Source to Sink: Broad and fine scale observations of terrestrial vs marine derived carbon in a Scottish sea loch (fjord).
Abstract:
We present the results of a sediment source identification study which utilised bulk elemental analysis (OC, IC & N) and isotopic tracers (δ13C & δ15N) combined with a linear isotopic end-member model and a new Bayesian mixing model methodology.
The study focused on Loch Sunart a sea loch on the west coast of Scotland; the loch is split into 3 sedimentary basins by 2 sills; each basin has unique sedimentary characteristics. A high density sampling campaign was undertaken resulting in 85 surface samples from the 3 basins. Through mapping the quantities of N, IC and OC (Fig.1) we gained or first insights into the distribution of C within the loch; clear patterns emerged with the highest amounts of OC found at the mouth of streams and rivers. The OC in these areas is clearly terrestrial in origin but the balance of terrestrial vs marine carbon in the wider loch is more complex.
To determine the balance of terrestrial vs marine carbon held within the surface sediments a simple linear mixing model and a new specialised isotopic Bayesian end-member mixing model (MixSIAR) were employed. Through sampling of the lochs catchment and local marine environment we compiled isotopic values for both terrestrial and marine carbon sources; the use of these values and the Bayesian mixing model allowed us to further constrain the balance of terrestrial vs marine carbon.
The results from the analysis allowed further high resolution spatial mapping of the surface sediment to be undertaken when this is compared to bathymetry, seismic geophysics, meteorological, hydrological and land use data we can determine which of these mechanisms have the greatest impact on the spatial distribution of the terrestrial vs marine carbon.