Changes in the Arctic Ocean carbon cycle with diminishing ice cover

Abstract

Less than three decades ago only a small fraction of the Arctic Ocean (AO) was ice free and then only for short periods. The ice cover kept sea surface pCO 2 at levels lower relative to other ocean basins that have been exposed year round to ever increasing atmospheric levels. In this study, we evaluate sea surface pCO 2 measurements collected over a 6-year period along a fixed cruise track in the Canada Basin. The measurements show that mean pCO 2 levels are significantly higher during low ice years. The pCO 2 increase is likely driven by ocean surface heating and uptake of atmospheric CO 2 with large interannual variability in the contributions of these processes. These findings suggest that increased ice-free periods will further increase sea surface pCO 2 , reducing the Canada Basin's current role as a net sink of atmospheric CO 2 .Plain Language Summary The Arctic Ocean (AO) ice cover is decreasing, exposing the sea surface to exchange with the gases in the atmosphere. Consequently, anthropogenic CO 2 that has accumulated in the atmosphere can now more readily enter the AO. It is expected that this will lead to an increase in CO 2 in the AO but because of a lack of data in the region, a clear relationship has not been established. We have measured the partial pressure of CO 2 (pCO 2 ) in the Canada Basin of the AO during five cruises spanning 2012-2017. These data have revealed that the pCO 2 is higher during years when ice concentration is low, supporting the previous hypothesis. Using a model, we have shown that while uptake of atmospheric CO 2 has increased pCO 2 , heating has also been important. These processes vary significantly from year to year, masking the likely increase in pCO 2 over time. Based on these results, we can expect that while the Canada Basin has been a sink for atmospheric CO 2 , the uptake of atmospheric CO 2 will diminish in the coming years.

The Changing CO2Sink in the Western Arctic Ocean From 1994 to 2019

“…Maximum p CO 2 appears in the late spring before the growing season start whereas minimum p CO 2 appears in the early summer. In contrast, the modeled climatological monthly p CO 2 deviated more from the observed seasonality of p CO 2 in the Canada Basin because the climatological monthly means can lump the interannual variations in p CO 2 , which primarily depends on the interannual variation in ice conditions (DeGrandpre et al., 2020). From the simulated results, we noticed that the seasonality of p CO 2 changes in both phase and magnitude in the periods before and after the year 2007, in which the western Arctic Ocean experienced a massive sea ice retreat.…”

Remote Sensing Systems for Ocean: A Review (Part 2: Active Systems)

“…SI cover is important for the Arctic environment and plays a pivotal role in the world's climate systems. Moreover, it has significant effects on maritime activities and navigation in the glacial areas [223]. Therefore, monitoring the SI through classification and charting grabbed decision-makers' attention to guarantee safety and economic activities without any possible damage to the environment.…”

Summer Surface CO2 Dynamics on the Bering Sea and Eastern Chukchi Sea Shelves From 1989 to 2019

“…On one hand, increasing open water area favors oceanic uptake of CO 2 by allowing more light penetration to enhance productivity and by removing the mechanical barrier for sea‐air CO 2 exchange (Arrigo et al., 2008; Arrigo & van Dijken, 2015; Bates et al., 2006; Bates & Mathis, 2009; Lewis et al., 2020). However, meltwater can also increase surface stratification, which limits the ocean's capacity for surface storage of CO 2 , suppresses nutrient replenishment from depth, and depresses the efficiency of biological carbon pump (Cai et al., 2010; DeGrandpre et al., 2020; Lannuzel et al., 2020; Ouyang et al., 2020). Further nuance results from ongoing warming that favors permafrost thaw and changes the riverine and groundwater flux of carbon and nutrients to Alaskan waters (Schuur et al., 2015; Tank et al., 2016; Vonk et al., 2015; Walvoord & Striegl, 2007).…”