DataSheet_1_Using Radiocarbon Measurements of Dissolved Inorganic Carbon to Determine a Revised Residence Time for Deep Baffin Bay.pdf

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 (δ¹³C) and radiocarbon (Δ¹⁴C) values of dissolved inorganic carbon (DIC) collected aboard the CCGS Amundsen in 2019. DIC δ¹³C and Δ¹⁴C values between ranged between -0.7‰ to +1.9‰ and -90.0‰ to +29.8‰, respectively. Surface DIC δ¹³C values were between +0.7‰ to +1.9‰, while deep (>100m) values were 0.0 to -0.7‰. Surface DIC Δ¹⁴C values ranged between -5.4‰ to +22.9‰, while deep DIC (>1400m) DIC Δ¹⁴C averaged -82.2 ± 8.5‰ (n = 9). To constrain natural DIC Δ¹⁴C values, we quantified the amount of atmospheric “bomb” ¹⁴C in DIC (Δ¹⁴C_bomb; using the potential alkalinity method; P_alk) and anthropogenic DIC (DIC_anth; using the ΔC^* method). Both proxies indicate an absence of Δ¹⁴C_bomb and DIC_anth below 1000m. Using two previously proposed deep water formation mechanisms and our corrected DIC Δ¹⁴C_natural values, we estimated a ¹⁴C-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.