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High-resolution mapping reveals ocean carbon sink detail

As atmospheric carbon dioxide levels continue to rise, the ocean plays a crucial role in helping to reduce the full impact of human-driven climate change by absorbing roughly a quarter of the carbon dioxide emitted by human activity.

However, this uptake is far from uniform across the global ocean. A new satellite-based product can now map the ocean carbon sink at unprecedented resolution, offering unique insights into this highly variable and complex component of Earth's climate system.

The global ocean has so far acted as a brake on climate change, having absorbed approximately 90% of the excess heat and around 25% of the carbon dioxide that has been released into the atmosphere through human activities such as the burning of fossil fuels.

Although the oceanic sink for the human-induced carbon dioxide reduces global warming, there are significant biogeochemical consequences. This uptake leads to a reduction in seawater pH and alters the carbonate chemistry of the ocean. These changes in ocean chemistry, often collectively referred to as ocean acidification, impact marine organisms and alter marine ecosystems.

With the health of our oceans at stake—and far-reaching consequences for the entire planet—it is crucial to understand the complexities and significant variability inherent in ocean carbon sink processes.

Although scientists have made significant progress in understanding how the global ocean carbon sink changes over seasons and decades, its short-term variability is still not well understood.

Most global datasets currently used to study the ocean carbon sink only provide monthly data and have a resolution of about 100 by 100 kilometers. This limited temporal and spatial resolution makes it difficult to capture the finer, more dynamic changes governing the ocean sink.

Nicolas Gruber, from the ETH Zurich University in Switzerland, said, "Increasing the resolution of these global datasets is challenging because the number of direct measurements of carbon dioxide at the ocean's surface is rather sparse across all regions and times.

"To address this, we came up with a creative mix of machine learning methods to develop a new version of our OceanSODA-ETHZ product—a global, gridded dataset of surface ocean carbon dioxide and the ocean carbonate system, designed for studying the ocean carbon sink and ocean acidification over seasonal to decadal timescales.

"This new version maps the parameters of the ocean carbon system every eight days at a resolution of about 25 by 25 kilometers, more than 30 times finer than previous products. A critical part of the approach is the use of satellite data, which provides detailed information to interpolate the measurements in time and space."

This result has been visualized in the animation above, which shows differences in the exchange of carbon dioxide between the air and the sea over a period encompassing numerous hurricanes in the Atlantic Ocean.

Regions in blue indicate carbon dioxide uptake by the ocean, while regions in red are where carbon dioxide is being released to the atmosphere. Arrows depict winds at the surface ocean.

At ESA's Living Planet Symposium this week, scientists have been learning how this new high-resolution product can also reveal the effects of short-lived but powerful events in the ocean.

Professor Jamie Shutler, from the University of Exeter's Department of Earth and Environmental Science, said, "Thanks to its fine detail, the dataset can help us separate and understand the influence of events like hurricanes—where deep water, often high in carbon can be forced to rise to the surface—which can cause sudden spikes or changes in surface ocean carbon dioxide levels."

By capturing these small-scale changes, the product opens up new opportunities to study how the ocean absorbs carbon and how this process might change in the future against the backdrop of climate change.

ESA Earth Observation Ocean Scientist, Roberto Sabia, said, "The fact that we can use this method to gain new insights into the exchange of carbon dioxide between the ocean and atmosphere—and on ocean acidification altogether—is a great step forward in ocean science. We thank the team for all their hard work and look forward to more new discoveries."