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 (delta C-13) and radiocarbon (Delta C-14) values of dissolved inorganic carbon (DIC) collected aboard the CCGS Amundsen in 2019. DIC delta C-13 and Delta C-14 values between ranged between -0.7 parts per thousand to +1.9 parts per thousand and -90.0 parts per thousand to +29.8 parts per thousand, respectively. Surface DIC delta C-13 values were between +0.7 parts per thousand to +1.9 parts per thousand, while deep (>100m) values were 0.0 to -0.7 parts per thousand. Surface DIC Delta C-14 values ranged between -5.4 parts per thousand to +22.9 parts per thousand, while deep DIC (>1400m) DIC Delta C-14 averaged -82.2 +/- 8.5 parts per thousand (n = 9). To constrain natural DIC Delta C-14 values, we quantified the amount of atmospheric "bomb" C-14 in DIC (Delta C-14(bomb); using the potential alkalinity method; P-alk) and anthropogenic DIC (DICanth; using the Delta C* method). Both proxies indicate an absence of Delta C-14(bomb) and DICanth below 1000m. Using two previously proposed deep water formation mechanisms and our corrected DIC Delta C-14(natural) values, we estimated a C-14-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.