Strong <i>p</i>CO₂ Undersaturation in an Arctic Sea: A Decade of Spatial and Temporal Variability in Baffin Bay

Abstract Utilizing an 11‐year (2011–2021) data set, we report surface‐ocean p CO 2 in Baffin Bay during the open‐water season (June–October) to establish a baseline understanding of surface seawater carbon dynamics in this region. We found p CO 2 was strongly undersaturated (70–130 μatm below saturation, depending on year), albeit with substantial regional variability. Though temperature was found to be a generally strong control of p CO 2 , sea‐ice dynamics and other non‐thermal drivers controlled p CO 2 at certain times and in certain regions. The Baffin Island Current region (western Baffin Bay) experienced relatively high p CO 2 during instances of high sea‐ice cover, usually in early spring. Average p CO 2 was comparatively lower in the West Greenland Current region (eastern Baffin Bay) which is ice‐free substantially longer (by 3–4 months) and where temperature acted as the dominant control to p CO 2 . With respect to temporal variations, June had the lowest p CO 2 of the open‐water season, coinciding with active sea‐ice melt. Surface‐ocean p CO 2 then increased month‐to‐month through July and August due to warming and decreased meltwater dilution, increasing again into September before stabilizing into October. Generally, non‐thermal controls acted to decrease p CO 2 during mid‐summer (possibly primary production, sea‐ice melt, and circulation), but acted to increase p CO 2 during early fall (vertical mixing). Despite spatial and temporal variation over the open‐water season, persistent undersaturation suggests that Baffin Bay is a potentially strong CO 2 sink, even in comparison to other uptake regions across the western Arctic.