Deep-sea currents transfer sediment, nutrients, and pollutants, which drive climatic, ecological and geomorphological variation in the global ocean. The complex interaction of downslope currents and internal tides in submarine canyons has meant that interpreting their stratigraphic record and therefore reconstructing oceanic environments through geological time has proven challenging. We integrate flow measurements with sediment core observations from the Whittard Canyon, to determine whether the stratigraphic signature of turbidity current and internal tide interaction is preserved. Sand is transported by turbidity currents and re-worked by internal tides, forming a suite of characteristic deposits; near-bed flow measurements show that turbidity currents superposed on internal tides collectively exceed a critical bed shear stress for mobilizing fine sand at least 1% of a year, suspending sediment tens of meters above the bed over longer periods. Using these observations, we present a framework to recognize this interaction in the stratigraphic record.

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.