A team of researchers from different countries has conducted a study that could help better understand how climate warming impacts the burial of organic carbon deposits underneath the world’s oceans.
Air Pollution
According to the research published in Nature, climate change seems to decrease organic carbon burial in oceans. This, in turn, brings about an increase in the amount of carbon that is released into the atmosphere.
“What we’re finding is that burial of organic carbon is very active,” said Rice University’s Dr. Mark Torres, a co-author of the study. “It changes a lot, and it responds to the Earth’s climatic system much more than scientists previously thought.”
This research hints that scientists still have a lot to learn about the dynamics of the long-term carbon cycle of Earth. It is believed to offer the most detailed report of organic carbon burial in the last 30 million years, yet.
Researchers from Texas A&M University, the University of Bremen, and the University of Leeds were also involved in the study.
Organic carbon burial and calculation
As the foundation of biological molecules, carbon cycles through ecosystems, the atmosphere, and the oceans—shaping Earth’s climate over millennia. It is naturally available in great abundance, and life on Earth is impossible without it. Its compounds are continually cycling between the atmosphere and biosphere of Earth as both plants and animals develop, die, and decompose.
Scientists say carbon’s cycle through the Earth can take millions of years, starting at tectonic subduction zones.
Drilled cores from the floor of the oceans have shown sediment layers that were formed many millions of years ago. For a long time, scientists have been probing the levels of carbon buried in these ocean sediments.
Researchers can find out when certain sediments were laid down with the aid of radiometric dating and other techniques. It is also possible to learn a great deal about past Earth conditions by examining minerals and microscopic organism skeletons in sediments.
Torres noted that there are two carbon isotopes: carbon-12 and carbon-13. One isotope (carbon-13) is a neutron heavier, but that’s enough to impact its absorption.
“So life prefers the lighter isotope, carbon-12,” said Torres, who described life as “lazy.” “And if you grow a plant and give it CO2, it will actually preferentially take up the lighter isotope. That means the ratio of carbon-13 to -12 in the plant will be lower – contain less 13 – than in the CO2 you fed the plant.”
Isotopic ratios have been the preferred choices for probing the amounts of carbon (both organic and inorganic) that were being buried at certain points in the history of Earth. Based on this, scientists have mostly held that carbon burial has not changed much over the last 30 million years in terms of amount.
The team in this new research thought something was amiss with the popular opinion. To challenge these long-held assumptions, the researchers took a different path.
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A different approach and surprising findings
Torres and his colleagues described the conventional method for isotopic calculations as being more “top-down.” So they proposed a “bottom-up” approach to ascertain if those calculations were right or otherwise. The team set out to use real data to work out the rates of organic carbon burial and estimate global carbon burial.
These researchers went on to acquire data collected across more than 50 years of scientific seafloor-drilling expeditions. Specifically, they obtained and analyzed sediment data gathered during 81 shipboard expeditions by the International Ocean Discovery Program (IODP) and its forerunners.
This first-of-its-kind research produced results that were “very different” from what traditional isotope calculations suggested.
Dr. Yige Zhang, the study’s corresponding author and an oceanographer at Texas A&M, pointed out that the calculations for the mid-Miocene period (roughly 15 million years ago) were especially wrong. Scientists previously thought that a huge amount of organic carbon was buried around this period. The Monterey Formation in California, rich in organic carbon, was previously thought to reflect widespread burial at the time. However, the new data suggest it may be an exception rather than the rule.
Findings in this study, however, show that the least organic carbon over the past 23 million years, or thereabout, was buried during the mid-Miocene.
Study results show that organic carbon burial is influenced a lot more by the climate than scientists previously believed.
As less organic carbon is buried in ocean sediments, more of it remains in the atmosphere as CO₂. This reduces the Earth’s ability to naturally sequester carbon, accelerating the greenhouse effect and global warming. The findings suggest climate change could be making the Earth’s carbon sink weaker over time.
The researchers expressed the hope that their findings could improve the understanding of the organic carbon cycle. Their results could help to better tackle the climate crisis. Understanding burial variability helps scientists refine global carbon budgets. If models assume steady burial rates when they’re actually declining, emissions targets and long-term climate predictions could be way off.
FAQs: Climate Change and Ocean Carbon Burial
What is organic carbon burial in the ocean?
It’s when dead marine life and plants sink and get trapped in seafloor sediments, storing carbon long-term.
Why does it matter for climate change?
It’s a natural way Earth removes CO₂ from the atmosphere, helping to stabilize global temperatures.
How does climate change affect this process?
Warming oceans speed up bacterial activity, which breaks down organic matter before it can be buried, releasing more carbon into the air.
What’s new about this study?
It found that carbon burial is much more sensitive to climate shifts than previously thought, especially over the last 30 million years.
How did researchers figure this out?
By analyzing real-world data from 81 ocean drilling expeditions instead of relying only on isotope models.
What’s the deal with the mid-Miocene period?
It was long thought to be a peak burial period, but new data show it actually had one of the lowest carbon burial rates.
What does this mean going forward?
It means we may need to adjust climate projections if oceans continue to store less carbon, adding pressure to cut emissions faster.
The Bottom Line
This study shows that organic carbon burial in the ocean isn’t as stable as once thought — it changes with climate. As the planet warms, less carbon is being stored in seafloor sediments.
This raises a practical question: How should climate models adjust if one of Earth’s long-term carbon sinks is becoming less effective?
References
Li, Z., Zhang, Y.G., Torres, M. et al. Neogene burial of organic carbon in the global ocean. Nature 613, 90–95 (2023). https://doi.org/10.1038/s41586-022-05413-6
