5.3. What is the terrestrial OC burial efficiency of Bute Inlet and how does it compare with other fjords?
Comparison between OC river input (23 ± 5 Kt OC/yr) and terrestrial OC burial rate in Bute Inlet (11.7 to 16.3 Kt OC/yr), suggests that Bute Inlet has a terrestrial OC burial efficiency ranging between 50 and 70 % (60 ± 11 % on average) when estimated over decennial and centennial timescales, respectively.
No study has closed budgets between river sources and fjord sediments before, so it is not possible to compare this value with other river-fed fjords. However, we can compare our results in Bute Inlet with previous fjord studies, by normalizing OC burial rates to the Bute Inlet’s total surface area. By doing so, the burial of terrestrial OC in Bute Inlet ranges between 72 and 100 t C/km2/yr. This range lies between previous estimates of OC fluxes of 57 to 107 t C/km2/yr in Scottish and Irish fjords that were described as having heterogeneous seafloors (Smeaton and Austin, 2020). Importantly, our results from Bute Inlet suggest that fjords characterised by sandy turbidity current systems may bury over three times more terrestrial OC compared to previous global estimates based on muddy cores from fjords without any identified turbidity current channels (22 t C/km2/yr; Smith et al., 2015, Cui et al., 2016).