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UCI scientists analyze first direct images of dissolved organic carbon from the ocean

Joint research project furthers understanding of important CO2 reservoir

June 5, 2018
UCI scientists analyze first direct images of dissolved organic carbon from the ocean
This image of a small marine dissolved organic carbon molecule was obtained by UCI, IBM Research-Zurich, University of Zurich and UC Santa Cruz researchers using atomic force microscopy, a technique developed by IBM in 2009. IBM Research-Zurich

Irvine, Calif., June 5, 2018 – In a first, researchers from the University of California, Irvine – as well as Switzerland’s University of Zurich, IBM Research-Zurich and UC Santa Cruz – have obtained direct images of dissolved organic carbon molecules from the ocean, allowing better analysis and characterization of compounds that play an important role in the Earth’s changing climate.

Using an atomic force microscopy technique developed by IBM, the team was able to visualize individual atoms and bonds, yielding clues about their persistence in the marine environment. Findings were published today in the American Geophysical Union journal Geophysical Research Letters.

“To understand processes happening on the scale of ocean basins, it is sometimes necessary to view objects that are orders of magnitude smaller,” said study co-author Ellen Druffel, professor and Fred Kavli Chair of Earth System Science at UCI. “By seeing with our own eyes the double bonds and rings of dissolved organic carbon molecules, we are better equipped to explain how they remain in the ocean for tens of thousands of years.”

The molecules that were imaged were collected by UC Santa Cruz researchers from waters in the northern central Pacific Ocean.

The marine dissolved organic carbon pool, comparable in size to the atmospheric CO2 reservoir, is about 200 times larger than the amount of carbon contained in all the plants and animals on the planet. Because of its complexity, diverse origins and varied reactions to environmental conditions, only about 10 percent of DOC has been characterized.

This image of a small marine dissolved organic carbon molecule shows a flat ring of six-carbon atoms that is very stable and does not break apart easily. It includes aromatic carbon-carbon bonds (white) and two attached methyl groups (green). IBM Research-Zurich

“We are still trying to figure out how the vast majority of this substance is going to be impacted by the ongoing addition of new CO2 from fossil fuel burning and from increasing temperatures due to global climate change,” said co-author Brett Walker, a UCI assistant researcher in Earth system science.

Most DOC near the ocean surface is derived from the remains of recently living phytoplankton. However, radiocarbon dating of DOC in the deep ocean shows it to be much older than expected – by as much as 4,500 years – indicating that a portion of this DOC survives multiple ocean mixing cycles.

Researchers have suggested that the chemical structure of DOC is responsible for its endurance in the environment, and through the atomic force microscopy technique, scientists are now able to see real-space images of the bound atoms in these compounds. The team has found that molecules from the deep ocean frequently exhibit aromaticity, meaning they’re flat rings of atoms that are very stable and do not break apart easily.

“These atom-scale visualizations help demonstrate that the old age of small DOC molecules in the deep ocean has to do with their chemical structure, which bacteria do not seem to utilize,” Walker said. “This is a crucial finding that will help researchers better understand the cycling of carbon in the oceans and the overall health of our planet’s marine environments.”

The work was funded by the University of Zurich, IBM Research-Zurich, the National Science Foundation and the American Chemical Society.

About the University of California, Irvine: Founded in 1965, UCI is the youngest member of the prestigious Association of American Universities. The campus has produced three Nobel laureates and is known for its academic achievement, premier research, innovation and anteater mascot. Led by Chancellor Howard Gillman, UCI has more than 30,000 students and offers 192 degree programs. It’s located in one of the world’s safest and most economically vibrant communities and is Orange County’s second-largest employer, contributing $5 billion annually to the local economy. For more on UCI, visit www.uci.edu.

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