Coastal blue carbon

Blue carbon will not solve climate change. The effect is too small; existing sediment carbon stock is a liability; and there is a timescale mismatch between ancient fossil fuel emissions and uptake by vegetation. Clearer communication would support informed decision-making.

Geomorphic and ecological factors shape the effects of sea level rise on the coastal carbon sink. This Review discusses how reductions in greenhouse gas emissions compensate for losses in carbon sequestration as ecosystem boundaries change rapidly in the coastal zone.

Mangroves, tidal marshes and seagrass meadows have historically been lost or degraded, threatening their ability to store carbon and provide ecosystem services. This Review details the global potential of blue carbon ecosystem protection and restoration in climate change mitigation, through carbon sequestration and co-benefit production.

A 23% decrease of seagrass in the western Gulf of Mexico over a five-year period, including the local decline of two seagrass species, was likely due to insufficient light availability from rapid sea level rise, according to long term survey and field monitoring programs.

Global observations from mangroves and saltmarshes unravel hidden carbon pathways. Inorganic carbon outwelling is revealed to dominate carbon budgets, impact coastal pH, and enhance the climate mitigation potential of blue carbon ecosystems.

Seagrass meadows in The Bahamas store 0.42 to 0.59 Pg organic carbon in the top meter of sediments and represent an important, but declining, global blue carbon hotspot, suggest sediment core analyses of 10 seagrass meadows across an extensive island chain in The Bahamas.

Landward barrier migration facilitates erosion of shoreface-exposed marsh and lagoon carbon stocks at rates outpacing backbarrier carbon accumulation, thus demonstrating the ephemeral nature of blue carbon storage along transgressive coasts.

Sustainable development of blue carbon has increased globally over the past two decades. Global cooperation could enable countries to improve blue carbon sustainable development, increase carbon sequestration, and generate up to $136.34 million in 2030 in economic benefits.

Multi-scale spatial machine learning of soil carbon stocks in Australia’s terrestrial and coastal marine ecosystems reveals eight bio-regions and their underlying subregional drivers that can help inform strategies for conservation and climate change mitigation.

Cultivating 1 million km² of the most productive exclusive economic zones, which are in the equatorial Pacific, could produce 1 Gt of seaweed carbon per year; however, beyond these productive waters carbon harvest efficiency drops dramatically, according to global dynamic seaweed growth simulations.

Coastal vegetated ecosystems have experienced rapid changes in climate and environmental conditions. These changes have caused disturbances to the amount of carbon they store in soils by altering the decomposition process of organic carbon.

Macroalgae can be transported across the open ocean, and substantial amounts can reach the seafloor at 4,000 m depth, according to analyses of metagenome data from global expeditions. Macroalgae are a potentially important oceanic carbon sink globally.

The coastal ocean is a dynamic environment, and CO₂ uptake is increasing faster than in the open ocean. Incorporating coastal processes into a global model shows that biological responses to climate-induced circulation changes and riverine nutrient inputs are key to the enhanced uptake.

Carbon sequestration in mangroves has been proposed as a mitigation strategy for climate change, yet the benefits of carbon burial may be offset by methane emissions. This study shows that methane offsets are small in saline and tropical mangroves, leading to greater net carbon sequestration.

An assessment of blue carbon strategies in Belize shows how quantifying fisheries, tourism and coastal risk co-benefits alongside carbon benefits can inform spatial and temporal target setting for nationally determined climate contributions that simultaneously provide societal benefits.

The authors show that estuarine and coastal vegetation are collectively a greenhouse gas (GHG) sink for the atmosphere, but methane and nitrous oxide emissions counteract the carbon dioxide uptake. Critical coastal GHG sink hotspots are identified in Southeast Asia, North America and Africa.