Ocean Acidification

Rivers deliver freshwater, nutrients, and carbon to Earth’s oceans, influencing the chemistry of coastal seawater worldwide. Notably, a river’s alkalinity and the levels of dissolved inorganic carbon it brings to the sea help to shape regional conditions for marine life, including shellfish and corals. These factors also affect the ability of coastal seawater to absorb carbon dioxide from Earth’s atmosphere—which can have major implications for climate change.

However, the factors influencing river chemistry are complex. Consequently, models for predicting worldwide carbon dynamics typically simplify or only partially account for key effects of river chemistry on coastal seawater. That could now change with new river chemistry insights from Da et al. By more realistically accounting for river inputs, the researchers demonstrate significant corrections to overestimation of the amount of carbon dioxide absorbed by the coastal ocean.

The researchers used real-world data on rivers around the world to analyze how factors such as forest cover, carbonate-containing rock, rainfall, permafrost, and glaciers in a watershed influence river chemistry. In particular, they examined how these factors affect a river’s levels of dissolved inorganic carbon as well as its total alkalinity—the ability of the water to resist changes in pH.

Climate change is nowhere more apparent in its disruptions than in the world’s oceans. The vast bodies of water that make our planet unique are currently undergoing fast and extensive transformations that are unlike anything scientists have seen before, according to a study published Tuesday in the journal Nature Climate Change.

Researchers from the Institute of Atmospheric Physics at the Chinese Academy of Sciences in Beijing, Mercator Ocean International in Toulouse, France, and the Laboratoire de Météorologie Dynamique at the École Normale Supérieure in Paris created a framework and tool to standardize and assess ocean variables and figure out when those variables are changed due to the warming climate.

The scientists examined how “compound changes” — the simultaneous effects of the Earth’s oceans losing oxygen, acidifying and becoming saltier or fresher — are pushing ecosystems past the point where adaptation is possible. And different layers of the pelagic world — a place where scientists have estimated over two million species reside, with approximately only 250,000 known to humanity — are affected to various degrees.

“For example, some specific species, e.g. some kind of fish, may be okay if their living environment is only saltier, but may become more vulnerable if they are exposed to the ‘compound change,’” Zhetao Tan, lead author of the study and a researcher at the Laboratoire de Météorologie Dynamique at the École Normale Supérieure, said in an email.

New research from the university of St Andrews has found that some coastal areas will become much more acidic than previously anticipated.

Because atmospheric CO₂ and ocean pH (acidity) are tightly coupled, the more CO₂that is released into the atmosphere, the more is absorbed by seawater, making the ocean progressively more acidic.   However,  in a paper published in Nature Communications,  researchers, using the California Current as an example, show that oceanic upwelling systems actually amplify ocean acidification.   

Upwelling is where nutrient- rich and already acidic  waters from deep in the oceans rise along the coast. When organic matter from the surface ocean sinks to the deep ocean, microbes gradually break it down in a chemical reaction that releases CO₂ and increases seawater acidity. When this deep water upwells, it brings the acidity to the surface, where it further reacts with the atmospheric CO₂, which makes these water masses even more acidic.  

The researchers used historic coral samples and boron isotope signatures recorded in their skeletons to reconstruct how acidity changed over the 20^th century, and then applied a regional ocean model to predict how acidity will change during the 21^st century.   The study showed that in these upwelling regions of the ocean, ocean acidification outpaces the level “expected” from rising atmospheric CO₂alone. This is because the upwelled water masses are acidic to start with and anthropogenically rising CO₂ exacerbates the acidity.   

Upwelling systems are among the most productive systems on our planet and support much of the world’s fisheries. Understanding how they respond to rising CO₂₂ is therefore not only critical for ocean science, but also carries major implications for fisheries and their potential vulnerabilities.  

Co Author Dr Hana Jurikova, Senior Research Fellow in from the School of Earth and Environmental Science, said: “Predicting how upwelling systems will respond to climate change is highly complex, as anthropogenic influences interact with natural sources of ocean acidification. Our research shows that such interactions can amplify environmental change in the California Current System, highlighting the need for similar studies in other regions to better anticipate future change.” 

The California Current can be used as an example of other upwelling systems. Other important areas of coastal upwelling around the world include the Humbold Current off the coast of Peru or the Benguela and Canary Currents off the coast of west Africa.   

Co Author Dr James Rae, Reader in the School of Earth and Environmental Science, said: “the ocean becoming more acidic poses major risks to marine ecosystems and the communities and economies they support. The solutions we now have for climate change, like heat pumps and electric vehicles, also fix ocean acidification, so it’s critical that we support them”.   

Human greenhouse gas emissions are raising temperatures and sea levels, collapsing ice sheets and acidifying oceans. Now, research maps out the range of emissions pathways that can limit these changes.

How much greenhouse gas can be emitted before the Earth changes beyond the natural world’s ability to adapt? One approach to answer this involves looking at the characteristics of the world humans evolved in and establish limits to preserving these ecosystems¹. There are many of these ‘planetary boundaries’ proposed, and previous work has mapped out how to stay within them². However, in reality, many of the targets interact in complex ways — for instance, the amount of carbon dioxide that can be released while staying below a temperature target can be increased if more cooling sulfates are emitted³, but these sulfates can increase acid rain. Now, writing in Nature Climate Change, Gasser and colleagues⁴ propose a framework to address these interconnections that assesses a range of climate targets and produces a set of compatible emissions pathways with different degrees of climate uncertainty.

The ocean’s smallest engineers, calcifying plankton, quietly regulate the Earth’s thermostat by capturing and cycling carbon. However, a new review published this week in Science by an international team led by the Institute of Environmental Science and Technology at the Universitat Autònoma de Barcelona (ICTA-UAB) (Spain) finds that these organisms, coccolithophores, foraminifers, and pteropods, are oversimplified in the climate models used to predict our planet’s future.

By omitting these plankton, current models may underestimate key processes in the global carbon cycle and the ocean’s capacity to respond to climate change. Calcifying plankton build minute shells of calcium carbonate (CaCO₃), a critical component of the ocean’s carbon cycle. These organisms influence seawater chemistry and facilitate the transfer of carbon from the atmosphere to the deep ocean. This “carbon pump” helps regulate Earth’s climate and influences everything from ocean chemistry to the fossil record. 

“Plankton shells are tiny, but together they shape the chemistry of our oceans and the climate of our planet,” said Patrizia Ziveri, ICREA research professor at ICTA-UAB and lead author of the study. “By leaving them out of climate models, we risk overlooking fundamental processes that determine how the Earth system responds to climate change.”

The Deep Acoustic Lander recorded sound at the Challenger Deep, nearly 11,000 meters below sea level, in 2021. David Barclay

The ocean is a noisy place. Ship propellers and whale songs reverberate at the lowest pitches, while at higher tones dolphins click and shrimp snap their claws. Between these frequencies are the sounds of the churning sea itself, generated as waves, wind, and rain roil its surface. Researchers have now used this ambient noise to probe the rising acidity of the ocean. The acoustic technique, published last week in the Journal of Geophysical Research: Oceans, could make it easier to measure this key parameter of ocean health across vast distances rather than relying on point measurements.

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The carbon emissions that are warming the globe also acidify seawater. The ocean naturally absorbs about one-third of annual carbon dioxide emissions; as this gas dissolves and reacts, it creates bicarbonate and hydrogen ions. The hydrogen lowers the pH of seawater, increasing ocean acidity, which can harm sea life and slow future carbon uptake. Ship-based measurements in shallow parts of the ocean have found that, since 1985, pH has already dropped from 8.11 to 8.04.

The waters of the ocean are layered, however, and measurements at one depth may not apply to others. Adding pH sensors to the thousands of robotic Argo floats that patrol the seas, diving as deep as 2000 meters, is one way to get a broader picture of acidity. But David Barclay, an acoustical oceanographer at Dalhousie University, and his co-authors found a way to measure average pH across even greater depth ranges, by taking advantage of the intrinsic physics of sound.

In the vast and intricate ecosystems of coral reefs, a hidden danger lurks, posing threats not just to the colorful corals themselves but to entire marine environments. Recent research spearheaded by Liu, PY., Chiu, WC., Lim, S.L., and their collaborators has shed light on the mysterious and pervasive sponge known as Terpios hoshinota. This sponge, infamous for its destruction of coral reefs, exhibits a remarkable ability to thrive under extreme environmental stressors, raising crucial questions about the future of coral ecosystems worldwide.

The study culminated from a comprehensive genomic analysis that aimed to unravel the underlying mechanisms behind the resilience and adaptability of T. hoshinota. As climate change continues to push marine environments to their limits, understanding how this sponge flourishes in conditions that would otherwise be detrimental to many marine organisms is not just interesting—it’s essential.

The research focuses on the genetic underpinnings that allow T. hoshinota to prosper in the face of rising sea temperatures, ocean acidification, and various pollutants. It is now well established that climate change has dire implications for marine biodiversity. The stressors these ecosystems endure can catalyze shifts that drastically alter their composition. As corals struggle, T. hoshinota capitalizes, spreading across coral reefs and frequently leading to mass coral die-offs.

One of the surprising findings of the research was that T. hoshinota possesses a unique set of genes that facilitate the breakdown of harmful substances in its environment. These genes effectively enable the sponge to withstand conditions that would typically weaken or kill other marine organisms. The genomic data indicates that this sponge has evolved sophisticated biochemical pathways, granting it a metabolic edge in nutrient acquisition even when resources are scarce.

Perhaps more alarming is the sponge’s ability to adapt rapidly to changing environmental conditions. The study highlights the sponge’s remarkable genomic plasticity, allowing for quick responses to stress. While many coral species take years or decades to make adaptations, T. hoshinota seems to have a genetic toolkit that allows for swift modifications. This adaptability could mean that the sponge will remain a dominant presence within marine ecosystems, further complicating conservation efforts targeting coral health.