Variability of Surface Water pCO2 in the Canadian Arctic Archipelago From 2010 to 2016

This study provides 6years of high-resolution underway measurements of the sea surface partial pressure of CO2 (pCO(2sw)), sea surface temperature, and salinity across the Canadian Arctic Archipelago (CAA). Observed pCO(2sw) varied regionally, with the northern and central channels of the CAA undersaturated in pCO(2sw) (with respect to the atmosphere), while the western regions were typically saturated to supersaturated in pCO(2sw). This apparent spatial variability was caused to some extent by the timing of our ship transit through the CAA, as we also found a general seasonal trend of pCO(2sw) being undersaturated in the early summer, followed by saturation to supersaturation in late summer, and a return to undersaturation during the autumn. Sea surface temperature was significantly correlated with pCO(2sw) at various locations across the CAA, but we also observed the effects of other regional processes like upwelling, primary production, riverine input, and sea ice melt. These processes are linked to each other, and hence, it is impossible to pinpoint only one dominant factor controlling pCO(2sw) variability in the CAA. However, we found that sea ice dominates the seasonal cycle of all these processes, thus making the timing of sea ice breakup a useful predictor of pCO(2sw) variability in the CAA. We calculated an average net oceanic sink of 14mmolCO(2<bold>)m(</bold>-2<bold>)day(</bold>-1) for the CAA during the summer and autumn seasons, but caution that a more rigorous budgeting approach is required to fully account for biases in dates and locations of our measurements. Plain Language Summary Studying seawater carbon dioxide (CO2) concentration in the Arctic Ocean helps us understand the impact of ocean acidification and estimate the region's response to increased human emissions. This study presents 6years of data from icebreaker research cruises to study the main factors responsible for differences in measured seawater CO2 concentration in the Canadian Arctic Archipelago (CAA). Overall, we found that the seawater CO2 concentration is low with respect to CO2 in the atmosphere during the summer and autumn seasons due to influences of increasing water temperature and sea ice melt, as well as the regional effects of other variables such as river inputs and biological activity. We observed that the CAA was absorbing atmospheric CO2, acting as a net oceanic sink. However, it is important to note that the ship sampling was limited to specific locations and timing every year due to logistical difficulties associated with navigating sea ice. Therefore, we cannot say that the entire CAA acts as an atmospheric CO2 sink in the same way everywhere. To solve this problem, we found a significant relationship between sea ice conditions and seawater CO2 concentration that could be very useful in estimating the seawater CO2 concentration elsewhere in the CAA.