Carbon budgets and potential blue carbon stores

The main findings of the SNH report are:

• Coastal and offshore sediments are the main repositories for carbon in Scotland’s marine environment.
• An estimated 18 million tonnes (MtC) of organic carbon are stored in the top 10cm of sediments across the 470 000 sq.km area of Scotland’s seas.
• An estimated 1738 million tonnes (MtC) of inorganic carbon are similarly stored as non-living shell material.
• Deposition of organic carbon amounts to 7.2 MtC/yr and inorganic carbon 0.5 MtC/yr in Scotland’s marine sediments.
• The main producer of carbon entering long-term storage in sediments is phytoplankton, 3.9 MtC/yr, with coastal plants (predominantly kelp) potentially contributing a further 1.8 MtC/yr.
• Habitat-forming species on the coast (seagrasses, saltmarsh, bivalve beds), are highly productive but their contribution to the overall carbon budget is very small because of the limited extent of each habitat.
• Maerl beds and cold water coral reefs contribute 0.5MtC of inorganic carbon to the standing stock. While their growth rates are relatively slow providing small annual sequestration capacity of inorganic carbon, their longevity (centuries) means that sequestered carbon is locked away at geological time scales.
• Sea lochs contain 0.33 MtC and have a sequestration capacity for sediment organic carbon of 0.07 MtC/yr.

See SNH Commissioned Report 957: Assessment of Blue Carbon Resources in Scotland's Inshore Marine Protected Area Network for further work on blue carbon. Layers associated with this (figures 5.1 - 5.4) are also on MS Maps NMPi.