Researchers are taking a deep dive into the carbon cycle and investigating how carbon moves from the ocean surface to greater depths and then remains there for hundreds of years. The findings could be critical as scientists work to better understand climate change and how much carbon the Earth’s atmosphere and oceans can store.
The new study, led by a scientist at Florida State University (FSU), included several researchers from Scripps Institution of Oceanography at the University of California San Diego.
In the paper recently published in the Proceedings of the National Academy of Sciences, FSU Assistant Professor and the study’s lead author Michael Stukel, a Scripps alumnus, explains how carbon is transported to deeper waters and why it is happening more rapidly in certain areas of the ocean.
“Algae in the surface ocean contribute half of the Earth’s photosynthesis, but most of the carbon dioxide they take up gets released back to the atmosphere when they die,” Stukel said. “The only way for this carbon to stay out of the atmosphere for a long period of time is to get it into the deep ocean. If it’s in the deep ocean, it can stay put for hundreds to thousands of years. As the climate gets warmer, will the ocean take up more carbon dioxide or less? That’s what we ultimately need to know. But first we have to figure out how this natural process of oceanic carbon storage works.”
Stukel has long engaged in studying how the carbon cycle functions. Specifically, he wants to understand the processes that move carbon into the deep ocean where it will not re-enter the atmosphere. Understanding these processes will be critical as the Earth grows warmer and more carbon dioxide is present.
Stukel, who is part of the California Current Ecosystem Long Term Ecological Research (CCE-LTER) project, set out with the CCE team to find answers to some of these questions while on a research cruise off the California coast in 2012.
Stukel and his colleagues suspected that certain areas of the sea were biological hotspots for carbon transport. Much like meteorological fronts converge to create a storm, there are fronts in bodies of water. These fronts typically form where there is a break in temperature or salinity. In these areas, scientists typically find dense and varied aquatic life.
“These results are highly relevant to the long-term mission of the site, because we know from another CCE-led study that these ocean fronts are becoming more common in this region,” said Scripps professor Mark Ohman, lead principal investigator of CCE-LTER and a co-author of the study. “So we expect front-related carbon export—and perhaps sequestration in the deep sea—to become increasingly important in the future. Our research group is developing the understanding needed to forecast future states of our marine ecosystem.”
Stukel and colleagues examined one such front off the west coast of Pt. Conception by setting sediment traps to measure how much carbon was being transported to the deep ocean in these areas. Stukel also used isotopic tracers to measure carbon flux.
The researchers found that double the amount of carbon was sinking to greater depths along this front than in other areas of the ocean, and the front itself acted as a giant conduit moving even non-sinking carbon to deeper depths.
One of the reasons for the higher sinking rates may deal with algae health. The CCE group observed that diatoms—a type of algae that makes glass-like shells out of silicon—found at this front were not healthy and were making much denser shells than normal. Diatoms typically also absorb high amounts of carbon dioxide. Copepods, krill, and other small crustaceans feed on these diatoms, and their fecal pellets then sink, taking large amounts of carbon with them. Because they are absorbing higher rates of silicon at these fronts, they are heavier and sinking to greater depths in the ocean.
“A lot of the carbon transport is mediated by these crustaceans,” Stukel said.
Stukel said the information this team uncovered can now be used by scientists who develop models that predict exactly how much carbon dioxide can be stored in the deep ocean. Stukel will also follow up on this work by examining other fronts to see if what he found off the coast of Santa Barbara is a widespread phenomenon.
“This study, led by Prof. Stukel, is a beautiful example of the power of a collaborative team of scientists working toward a goal,” said Ohman.
The researchers who contributed to the research are Lihini Aluwihare, Katherine Barbeau, Ralf Goericke, Arthur J. Miller, Mark D. Ohman, Angel Ruacho, Brandon M. Stephens and Michael R. Landry from Scripps Institution of Oceanography at UC San Diego; Alexander Chekalyuk from Columbia University; and Hajoon Song from Massachusetts Institute of Technology. The work was funded by the National Science Foundation.
-- Adapted from a Florida State University news release
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