Abstract
The delivery and burial of terrestrial particulate organic carbon (OC)
in marine sediments is important to quantify, because this OC is a food
resource for benthic communities, and if buried it may lower the
concentrations of atmospheric CO2 over geologic
timescales. Analysis of sediment cores has previously shown that fjords
are hotspots for OC burial. Fjords can contain complex networks of
submarine channels formed by seafloor sediment flows, called turbidity
currents. However, the burial efficiency and distribution of OC by
turbidity currents in river-fed fjords had not been investigated
previously. Here, we determine OC distribution and burial efficiency
across a turbidity current system within a fjord, in Bute Inlet
(Canada). We show that 60 ± 10 % of the OC supplied by the two river
sources, is buried across the fjord surficial (2 m) sediment. The
sand-dominated submarine channel and its terminal lobe contain 63 ± 14
% of the annual terrestrial OC burial in the fjord. In contrast, the
muddy overbank and distal flat basin settings contain the remaining 37 ±
14 %. OC in the channel, lobe and overbank exclusively comprises
terrestrial OC sourced from rivers. When normalized by the fjord’s
surface area, at least three times more terrestrial OC is buried in Bute
Inlet, compared to the muddy parts of other fjords previously studied.
Although the long-term (>100 year) preservation of this OC
is still to be fully understood, turbidity currents in fjords appear to
be efficient in storing OC supplied by rivers in their near-surface
deposits.