Substantial stores of sedimentary carbon held in mid-latitude fjords

Quantifying marine sedimentary carbon stocks is
key to improving our understanding of long-term storage of
carbon in the coastal ocean and to further constraining the
global carbon cycle. Here we present a methodological approach
which combines seismic geophysics and geochemical
measurements to quantitatively estimate the total stock
of carbon held within marine sediment. Through the application
of this methodology to Loch Sunart, a fjord on the
west coast of Scotland, we have generated the first full sedimentary
carbon inventory for a fjordic system. The sediments
of Loch Sunart hold 26.90.5 Mt of carbon split between
11.50.2 and 15.00.4 Mt of organic and inorganic
carbon respectively. These new quantitative estimates of carbon
stored in coastal sediments are significantly higher than
previous estimates. Through an area-normalised comparison
to adjacent Scottish peatland carbon stocks, we have determined
that these mid-latitude fjords are significantly more
effective as carbon stores than their terrestrial counterparts.
This initial work supports the concept that fjords are important
environments for the burial and long-term storage of carbon
and therefore should be considered and treated as unique
environments within the global carbon cycle.