Breakthrough in modeling
First global study of coastal seas as carbon dioxide reservoirs possible
Coastal seas form a complex transition zone between the two largest CO2 sinks in the global carbon cycle: land and ocean. Ocean researchers have now succeeded for the first time in investigating the role of the coastal ocean in a seamless model representation. The team led by Dr. Moritz Mathis from the Cluster of Excellence for Climate Research CLICCS at Universität Hamburg and the Helmholtz-Zentrum Hereon was able to show: The intensity of CO2 uptake is higher in coastal seas than in the open ocean. This is evidenced by a study published in the journal Nature Climate Change.
In computational climate science, land and ocean, the Earth’s two major carbon reservoirs, have so far been considered separately. The transport of carbon into the coastal seas, for example via river inputs, coastal erosion and tidal flats, has been ignored. Coast-specific processes could only be considered in a limited and spatially coarse manner because climate models were developed for global scales. Due to the more realistic representation and higher resolution in the transition zone between land and ocean used in ICON-Coast, the model offers new possibilities to explore the effects of climate change on coastal areas and marine ecosystems, such as risks from heat waves, storms, or global sea level rise.
It is known from observations that the increase in atmospheric CO2 concentration enhances the uptake of CO2 into the ocean, thereby significantly mitigating climate change. Simulations with ICON-Coast now shed light on the causes and enable understanding of the function of coastal and marginal seas in the Earth’s climate dynamics: „Our analyses show that intense plankton growth is the key to enhanced CO2 uptake in the coastal ocean and that this uptake is higher than in the open ocean. This is due to climate-induced changes in the circulation and increasing nutrient inputs from rivers,“ says Dr Moritz Mathis, who led the study. The researchers also expect that the intensity difference between coastal seas and the open ocean will continue to strengthen further with ongoing CO2 emissions.
All the more important: „Coastal management strategies that disturb biological production could weaken the ocean’s CO2 uptake and make climate protection more difficult,“ emphasizes Mathis. „With the new model, we can also test approaches to CO2 avoidance such as offshore wind energy for their effectiveness and undesirable side effects.“ (Source: Hereon Press Release)
Read the complete Hereon Press Release:
==> Breakthrough in modeling
Mathis, M., Lacroix, F., Hagemann, S., Nielsen, D.M., Ilyina, T., & Schrum, C. (2024): Enhanced CO2 uptake of the coastal ocean is dominated by biological carbon fixation. Nat. Clim. Chang., doi: 10.1038/s41558-024-01956-w
Abstract:
Observational reconstructions indicate a contemporary increase in coastal ocean CO2 uptake. However, the mechanisms and their relative importance in driving this globally intensifying absorption remain unclear. Here we integrate coastal carbon dynamics in a global model via regional grid refinement and enhanced process representation. We find that the increasing coastal CO2 sink is primarily driven by biological responses to climate-induced changes in circulation (36%) and increasing riverine nutrient loads (23%), together exceeding the ocean CO2 solubility pump (41%). The riverine impact is mediated by enhanced export of organic carbon across the shelf break, thereby adding to the carbon enrichment of the open ocean. The contribution of biological carbon fixation increases as the seawater capacity to hold CO2 decreases under continuous climate change and ocean acidification. Our seamless coastal ocean integration advances carbon cycle model realism, which is relevant for addressing impacts of climate change mitigation efforts.
Another publication deals with the above-mentioned study and puts it into context:
Resplandy, L. (2024): Coastal sink outpaces open ocean. Nat. Clim. Chang., doi:10.1038/s41558-024-01968-6
“Mathis and co-authors provide a solid argument in support of a biologically strengthened coastal ocean sink that is at odds with the traditional view of a passive ocean sink controlled by the rise in atmospheric CO2”
