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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.

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