Pathways of blue carbon export from kelp and seagrass beds along the Atlantic coast of Nova Scotia

Coastal vegetated ecosystems are recognized for their role in cycling and
storing carbon in the world’s oceans (i.e., blue carbon); however, high
uncertainty in carbon sequestration rates are driven in part by an absence
of studies directly estimating carbon export to the deep sea. We modeled
export from nearshore kelp forests and seagrass beds, showing that export
varies by orders of magnitude across spatial scales (5 – 100s km), kelp
and seagrass species, seasons, and forms of carbon, raising caution in
using generalized export rates in blue carbon accounting. Our results are
also the first to show rapid (within 20-30 days) and extensive export of
neutrally buoyant dissolved organic carbon to the shelf break (up to 44%
within 90 days), contrasting sinking particulate organic carbon particles
that remained within 100 m water depth in the near shore. These results
improve estimates of carbon sequestration by nearshore vegetated
ecosystems and reveal contrasting patterns of export relative to other
regions of the globe.