14C-based deconvolution of relationships between carbon pools in Icelandic rivers and streams

Rivers are important agents in the lateral transfer of carbon from terrestrial to the marine realm, thus forming a key component of the global carbon cycle. Carbon sources and transformations along the land-ocean aquatic continuum are dynamic with a complex interplay between dissolved and particulate, and inorganic and organic carbon pools. Elucidating interrelationships between these pools is hindered by multiple sources and processes that influence the carbon signatures of these pools in a dissimilar fashion. Icelandic streams and rivers offer an opportunity to directly assess the fluvial carbon pool dynamics due to the virtual absence of sedimentary rocks (e.g., shales, carbonates with a radiocarbon dead signature) that otherwise “muddy the waters” with respect to apparent sources and turnover times.

In order to characterize carbon transport patterns of Icelandic rivers and streams, we collected water samples from 43 river systems with watersheds that cover a wide range of catchment properties such as size, water discharge, climate as well as landcover. Here we assess the concentrations as well as the isotopic composition (¹³C, ¹⁴C) of particulate and dissolved organic carbon (POC; DOC, respectively) as well as dissolved inorganic carbon (DIC) alongside stable water isotopes (δ²H, δ¹⁸O) and major ion geochemistry.
Radiocarbon content (reported as fraction modern; F¹⁴C) of POC, DOC and DIC show similar patterns: lower F¹⁴C values (i.e., highest radiocarbon ages) are mostly associated with glacial runoff while higher F¹⁴C values (younger carbon) correspond to higher soil organic carbon content within the respective catchment. This dataset is but a first glimpse at carbon transport patterns in Icelandic rivers. Biomarker concentrations and isotopic compositions such as leaf waxes (n-alkanes, n-alkanoic acids) and soil derived lipids (branched glycerol dialkyl glycerol tetraether) will be used to further investigate provenance, transport and storage mechanisms in the diverse suite of Icelandic catchments.