of carbon emissions

The ocean’s chemistry is changing at an unprecedented rate. By the end of this century the ocean is expected to be 150% more acidic than it is now. Acidification is threatening marine life. It’s killing baby oysters, deep-sea coral reefs and pteropods, tiny creatures, known as the potato chips of the sea. Human livelihoods are also in jeopardy. This film explores the alarming effects of ocean acidification, drawing on the expertise of scientists and the first-hand experiences of a Native Alaskan community. The film also looks at what can be done to lessen the problem.

The Economist, YouTube, 2 February 2023. Video.

A study of hypoxia and ocean acidification related physico-chemical parameters in selected coastal waters around Mauritius

Sea water samples were collected at five stations around Mauritius namely Flic-en-Flac, Albion, Mont Choisy, Trou-d’Eau-Douce and La Cambuse over 12 months from July 2021 to June 2022 for the analysis of dissolved oxygen (D.O), pHT and Total alkalinity (AT). Albion was the only open water system whereas the others were lagoons. Summer was from November 2021 to April 2022 while the period from July 2021 to October 2021, May 2022 and June 2022 were considered to be winter. The summer mean values of sea surface temperature (SST), D.O, pHT and AT varied from 28.2 ± 1.3 °C to 29.8 ± 2.2 °C, from 6.60 ± 1.15 mgL−1 to 8.11 ± 0.51 mgL−1, from 8.10 ± 0.09 to 8.20 ± 0.12 and from 2324.5 ± 110.6 μmol kg−1 to 2384.8 ± 118.6 μ mol kg−1, respectively. The winter mean values of these parameters varied from 24.7 ± 1.1 °C to 26.1 ± 1.4 °C, from 6.55 ± 1.21 mgL−1 to 8.26 ± 0.67 mgL−1, from 8.00 ± 0.08 to 8.13 ± 0.14 and from 2397.2 ± 84.9 μmol kg−1 to 2448.7 ± 108.5 μmol kg−1, respectively. The Two-way measures ANOVA and the post hoc analysis revealed that (1) the only two stations having a comparable mean pHT variability in the two seasons were Albion and La Cambuse, despite having opposite bearings and morphology, but their mean D.O variability was the contrary (2) the mean temporal variability in D.O and pHT at Mont Choisy were not significant due to the presence of sea grasses.

Continue reading ‘A study of hypoxia and ocean acidification related physico-chemical parameters in selected coastal waters around Mauritius’

Smithsonian scientists unearth signs of an ancient climate calamity buried beneath the seafloor

The research puts modern oceanic climate change in context

The research vessel JOIDES Resolution collecting samples in the Indian Ocean off the western coast of Australia in 2017. Gabriel Tagliaro

During the Cretaceous Period around 100 million years ago, Earth’s oceans were nearly unrecognizable. Below the waves swam marine reptiles: lizard-like mosasaurs, long-necked plesiosaurs and gargantuan sea turtles. These behemoths lived alongside squid-like ammonites encased in tightly-coiled shells and a slew of bizarre fish.

94 million years ago, these strange seas became nearly uninhabitable. Oxygen levels plummeted, and the ocean acidified during an episode known as the Oceanic Anoxic Event 2 (OAE2) that sent ripples through marine ecosystems worldwide. “As geologists, we’re drawn to times when things went wrong during the past,” said Matt Jones, a former research fellow at the National Museum of Natural History who now works with the United States Geological Survey. “We’re trying to understand why the oceans lost so much oxygen content in the mid Cretaceous.”

As they retrieved samples from the seafloor, the team noticed the pale-colored cores were punctuated by a green and black band of sediment several centimeters thick — a sign that something dramatic had happened to the oceanic environment. Based on its position in the core, they estimated that this band of dark sediment was deposited during the OAE2.

The black bands of mudstone in the cores represent periods when oxygen levels along the seafloor in the Mentelle Basin plummeted. Brian Huber, NMNH

Continue reading ‘Smithsonian scientists unearth signs of an ancient climate calamity buried beneath the seafloor’

Potential effects of climate change on the growth response of the toxic dinoflagellate Karenia selliformis from Patagonian waters of Chile

Northern Patagonia (41–44°S) is affected by climatic, hydrological and oceanographic anomalies, which in synergy with processes such as global warming and acidification of the coastal oceans may affect the frequency and intensity of harmful algal blooms (HABs). Greater frequency of HABs has been reported in the southeastern Pacific Ocean, including blooms of the toxic dinoflagellate Karenia selliformis, causing massive mortality of marine fauna in the oceanic and coastal areas of Patagonia. The objective of this study was to determine the effects of temperature and pH interaction on the growth of K. selliformis (strain CREAN_KS02), since these factors have wide seasonal fluctuations in the Patagonian fjord ecosystem. The CREAN_KS02 strain isolated from the Aysén Region (43°S) was used in a factorial experiment with five pH levels (7.0, 7.4, 7.7, 8.1 and 9.0) and two temperatures (12 and 17 °C) during a period of 18–21 days. Results indicated a significant effect of temperature and pH interaction on growth rate (range 0.22 ± 0.00 to 0.08 ± 0.01 d−1) and maximum density (range 13,710 ± 2,616 to 2,385 ± 809 cells mL−1) of K. selliformis. The highest density and growth of K. selliformis was found at 12 °C with a reduced pH (7.0–7.7). The results suggest that the current environmental conditions of coastal Patagonia, waters of low temperature and relatively low pH, may be favorable for the development of blooms of this species during autumn. We suggest that there is natural plasticity of K. selliformis in a wide pH range (7.0–8.1) but in a narrow low temperature range (10.6–12.9 °C), values that are typically recorded in the oceanic region of northern Patagonia. In contrast, in an extreme climate change scenario (ocean warming and coastal acidification) in northern Patagonia, a negative effect on the growth of K. selliformis may be expected due to amplification of the acidification effects caused by the thermal stress of high temperature water.

Continue reading ‘Potential effects of climate change on the growth response of the toxic dinoflagellate Karenia selliformis from Patagonian waters of Chile’

Effects of global environmental change on microalgal photosynthesis, growth and their distribution

Global climate change (GCC) constitutes a complex challenge posing a serious threat to biodiversity and ecosystems in the next decades. There are several recent studies dealing with the potential effect of increased temperature, decrease of pH or shifts in salinity, as well as cascading events of GCC and their impact on human-environment systems. Microalgae as primary producers are a sensitive compartment of the marine ecosystems to all those changes. However, the potential consequences of these changes for marine microalgae have received relatively little attention and they are still not well understood. Thus, there is an urgent need to explore and understand the effects generated by multiple climatic changes on marine microalgae growth and biodiversity. Therefore, this review aimed to compare and contrast mechanisms that marine microalgae exhibit to directly respond to harsh conditions associated with GCC and the potential consequences of those changes in marine microalgal populations. Literature shows that microalgae responses to environmental stressors such as temperature were affected differently. A stress caused by salinity might slow down cell division, reduces size, ceases motility, and triggers palmelloid formation in microalgae community, but some of these changes are strongly species-specific. UV irradiance can potentially lead to an oxidative stress in microalgae, promoting the production of reactive oxygen species (ROS) or induce direct physical damage on microalgae, then inhibiting the growth of microalgae. Moreover, pH could impact many groups of microalgae being more tolerant of certain pH shifts, while others were sensitive to changes of just small units (such as coccolithophorids) and subsequently affect the species at a higher trophic level, but also total vertical carbon transport in oceans. Overall, this review highlights the importance of examining effects of multiple stressors, considering multiple responses to understand the complexity behind stressor interactions.

Continue reading ‘Effects of global environmental change on microalgal photosynthesis, growth and their distribution’

Oregon shellfish farmers: perceptions of stressors, adaptive strategies, and policy linkages


  • Interviews were conducted with fifteen (79%) of oyster farmers in Oregon.
  • Farmers are most impacted by environmental, economic, and regulatory stressors.
  • Shellfish farmers had matching adaptive strategies to address these stressors.
  • Flexible aquaculture policies can help support these strategies.


In the United States, domestic oyster aquaculture production is insufficient to meet national demand, thus creating a reliance on international oyster imports for consumption. West coast shellfish farmers are threatened by climate change, including ocean acidification as well as socioeconomic challenges such as labor availability. To expand and enhance United States oyster production, and support domestic food security and livelihoods, a better understanding of the limitations that oyster farmers’ experience, and corresponding pathways forward for adaptation is needed. Through semi-structured interviews conducted with commercial Oregon shellfish farmers, we assess the environmental, economic, social and regulatory stressors impacting oyster growing operations, and the corresponding adaptive strategies employed or envisioned by aquaculture farmers. We find farmers are most impacted by environmental stressors (nuisance species that interact with oysters or oyster habitat negatively), followed by regulatory and economic stressors (permitting and regulations and labor availability). Farmers perceived ocean acidification as a risk, but primarily at the oyster larva stage rather than the juvenile or adult grow-out stage. Examples of farmer-identified adaptive strategies included streamlining permitting and regulations, incentivizing employee retention, and having flexibility in culture type to avoid nuisance species and other environmental stressors. An increase in targeted outreach related to aquaculture policies and engagement with industry, scientists, managers, and policy-makers could facilitate policies that support these and other adaptive strategies.

Continue reading ‘Oregon shellfish farmers: perceptions of stressors, adaptive strategies, and policy linkages’

Spatial distribution of seawater carbonate chemistry and hydrodynamic controls in a low-inflow estuary


  • Hydrodynamic exchange in low-inflow estuaries influences local carbonate chemistry.
  • Large tidal differences in alkalinity due to hypersaline conditions near bay head.
  • Flushing time largely explains spatial trends in carbonate chemistry.
  • Diel cycles and long flushing times minimized tidal differences in dissolved CO2.


Coastal and estuarine systems play an important role in the global carbon cycle and often have complex carbonate chemistry dynamics due to a multitude of biogeochemical and physical drivers. Compared to classic estuaries, mechanisms driving the distribution of carbonate parameters in low-inflow estuaries are understudied. The spatial distribution of carbonate chemistry and hydrodynamic parameters were characterized in Morro Bay, a short and seasonally hypersaline estuary on the Central California Coast, during the dry, low-inflow season to better understand in situ modifications. Sampling transects were completed in the main channel in June, August, and September of 2018, bracketing both a high and low tide on each date. Temperature, salinity, total alkalinity, and dissolved inorganic carbon all increased from the mouth to the back of the estuary, with larger values observed during the low tide. pH values decreased towards the back of the bay, and had little variation between high and low tide for June and August transects. Flushing times (estimated using a salt-budget model approach) also increased toward the back of the bay which led to hypersaline conditions. Salinity alone only explained 20–33% of observed changes in total alkalinity and 13–22% of observed changes in dissolved inorganic carbon throughout the bay. The remaining changes in total alkalinity and dissolved inorganic carbon were likely driven by biogeochemical modifications enhanced by extended flushing times, particularly in the back bay. Prior to this project, Morro Bay experienced a recent, rapid collapse of eelgrass, the major biogenic habitat. In the last four years eelgrass in Morro Bay appears to be on a recovery trajectory; therefore, this study provides a baseline whereby future studies can evaluate carbonate chemistry changes associated with potential eelgrass recovery and expansion. This study highlights the unique hydrodynamic exchange in seasonally low-inflow estuaries and its potentially large role in influencing local carbonate chemistry and ocean acidification.

Continue reading ‘Spatial distribution of seawater carbonate chemistry and hydrodynamic controls in a low-inflow estuary’

A universal framework to measure the impacts of ocean acidification on marine life

IOC/UNESCO’s efforts to advance towards the Sustainable Development Goal 14.3 “Minimize and address the impacts of ocean acidification, including through enhanced scientific cooperation at all levels’ involve its role as the custodian agency for the associated indicator 14.3.1, meaning that it is responsible for the compilation and sharing of global data on ocean acidification.

Ocean acidification is a significant environmental threat that is having a profound impact on marine life, including coral reefs, shellfish, and many other species. A lack of a global framework for measuring the effects of ocean acidification on marine life has made it difficult for the scientific community to effectively assess this issue.  

The publication of the new article “Unifying biological field observations to detect and compare ocean acidification impacts across marine species and ecosystems: What to monitor and why” by the GOA-ON Biological Working Group, supported by IOC/UNESCO, provides a global guiding framework for the scientific community to measure the impacts of ocean acidification on marine life.  It  proposes five broad classes of biological indicators that, when coupled with environmental observations including carbonate chemistry, would allow to observe and compare the rate and severity of biological change in response to ocean acidification globally. 

Such a novel observing methodology allows inclusion of a wide diversity of marine ecosystems in regional and global assessments and has the potential to increase the contribution of ocean acidification observations from countries with developing ocean acidification science capacity.

Read the paper online: 

IOC-UNESCO, 31 January 2023. Press release.

OA-ICC bibliographic database updated

An updated version of the OA-ICC bibliographic database is available online.

The database currently contains 10,040 references and includes citations, abstracts and assigned keywords. Updates are made every month.

The database is available as a group on Zotero. Subscribe online or, for a better user experience, download the Zotero desktop application and sync with the group OA-ICC in Zotero. Please see the “User instructions” for further details.

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Groundwater discharge and streams drive spatial alkalinity and pCO2 dynamics in two contrasting tropical lagoons

Coral reef lagoons are areas of complex carbon cycling, however, regional (e.g. land use) and global (e.g. climate) factors, including land runoff and ocean acidification, are adversely affecting carbonate-building coral reef systems. Coupled with this, surplus nutrients entering coastal waters can prompt excess algae growth, which can stimulate further carbon dioxide (CO2) production in the water column, thus enhancing coral/sediment dissolution. However, new inputs of alkalinity into coastal systems can buffer against acidification. By combining the natural groundwater tracer radon (222Rn) with carbonate chemistry in two contrasting Cook Island lagoons (the fringing Muri Lagoon on Rarotonga and the comparatively larger Aitutaki near-atoll lagoon), we were able to identify multiple drivers of coral reef acidification and regulation. Despite the lagoons having similar rates of submarine groundwater discharge (3.1 to 3.3 cm d−1; although the rate in Aitutaki is a maximum rate based on an assumed 100 m seepage face), groundwater inputs of CO2 and alkalinity were primarily driven by different sources (discrete offshore seeps in Muri Lagoon and dredged channels in Aitutaki Lagoon). Streams delivered low alkalinity water to both lagoons, but high pCO2 waters to the Aitutaki Lagoon in contrast to Muri Lagoon. Aragonite saturation states (ΩAr) ranged between 2.2 and 5.2, with areas of low ΩAr corresponding to areas of high radon and excess algal growth in Muri Lagoon, and areas that receive low alkalinity surface water in Aitutaki. Time-series sampling indicated that tidal heights and the ability of seawater to overtop the fringing reef influenced groundwater dynamics, lagoon hydrodynamics and carbonate chemistry. Groundwater discharge and stream flows were a significant freshwater source of new geologic CO2 and alkalinity to each lagoon, while recirculated seawater is likely a significant source of biologic CO2 driven by microbial respiration in sediments. The study found that while groundwater inputs of alkalinity may reduce acidification, they do not fully counteract ongoing acidification and CO2 inputs. This study also highlighted the need for future studies to undertake detailed spatial measurements to accurately characterise tropical island carbon dynamics due to the heterogeneous nature of these environments.

Continue reading ‘Groundwater discharge and streams drive spatial alkalinity and pCO2 dynamics in two contrasting tropical lagoons’

Dissolved CO2 and oxygen dynamics on coral reefs: from natural variability and impacts on calcification to projections under warming

Coral reefs globally are facing impacts from ocean warming, acidification, and oxygen loss as a result of anthropogenic climate change. Understanding the spatiotemporal patterns of reef carbonate chemistry and oxygen variability, as well as how low pH or oxygen conditions might affect coral physiology, is key to predicting how global reefs will be impacted in the future. In this dissertation, I leveraged dissolved oxygen data from autonomous sensors deployed at 32 sites around the world to explore present-day oxygen variability and project changes in hypoxia exposure under modeled ocean warming. I show that hypoxia is pervasive on global coral reefs, with 84 % of the reef habitats surveyed experiencing weak to moderate hypoxia and 13 % experiencing severe hypoxia under present-day conditions. Calculations of reef oxygen loss under 5 warming scenarios reveal that warming will increase the duration, intensity, and severity of hypoxic events on reefs, leading to severely hypoxic conditions on more than a third of these reef habitats by 2100. In case studies of reefs in Bermuda and Taiwan, I examined multidimensional variability in carbonate chemistry and oxygen across a reef and assessed the potential for seagrass beds to serve as refugia for corals from ocean acidification and deoxygenation. In Bermuda, data from spatial seawater surveys and a suite of autonomous sensors at the surface and benthos revealed strong signals of both benthic and water column productivity that interacted with local geomorphology and hydrodynamics to create the observed patterns in carbonate chemistry and oxygen across the reef. In Taiwan, strong gradients in temperature, pH, and oxygen across the seagrass bed were associated with significant differences in coral skeletal extension rate, density, and ∂13C isotopic composition measured from coral cores. However, there was no evidence that the presence of seagrass significantly impacted coral calcification rates along this gradient. Altogether, this dissertation provides projections of coral reef oxygen loss under rapid climate change and highlights the contributions of local conditions to observed variability in seawater chemistry with complex impacts on coral growth.

Continue reading ‘Dissolved CO2 and oxygen dynamics on coral reefs: from natural variability and impacts on calcification to projections under warming’

Scientists participate in ocean acidification annual community meetings in San Diego, California

Scientists from NOAA’s Atlantic Oceanographic and Meteorological Laboratory (AOML), and our cooperative institute partners, the University of Miami’s Cooperative Institute of Marine and Atmospheric Studies  and the Northern Gulf Institute, recently participated in Ocean Acidification Annual Community Meetings at the Scripps Institute of Oceanography in San Diego, California. Over the course of multiple days, scientists attended various meetings on ocean acidification research topics, visited laboratories, met with fellow scientists, learned about new ocean acidification technologies, and much more. 

Seven scientists wearing name tags pose for a photo with a green lawn, palm trees, and the Pacific Ocean in the background.
Molly Baringer, Leticia Barbero, Ian Enochs, Nastassia Patin, Luke Thompson, Kelly Goodwin, and Fabian Gomez attending the Ocean Acidification Annual Community Meeting at the Scripps Oceanographic Institute.

NOAA’s Ocean Acidification Program (OAP) seeks to better prepare society to respond to changing ocean conditions by understanding the processes of ocean acidification through interdisciplinary partnerships both nationally and internationally. The goals of the OAP community meeting are to shape the future of the OAP; to inform community members of OAP updates, encourage collaborations with the ocean acidification research community, discuss research gaps and how to address them, and to make ocean acidification research more diverse and accessible.

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