Seaweed and carbon storage
Researchers revealed: Seaweed forests are significant contributors to oceanic carbon storage
A groundbreaking study by an international team of researchers, including two scientists at Helmholtz-Zentrum Hereon, has revealed the role of seaweed for oceanic carbon storage. Their research estimates that the world’s seaweed forests transport 56 million tons of carbon (between 10 to 170 million tons) to deep ocean sinks each year. Between 4 and 44 million tons of this carbon could remain sequestered in these deep sinks for at least a hundred years. This discovery, published in the prestigious journal Nature Geoscience.
The study, led by Dr Karen Filbee-Dexter at the Norwegian Institute of Marine Research and the University of Western Australia, reveals that seaweed forests export about 15 percent of their captured carbon into deep ocean waters each year, where part of it can remain trapped for centuries. The study estimates that seaweed-carbon export below 200 m depth totaled 3 to 4 percent of the ocean carbon sink. The findings underscore the need to include macroalgae in the depictions of the global ocean carbon budget, which still ignores the contribution of marine vegetation.
The international team used global ocean models to track the fate of seaweed carbon from the coast to the deep ocean. The transport time for macroalgae to the deep ocean was compared to their degradation rate to estimate the fraction that would reach the deep sinks. The team identified hotspots of carbon export globally, for example in areas with extensive seaweed forests or coastal areas with canyons or narrow continental shelves that are close to the deep sea. The coastal ocean represents an important global carbon sink and is a focus for interventions to mitigate climate change and meet the Paris Agreement targets while supporting biodiversity. “Hopefully our findings will help motivate efforts to reduce emissions as well as the negative impacts of human activities in the coastal zone to ensure the longevity of seaweed forests and their contributions to carbon sequestration and marine biodiversity,” said Dr Daniel Carlson, coauthor on the study. (Source: Hereon News)
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==> Seaweed and carbon storage
Filbee-Dexter, K., Pessarrodona, A, Pedersen, M.F., Wernberg, T., Duarte, C.M., Assis, J., Bekkby, T., Burrows, M.T., Carlson, D.F., Gattuso, J.-P., Gundersen, H., Hancke, K., Krumhansl, K.A., Kuwae, T., Middelburg, J.J., Moore, P.J., Queirós, A.M., Smale, D.A., Sousa-Pinto, I., Suzuki, N., & Krause-Jensen, D. (2024): Carbon export from seaweed forests to deep ocean sinks. Nat. Geosci. (2024), doi:10.1038/s41561-024-01449-7
Abstract:
The depletion of sedimentary organic carbon stocks by the use of bottom-contacting fishing gear and the potential climate impacts resulting from remineralization of the organic carbon to CO2 have recently been heavily debated. An issue that has remained unaddressed thus far regards the fate of organic carbon resuspended into the water column following disturbance by fishing gear. To resolve this, a 3D-coupled numerical ocean sediment macrobenthos model is used in this study to quantify the impacts of bottom trawling on organic carbon and macrobenthos stocks in North Sea sediments. Using available information on vessel activity, gear components, and sediment type, we generate daily time series of trawling impacts and simulate 6 years of trawling activity in the model, as well as four management scenarios in which trawling effort is redistributed from areas inside to areas outside of trawling closure zones. North Sea sediments contained 552.2±192.4 kt less organic carbon and 13.6±2.6 % less macrobenthos biomass in the trawled simulations than in the untrawled simulations by the end of each year. The organic carbon loss is equivalent to aqueous emissions of 2.0±0.7 Mt CO2 each year, roughly half of which is likely to accumulate in the atmosphere on multi-decadal timescales. The impacts were elevated in years with higher levels of trawling pressure and vice versa. Results showed high spatial variability, with a high loss of organic carbon due to trawling in some areas, while organic carbon content increased in nearby untrawled areas following transport and redeposition. The area most strongly impacted was the heavily trawled and carbon-rich Skagerrak. Simulated trawling closures in planned offshore wind farms (OWFs) and outside of core fishing grounds (CFGs) had negligible effects on net sedimentary organic carbon, while closures in marine protected areas (MPAs) had a moderately positive impact. The largest positive impact arose for trawling closures in carbon protection zones (CPZs), which were defined as areas where organic carbon is both plentiful and labile and thereby most vulnerable to disturbance. In that scenario, the net impacts of trawling on organic carbon and macrobenthos biomass were reduced by 29 % and 54 %, respectively. These results demonstrate that carbon protection and habitat protection can be combined without requiring a reduction in net fishing effort.
