Tracing Pan-Canadian Arctic Water Masses and Dissolved Inorganic Carbon Cycling Using Stable and Radiocarbon Isotopes

The Canadian Arctic is warming four times faster than the global average, yet the impact of this perturbation on the marine carbon cycle remains unknown. Dissolved inorganic carbon (DIC) stable isotope (delta C-13) and radiocarbon (Delta C-14) values are powerful tools for tracing water mass transport, residence times and carbon cycling. While the hydrography of the Canadian Arctic Archipelago (CAA) is well documented, few DIC delta C-13 and Delta C-14 values exist for the region. Here, we present new DIC delta C-13 and Delta C-14 depth profiles from 19 stations across the CAA sampled in 2021 and place them into the context of five recently published Baffin Bay values. CAA DIC delta C-13 and Delta C-14 values ranged from -0.68 parts per thousand to +1.86 parts per thousand, and -90.7 to +49.5 parts per thousand, respectively. Several negative DIC Delta C-14 values (-44.7 parts per thousand and -51.9 parts per thousand) were observed near the Mackenzie River, indicating riverine permafrost carbon is actively incorporated into the nearshore DIC pool. "Bomb" DIC Delta C-14 values in the Kitikmeot Sea were attributed to enhanced tidal mixing and heterotrophy together with high regional water mass residence times. A comparison of historical DIC Delta C-14 depth profiles from 2009 to 2021 reveals significant dilution of "bomb" C-14 and minor contributions (2.1%-4.4%) of fossil anthropogenic CO2 within Pacific Summer Water (PSW), Pacific Winter Water (PWW) and Atlantic Fram Strait Water (ATLFS) in the Beaufort Sea. Finally, the contrast between deep Beaufort Sea and Baffin Bay DIC delta C-13 and Delta C-14 values reveal differences in residence time and carbon sources in the two regions.