Evaluating sources and cycling of particulate organic carbon in Baffin Bay:
a Δ14C and δ13C approach
Aislinn Fox, Brett Walker
Department of Earth and Environmental Sciences, University of Ottawa
a Δ14C and δ13C approach
Aislinn Fox, Brett Walker
Department of Earth and Environmental Sciences, University of Ottawa
The impact of global climate change on Arctic ecosystems and the marine carbon cycle is poorly constrained. Little data exists regarding carbon cycling in Baffin Bay, an important region that connects the Arctic and Atlantic. Currents flowing out from Baffin Bay influence meridional overturning circulation in the Labrador Sea. With the Canadian Arctic warming twice as fast as the rest of planet, constraining the biogeochemical cycling of the major marine carbon reservoirs in this region is critical. Particulate organic carbon (POC) is the carbon reservoir central to the biological pump, and is responsible for the export/removal of carbon fixed from our atmosphere by primary producers to the deep ocean where it is buried. Stable carbon and radiocarbon isotopic measurements are powerful tools for evaluating the sources and cycling of POC. Here we evaluate the stable carbon (δ13C) and radiocarbon (Δ14C) values of POC collected throughout Baffin Bay in 2019. POC concentrations, δ13C, and Δ14C values ranged from 2.9 to 10.7 μM C L-1, −21.6‰ to −29.5‰, and −41.8‰ to +76.8‰, respectively. Our results suggest that POC in Baffin Bay is comprised of multiple carbon sources. Autochthonous (in situ phytoplankton production) and allochthonous (resuspended marine sediment and/or advected suspended POC) components make up variable proportions of POC. POC isotopic values can be largely predicted by salinity, suggesting that surface currents and water mass endmembers exert a primary control on the δ13C and Δ14C signature of POC. POC from eastern Baffin Bay have similar Δ14C values to that of the Δ14C of surface dissolved inorganic carbon, suggesting a major POC contribution from primary production in this region. Positive POC Δ14C values in central Baffin Bay indicate the presence of “bomb” radiocarbon introduced in the 1960s from thermonuclear weapons testing. This suggests that some fraction of marine POC in Baffin Bay’s central gyre, associated with low temperature and salinity, is decades old. These data provide novel constraints on the cycling of POC in Baffin Bay, and represent baseline data for identifying future changes in carbon cycling in the Canadian Arctic.