Next generation climate scientists prepare for the future by studying past North Atlantic iceberg melting

Next generation climate scientists prepare for the future by studying past North Atlantic iceberg melting

By Grace Rodgers, Dec. 18, 2020 –

In a race against climate change, Yuxin Zhou, 26, is among the next generation of climate scientists studying the Earth’s responses to rapidly rising temperatures, threatening life on the planet.

As a fifth-year Ph.D. student at Columbia University’s Lamont-Doherty Earth Observatory, studying how the Earth’s climate behaved in the past is the best way for Zhou to understand the pace and consequences of climate change today.

In a similar way, to understand Zhou’s pathway into climate science, it’s important to look back on his journey to the present.

After graduating high school in Nanjing, China, Zhou moved to the United States to study computer science at the University of Southern California, Los Angeles. However, less than one year into the undergraduate program, he switched to geological sciences, inspired by his first earth science class.

“My deepest memory is my professor talking about his experience going into a submersible for research. He said it’s like looking down from an airplane onto New York City streets because it’s bustling with life,” Zhou said. “It was really that class that captured me and helped me become interested in earth science.”

Yuxin Zhou and Pablo Alasino working performing field work in Argentina.
While in Argentina as a University of Southern California undergraduate student, Zhou worked with professor Pablo Alasino (left) on geological mapping. (Yuxin Zhou//Columbia University)

While in undergrad, he also participated in multiple research opportunities in geochemistry, one of which was a summer fellowship at the Woods Hole Oceanographic Institution. He also gained publications in Nature Geoscience and Journal of Geophysical Research – Atmosphere.

From there, he moved cross-country to pursue a degree in earth and environmental sciences at Columbia University’s Lamont-Doherty Earth Observatory just outside of New York City.

“I just really wanted to continue to do the research, and earning a Ph.D. was the natural next step,” Zhou said.

As a current fifth-year Ph.D. student, Zhou’s research focuses on the factors destabilizing the circulation in the North Atlantic, spanning the past 150,000 years

Jerry McManus, a geochemistry professor and researcher at Lamont-Doherty, works closely with Zhou as his research advisor and has seen his growth as a young scientist in the field.

“He started his Ph.D. working on more recent climate issues, and then became interested in paleoclimate and in geochemistry. He’s gone up a learning curve and has done brilliantly,” said McManus. “I work with wonderful, bright junior people, and if I can stay out of their way and help them to do their great work, then that works out the best all-around.”

Yuxin Zhou standing at a podium presenting his research at the Goldschmidt geochemistry conference in Barcelona.
While at the Goldschmidt geochemistry conference in Barcelona, Zhou presented his research on the history of iceberg discharge in the western North Atlantic. (Athena Nghiem//Columbia University)

In early October, both Zhou and McManus presented their new research at the Comer Climate Conference, an annual summit where climate scientists from around the world gather to present emerging research.

Zhou’s presentation focused on his new method to track and measure the amount of freshwater released by melting icebergs following Heinrich events. Icebergs break off from glaciers into the ocean all the time, but Heinrich events are special in that a large number of icebergs do so in a short amount of time. These events can impact ocean circulation and in turn, weather temperatures, storms and rainfall across the globe.

Unlike existing research on iceberg melting in the North Atlantic, Zhou’s new method measures the amount of freshwater and the location of freshwater released. Much of his research is based on new and previously published measurements of sediment cores collected from ocean floors in the North Atlantic.

In measuring these sediment cores, Zhou can identify specific elements and isotopes within sections of the core that correlate to the amount of freshwater released by melting icebergs during a certain period of time. The correlations follow past ice ages and warm spells, which can help predict the pace of climate change today.

“I have the opportunity to use and apply cutting edge technologies to analyze the cores,” Zhou said. “It’s very inspiring to me because you’re not thinking about your own or your own generation’s scientific career, but 10s of years in the future.”

While at Lamont-Doherty, Zhou has worked alongside Celeste Pallone, a 2nd-year Ph.D. student.

“The biggest things I’ve learned from his work is both how he does lab work, but also how he organizes and prepares his data,” said Pallone. “I’ve learned what kind of statistical methods he uses to back up his claims, and just how to do good science.”

Yuxin Zhou standing at a booth with Jennifer Middleton presenting their research at the annual Lamont-Doherty Earth Observatory open house.
During the annual Lamont-Doherty Earth Observatory open house, Zhou worked with a team (right: Jennifer Middleton, a postdoc researcher) on an exhibition about iron availability in the ocean. (Yuxin Zhou//Columbia University)

In addition to earning his Ph.D., Zhou hopes to remain in academia, working with students in science. For the past two years, Zhou has volunteered for the nonprofit Girls Who Code, teaching high school girls how to create a website. He has also worked as the Graduate Student Committee chair at Lamont-Doherty Earth Observatory, advocating for student concerns to the department and pushing for student representation on hiring committees.

“Having an inclusive teaching environment and active learning experience is very important to me,” Zhou said. “We want to make sure that hiring has a certain voice on it, and hopefully, that will translate to more diversity, equity, and inclusion.”

Looking into the future, Zhou hopes to work with other climate scientists to help predict and mitigate the effects of climate change. Having comparisons between data observations and model simulations can be a very powerful tool to narrow down estimates on the freshwater fluxes and their impacts, Zhou said.

“What we’re seeing now is unprecedented. We do have some imperfect analogs of the current scenario in the past,” Zhou said. “But by better understanding those past events, we establish a baseline of what may happen in the future.”

For a deeper dive into Zhou’s research process, read “Breaking down clues to climate change from ocean floors to measure iceberg melting“on Medill Reports.

Grace Rodgers is health, environment and science reporters at Medill. You can follow her on Twitter at @gracelizrodgers.

Breaking down clues to climate change from ocean floors to measure iceberg melting

Breaking down clues to climate change from ocean floors to measure iceberg melting

By Grace Rodgers, Dec. 18, 2020 –

Melting freshwater icebergs raise critical questions about ocean circulation. However, to find answers to what’s happening on ocean surfaces, some scientists are searching ocean floors for evidence of past environments and clues to the pace of current climate change.

As a fifth-year Ph.D. student at Columbia University’s Lamont-Doherty Earth Observatory, Yuxin Zhou’s research focuses on the factors destabilizing the circulation in the North Atlantic, spanning the past 150,000 years. The majority of his findings are based on new and previously published measurements of long tubes of sediment cores collected from ocean floors in the North Atlantic.

“Model simulations can be a very powerful tool to narrow down the spread off of estimates we have on the freshwater fluxes,” Zhou said.

Prior to the pandemic, he spent long weekdays working at Lamont-Doherty in the Palisades near New York City. However, due to stay-at-home orders, he has been on campus for only three to four weeks in total since March.

When Zhou does travel to the campus, entering the laboratory requires an extensive sanitation protocol. He must change into the appropriate lab attire, which includes long pants, long sleeves, closed-toed shoes, gloves, goggles, a mask, and a lab coat. After stepping onto a sticky mat to remove dust particles from his shoes, Zhou can enter the lab and begin working.

Measuring 18 data points from one sediment core can take up to two weeks but provides key data on specific elements and isotopes within the sediment, and indicates the amount of freshwater released by melting icebergs during a certain period of time.

To begin the measuring process, Zhou begins by removing a small portion of the sediment core and places the solid sediment into a heat-and acid-resistant container. He then uses heat and several types of acids, including hydrofluoric acid, to gradually dissolve the solid sediment into a liquid solution.

Yuxin Zhou working on scientific processes at the Lamont-Doherty Earth Observatory laboratory.
While working in the Lamont-Doherty Earth Observatory laboratory, Zhou wears full personal protective equipment including a lab coat, face mask, goggles, and gloves. In the lab, Zhou works on various scientific processes including column chemistry (right). (Yuxin Zhou // Columbia University)

Once a dissolved liquid, it’s time to begin a chemical process called column chemistry, which filters and separates elements in the liquid. The chemical process results in a concentrated liquid containing three primary elements, which Zhou needs to measure the iceberg meltwater: thorium, protactinium, and uranium.

Finally, the concentrated liquid is placed into a machine to test the concentration of each isotope. With conclusive measurements, Zhou can determine the amount and location of freshwater released by icebergs in the North Atlantic.

The remainder of the sediment core is archived in the Lamont-Doherty’s core repository, one of the largest such repositories in the world. With accessibility to decades of core sediments collected from around the world, Zhou hopes his new method will contribute to scientist’s global efforts to predict and mitigate the effects of climate change.

“The best minds in the world have been working on this for a very long time,” Zhou said. “The scientists have nothing other than the best interest of science and the human society when they devote their careers to these questions about climate change.”

For the full story on Zhou and his journey to the present, read “Next generation climate scientists prepare for the future by studying past North Atlantic iceberg melting” on Medill Reports.

Grace Rodgers is health, environment and science reporters at Medill. You can follow her on Twitter at @gracelizrodgers.

A new glacial chronology lays the groundwork for understanding how modern ice sheets respond to climate change

A new glacial chronology lays the groundwork for understanding how modern ice sheets respond to climate change

By Grace Rodgers, Dec. 18, 2020 –

Researchers have long tracked the timing and retreat patterns of the North American Laurentide ice sheet, the greatest ice sheet to exist in the Ice Age. During that time, nearly two-thirds of the rise in the global sea level was caused by the melting of the Laurentide — the majority of which occurred over 10,000 years.

“That’s an interesting, dynamic problem. In many senses, they’re very few other elements that size on the planet that change that rapidly,” said Thomas Lowell, a geology professor at the University of Cincinnati.

For over 40 years, Lowell has studied the Laurentide and tracked two key behaviors the ice sheet exhibited during climate changes: the amount of meltwater and ice margin retreat. Lowell presented his most recent research on these two behaviors at the annual Comer Climate Conference, an annual summit where climate scientists from around the world gather to present emerging research.

Over a five-year research process, Lowell and a team of scientists assembled the first-ever annual chronology tracking the amount of meltwater released and the rate at which the Laurentide retreated. The chronology begins nearly 12,700 years ago and spans a 1,500-year transition between the late Younger Dryas, a geologic interval of colder temperatures, and the Holocene boundary, a geologic interval of warmer temperatures.

Lowell predicted the measurements would show a slower retreat rate and less meltwater during the cold interval, and a faster retreat rate and more meltwater during the warm interval. However, the chronology revealed the meltwater doubled at the transition between the cold and warm interval, while the ice sheet retreated at a constant rate.

“If you melt a glacier more, you expect it to shrink faster. But the interval that we recorded, [the retreat rate] didn’t seem to be paying attention [to the temperature],” said Lowell. “Even though it was melting faster, it was still backing up and retreating at the same rate.”

While melting in warmer temperatures was expected, Lowell was surprised the glacier retreated at the same rate despite the higher meltwater.

“There’s nothing super exciting about the [meltwater] findings, but coupled with the [retreat rate] findings, they seemingly conflict with each other,” said Lowell.

The team of scientists working on the frozen ice using measuring equipment.
The team of scientists spent roughly four weeks researching and plotting core sites for the varve chronology. Afterward, the team spent roughly six weeks collecting the sediment cores across frozen lakes in Central North America. (Dr. Andy Breckenridge//University of Wisconsin)

To quantify the amount of glacial meltwater, Lowell and the team of scientists recovered roughly 1,000 meters total of sediment cores, one meter at a time across lakes in Central North America. Back in the lab, scientists measure the core’s “varves”, the thickness of sediment layers deposited in one year. Each varve indicates the amount of melting that occurred in one year: the thicker the layer, the more meltwater.

Altogether, the sediment cores serve as a chronology of meltwater. Measuring varve units can be critical for assessing the response of both past and present ice sheets to climate change.

“[Varves] were an archive that we really needed to understand the ice,” said Dr. Andy Breckenridge, lead author and a geology professor at the University of Wisconsin. “We knew the record was there and we designed a strategy where we were going after modern lakes to reconstruct it.”

The Geographic Information System equipment taking a photo of a sediment core.
Using a Geographic Information System at the University of Minnesota, Breckenridge captures a high-resolution image of the sediment cores to measure each varve. (Dr. Andy Breckenridge//University of Wisconsin)

Breckenridge measured each sediment core, beginning by taking high-resolution scans to survey the varve thickness and color. Lighter layers indicate summer seasons, meaning the sediment is coarser due to warmer temperatures. Darker layers indicate winter seasons, meaning the sediment finer grain due to colder temperatures. Once tallied on a spreadsheet, Breckenridge identifies thickness patterns to organize the varve chronology.

While one half of the cores are used for data collection, the other half is stored in a refrigerated warehouse allowing researchers from around the world to come and study the chronological cores.

“[Other researchers] are going to be able to request samples from our cores,” Breckenridge said. “And that’s already happened at some of our sites. I know some of our cores have been used for a carbon storage question”

Now that these findings are published, Lowell’s current research question asks: are these melting patterns a behavior of the whole ice sheet or just a small part of it, and if so, is that small part important. Further research into past and present glacial melting is critical to help us understand sea level change that threatens the livelihood of millions around the world.

“The ice sheets have the potential to change sea level, enough to really matter to society,” said Lowell.

Grace Rodgers is health, environment and science reporters at Medill. You can follow her on Twitter at @gracelizrodgers.

Trump warns the Green New Deal will ‘take out the cows.’ Here’s the science showing why that’s a myth.

Trump warns the Green New Deal will ‘take out the cows.’ Here’s the science showing why that’s a myth.

By Carlyn Kranking and Grace Rodgers, Nov. 19, 2020 –

At the first 2020 Presidential debate, President Donald Trump said that Green New Deal supporters “want to take out the cows” to reduce greenhouse gas emissions.

Not only is this claim untrue, but eliminating cows, which notoriously produce the greenhouse gas methane, isn’t necessary to address climate change, according to University of Oxford researchers.

“It would be good if you maybe ate less beef, had less milk — but we don’t need to completely get rid of all the cows,” said John Lynch, postdoctoral researcher at the University of Oxford.

Lynch studies ways to anticipate the impacts of greenhouse gases and suggests that the greenhouse gas carbon dioxide is more important to address than methane. It takes much less time to reverse the impact of methane emissions than it does to undo the effects of carbon dioxide, so it’s possible to delay addressing methane, he said. His suggestion has huge implications, because the way greenhouse gases are reported and compared in policies today doesn’t make it clear how differently these gases behave.

The Global Warming Potential (GWP) is a metric used to compare how much different greenhouse gases will warm the atmosphere across a given period into the future. Organizations including the U.S. Environmental Protection Agency and U.N. Intergovernmental Panel on Climate Change publish the GWP in their reports.

However, Lynch’s research shows that, for some purposes, the GWP metric may be misleading. Reporting all gases as though they were on the same playing field, experts say, does not account for key differences between them, especially between methane and carbon dioxide.

“Metrics that try and treat the gases in the same way are always going to have limitations,” Lynch said.

A figure from Lynch’s report demonstrates the differing effects of carbon dioxide and methane on warming over time.

In the first few decades after it’s emitted, methane causes more warming per kilogram than carbon dioxide does. Methane, however, breaks down after about 12 years, while carbon dioxide accumulates in the atmosphere, warming the planet for millennia.

Calculating warming potential over 100 years, for instance, does not account for how strongly methane warms the planet initially, nor does it account for the full effects that CO2 emissions will have.

So, if the GWP measurement is misleading, what does this mean for potential policies based on that statistic?

It would be best to cut both carbon dioxide and methane emissions, Lynch said. But because governments have limited will and resources to address the problem, he said it is more important to achieve net zero carbon emissions before cutting methane.

“If we prioritize the methane, first we will have a large quick benefit” as methane levels in the atmosphere rapidly fall, Lynch said. “But in the meantime, we will have carried on emitting all the CO2 that we decided not to bother with because methane looks easy. And then, in a couple of decades, we’ll be stuck with that CO2 warming, whereas if we just delayed our action on methane, we’d still be able to reverse that.”

Still, governments should not ignore methane emissions in climate policy, as all greenhouse gases warm the planet, Lynch said. But ultimately, the most important thing to do is to get to net zero carbon dioxide, because that’s the gas with the longest-lasting and biggest impact on global warming.

“There’s a lot of harm in delaying things that address carbon emissions,” said physicist Raymond Pierrehumbert, a professor and statutory chair in the physics department at the University of Oxford.

These long-lasting emissions will warm the planet, causing more extreme weather conditions, droughts, floods and rising sea levels. The longer it takes to reach net-zero CO2 emissions, the more severe these effects will be.

That’s why Lynch feels we “don’t really have a choice” on whether or not to decrease carbon emissions.

“All of your energy needs to be decarbonized,” Lynch said. “If we don’t, we’ll never stop the temperature going up.”

Carlyn Kranking and Grace Rodgers are Health, Environment and Science reporters at Medill. You can follow them on Twitter at @carlyn_kranking and @gracelizrodgers. 


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