Researchers at UC Santa Barbara are shedding new light on the ocean’s role in storing carbon. Led by microbial oceanographer Alyson Santoro, the team has challenged traditional views about how carbon dioxide is absorbed in the dark depths of the sea. Their findings, published in Nature Geoscience, aim to clarify the relationship between nitrogen availability and carbon fixation in these waters.
Santoro highlights the importance of understanding how much carbon the ocean captures. “We want to know how carbon moves through the deep ocean,” she explains. The ocean absorbs about a third of human-made carbon emissions, making its carbon storage capacity vital for regulating global temperatures.
Traditionally, scientists believed that most carbon fixation happened in sunlit surface waters through photosynthetic phytoplankton. In deeper waters, it was thought that archaea (a type of microorganism) performed the fixation by oxidizing ammonia. However, inconsistencies in existing data puzzled researchers. There appeared to be insufficient nitrogen energy to support the high rates of carbon fixation that were observed.
This disconnect has engaged Santoro and lead author Barbara Bayer for nearly a decade. Their earlier work tested whether the archaea might be more efficient in carbon fixation than previously thought. But that theory didn’t add up.
In their latest study, they redirected their focus to the role of ammonia-oxidizing microbes. Bayer designed an experiment to precisely inhibit these organisms in the deep ocean. To their surprise, when the activity of these archaea was limited, the expected drop in carbon fixation didn’t occur. This led the researchers to rethink who really contributes to carbon fixation in these depths.
If archaea are not the main players, other types of microbes, particularly certain bacteria, could be stepping up to fill the gap. “Heterotrophic microorganisms, which feed on organic matter, might also fix inorganic carbon,” Santoro says. This research provides a new perspective on the deep ocean’s food web and how it operates.
“We’re trying to understand the fundamental structure of this food web,” she adds. This deeper understanding could have broader implications for marine ecosystems. It suggests a more complex relationship between different types of microbes and carbon, which could ultimately impact our approach to climate change and ocean conservation.
As scientists continue to investigate, they will also look into how the nitrogen cycle interacts with other essential cycles in the ocean, including those involving iron and copper. Understanding these interactions is crucial for comprehending not just carbon fixation but also the overall health of marine ecosystems.
This study has far-reaching implications, shedding light on the hidden complexities of our ocean ecosystem—an ecosystem that plays a crucial role in fighting climate change.
For more information on the ocean’s carbon cycle, check out the National Oceanic and Atmospheric Administration (NOAA) website.
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