Abstract
AbstractThe Mackenzie River Basin (MRB) delivers large quantities of organic carbon (OC) into the Arctic Ocean, with significant implications for the global C budgets and ocean biogeochemistry. The amount and properties of OC in the Mackenzie River's delta have been well monitored in the last decade, but the spatial variability in OC sources transported by its different tributaries is still unclear. Here we present new data on the radiocarbon (14C) content of dissolved and particulate OC (Δ14C‐DOC and Δ14C‐POC) across the mainstem and major tributaries of the MRB, comprising 19 different locations, to identify factors controlling spatial patterns in riverine OC sources. The Δ14C‐DOC and Δ14C‐POC varied across a large range, from −179.9‰ to 62.9‰, and −728.8‰ to −9.0‰, respectively. Our data reveal a positive spatial coupling between the Δ14C of DOC and POC across the MRB, whereby the most 14C‐depleted waters were issued from the mountainous west bank of the MRB. This 14C‐depleted DOC and POC likely originates from a combination of petrogenic sources, connected with the presence of kerogens in the bedrock, and biogenic sources, mobilized by thawing permafrost. Our analysis also reveals intriguing relationships between Δ14C of DOC and POC with turbidity, water stable isotope ratio and catchment elevation, indicating that hydrology and geomorphology are key to understanding riverine OC sources in this landscape. A closer examination of the specific mechanisms giving rise to these relationships is recommended. For now, this study provides a road map of the key OC sources in this rapidly changing river basin.
Highlights
The Mackenzie River Basin (MRB) is the fourth largest source of freshwater to the Arctic Ocean
Results are reported here as Δ14C values in ‰, which expresses the relative difference in 14C activity between the absolute international standard and the sample activity corrected for age and normalized to δ13C = 25‰ (Stuiver & Polach, 1977)
The measured Δ14C‐DOC and Δ14C‐POC in each sample are in effect weighted averages for a mixture of organic carbon (OC) components with possibly different 14C contents
Summary
The Mackenzie River Basin (MRB) is the fourth largest source of freshwater to the Arctic Ocean. The region is experiencing one of the fastest rate of warming across the globe, with the Mackenzie River delta having warmed by ~3°C (>4.5°C in winter) since the midtwentieth century (Bush & Flato, 2019). This warming is profoundly transforming the landscape and hydrology of the MRB through accelerated thawing of permafrost, thermokarst development, riverbank slumping, greater forest fire activity and a northward migration of the tree line (Burn & Kokelj, 2009; Guay et al, 2014; St. Jacques & Sauchyn, 2009). The sources of OC mobilized by its different tributaries, together with their spatial controls, remain to be fully resolved
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
