The Earth’s oceans are helping to slow global warming by absorbing carbon from our atmosphere. However, it is difficult to fully observe this crucial process in the upper ocean and in the lower atmosphere, as measurements are not taken where they occur, but at the surface of the sea, but several meters below. New research uses data from ESA, NASAand NOAA satellites to correct this, finding that far more carbon is being absorbed by the oceans than previously thought.
There is an ongoing effort to collect and compile on site Measurements of the ocean sink in the form of the Surface Ocean CO₂ Atlas (SOCAT), which contains over 28 million international observations of our oceans and coastal seas from 1957 to 2020. By searching SOCAT’s extensive database, scientists can determine how much carbon is being sucked from the atmosphere and stored by our seas.
Much of the carbon dioxide released into the atmosphere by human activities is absorbed by our oceans. This helps regulate our climate change by trapping this warming gas and acting as a carbon sink. Recent research has shown that the amount of carbon absorbed by our oceans is underestimated by up to 0.9 gigatons per year. The researchers used satellite data to correct measurements of ocean carbon compiled by the Surface Ocean CO ocean Atlas (SOCAT). Instead of being collected where carbon flows into the ocean – on the surface – it is being taken in a few meters deeper, leading to an incomplete understanding of this crucial process. By combining SOCAT data with observations from a number of satellites, the researchers were instead able to identify the process at the ocean surface. The results are consistent with independent estimates of the size of the oceanic carbon sink, and therefore provide a more certain characterization of the way Earth’s oceans are capturing this gas.
“There is a catch, however: the measurements are not carried out directly on the sea surface, where they are needed, but from a depth of a few meters,” explains Andrew Watson from the University of Exeter, UK, lead author of the new study. Although the difference can be only a few meters, the sea surface temperature changes with depth – and with it the associated ability to absorb carbon from the atmosphere.
“Previous studies have ignored the small temperature differences between the ocean surface and the sample depth, but we know that this has a significant impact on how carbon is held by the oceans in terms of salinity, solubility, stability, etc. Andrew adds. “But satellites can measure the temperature at the ocean surface more or less accurately – and when we do that we find that it makes a big difference.”
By applying satellite corrections to SOCAT data from 1992 to 2018 to take into account temperature differences between the surface and a few meters below the surface, the researchers found a much higher uptake of carbon dioxide in the oceans than previously assumed. They achieved this thanks to data from a number of satellites such as Envisat from ESA, AVHRR from NOAA, MetOp series from EUMETSAT and the Copernicus Sentinel-3 mission, initially as part of the OceanFlux research project (part of ESA’s Science for Society program) ) and then continued within two EU-funded projects.
The corrected figures show that the net flow of carbon into the oceans is underestimated by up to 0.9 gigatons of carbon per year – a significant amount that at times doubles uncorrected values.
“These results are consistent with independent estimates of the size of the oceanic carbon sink based on global ocean surveys by research vessels,” added co-author Jamie Shutler, also from the University of Exeter. “Now that these two separate estimates of the size of the carbon dioxide ocean sink agree pretty well, we can view and use their results with greater confidence and trust that they will most likely give us an accurate picture of what is going on.”
Andrew and Jamie were both part of a pan-European research team – including researchers from Heriot-Watt University and UHI in Scotland – who previously used SOCAT data to estimate how carbon flows in and out of our oceans in unprecedented ways accuracy. They found that three gigatons of carbon were drawn into the ocean in 2010 alone: about a third of the emissions caused by human activities. This finding contrasted with earlier estimates of a quarter, and led Andrew, Jamie and colleagues to conclude – as in this study – that the role of the oceans in capturing atmospheric carbon is underestimated.
While this can bring positive benefits in reducing the warming of the atmosphere due to climate change, as more carbon dioxide is removed from the air, the oceans are affected by the carbon they absorb. They become more acidic, which threatens the health of marine ecosystems and makes marine life increasingly difficult to survive.
“The importance of our oceans in regulating the climate and promoting biodiversity cannot be overstated,” added Craig Donlon of ESA. “In all of ESA’s Earth observation activities, it is our aim to fully consider the role of our oceans in relation to the carbon cycle. This key result, together with others based on the commitment and excellent collaboration of the ESA OceanFlux team, forms a solid foundation for this and will help us to more accurately characterize and better understand the changing climate of our planet. ”
The paper published in Communication with natureis titled: “Revised estimates of the CO2 flux in the ocean atmosphere are consistent with the carbon inventory of the oceans.”
For more information on this climate science news, see Oops! The world’s oceans absorb far more carbon than most scientific models suggest.
Reference: “Revised estimates of CO in the ocean atmosphere2 Flux Corresponds to the Carbon Inventory of the Oceans “by Andrew J. Watson, Ute Schuster, Jamie D. Shutler, Thomas Holding, Ian GC Ashton, Peter Landschützer, David K. Woolf and Lonneke Goddijn-Murphy, September 4, 2020, Nature communication.
DOI: 10.1038 / s41467-020-18203-3
