Blue refers to the marine environment, which refers to everything in the deep ocean, through to the land and areas that are influenced by the salty water of the sea, and the soils and sediments below them. The carbon aspect refers to the carbon contained in the bodies of marine organisms, ranging from tiny microscopic phytoplankton through to the largest creatures on the planet such as whales, and everything in between. This includes the biomass in living organisms, and also those that have died and are incorporated into the seabed (source: National Oceanography Centre).
Vegetated coastal habitats, particularly saltmarsh and seagrass, have the capacity to store and sequester considerable amounts of carbon through photosynthesis and subsequent burial in soils and sediments, as well as trapping and storing carbon transported from terrestrial and other marine habitats. When undisturbed, some marine and coastal habitats have the capacity to store carbon long-term.
Natural England have published a report on Carbon Storage and Sequestration by Habitat 2021 (NERR094) which includes detailed information on marine and coastal habitats. It notes that saltmarshes are large carbon stores, although they are subject to erosion and accretion through natural coastal processes, and are affected by rising sea levels. Sea grass meadows also have the potential to store large quantities of carbon within the sediments if undisturbed. Their vegetation can also sequester significant amounts of carbon in situ, as well as acting to trap and store carbon released from elsewhere. There are significant evidence gaps in our understanding of carbon cycling for many marine and coastal habitats. However, the protection and re-establishment of coastal habitats will also provide climate change adaptation benefits in addition to those for mitigation.
A further Natural England desk-based study maps the extent and distribution of blue carbon habitats in English waters and estimates the associated carbon accumulation and storage rates. The potential for recovery and restoration of coastal blue carbon habitats is explored alongside the key pressures that are driving habitat loss and inhibiting recovery, to identify risks to existing blue carbon stocks and opportunities. The results show that the coastal blue carbon habitats (saltmarsh, intertidal mud and seagrass) are the richest in terms of carbon accumulation rates and storage per unit area, but that the largest stocks are held in the subtidal sediments, due to their vast habitat extents.
This report also notes that coastal and marine habitats are receiving increasing attention due to their potential to store and sequester large quantities of carbon. The coastal and marine contribution to the global anthropogenic carbon dioxide budget is now recognised and reported by the Intergovernmental Panel on Climate Change (IPCC) and other international bodies, highlighting the increasing importance of these ecosystems in mitigating against climate change. However, in comparison to terrestrial systems, the role of coastal and marine habitats as a source and sink of greenhouse gases is comparatively under-studied.
In 2021, the Environment Agency have published a report that reviews the evidence behind carbon offsetting looking at a wide range of different offsetting approaches which could be used in the UK. See: Achieving net zero - a review of the evidence behind carbon offsetting - summary. An infographic summarises the findings for the public.
Blue Marine (BLUE) has developed a blue carbon programme with several workstreams.They are seeking to quantify the carbon sequestration and storage potential in a number of our projects in partnership with the University of Exeter. They are funding carbon mapping and seeking to better understand the impacts of mobile contact bottom fishing on carbon stocks and the carbon cycle. They have conducted a discovery phase to explore the potential for a large investment in blue carbon projects, on behalf of a corporate partner and are involved in answering key scientific questions to remove the barriers to blue carbon projects.
In 2022, BLUE Marine published a report which aims to explore the global scale and opportunity for blue carbon habitats to act as a climate change solution. See: Blue-Carbon-UK-Report.pdf (bluemarinefoundation.com).