Ocean Acidification

The way Philip Gravinese, Ph.D., sees it, research is important not just for what can be discovered but for how that information can be shared.

In keeping with that philosophy, Gravinese, an Eckerd College assistant professor of marine science, recently co-authored a paper titled “Do pH-Variable Habitats Provide Refuge for Stone Crabs from Coastal Acidification?” It was published Nov. 15 in the journal Oceanography.

“The paper is a lesson developed for educators that is based on some of the ongoing research I’ve been doing near Fort De Soto Park,” Gravinese explains. “In this work we are looking at stone crab reproductive success between sandy habitats (narrow pH range) and seagrass habitats (wider pH range) to see if the pH range between those habitats provides the stone crab with any reproductive advantage under future climate change reductions in seawater pH.”

The project is being funded by the Tampa Bay Estuary Program.

Last year, Gravinese and two researchers from Louisiana State University were awarded a four-year, $922,000 grant from the National Science Foundation to study the impact of climate change on stone crabs. The goal is to investigate and model how rapidly changing ocean temperatures and pH levels disrupt stone crab larval development, behavior and dispersal among habitats along the Florida coasts. Gravinese’s previous work has shown that stone crabs can be sensitive to environmental stressors throughout their larval development.

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The urgent need to remove excess carbon dioxide from Earth’s environment could include enlisting some of our planet’s smallest inhabitants, according to an international research team led by Michael Hochella of the Department of Energy’s Pacific Northwest National Laboratory.

Hochella and his colleagues examined the scientific evidence for seeding the oceans with iron-rich engineered fertilizer particles near ocean plankton. The goal would be to feed phytoplankton, microscopic plants that are a key part of the ocean ecosystem, to encourage growth and carbon dioxide (CO₂) uptake. The analysis article appears in the journal Nature Nanotechnology.

“The idea is to augment existing processes,” said Hochella, a Laboratory fellow at Pacific Northwest National Laboratory. “Humans have fertilized the land to grow crops for centuries. We can learn to fertilize the oceans responsibly.”

In nature, nutrients from the land reach oceans through rivers and blowing dust to fertilize plankton. The research team proposes moving this natural process one step further to help remove excess CO₂ through the ocean. They studied evidence that suggests adding specific combinations of carefully engineered materials could effectively fertilize the oceans, encouraging phytoplankton to act as a carbon sink.

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More information: Peyman Babakhani et al, Potential use of engineered nanoparticles in ocean fertilization for large-scale atmospheric carbon dioxide removal, Nature Nanotechnology (2022). DOI: 10.1038/s41565-022-01226-w

A bryozoan, at 32m depth at Signy Island, Antarctica. Credit: David Barnes, British Antarctic Survey

A new study led by the Institut de Ciències del Mar (ICM-CSIC), with colleagues from the British Antarctic Survey, the Institute of Oceanology, the Polish Academy of Sciences and the University of Gdańsk have also participated has revealed that global warming and ocean acidification threaten marine organisms that build their skeletons and shells with calcium carbonate (chalk) such as corals, bryozoans, molluscs, sea urchins or crustaceans.

The work, recently published in the journal Ecography, focuses on organisms with calcium carbonate skeletons from around Antarctica in the Southern Ocean. Calcium carbonate is more soluble in more acidic waters which contain more carbon dioxide (CO₂), such as the colder waters of the polar regions, making it harder for these creatures to build their skeletons.

Bryozoans, key for understanding the global change impacts on calcifying organisms

To carry out the study, researchers analysed the skeleton of a group of marine creatures called bryozoans (commonly known as moss animals), which are small filter-feeding invertebrates that live on the seafloor and can create complex habitats that enhance biodiversity.

In this sense, the expert explains that the bryozoan skeletons are made of the two main types of calcium carbonate, calcite or aragonite, but they can also incorporate magnesium, which can make the skeletons more vulnerable to acidification.

Through mineralogical analyses, researchers identified the different types of minerals and determined the levels of magnesium found in Antarctic bryozoan skeletons, creating the largest dataset for Southern Ocean bryozoans ever produced. Then, they included these mineral signatures with existing data from almost 500 species found in the Southern Hemisphere and compared the distribution of the different mineral types and levels of magnesium in their skeletons with the temperature of the seawater that they lived in.

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Ocean warming and ocean acidification driven by climate change decrease the nutritional quality of some marine organisms, causing disruptions to the ocean food web.

This is the main conclusion of a study conducted by the Institute of Environmental Science and Technology of the Universitat Autònoma de Barcelona (ICTA-UAB) in collaboration with the Roscoff Marine Station (France) that analyzes the increase in temperature and ocean acidification on the nutritional content of coccolithophores, a unique and abundant type of phytoplankton able to calcify and cover the cell with elaborate calcite elements.

Ocean warming and acidification are the result of the rapid accumulation of carbon dioxide in the atmosphere. While ocean warming is predicted to cause changes in the distribution of species, which will have impacts on marine ecosystems, calcifying marine organisms are predicted to respond negatively to ocean acidification as it makes it more difficult for them to build their skeleton or shells. Although these impacts are expected to affect the marine food web, there is a lack of knowledge as to what these specific effects will be.

Coccolithophores are at the base of the marine food web and are a food source for many zooplankton species by providing energy to these organisms in the form of fats (lipids) and other nutrients. Like other marine organisms, acidification is expected to negatively affect their shells.

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The Minister for Science and Industry Ed Husic and the Minister for the Environment and Water Tanya Plibersek today launched the State of the Climate Report 2022.

The report underlines why the Australian Government is acting with urgency to tackle climate change in line with our international obligations and the expectations of the Australian people.

It was prepared by two of Australia’s leading climate research agencies, the CSIRO and the Bureau of Meteorology.

State of the Climate has found changes to weather and climate extremes are happening at an increased pace across Australia.

The report, released every two years, shows an increase in extreme heat events, intense heavy rainfall, longer fire seasons and sea level rise. The report draws on the latest climate monitoring, science and projection information to detail Australia’s changing climate now and into the future. 

The report details that concentrations of greenhouse gases, such as carbon dioxide, are at the highest levels seen on Earth in at least two million years. This is causing Australia’s climate to warm. 

The report also documents the continuing acidification of the oceans around Australia, which have also warmed by more than one degree since 1900.  

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By comparing data from a long list of Arctic expeditions, researchers have been able to see how the pH of the ocean north of Alaska and Siberia has decreased rapidly. In recent decades, the rate of acidification of the Arctic Ocean has been 3–4 times faster than in other oceans. This is because more carbon dioxide is taken up by the sea water when the surface is in direct contact with the atmosphere without a barrier of ice. In the past, the sea ice has kept the sea water close to the North Pole from being saturated with carbon dioxide.

“The time-series of pH measurements made in the Arctic Ocean is long. The oldest are from an expedition in 1994, when the ice sheet was extensive and thick, and measurements were taken in the leads between the ice floes. On the expedition in 2014, the icebreaker Oden was able to travel in open water half way from Siberia to the North Pole,” says Leif Anderson, researcher in marine chemistry at the University of Gothenburg and one of the authors of the study.

The measured acidification over the last 30 years corresponds to about 0.1 on the pH scale. The researchers estimate that the pH value will decrease a further 0.3 by the next turn of the century if carbon dioxide levels continue to rise in the atmosphere as they are today. The impact will be greatest in the coldest oceans. Water temperature determines how much carbon dioxide can be dissolved in the ocean. More freshwater from melted sea ice also result in a larger acidification effect by the uptake of carbon dioxide from the atmosphere due to changes in the seawater chemistry.

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Article in Science: Climate change drives rapid decadal acidification in the Arctic Ocean from 1994 to 2020

Through fossil fuel combustion, deforestation, and other industrial and agricultural activities, humans have raised global atmospheric carbon dioxide (CO₂) levels to more than 415 parts per million. That concentration represents a 135-parts-per-million increase since preindustrial times in the late 18th century. It is often assumed that this CO₂ increase consists entirely of anthropogenically emitted CO₂, but a new study challenges that assumption.

To investigate the standard narrative about the fate of anthropogenically emitted carbon, Holzer and DeVries labeled CO₂ as it was emitted and tracked it with a data-assimilated ocean circulation model. This method allowed them to partition the net changes in atmospheric and oceanic carbon inventories as either anthropogenically emitted or natural carbon. The model followed the journey of emitted carbon from 1780 to 2020 using what is called a linear labeling tracer. Researchers have used this labeling technique in other applications but never to track anthropogenic carbon.

The modeling revealed that only 45% of the increase in atmospheric carbon over the past few centuries originated as emitted carbon and that outgassed natural carbon from the ocean accounts for the other 55%. The researchers also found that the ocean has accumulated nearly twice as much emitted carbon as previously assumed.

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Under a worst-case scenario, half of coral reef ecosystems worldwide will permanently face unsuitable conditions in just over a dozen years, if climate change continues unabated. That is one of the findings from new research published on October 11, in PLOS Biology by University of Hawaiʻi at Mānoa researchers. Unsuitable conditions will likely lead to the corals dying off and other marine life will struggle to survive due to disruptions in the food chain.

“While the negative impacts of climate change on coral reefs are well known, this research shows that they are actually worse than anticipated due to a broad combination of climate change-induced stressors,” said lead author Renee O. Setter, a doctoral student in the Department of Geography and Environment in the College of Social Sciences. “It was surprising to find that so many global coral reefs would be overwhelmed by unsuitable environmental conditions so soon due to multiple stressors.”

Using an ensemble of global climate change models, the researchers compared scenarios of five environmental stressors projected from the 1950s through the year 2100. These stressors included sea surface temperature, ocean acidification, tropical storms, land use and human population. From prior studies, threshold values for the stressors that led to unsuitable environmental conditions for coral reefs were identified.

Ocean acidification is a major concern related to climate change, with the oceans currently absorbing around a quarter of the carbon dioxide that is released into the atmosphere. The increased CO ₂ that is absorbed by the ocean in turn decreases its pH, making the waters more acidic. These more acidic conditions put marine organisms that create calcium carbonate shells and skeletons at risk.

New research that will be presented Monday at the Geological Society of America’s GSA Connects 2022 meeting evaluated a strategy based on Indigenous techniques that may help to mitigate the effects of ocean acidification on calcifying organisms.

Hannah Hensel, a Ph.D. candidate at the University of California, Davis, led a study that tested whether adding shell hash—pulverized clam shells—to sediments could help raise the pH of pore waters and aid in calcification for infaunal marine organisms.

“One of the things that marine invertebrates have to deal with regarding climate change is ocean acidification,” said Hensel. “When researching marine invertebrates that build shells and skeletons out of calcium carbonate, I came upon some research by a diverse group of people up in British Columbia working in clam gardens, an Indigenous shellfish management practice.”

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Over the past 200 years, our planet’s oceans have absorbed more than a quarter of all anthropogenic carbon dioxide from the atmosphere. As a result, their acidity has increased by nearly 30 percent their acidity has increased by nearly 30 percent since the beginning of the Industrial Revolution. In this regard, the water’s pH value isn’t constant; it varies both seasonally and regionally. The lowest values naturally occur in winter. But that could soon change, since they could be shifted to the summer by climate change, as an international team including experts from the Alfred Wegener Institute recently demonstrated. If this comes to pass, it could have far-reaching consequences for life in the ocean, as they report in the journal Nature.

The biological activity of marine organisms normally reaches its zenith in summer, as the season is normally characterised by optimal conditions for survival, finding food and reproducing. However, climate change is now threatening this status quo by shifting the point at which the pH values are lowest from winter to summer, as experts from the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI) and France’s Laboratory for Sciences of Climate and Environment (LSCE, part of the CEA); LOCEAN – Laboratory of Oceanography and Climatology; and Institute Pierre-Simon Laplace (IPSL) recently determined. In a new study, they conclude that summer acidification could intensify by up to 25 percent by the end of the century. Some organisms living in the Arctic Ocean would be severely affected by this change, reducing their ability to cope with more intensive summertime warming.

This seasonal shift is due to the more intense rise in CO₂ in warmer water. In summer, atmospheric temperatures rise in the Arctic, more sea ice melts, and the surface water grows warmer. This warming process becomes so intense that the acidification of the seawater increases much more rapidly and can no longer be compensated for by the photosynthesis of marine algae. “These new findings spell trouble for some types of Arctic fish, like the polar cod, which are already threatened by climate change,” says co-author Hans-Otto Pörtner, a biologist and climate researcher at the AWI. “The projected high temperatures will push Arctic fauna to their thermal limits or even beyond, particularly with regard to life stages in which they’re more fragile.” First author James Orr from the LSCE and IPSL adds: “Who would have thought that climate change could shift the time of maximum acidification by six months, when studies on seasonal biological rhythms only projected shifts of up to roughly a month?” “The fascinating thing about this study is the fact that the chemical winters will actually become chemical summers,” says Lester Kwiatkowski, a co-author from LOCEAN and the IPSL.

In their study, the experts analysed simulations of 27 Earth system models and prepared future climate scenarios. While doing so, for the first time they assessed the potential for seasonal shifts in acidification, including all related variables. Why? Because the degree of acidification isn’t determined by just one factor; it’s a complex interplay of physical and biological processes, influenced by the more intense warming of surface water in summer. These changes were more pronounced in scenarios with moderate and high greenhouse-gas emissions and were far milder in those with lower emissions. In the researchers’ eyes, this represents a glimmer of hope that key elements of the Arctic Ocean’s ecosystem can be preserved if mean global warming can be kept below 2°C.

Ocean temperatures in the Gulf of Mexico and the Caribbean Sea are on pace to surpass critical thresholds for coral health by mid-century, but rapid action to significantly reduce emissions could slow warming, giving corals and coral conservation programs as much as 20 more years to adapt, according to new research.

Climate scientists and marine biologists from Rice University, the University of Colorado Boulder and Louisiana State University used computer models to simulate climate warming from 2015-2100 under both a “business as usual” scenario with very high emissions and a scenario in which emissions were reduced to high levels. Their study and analysis of ocean warming and ocean acidification levels for specific regions in the Gulf of Mexico and Caribbean under each scenario is published in the Journal of Geophysical Research: Biogeosciences. The researchers found reducing emissions could delay the onset of critically warm ocean temperatures in some areas where reefs are still healthy.

“There are reefs in the Gulf that are really worth saving,” said Rice University marine biologist Adrienne Correa, a co-author of the study. “Some of the healthiest reefs that we still have in the United States are in the areas covered by these projections.”

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University of Adelaide research shows that in cases where biodiversity metrics show no change or little change, there may still be reorganisation of ecological communities in our oceans.

“The belief that climate change will alter global marine biodiversity is one of the most widely accepted,” said Professor Ivan Nagelkerken from the University of Adelaide’s Environment Institute and Southern Seas Ecology Laboratories.

“Commonly used biodiversity measures don’t pick up reorganisation of marine communities due to ocean acidification because new species replace species that are lost.

“Little or no biodiversity change is detected when one community of marine species is replaced by another even under significant habitat loss.”

The team looked at research undertaken into how species communities located around undersea volcanic CO₂ vents and in laboratory mesocosms respond to changes in climate. They reviewed 58 research studies that examined communities in different types of temperate reefs, coral reefs and seagrass beds, and 23 studies carried out in outdoor experimental environments or laboratories.

Climate change due to human activity has a direct impact on marine species. It alters their abundance, diversity, distribution, feeding patterns, development and breeding, and the relationships between species are affected.

The University of Adelaide’s Professor Sean Connell, who is also from the Environment Institute and Southern Seas Ecology Laboratories, co-authored the study.

“Experiments done in the laboratory are weak in detecting biodiversity change, so natural systems experiencing advanced ocean acidification are emerging as an innovative way of studying biodiversity responses,” he said.

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The study was published in the journal Global Change Biology .

Wei-Jun Cai, an expert in marine chemistry at the University of Delaware, is sounding new alarm bells about the changing chemistry of the western region of the Arctic Ocean, where he and an international team of collaborators have found acidity levels increasing three to four times faster than ocean waters elsewhere.

They also identified a strong correlation between the accelerated rate of melting ice in the region and the rate of ocean acidification, a perilous combination that threatens the survival of plants, shellfish, coral reefs and other marine life and biological processes throughout the planet’s ecosystem.

The new study, published on Thursday, Sept. 30 in Science, the flagship journal of the American Association for the Advancement of Science, is the first analysis of Arctic acidification that includes data from more than two decades, spanning the period from 1994 to 2020.

Scientists have predicted that by 2050 — if not sooner — Arctic sea ice in this region will no longer survive the increasingly warm summer seasons. As a result of this sea-ice retreat each summer, the ocean’s chemistry will grow more acidic, with no persistent ice cover to slow or otherwise mitigate the advance.

That creates life-threatening problems for the enormously diverse population of sea creatures, plants and other living things that depend on a healthy ocean for survival. Crabs, for example, live in a crusty shell built from the calcium carbonate prevalent in ocean water. Polar bears rely on healthy fish populations for food, fish and sea birds rely on plankton and plants, and seafood is a key element of many humans’ diets.

That makes acidification of these distant waters a big deal for many of the planet’s inhabitants.

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The oceans take up around 10% more of humanity’s carbon emissions than previously thought. This uptake slows global warming but worsens problems such as ocean acidification.

Researchers think the oceans absorb roughly one-quarter of CO₂ emissions from human activities. But estimates of the precise size of this ‘carbon sink’ vary.

Jens Terhaar at the University of Bern in Switzerland and his colleagues analysed models and observations of carbon flowing in and out of the ocean. They found three factors that influence the size of the carbon sink.

One is how salty the waters are in a particular zone in the Southern Ocean around Antarctica. A second is the strength of an ocean-current pattern in the North Atlantic Ocean. The third is a measure of how much CO₂ seawater can absorb in given atmospheric conditions. By focusing on how these three factors feed into climate models, the scientists were able to match the models to observations more accurately, thus reducing uncertainties in the size of the carbon sink.

The extra uptake would balance out only two to four years of global CO₂ emissions at current rates.

Copepods are among the most important organisms in the ocean. The millimeter-small animals are food for many fish species and are therefore of central importance for life in the sea. Marine biologists fear that climate change could affect the small crustaceans in the future – and that this could decimate the most important food source for fish and many other marine animals. A team from GEOMAR Helmholtz Centre for Ocean Research Kiel, the University of Connecticut, and the University of Vermont has therefore investigated for the first time in more detail whether copepods can genetically adapt to changing living conditions over the course of evolution. In doing so, they have taken into account both the effect of higher water temperatures and ocean acidification. The work of the U.S.-German group is special because it was one of the first to expose marine animals to multiple stressors in the lab.

The results, recently published in the scientific journal Proceedings of the National Academy of Sciences, are cautiously optimistic. The team, led by Professor Dr. Reid Brennan, marine ecologist at GEOMAR, and Professor Dr. Melissa Pespeni of the University of Vermont, found through detailed genetic analysis that the small crustaceans can indeed adapt to the new conditions over the course of about 25 generations – which corresponds to a period of just over one year, since several generations of crustaceans can mature in a year at moderate water temperatures. The researchers found that as water temperatures rise and conditions become more acidic, gene variants become prevalent in the copepods’ genome that result in the animals being better able to withstand environmental stress. “These mechanisms help, among other things, to ensure that copepod eggs develop properly despite unfavorable environmental conditions and that important metabolic processes continue,” says Reid Brennan.

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Overreliance on fossil fuels has led to a buildup of greenhouse gasses like carbon dioxide (CO₂) in the atmosphere. But CO₂ doesn’t only stay in the air; it also dissolves into the ocean, where it decreases the pH of the water and leads to ocean acidification. Corals are especially vulnerable to damage from ocean acidification, and rising CO₂ levels jeopardize the future of coral reefs globally. However, a new study from researchers at the University of Pennsylvania and Australia’s University of Queensland, reports certain corals may do better than others at withstanding ocean acidification.

The study was published in Proceedings of the Royal Society B. Using samples from the Great Barrier Reef, the researchers studied how coral from environments with greater CO₂ variability respond to increasing acidification.

Ocean acidification threatens coral because it breaks down the rocky, calcified skeletons that give coral its distinctive structure, says Katie Barott, an assistant professor of biology in Penn’s School of Arts & Sciences and senior author on the study. When water CO₂ levels surge, corals can no longer grow or maintain their skeletons.

While ocean acidification is a consequence of climate change, there are also regular fluctuations in water pH that occur regardless of greenhouse gas emission levels. These fluctuations are driven by respiration from the coral and photosynthesis from the coral’s symbiotic algae.

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A new study led by the Institut de Ciències del Mar (ICM-CSIC) in Barcelona has revealed that plastic degradation contributes to ocean acidification via the release of dissolved organic carbon compounds from both the plastic itself and its additives.

“Thanks to this study we have been able to prove that in highly plastic-polluted ocean surface areas, plastic degradation will lead to a drop of up to 0.5 pH units, which is comparable to the pH drop estimated in the worst anthropogenic emissions scenarios for the end of the 21st century,” points out Cristina Romera-Castillo, ICM-CSIC researcher and first author of the study, which has been published this week in the journal Science of the Total Environment.

Acidification and plastic pollution are two of the major problems facing the ocean today. Since the industrial revolution, the increase in ocean acidity has made it more difficult for some calcifying organisms, such as corals, to maintain their skeletons. Every year up to 13 million tons of plastic reach the sea.

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What is measured

Ocean acidification describes the long-term decrease in the pH of our oceans and coastal waters. This indicator measures:

• change in pH, acidity, and pCO₂ (partial pressure CO_2, which is a measure of dissolved carbon dioxide) in New Zealand’s subantarctic surface waters (Munida Transect) from 1998 to 2020
• pH at selected coastal sites (New Zealand Ocean Acidification Observing Network, NZOA-ON) from 2015 to 2021.

Why it is important

The oceans are a large carbon sink and have very likely absorbed 20–30 percent of the carbon dioxide (CO₂) emitted by human activities in the last two decades (Bindoff et al., 2019). CO₂ absorption reduces atmospheric greenhouse gas concentrations. However, when seawater absorbs CO₂ from the atmosphere, chemical reactions produce hydrogen ions that acidify the seawater and decrease its pH.

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The ocean plays a key role in mitigating climate change by absorbing about 25 percent of the carbon dioxide gas (CO2) released into the atmosphere each year by human activities. However, this comes at a cost to ocean health because the uptake of this human-released carbon causes changes in ocean chemistry, called ocean acidification (OA), that can be detrimental to marine ecosystems. 

A University of California – Santa Cruz (UCSC) and NOAA led research team set out to understand how OA metrics, such as pH and the partial pressure of CO2 (pCO2), have changed below the surface waters of the open North Pacific Ocean and coastal California Current System since industrialization (~1750). The California Current Large Marine Ecosystem along the US West Coast is a highly productive coastal ecosystem fueled by seasonal upwelling of cold, nutrient-rich water that supports important fisheries, tourism, and cultural heritage. 

This new research, led by Mar Arroyo, graduate student at UCSC, used observational data from research cruises as part of the GO-SHIP and West Coast Ocean Acidification surveys as well as output from a regional ocean model. The findings were published in the journal Geophysical Research Letters. 

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