This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: The use of fossil fuels alters both the concentration and the carbon isotope composition of carbon dioxide in the atmosphere. Since surface water exchanges carbon dioxide with the atmosphere, this also alters the isotopic composition of the carbon dissolved in the ocean.
In a new study, a team from MARUM—Center for Marine Environmental Sciences at the University of Bremen has now determined how deep this so-called Suess effect has already penetrated into the North Atlantic. In its stable form, carbon consists of the isotopes C-12 and C-13. During photosynthesis, plants preferentially fix the lighter C-12.
Because fuels consist predominantly of fossil plant material, they contain comparatively little of the heavy carbon isotope C-13. As a result of their combustion, the ratio of C-13 to C-12 in the atmosphere decreases. Through exchange with the atmosphere, surface water increasingly takes on this altered isotopic signature.
Through vertical mixing and the formation of deep water, anthropogenic carbon can be transported deep into the ocean. New measurements show how far this anthropogenic carbon signal has already penetrated into the deep-water masses of the North Atlantic. For their study, published in the journal Geophysical Research Letters, the team led by Emma Bavoux analyzed carbon isotope ratios in water samples collected during two expeditions aboard the research vessel MARIA S.
MERIAN in 2017 and 2018 along a transect at approximately 48° north across the entire North Atlantic. In addition, the researchers used earlier measurements of the trace gas sulfur hexafluoride (SF₆)—which is also produced by human activities—to estimate the human-induced component in the carbon isotope ratio. "We were surprised by how significant the Suess effect already is in the deep-water masses of the North Atlantic," Bavoux says.
The Suess effect is now detectable in nearly all the North Atlantic water masses studied. Young subsurface water masses in the North Atlantic—or those that had most recently been in contact with the atmosphere—exhibited the strongest Suess effect. The Suess effect was extremely weak or undetectable in deep, ancient water masses such as the Northeast Atlantic Deep Water, which likely have had no contact with the atmosphere for several hundred years.
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