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The work, published in Nature Communications, could provide insight into the future location and potential impacts of low-oxygen regions in Earth’s warmer oceans. In particular, the work anticipates more dead zones in the North Atlantic.
Minimum oxygen zones, or MOZ, are areas of the ocean where oxygen levels in the midwaters (100 to 1,000 meters below the surface) are too low to support most marine life. These dead zones play an important role in the overall health of the oceans.
“MOZs are very important for ocean geochemical circulation,” says Katherine Davis, associate professor of marine, earth and atmospheric sciences at North Carolina State University and corresponding author of the paper. “They are produced in areas that do not have access to sunlight and atmospheric oxygen. Their location determines the availability of carbon and nitrogen (an essential nutrient for life on Earth) in the ocean, so they are important drivers of nutrient cycles.”
The ability to predict the location of OMZs is important not only for understanding the nutrient cycle, but also for their effects on marine life. Oceanic dead zones restrict the range of animals to the shallow surface of the ocean, where oxygen is most abundant.
Davis and his colleagues wanted to know how a warmer climate might affect future OMZs. To do this, they went back to the Pliocene epoch (between 5.3 and 2.6 million years ago), when carbon dioxide levels in Earth’s atmosphere were comparable to today.
“The Pliocene is the last time we had a stable, warm climate globally, and the average global temperature was 2-3C warmer than it is now, which scientists predict could be about 100 years from now,” Davis says. From now. years.”
To determine where the Pliocene OMZs were located, the researchers used tiny fossilized plankton called foraminifera. Foraminifera are single-celled organisms the size of a grain of sand. They form hard calcium carbonate shells that can remain in marine sediments.
One species in particular, Globorotaloides hexagonus, is found only in areas with little oxygen. By using trawling Pliocene sediment databases to locate those species, the team was able to map the Pliocene OMZs. They superimposed their map on a computer model of Pliocene oxygen levels and found that the two were identical.
Especially in the North Atlantic
The OMZ map showed that during the Pliocene, oxygen-depleted waters were more prevalent in the Atlantic Ocean, especially in the North Atlantic. In contrast, in the North Pacific Ocean there were fewer regions of low oxygen content.
“This is the first global spatial reconstruction of oxygen minimum regions in the past,” says Davis. “And it matches what we’re already seeing in the Atlantic Ocean in terms of lower oxygen levels. Warmer water has less oxygen.” A map of Pliocene dead zones can give us an idea of what the Atlantic Ocean might look like 100 years from now on a much warmer Earth.”
What does a future with less oxygen in the Atlantic mean? According to Davis, it could have a huge impact on everything from carbon storage and nutrient cycling in the ocean to fisheries and marine species management.
OMZs serve as a ‘floor’ for marine animals, which are crushed to the surface,” Davis explains. “So fishermen can suddenly see a lot of fish, but that doesn’t mean there are more than usual, it just means they are forced to occupy a smaller area. Fisheries will need To take into account the influences of OMZs when managing stocks.
“Silent but far-reaching changes are also possible in the amount of nutrients available to life in those surface waters, as well as in where carbon dioxide captured by the ocean is stored.”
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