Malformed seashells, ancient sediment provide clues about Earth’s past

A drone photo of the JOIDES Resolution in the Mentelle Basin, where Northwestern scientists drilled for ancient sediment.
Photo Credit: Gabriele Tagliaro, University Sao Paulo

Scientific Frontline: Extended "At a Glance" Summary: Ocean Anoxic Event 2 and Ocean Acidification

The Core Concept: Ocean Anoxic Event 2 (OAE2) was a major global environmental crisis approximately 100 million years ago marked by severe ocean deoxygenation and widespread acidification driven by massive volcanic carbon dioxide emissions.

Key Distinction/Mechanism: Unlike typical modern warming trends, OAE2 featured a unique feedback loop where extreme ocean acidification temporarily suppressed calcification rates, allowing seawater alkalinity to accumulate and ultimately triggering a transient cooling period known as the Plenus Cold Event.

Major Frameworks/Components:

• Calcium isotope ratio analysis of fossilized planktonic foraminifera to evaluate physiological stress caused by ocean acidification.
• Deep-sea sedimentary core analysis identifying abrupt depletions in calcium carbonate minerals.
• Integration of geological outcrop data from Gubbio, Italy, and the Western Interior Seaway.
• Geochemical modeling linking ocean alkalinity accumulation to carbon dioxide drawdown during the Plenus Cold Event.

Fossils Link Ocean Acidification to Mass Extinction

Jonathan Chen, the study's lead author, examines foraminifera fossils under a microscope.
Photo Credit: Northwestern University

Scientific Frontline: Extended "At a Glance" Summary: Cretaceous Planktic Foraminifera Extinction

The Core Concept: A 113-million-year-old mass extinction event of marine planktic foraminifera was driven by severe ocean acidification caused by massive volcanic carbon dioxide emissions. Microscopic fossil evidence confirms that acidic surface waters dramatically reduced the ability of these organisms to build calcium carbonate shells.

Key Distinction/Mechanism: By measuring calcium isotope ratios within individual microfossils, researchers differentiated between the severe calcification stress experienced by surface-dwelling plankton and the milder impact on deep-sea benthic organisms, proving that atmospheric carbon dioxide acidified surface waters before reaching the ocean floor.

Origin/History: During the Early Cretaceous period, specifically at the Aptian-Albian boundary, the massive Kerguelen Plateau volcanic province erupted in the southern Indian Ocean, spewing vast quantities of carbon dioxide into the atmosphere.

Major Frameworks/Components:

• Isotope Geochemistry: The use of calcium isotope ratios as a geochemical proxy to measure historical biocalcification rates and physiological stress in shell-building organisms.
• Carbon Sequestration: The role of foraminifera in the natural carbon cycle, locking away carbon within external, solid calcium carbonate shells.
• Volcanic Forcing: The mechanism by which large igneous provinces, such as the Kerguelen Plateau, emit atmospheric carbon dioxide that subsequently dissolves into surface seawater and lowers its pH.
• Biocalcification: The biological process by which marine organisms construct shells from carbonate ions, a process significantly hindered by increased seawater acidity.

What Is: Ocean Acidification

Scientific Frontline: Extended "At a Glance" Summary: Ocean Acidification

The Core Concept: Ocean acidification is a systemic, ongoing global environmental crisis in which anthropogenic carbon dioxide emissions dissolve into the ocean, fundamentally altering its thermodynamic equilibrium, lowering its pH, and depleting the bioavailable carbonate ions essential for marine life.

Key Distinction/Mechanism: Unlike the atmospheric and oceanic warming driven by climate change, ocean acidification is a direct chemical reaction. Dissolved \(CO_2\) reacts aggressively with seawater to form unstable carbonic acid (\(H_2CO_3\)), which rapidly dissociates into bicarbonate (\(HCO_3^-\)) and free hydrogen ions (\(H^+\)). These excess hydrogen ions bind with vital carbonate ions (\(CO_3^{2-}\)), severely limiting the ability of marine organisms to precipitate calcium carbonate (\(CaCO_3\)).

Origin/History: Since the onset of the Industrial Revolution, the global average surface ocean pH has fallen from a pre-industrial baseline of 8.20 to approximately 8.10. While geochemists compare this event to the Paleocene-Eocene Thermal Maximum (PETM) 56 million years ago, modern anthropogenic carbon emissions are driving this chemical shift at an unprecedented rate, estimated to be ten times faster than the peak of the PETM.

Research finds grave concern for coral reefs

 

Sabine evaluating a potential deployment site for a mooring in Palau.

Similar to a giant sponge, the ocean absorbs a quarter of the excess CO2 produced every year from human activities (anthropogenic carbon) around the world. Carbon dioxide dissolves in the surface water and through the overturning circulation of ocean currents and mixing processes, is slowly transported into the ocean’s interior—which allows the surface ocean to absorb more CO2. In this cycle, CO2 reacts with the water molecules in the ocean to form carbonic acid in a process known as ocean acidification. Like ocean warming, an increase in ocean acidification can also have a profound impact on marine ecosystems.

University of Hawaiʻi at Mānoa Oceanography Professor Christopher Sabine has devoted his life to understanding the connections between the ocean and anthropogenic carbon. After earning his PhD in chemical oceanography at UH Mānoa in the early 1990s, Sabine spent the next decade conducting high-quality carbon measurements in an effort to better understand where inorganic carbon is stored in the ocean.

Carbon-rich waters are becoming even more acidic as atmospheric CO2 levels rise

Orange cup corals, pictured growing on rocks above, are native to the Pacific Ocean. As they grow, corals incorporate minerals from seawater, leaving a valuable historical record in their skeletons. In this University of Washington-led study, researchers compare preindustrial corals to modern specimens to show how quickly the ocean is acidifying.
Photo Credit: Alexander Vasenin
(CC BY-SA 4.0)

Scientific Frontline: Extended "At a Glance" Summary: Ocean Acidification in the California Current

The Core Concept: Carbon-rich waters along the North American coastline are acidifying at an accelerated rate due to rising atmospheric carbon dioxide and coastal upwelling processes.

Key Distinction/Mechanism: Unlike open ocean surface acidification, the Northeastern Pacific features the California Current system, which brings upwelled subsurface water rich in dissolved carbon dioxide, amplifying local acidification beyond global averages.

Origin/History: Researchers analyzed 54 museum and laboratory samples of orange cup corals collected between 1888 and 1932, comparing them with modern specimens gathered in 2020 to establish historical baseline water chemistry.

Major Frameworks/Components:

• Chemical analysis of boron ratios in historical and modern coral skeletons to reconstruct past seawater acidity.
• Integration of historical handwritten museum and laboratory logbooks to pinpoint exact sample collection sites.
• Evaluation of the California Current and coastal upwelling dynamics that cycle deep, decomposing organic-rich water to the surface.

Acidification Ruins Reef Fish Social Lives

Photo Credit: Francesco Ungaro

Scientific Frontline: Extended "At a Glance" Summary: Ocean Acidification and Reef Fish Social Structures

The Core Concept: Ocean acidification, driven by climate change, degrades the physical complexity of reef habitats, causing small reef fishes to gather in smaller, less protective shoals. This reduction in group size compromises their survival strategies and alters both collective and individual behaviors.

Key Distinction/Mechanism: The research highlights a critical distinction between direct and indirect climate impacts: the direct physiological effects of warming and lower pH on individual fish behavior are minimal. Instead, the mechanism of harm is indirect, where the loss of complex reef structures forces the breakdown of social systems, reducing the fishes' boldness, foraging efficiency, and shared vigilance.

Major Frameworks/Components: 

• Habitat Complexity Degradation: The physical breakdown of reef environments caused by increased ocean acidity.
• Shoal Dynamics: The behavioral and survival benefits of large fish groups, which allow individuals to forage more efficiently, stay in the open longer, and better detect predators.
• Natural Climate Analogues: The methodological framework of using volcanic \(\mathrm{CO_2}\) seeps to observe ecological questions in a natural, naturally acidified setting.
• Indirect vs. Direct Climate Stress: The theoretical pillar demonstrating that environmental context and social structures are just as vulnerable to climate change as the physiological limits of the animals themselves.

Under Ocean Acidification, Embryos of a Key Forage Fish Struggle to Hatch

This photo shows sand lance embryos that have and have not hatched. Sand lance have trouble hatching at future ocean \(\mathrm{CO_2}\) levels
Image Credit: Emma Cross.

Scientific Frontline: Extended "At a Glance" Summary: Impact of Ocean Acidification on Sand Lance Embryos

The Core Concept: Ocean acidification, driven by the absorption of atmospheric carbon dioxide into seawater, significantly reduces the hatching success of sand lance embryos by impairing the enzymes required to break through their eggshells.

Key Distinction/Mechanism: While many near-shore fish species exhibit resilience to daily and seasonal pH fluctuations, offshore-spawning fish like the sand lance inhabit more stable environments, making them exceptionally sensitive to elevated carbon dioxide levels and compromised hatching enzyme efficacy.

Major Frameworks/Components: Anthropogenic carbon dioxide uptake acting as a seawater carbon sink; physical oceanography modeling of projected carbon dioxide levels in the Gulf of Maine for 2050 and 2100; serial experimentation methodology involving repeated laboratory rearing of embryos; and biochemical mechanisms involving impaired chorion-splitting enzymes.

Sea butterfly life cycle threatened by climate change

An adult sea butterfly, a tiny free swimming sea snail.
Photo Credit: Victoria Peck – British Antarctic Survey

Shelled pteropods, commonly known as sea butterflies, are increasingly exposed to ocean changes, but some species are more vulnerable to this threat. In a new study, published this month in the journal Frontiers in Marine Science, British Antarctic Survey (BAS) scientists examining pteropod life cycles in the Southern Ocean have found that some species might be more vulnerable to this threat due to different timings of their life cycle.

Sea butterflies are tiny, free-swimming sea snails, which are an important part of the marine ecosystem. They are also vulnerable to climate change as their shells are sensitive to ocean acidification. Now, a team of researchers led by BAS has examined the life cycles of two free-swimming sea snail species. They found that one is less vulnerable to changes in the Southern Ocean than the other, which could affect the sea snails on a population level and in turn impact the marine ecosystem.

The world’s oceans absorb approximately a quarter of all carbon dioxide (CO2) emissions. During absorption, CO2 reacts with seawater and oceanic pH levels fall. This is known as ocean acidification and results in lower carbon ion concentrations. Certain ocean inhabitants use carbon ions to build and sustain their shells. Pteropods, which are important components of the marine ecosystem, are among them.

Bladderwrack at risk of destruction as ocean acidity rises

Bladderwrack is one of the most common macroalgae growing along Sweden’s coasts. It is widespread up to the Bothnian Sea. In Europe, it grows all the way down to Portugal’s Atlantic coast.
Photo Credit: Alexandra Kinnby

Climate change is increasing carbon dioxide levels in the sea, causing bladderwrack seaweed to grow more quickly and to increase in size along the coast. However, a scientific study by researchers from the University of Gothenburg shows that this growth is illusory as, in more acidic seas, the seaweed will be unable to withstand storms and powerful waves.

Ocean acidification is a consequence of the oceans absorbing a large proportion of the carbon dioxide that is being released into the atmosphere. The drop in pH changes the conditions for the plants and animals that live in our seas. The ocean has already become more acidic and the worst-case scenario from the IPCC predicts an even further drop in pH, from 8.1 today down to around 7.7 by the end of this century.

“That might not sound very much, but pH is a logarithmic scale so it’s a big difference. We are already seeing calcifying species such as shellfish finding it more difficult to survive today,” says Alexandra Kinnby, a marine biologist at the University of Gothenburg.

Oceanography: In-Depth Description

Oceanography is the comprehensive, interdisciplinary study of the Earth's oceans and seas, encompassing their physical properties, chemical composition, biological ecosystems, and geological structures. Its primary goal is to understand the complex, dynamic processes that govern the marine environment, how the ocean interacts with the atmosphere to regulate global climate, and the mechanisms that shape the seafloor and coastal margins.

Extreme events stress the oceans

Sea snails - the picture shows a pteropod - play an important role in the marine food web. They are especially sensitive to ocean warming and acidification.
Source: Universität Bern Credit: Charlotte Havermans

Scientific Frontline: Extended "At a Glance" Summary: Compound Marine Extreme Events

The Core Concept: Compound marine extreme events refer to the simultaneous or combined occurrence of multiple environmental stressors, such as marine heatwaves and extreme ocean acidity, which severely amplify pressure on marine ecosystems.

Key Distinction/Mechanism: Unlike isolated climate anomalies, compound events involve interacting physical and chemical oceanographic drivers—such as temperature increases correlating with higher proton concentrations or altered water column mixing—that exponentially worsen environmental stress.

Major Frameworks/Components:

• Marine heatwaves characterized by prolonged sea surface temperature anomalies significantly exceeding historical averages.
• Extreme ocean acidity defined by elevated proton concentrations within seawater.
• Earth system model simulations projecting exponential increases in co-occurring extreme days under future global warming scenarios.
• Regional ocean dynamics, including thermal expansion, subsurface water circulation, and localized chemical interactions.

Algae bio hacks itself in adapting to climate change

Phytoplankton - the foundation of the oceanic food chain.
Photo Credit: NOAA

Clear evidence that marine phytoplankton are much more resilient to future climate change than previously thought is the focus of a study published in Science Advances by an international team of scientists, including University of Hawaiʻi at Mānoa oceanography professor David Karl.

“Knowing how marine algae will respond to global warming and to associated decline of nutrients in upper ocean waters is crucial for understanding the long-term habitability of our planet,” said Karl.

Combining data from the long-term Hawaiʻi Ocean Time-series program at UH Mānoa with new climate model simulations conducted on one of South Korea’s fastest supercomputers, the scientists revealed that a mechanism, known as nutrient uptake plasticity, allows marine algae to adapt and cope with nutrient-poor ocean conditions that are expected to occur over the next decades in response to global warming of the upper ocean.

Climate change will destroy familiar environments, create new ones and undermine efforts to protect sea life

 A healthy coral reef in 2012 in the Northern Mariana Islands. A year later, the reef was dead. The reef is a symbol of how climate change is already transforming ocean environments.
Credit: Steven Mana‘oakamai Johnson

Climate change is altering familiar conditions of the world’s oceans and creating new environments that could undermine efforts to protect sea life in the world’s largest marine protected areas, new research from Oregon State University shows.

The changing conditions also have cultural and economic implications for the people whose traditions and livelihoods are dependent on ocean resources, said James Watson, an assistant professor in OSU’s College of Earth, Ocean, and Atmospheric Sciences and the paper’s co-author.

“What we’re looking at here is the potential extinction of a whole environment,” said Watson, who specializes in marine social-ecological systems and understanding complex adaptive systems. “In some places, the environments we have today are not going to exist in the future. We won’t be able to go visit them or experience them. It is an environmental, cultural and economic loss we can’t replace.”

The researchers’ analysis of multiple climate scenarios showed:

• 60% to 87% of the ocean is expected to experience multiple biological and chemical changes, such as increases in water temperature, higher levels of acidity and changes in oxygen levels, by the year 2060.
• The rate of change is expected to be even higher, 76% to 97%, in very large marine protected areas such as Australia’s Great Barrier Reef Marine Park and the Galapagos Marine Reserve in Ecuador.
• Increases in pH, which measures ocean acidity, are expected as soon as 2030. Ocean acidification reduces the amount of carbonate in seawater, which is necessary for marine organisms, such as corals and mollusks like oysters, to develop their shells and skeletons.

Coral reef biodiversity predicted to shift as climate changes

 

Experimental set up at HIMB with mesocosms. (Photo credit: Chris Jury)

Coral reefs are among the most biologically diverse, complex and productive ecosystems on the planet. Most of coral reef biodiversity consists of tiny organisms living deep within the three-dimensional reef matrix. Although largely unseen, this diversity is essential to the survival and function of coral reef ecosystems, and many have worried that climate change will lead to dramatic loss of this diversity.

New research led by scientists at the University of Hawaiʻi at Mānoa reveals that the species which dominate experimental coral reef communities shift due to climate change, but the total biodiversity does not decline under future ocean conditions of warming and acidification predicted by the end of the century.

The study was published in the Proceedings of the National Academy of Science.

“Rather than the predicted collapse of biodiversity under ocean warming and acidification, we found significant changes in the relative abundance, but not the occurrence of species, resulting in a shuffling of coral reef community structure,” said Molly Timmers, lead author who conducted this study during her doctoral research at the Hawaiʻi Institute of Marine Biology (HIMB) at UH Mānoa’s School of Ocean and Earth Science and Technology (SOEST).

Important but overlooked organisms

“The tiny organisms living in the reef structure are known as the cryptobiota, which are analogous to the insects in a rainforest,” said Timmers. “They play essential roles in reef processes such as nutrient cycling, cementation and food web dynamics—they are an important diet of many of the fishes and invertebrates that make coral reef ecosystems so dynamic.”

Despite their critical importance to coral reef ecosystems, these cryptobiota are often overlooked in climate change research due to the challenges associated with surveying them using visual census and in identifying this highly diverse and understudied community.

“As a result, our perceptions of coral reef biodiversity across marine gradients and how biodiversity will respond to climatic change has been primarily based on a handful of observable surface-dwelling taxa, such as corals and fish,” said Timmers.

Experimental designs

To assess the responses of the understudied cryptobiota to future ocean conditions, Timmers and colleagues at HIMB devised an experiment wherein tiered settlement plates were placed in experimental flow-through tanks. These mesocosms received unfiltered seawater from a nearby reef slope off the shore of HIMB and were treated with end-of-the-century predicted ocean warming and/or ocean acidification conditions. After two years of exposure, the team examined the organismal groups that had developed on the settlement plates using DNA metabarcoding techniques.

“This two-year experimental mesocosm study is unprecedented for climate change research and is the first one to examine the diversity of the entire coral reef community from microbes and algae to the corals and fishes,” said Chris Jury, the author who developed and maintained the mesocosm system.

Source/Credit: University of Hawaiʻi

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Shrinking Shellfish? Risks of Acidic Water in the Indian River Lagoon

FAU researchers measured aragonite saturation – a key indicator of water’s ability to support calcifying organisms like clams and oysters – throughout the Indian River Lagoon.
Photo Credit: Courtesy of Florida Atlantic University

Scientific Frontline: "At a Glance" Summary

• Main Discovery: Elevated nutrient runoff, freshwater discharges, and harmful algal blooms are accelerating coastal acidification in Florida's Indian River Lagoon, resulting in critically low levels of aragonite saturation necessary for shell-building organisms to survive.
• Methodology: Researchers performed a comprehensive spatial survey of the entire lagoon alongside weekly monitoring at three distinct central sites—an urban canal, a river mouth, and a natural reference area—between 2016 and 2017 to measure water chemistry and correlate aragonite saturation (\(\Omega_{arag}\)) with environmental stressors.
• Key Data: The study established a strong positive correlation between aragonite saturation and salinity, with data showing that nutrient-dense northern regions and freshwater-impacted southern areas consistently exhibited saturation levels insufficient for healthy shell development.
• Significance: Depleted aragonite levels inhibit the growth and structural integrity of calcifying species like oysters and clams, making them more vulnerable to predation and disease, which threatens the stability of the entire estuarine food web and local economy.
• Future Application: These findings provide a baseline for new ecosystem management strategies focused on controlling nutrient inputs and freshwater flows, supported by real-time pH and \(\mathrm{CO_2}\) monitoring via the upgraded Indian River Lagoon Observatory Network of Environmental Sensors (IRLON).
• Branch of Science: Marine Biogeochemistry and Estuarine Ecology
• Additional Detail: This research represents the first complete documentation of aragonite saturation distribution across the entire Indian River Lagoon, identifying specific "hotspots" where local anthropogenic pressures amplify global ocean acidification trends.

How Gravity Helps Oyster Larvae Feed

Eastern oysters (Crassostrea virginica) are native to the Atlantic coast of North America and are an important species for coastal ecosystems and fisheries.
Photo Credit: Daniel Hentz, ©Woods Hole Oceanographic Institution

Scientific Frontline: Extended "At a Glance" Summary: Oyster Larvae and Gravity-Driven Feeding

The Core Concept: A new study reveals that the dense calcium carbonate shells of tiny eastern oyster larvae make them heavier than seawater, allowing gravity to drive the currents they use to bring food to their mouths.

Key Distinction/Mechanism: It was previously assumed that microscopic larvae rely on the drag produced by swimming to create feeding currents. This research demonstrates that for oyster larvae, gravity (due to their shell's density) is the primary force, placing them in a feeding regime typically associated with larger marine organisms.

Major Frameworks/Components:

• Micro-particle image velocimetry: Used to track tracer particles and measure the invisible feeding currents generated by the larvae.
• High-speed microscale imaging system (HSMIS): A custom setup using a low-heat red LED and a camera recording at 2,000 frames per second to observe larvae in a larger volume of water without heat disruption.
• The interaction of shell density, gravity, and fluid dynamics in generating feeding currents.

Growth of coral reefs likely cannot keep pace with rising sea level

The upper panel shows a coral reef margin in Belize with living branched Acropora (elkhorn) and platy Millepora (fire) corals, which are both competitive and fast-growing. The lower panel shows broken branches of dead Acropora corals overgrown by weedy, fertile hill and finger corals (Porites) as well as fleshy algae.
Photo Credit: E. Gischler.

In identifying and dating coral remains in drill cores taken from Belize reefs, a team of experts from Goethe University Frankfurt and partners from Germany, the USA and Canada has shown the importance of specific types of coral for reef-building during the current Holocene geological epoch, dating back some 12,000 years. The scientists found that certain coral species disappeared for longer periods in the past due to climate changes, and identified another climate-related threat to coral reefs: In addition to warming and ocean acidification, among others, the rising sea level also threatens coral reefs, whose growth rates cannot keep up. 

Tropical coral reefs could end up being one of the first victims of climate change. The marine diversity hotspots are threatened by and declining as a result of global warming, ocean acidification, a deterioration of water quality, as well as diseases of reef-building organisms, and their growth is unable to keep up with the projected rise in sea levels. These are some of the conclusions drawn by an interdisciplinary team of scientists from Goethe University Frankfurt's Institute of Geosciences, the company ReefTech Inc., the GEOMAR Helmholtz Center of Ocean Research, the University of Ottawa's Department of Earth and Environmental Sciences, and the GSI Helmholtz Center of Heavy Ion Research. Their findings are based on an examination of 22 drill cores collected from the Belize barrier reef and atolls, the largest reef system in the Atlantic Ocean, which focused on identifying and dating coral growth and accretion rates over the past 9,000 years. 

Marine Biology: In-Depth Description

Photo Credit: Neeraj Pramanik

Marine Biology is the scientific study of organisms in the ocean and other brackish bodies of water. This discipline encompasses a vast spectrum of life forms, ranging from microscopic picoplankton to the blue whale, the largest animal on Earth. It is an integrative field that combines elements of geology, chemistry, physical oceanography, and biology to understand the physiology, behavior, and ecological roles of marine organisms, as well as their complex interactions with the high-salinity environment.

Marine Ecology: In-Depth Description

Photo Credit: Ekaterina Zlotnikova

Marine ecology is the scientific study of marine ecosystems, focusing on the interactions between marine organisms and their physical, chemical, and biological environments. Its primary goal is to understand the complex dynamics of ocean habitats, from microscopic phytoplankton to massive cetaceans, mapping how energy flows and how environmental factors shape the distribution, abundance, and behavior of life in the sea.

All West Coast Abalones at Risk of Extinction on the IUCN Red List

A red abalone is surrounded by a barren of purple sea urchins.
Photo Credit: Katie Sowul/California Department of Fish and Wildlife

All seven of the United States’ abalone species that live on the West Coast are now listed as Critically Endangered or Endangered on the International Union for Conservation of Nature, or IUCN, Red List of Threatened Species. These listings were based on a West Coast abalones assessment led by Laura-Rogers Bennett of the California Department of Fish and Wildlife, or CDFW, and University of California, Davis.

Six species — red, white, black, green, pink and flat abalone — are listed by IUCN as critically endangered. The northern abalone, also known as threaded or pinto abalone, is listed as endangered.

The IUCN Red List is considered the world’s most comprehensive inventory of the global conservation status of species. While the listing does not carry a legal requirement to aid imperiled species, it helps guide and inform global conservation and funding priorities.