To paraphrase Mark Twain, reports of declining phytoplankton in the North Atlantic may have been greatly exaggerated. A prominent 2019 study used ice cores in Antarctica to suggest that during the industrial era, with worrying implications that the trend might continue.

But new research led by the 91̽�� shows that marine phytoplankton — on which larger organisms throughout the marine ecosystem depend — may be more stable than believed in the North Atlantic. The team’s analysis of an ice core going back 800 years shows that a more complex atmospheric process may explain the recent trends.

The was published the week of Nov. 13 in the Proceedings of the National Academy of Sciences.

Tiny floating photosynthetic organisms known as phytoplankton form the base of the marine ecosystem. These microscopic creatures are also important to the planet as a whole, producing roughly half the oxygen in Earth’s atmosphere.

Since phytoplankton are hard to count, scientists attempt to measure their abundance in other ways. Phytoplankton emit dimethyl sulfide, an odorous gas that gives beaches their distinctive smell. Once airborne, the dimethyl sulfide converts to methanesulfonic acid, or MSA, and sulfate. These eventually fall out onto land or snow, making ice cores one way to measure past population sizes.

“Greenland ice cores show a decline in MSA concentrations over the industrial era, which was concluded to be a sign of declining primary productivity in the North Atlantic,” said lead author , a 91̽��doctoral student in atmospheric sciences. “But our study of sulfate in a Greenland ice core shows that MSA alone can’t tell us the whole story when it comes to primary productivity.”

Since the mid-1800s, factories and tailpipes have also been spewing sulfur-containing gases into the air. Those gases have slightly different forms of sulfur atoms that make it possible to distinguish the marine and land-based sources in ice cores.

The new study goes further back than the previous study by measuring several sulfur-containing molecules in an ice core from central Greenland with layers spanning the years 1200 to 2006. The authors show that human-generated pollutants changed the atmosphere’s chemistry. This, in turn, altered the fate of the gases emitted by phytoplankton.

“When looking at the ice cores, we found that sulfate derived from phytoplankton increased during the industrial era,” Jongebloed said. “In other words, the decline in MSA is ‘offset’ by the simultaneous increase in phytoplankton-derived sulfate, indicating that phytoplankton-derived sulfur emissions have remained stable overall.”

When that balance is included in the calculations, the phytoplankton populations seem fairly stable since the mid-1800s. The researchers caution, however, that marine ecosystems remain under threat from many directions.

“Measuring both MSA and phytoplankton-derived sulfate gives us a fuller picture of how the emissions from marine primary producers have changed — or not changed — over time,” said senior author , a 91̽��professor of atmospheric sciences.

“Ice core measurements along with other independent estimates of phytoplankton abundance (such as chlorophyll measurements) and paired with modeling studies (which help us estimate how atmospheric chemistry and climate change over time) can help us understand how marine productivity has changed in the past and how productivity might change in the future.”

Other co-authors are research scientist , doctoral student and former undergraduates and at the UW; Jihong Cole-Dai and Carleigh Larrick at South Dakota State University; William Porter and Linia Tashmim at the University of California, Riverside; and Lei Geng at the University of Science and Technology of China.

The study was funded by the National Science Foundation and the National Natural Science Foundation of China.

For more information, contact Jongebloed at ujongebl@uw.edu or Alexander at beckya@uw.edu.

The American Geophysical Union Sept. 13 that five 91̽�� faculty members have been elected as new fellows, representing the departments of astronomy, Earth and space sciences, oceanography, global health, and environmental and occupational health sciences.

The Fellows program recognizes AGU members who have made exceptional contributions to Earth and space sciences through a breakthrough, discovery or innovation in their field. The five 91̽��honorees are among 54 people from around the world in the 2023 Class of Fellows. AGU, the world’s largest Earth and space sciences association, annually recognizes a select number of individuals nominated by their peers for its highest honors. Since 1962, the AGU Union Fellows Committee has selected less than 0.1% of members as new fellows.

Also honored by AGU this year are three 91̽��faculty members, from the departments of Earth and space sciences and atmospheric sciences, who have received other awards.

Here are the UW’s five new AGU Fellows:

, professor of Earth and space sciences, studies which characteristics of Earth help this planet support life, and whether life might be found on other planets. His work spans astronomy, biology and geology, on planetary environments including Earth, Mars, Venus and icy moons, as well as planets outside this solar system. He is the author of “Astrobiology: A Very Short Introduction” for the layperson and “Atmospheric Evolution on Inhabited and Lifeless Worlds” for researchers.

, who holds the Karl M. Banse Endowed Professorship in oceanography, explores the limits and ecological contributions of microbial life in deep ocean and polar regions, focusing in recent years on how microbes adapt to the extreme conditions of Arctic sea ice. In addition to a research and teaching career, Deming founded what is now the 91̽��Center for Environmental Genomics and helped establish the nation’s first graduate training program in astrobiology.

, professor of global health and of environmental and occupational health sciences, has been conducting research on the health risks of climate variability and change for nearly 30 years. She focuses on estimating current and future health risks of climate change, designing adaptation policies and measures to reduce risks in multi-stressor environments, and estimating the health co-benefits of mitigation policies. Ebi is also founding director of the 91̽��, or CHanGE.

, professor of astronomy, is an astrobiologist and planetary astronomer whose research focuses on predicting, acquiring and analyzing observations of planetary atmospheres and surfaces. In addition to studying planets within our solar system, she is interested in exoplanets — those outside the solar system — and how they might reveal the presence of life. With the UW’s Virtual Planetary Laboratory, she uses models of planets and planet-star interactions to generate plausible planetary environments and spectra for extrasolar terrestrial planets and the early Earth.

, professor and chair of Earth and space sciences, is a geochemist and glaciologist whose research focuses on polar climate and ice sheets in the Arctic and in Antarctica. He is best known for his analyses of Antarctic ice cores using measurements of oxygen and hydrogen in the ice to better understand how climate has varied in the past, over hundreds to thousands of years.

In addition to the newly elected fellows, 91̽��faculty members are also recognized in several subject-specific awards and lectures:

, professor of atmospheric sciences, will deliver the in December at the AGU’s fall meeting. Alexander studies the relationship between climate change and the chemical composition of the atmosphere. She looks at the pathways by which atmospheric pollutants form, how those chemical pathways can vary, and what that means both for present-day air quality and for the future of climate change.

, research assistant professor of Earth and space sciences, has received the for his research modeling natural disasters using geodesy, or the shape of the Earth’s surface, and seismology. Crowell pioneered ways to use GPS and related data in earthquake and tsunami early warning systems. He is currently using this data to better understand natural disasters as they unfold and develop a risk-mitigation framework for coastal hazards such as tsunamis.

, research assistant professor of Earth and space sciences, has received the . Journaux uses modeling and experiments to explore the conditions in extreme environments on other planets, and how that might affect their ability to harbor life. He is a member of the science team for NASA’s upcoming Dragonfly mission, which will characterize the chemistry and habitability of Saturn’s largest moon, Titan.

, a researcher at the Pacific Northwest National Laboratory with an affiliate 91̽��faculty position in oceanography, has received the .

All honorees will be recognized in December at the AGU’s fall meeting in San Francisco.

Volcanoes draw plenty of attention when they erupt. But new research shows that volcanoes leak a surprisingly high amount of their atmosphere- and climate-changing gases in their quiet phases. A Greenland ice core shows that volcanoes quietly release at least three times as much sulfur into the Arctic atmosphere than estimated by current climate models.

The , led by the 91̽�� and published Jan. 2 in Geophysical Research Letters, has implications for better understanding Earth’s atmosphere and its relationship with climate and air quality.

“We found that on longer timescales the amount of sulfate aerosols released during passive degassing is much higher than during eruptions,” said first author , a 91̽��doctoral student in atmospheric sciences. “Passive degassing releases at least 10 times more sulfur into the atmosphere, on decadal timescales, than eruptions, and it could be as much as 30 times more.”

The international team analyzed layers of an ice core from central Greenland to calculate levels of sulfate aerosols between the years 1200 and 1850. The authors wanted to look at the sulfur emitted by marine phytoplankton, which were previously believed to be the biggest source of atmospheric sulfate in pre-industrial times.

“We don’t know what the natural, pristine atmosphere looks like, in terms of aerosols,” said senior author , a 91̽��professor of atmospheric sciences. “Knowing that is a first step to better understanding how humans have influenced our atmosphere.”

The team deliberately avoided any major volcanic eruptions and focused on the pre-industrial period, when it’s easier to distinguish the volcanic and marine sources.

“We were planning to calculate the amount of sulfate coming out of volcanoes, subtract it, and move on to study marine phytoplankton,” Jongebloed said. “But when I first calculated the amount from volcanoes, we decided that we needed to stop and address that.”

The location of the ice core at the center of the Greenland Ice Sheet records emissions from sources over a wide swath of North America, Europe and surrounding oceans. While this result applies only to geologic sources within that area, including volcanoes in Iceland, the authors expect it would apply elsewhere.

“Our results suggest that volcanoes, even in the absence of major eruptions, are twice as important as marine phytoplankton,” Jongebloed said.

The discovery that non-erupting volcanoes leak sulfur at up to three times the rate previously believed is important for efforts to model past, present and future climate. Aerosol particles, whether from volcanoes, vehicle tailpipes or factory chimneys, block some solar energy. If the natural levels of aerosols are higher, that means the rise and fall of human emissions — peaking with the acid rain of the 1970s and then dropping with the Clean Air Act and increasingly strict air quality standards — have had less of an effect on temperature than previously believed.

“There’s sort of a ‘diminishing returns’ effect of sulfate aerosols, the more that you have, the less the effect of additional sulfates,” Jongebloed said. “When we increase volcanic emissions, which increases the baseline of sulfate aerosols, we decrease the effect that the human-made aerosols have on the climate by up to a factor of two.”

That means Arctic warming in recent decades is showing more the full effects of rising heat-trapping greenhouse gases, which is by far the main control on Earth’s average temperature.

“It’s not good news or bad news for climate,” Jongebloed said of the result. “But if we want to understand how much the climate will warm in the future, it helps to have better estimates for aerosols.”

Better estimates for aerosols can improve global climate models.

“We think that the missing emissions from volcanoes are from hydrogen sulfide,” said Alexander, referring to the gas that smells like rotten eggs. “We think that the best ways to improve these estimates of volcanic emissions is to really think about the hydrogen sulfide emissions.”

The study was funded by the U.S. National Science Foundation, NASA and the National Natural Science Foundation of China. Other 91̽��co-authors are undergraduate students Sara Salimi and Shana Edouard, doctoral student Shuting Zhai, research scientist Andrew Schauer, and professor Robert Wood. Other co-authors are Lei Geng, a former 91̽��postdoctoral researcher now at the University of Science and Technology of China; Jihong Cole-Dai and Carleigh Larrick at South Dakota State University; Tobias Fischer at the University of New Mexico; and Simon Carn at Michigan Technological University.

For more information, contact Jongebloed at ujongebl@uw.edu or Alexander at beckya@uw.edu.

The air in the United States and Western Europe is much cleaner than even a decade ago. Low-sulfur oil standards and regulations on power plants have successfully cut sulfate concentrations in the air, reducing the fine particulate matter that harms human health and cleaning up the environmental hazard of acid rain.

Despite these successes, sulfate levels in the atmosphere have declined more slowly than sulfur dioxide emissions, especially in wintertime. This unexpected phenomenon suggests sulfur dioxide emission reductions are less efficient than expected for cutting sulfate aerosols. A new study led by the Tokyo Institute of Technology, Hokkaido University and the 91̽�� explains why. The was published May 5 in Science Advances.

When concentrations of acidic sulfate from fossil fuel emissions decrease while the concentration of more basic ammonium molecules in the atmosphere stay constant, liquid water droplets in clouds become less acidic. This makes conversion of sulfur dioxide to sulfate more efficient. So, even though air quality regulations have reduced the supply of sulfur dioxide from power plants and shipping, the total amount of sulfate particulates that harm human health has dropped more slowly.

“It does not mean that the emissions reductions aren’t working. It’s just that there is a reaction which partially mitigates the reductions,” said co-author , a 91̽��professor of atmospheric sciences. “We need to understand this multiphase chemistry in the atmosphere to make an efficient strategy to manage air pollution and accurately predict future air pollution and climate change impacts.”

During most of the 20^th century, sulfur dioxide emissions increased with industrialization in many parts of the world. But recently that trend has reversed in response to regulations, while ammonium emissions from animals and agriculture continue at the same rate. These trends are expected to continue.

Data from an ice core in Greenland that preserves past years’ atmospheres show that the proportion of sulfate containing oxygen with one extra neutron, or oxygen-17, increased in the 1980s after countries began to regulate emissions. The authors’ analysis shows this is due to faster sulfate formation in the liquid phase in the atmosphere, which occurs largely within clouds, under less-acidic conditions.

“After the SO₂ emission control, relatively lower atmospheric acidity promotes the efficiency of sulfate production in the atmosphere, which weakens the response of sulfate level to the SO₂ reduction,” said lead author at the Tokyo Institute of Technology. “Our unique isotopic techniques applied for the Greenland ice core records identify the key process of the weakened response of sulfate to SO₂ emissions reduction.”

The data came from an ice core drilled in southeast Greenland (SE-Dome) as part of a project led by Hokkaido University. The oxygen trapped in this ice provided evidence of sulfate composition from 1959 to 2015, without contamination from local pollution.

“Based on a continuous and high-resolution ice core record from SE-Dome, we could obtain reliable records for atmospheric aerosols without second modification after deposition,” said co-author and leader of SE-Dome ice core project at Hokkaido University. “We plan to drill a second ice core at the same location this year, and try to reconstruct the aerosol history back to the 1750s.”

The ice core does not contain separate data for summer and winter, but models show that other, gas-phase chemical reactions for sulfur dioxide become more important in summer, reducing the summertime impact of changing cloud acidity. Knowing how these molecules react will help improve the atmospheric models used to forecast air quality and project climate change.

The research was funded by the Japan Society for the Promotion of Science and the National Science Foundation. , a graduate student in atmospheric sciences at the UW, is among the other co-authors.

For more information, contact Alexander at beckya@uw.edu or Hattori at hattori.s.ab@m.titech.ac.jp.

Adapted from a press release by Tokyo Institute of Technology.

The main molecules responsible for breaking down all these emissions are called oxidants. The oxygen-containing molecules, mainly ozone and hydrogen-based detergents, react with pollutants and reactive greenhouse gases, such as methane.

A 91̽�� published May 18 in the journal finds that during large climate swings, oxidants shift in a different direction than researchers had expected, which means they need to rethink what controls these chemicals in our air.

“Oxidants are very reactive, and they react with pollutants and greenhouse gases and clean up the atmosphere,” said corresponding author , a 91̽��associate professor of atmospheric sciences. “We wanted to see how the ability of the atmosphere to clean itself might change with climate.”

First author , a former 91̽��postdoctoral researcher now at Grenoble Alpes University, analyzed slices from a Greenland ice core in the UW’s . The 100,000-year core begins in a relatively warm period, covers a full ice age and ends in the present day, with several shorter temperature swings along the way. The researchers used a new method to get a first-ever read on changes in atmospheric oxidants — volatile chemicals that are not directly preserved in ice cores.

The researchers fed meltwater to bacteria that drank the liquid and then excreted a gas that can be measured by machines that track isotopic composition of gas. Looking at the weight of oxygen atoms from the meltwater let the team see how many had come from the two main oxidants: ozone, which varies in the atmosphere over time, versus the detergent molecules, which are expected to stay fairly constant.

“We found that the sign of the change was the complete opposite of what we expected,” Alexander said. “And that indicates that what we thought were the main drivers for the abundance of oxidants were not actually the main controls, and we had to come up with some other mechanisms.”

Atmospheric scientists had believed that ozone levels rise as the temperature increases. Ozone is produced with water vapor and emissions from plants, soil bacteria and other living things. All of these go up as the temperature warms. So the authors expected to find more ozone in the warmer climates.

Instead, the proportion of ozone actually increased in colder climates. When the temperature changes were small, ozone did increase with temperature, but for big temperature swings that relationship flipped, with more ozone in the cold periods.

One hypothesis proposed by the authors is a change in the circulation between the troposphere, the air above our heads, and the stratosphere, the higher-elevation layer close to where most airplanes fly. Air circulates between these two, moving up in the tropics and dropping back down at the poles. The stratosphere contains more ozone that is largely formed at those elevations in the tropics, so if the circulation quickens, then more ozone from the stratosphere would get carried down to the surface.

“There is evidence — strong evidence — showing that the became stronger during the last glacial maximum,” said co-author , a 91̽��professor of atmospheric sciences. “That means there was less stratospheric ozone in the tropics but more in the high latitudes, and then more ozone going down from the stratosphere to the troposphere.”

That’s one explanation for why ozone would go up at the surface during cold climates. This shift in circulation would also cause more ultraviolet radiation to hit the tropics, and UV and water vapor are the main drivers for the formation of the other main group of oxidants, the detergents. The ice-age tropics could then become a rich source of detergents, which break down pollution and greenhouses gases like methane.

“Traditionally, ice-core methane records have been interpreted solely as a change in the source,” Alexander said. “But land-surface models have not been able to simulate the full scale of the change of methane seen in ice cores. That suggests that maybe the lifetime of methane has changed, and the only way to do that is to change the amount of detergent in the atmosphere.”

A second possible explanation for the puzzling ozone trend, researchers said, is a less-understood group of oxidants: halogens. These molecules are poorly studied, and it’s not fully known how they influence climate, but researchers suspect they could react to affect the levels of other oxidants.

“The largest source of halogens is from sea salt, and we know from ice cores that sea salt is much higher in colder climates,” Alexander said. “Sea ice also changes with climate, of course.”

The authors suspect that both mechanisms — the high-level circulation and chemical reactions with halogens — could affect oxidants during big swings in Earth’s temperature.

“The changes we measured in ozone levels seem to be quite large if you only consider one mechanism at a time, suggesting that they might be acting simultaneously, and not necessarily independently from one another,” Alexander said.

The research was funded by the National Science Foundation. Geng will soon begin a position at the University of Science and Technology of China in Hefei. Other co-authors are at the UW, at the University of Rochester, at Harvard University and at Princeton University.

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For more information, contact Alexander at 206-543-0164 or beckya@uw.edu, Geng at genglei@ustc.edu.cn and Fu at 206-685-2070 or qfu@atmos.washington.edu.

More photos are posted .

NSF grants: AGS 1103163, PLR 1106317, PLR 1244817, AGS 1102880

By analyzing samples from the Greenland ice sheet, 91̽�� atmospheric scientists found clear evidence of the U.S. Clean Air Act. They also discovered a link between air acidity and how nitrogen is preserved in layers of snow, according to a published this week in the .

Forty-five years ago, acid rain was killing fish and dissolving stone monuments on the East Coast. Air pollution rose beginning with the Industrial Revolution and started to improve when the U.S. Clean Air Act of 1970 required coal power plants and other polluters to scrub sulfur out of their smokestacks.

91̽��researchers began their study of ice cores interested in smog, not acid rain. They discovered a link between the two forms of pollution in the geologic record.

Nitrogen is emitted as a short-lived compound, NOx, which causes ground-level ozone, the main ingredient in smog, and relates to compounds that are the “detergent” of the atmosphere. Sources of NOx include smokestacks and vehicle tailpipes, as well as wildfires, soil microbes or reactions triggered by lightning strikes.

Teasing out the sources of NOx through history might tell us about the atmosphere of the past, how methane, ozone and other chemicals change in the atmosphere, and also provide a measure of global human emissions.

“How much the nitrate concentrations in ice core records can tell about NOx and the chemistry in the past atmosphere is a longstanding question in the ice-core community,” said lead author , a 91̽��postdoctoral researcher in atmospheric sciences.

Unlike other gases, short-lived NOx can’t be measured directly from air bubbles trapped in ice cores. Within a day or two most of the NOx changes into nitrate, a water-soluble molecule essential to life that gets deposited in soil and snow.

by co-author , a 91̽��professor of Earth and space sciences, suggested that comparing amounts of the two stable forms of nitrogen – nitrogen-15 and nitrogen-14 – in nitrate could pinpoint the emission sources of NOx. Ice cores from Greenland and North American lake sediments showed the nitrogen-15 ratio gradually decreasing since 1850, suggesting a corresponding rise in human emissions.

The new research says: not so fast. The detailed measurements of nitrate, NOx and sulfur show the nitrogen isotope ratio leveling off in 1970, and suggests that ratio is sensitive to the same chemicals that cause acid rain.

“This shows that the relationship between emissions and the isotopes is less direct than we thought, and the final signal recorded in the Greenland ice cores is actually not just the nitrogen emission, but the combined effect of sulfur and nitrogen emissions,” Steig said.

The ice cores used in the study were collected in 2007 at Summit Station, Greenland. Total amounts of nitrate for each year were measured and calculated at South Dakota State University, where Geng did his doctoral work. The different forms, or isotopes, were measured in UW’s .

Geng’s work showed that the long-term decrease in the nitrogen-15 isotope since 1850, and its leveling off in 1970, are linked to changes in air chemistry. Airborne nitrate can exist as a gas or a particle, and nitrate with lighter isotopes tends to exist as a gas. But he found that the total fraction of nitrate present as gas or particle varies with the acidity of the atmosphere, and the acidic air causes more of the light isotopes to exist as a gas.

“The isotope records really closely follow the atmospheric acidity trends,” said co-author , a 91̽��associate professor of atmospheric sciences. “You can really see the effect of the Clean Air Act in 1970, which had the most dramatic impact on emission of acid from coal-fired power plants.”

What’s more, airborne nitrate dissolves in water and falls at the poles as snow. While that snow sits on the ground, sunlight bouncing off the surface triggers chemical reactions that send some of it back into a gas form. Acid air can also influence the reactivity of nitrate in snow and thus the preservation of nitrate in ice cores.

Other ice core records might also be affected by acidity in air, Alexander said. No effect would be expected for stable gases like carbon dioxide and oxygen, or for the water molecules used to calculate temperature variations through time. But acidity in air could influence deposition and preservation of other volatile compounds such as chlorine, mercury or organic materials in ice cores.

Eventually, better understanding of the air chemistry during formation of the layers could allow researchers to correct for the effect, extracting better information of the past from these compounds in the geologic record.

The research was funded by the National Science Foundation. Other co-authors are Eric Sofen and Andrew Schauer at the UW, Jihong Cole-Dai at South Dakota State University and Joël Savarino at University of Grenoble in France.

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For more information, contact Geng at 206-543-4596 and leigeng@uw.edu, Alexander at 206-543-0164 or beckya@uw.edu or Steig at 206-685-3715 or steig@uw.edu.