Using Radiocarbon Measurements of Dissolved Inorganic Carbon to Determine a Revised Residence Time for Deep Baffin Bay

The Canadian Arctic is warming at three times the rate of the rest of the planet and the effects of climate change on the Arctic marine carbon cycle remains unconstrained. Baffin Bay is a semi-enclosed, Arctic basin that connects the Arctic Ocean to the north to the Labrador Sea to the south. While the physical oceanography of surface Baffin Bay is well characterized, less is known about deep water formation mechanisms within the Basin. Only a few residence-time estimates for Baffin Bay Deep Water (BBDW) exist and range from 20 to 1450 years. Better residence time estimates are needed to understand the oceanographic significance of Baffin Bay. Here we report stable carbon (δ 13 C) and radiocarbon (Δ 14 C) values of dissolved inorganic carbon (DIC) collected aboard the CCGS Amundsen in 2019. DIC δ 13 C and Δ 14 C values between ranged between -0.7‰ to +1.9‰ and -90.0‰ to +29.8‰, respectively. Surface DIC δ 13 C values were between +0.7‰ to +1.9‰, while deep (>100m) values were 0.0 to -0.7‰. Surface DIC Δ 14 C values ranged between -5.4‰ to +22.9‰, while deep DIC (>1400m) DIC Δ 14 C averaged -82.2 ± 8.5‰ ( n = 9). To constrain natural DIC Δ 14 C values, we quantified the amount of atmospheric “bomb” 14 C in DIC (Δ 14 C bomb ; using the potential alkalinity method; P alk ) and anthropogenic DIC (DIC anth ; using the ΔC * method). Both proxies indicate an absence of Δ 14 C bomb and DIC anth below 1000m. Using two previously proposed deep water formation mechanisms and our corrected DIC Δ 14 C natural values, we estimated a 14 C-based residence time of 360-690 years for BBDW. Based on these residence times, we infer carbon is likely stored for centuries in deep Baffin Bay.