Data from: Blue Carbon stocks of Great Barrier Reef deep-water seagrasses

Shallow-water seagrasses capture and store globally-significant quantities
of organic carbon (OC), often referred to as ‘Blue Carbon’; however, data
is lacking on the importance of deep-water (>15 m) seagrasses as
Blue Carbon sinks. We compared OC stocks from deep-, mid- and
shallow-water seagrasses at Lizard Island within the Great Barrier Reef
Lagoon. We found deep-water seagrasses (Halophila species) contained
similar levels of OC as shallow-water species (e.g Halodule uninervis)
(0.64 ± 0.08% and 0.9 ± 0.1 mg C cm3, 0.87 ± 0.19% and 1.3 ± 0.3 mg C cm3,
respectively), despite being much sparser and smaller in stature.
Deep-water seagrasses sediments contained significantly higher levels
(~9-fold) of OC than surrounding bare areas. Inorganic carbon (CaCO3)
levels were relatively high in deep-water seagrass sediments (8.2 ± 0.4%),
and if precipitated from epiphytes within the meadow, could offset the
potential CO2-sink capacity of these meadows. The δ13C signatures of
sediment samples varied among depths and habitats (-10.9 and -17.0),
reflecting contributions from autochthonous and allochthonous sources. If
the OC stocks reported in this study are similar to deep-water Halophila
meadows elsewhere within the GBR lagoon (total area 31,000 km2), then OC
bound within this system is roughly estimated at 27.4 million tonnes. The
dataset published in Dryad Digital Repository (doi:10.5061/dryad.kj239),
has been updated with the corrected data values for mg Corg cm−3.