Increase in CO₂ Uptake Capacity in the Arctic Chukchi Sea During Summer Revealed by Satellite‐Based Estimation

Abstract

The Chukchi Sea is a globally important sink of atmospheric carbon dioxide (CO 2 ), accounting for ∼5-8% of the coastal sink of CO 2 (Bates, 2006;Borges et al., 2005;Laruelle et al., 2014). The budget and temporal variability of the CO 2 sink in Chukchi Sea have been calculated and examined (Bates, 2006;Evans et al., 2015;Laruelle et al., 2014;Manizza et al., 2019), but most of these studies are based on scarce data of uneven spatial and temporal distribution, which is subject to large uncertainties. The Arctic Ocean has experienced dramatic physical and ecological changes due to the rapid climate change, inducing sea ice retreating (Screen & Simmonds, 2010), freshwater storage increasing (Li et al., 2009), warming of the sea surface temperature (Steele et al., 2008), and increasing of phytoplankton primary production (Lewis et al., 2020). All these changes profoundly influence the sea surface partial pressure of CO 2 (pCO 2 ). The difference between sea surface and atmospheric pCO 2 , namely ∆pCO 2 , determines the direction of the air-sea CO 2 gas exchange. Yet, long-term trend of CO 2 sink capacity in response to climate change in this area is rarely studied primarily due to a lack of long-term continuous pCO 2 measurements. A few studies (Bates, 2006;Ouyang et al., 2020) found the potential increase in CO 2 uptake under climate change on the Chukchi shelf;

RETRACTED: Rapid Acidification of the Arctic Chukchi Sea Waters Driven by Anthropogenic Forcing and Biological Carbon Recycling

“…The contribution of air‐sea CO 2 exchange to DIC increase can be estimated from CO 2 flux: $$${\mathrm{dDIC}}_{ex}={\text{FCO}}_{2}/\text{MLD}$$$ where dDIC ex is the change in DIC attributed to air‐sea CO 2 exchange, FCO 2 is the air‐sea CO 2 flux, and MLD is the mixed layer depth (data adopted from Tu et al., 2021). The following equation shows the calculations of FCO 2 : $$${\text{FCO}}_{2}=\hspace*{.5em}f\times k\times {K}_{H}\times {\Delta}p{\text{CO}}_{2}$$$ where f is the correction term for sea ice, f = (1−ice%); k and K H are CO 2 gas transfer velocity and the solubility of CO 2 (calculated from temperature and salinity following Weiss, 1974), respectively.…”

“…Strengthened air-sea CO 2 exchange due to sea-ice melt and enhanced organic matter respiration due to inflow of Pacific waters are the most likely causes. The increased uptake of atmospheric CO 2 from 2002 to 2019 would reduce pH and Ω arag by −0.0038 years −1 and −0.012 years −1 (following Tu et al, 2021), respectively, which contributes to about 79% and 71% of the total pH and Ω arag long-term trends in the Chukchi Sea. The contribution from respiration was…”

“…where dDIC ex is the change in DIC attributed to air-sea CO 2 exchange, FCO 2 is the air-sea CO 2 flux, and MLD is the mixed layer depth (data adopted from Tu et al, 2021). The following equation shows the calculations of FCO 2 :…”

“…The Chukchi Sea, as an important inflow continental shelf of the Arctic Ocean, has experienced more dramatic climate‐driven changes. Rapid sea‐ice retreat (Screen & Simmonds, 2010; Wang & Overland, 2009) and increased inflow of nutrient‐rich surface water from the Pacific Ocean (Woodgate & Rebec Ca, 2017; Woodgate et al., 2012) resulted in an increase in primary production (Lewis et al., 2020), and the increasing carbon sink accounting for more than 50% of the overall Arctic Ocean CO 2 sink and 8% of the global marginal sea CO 2 sink (Bates et al., 2006; Ouyang et al., 2020; Tu et al., 2021). Sea‐ice loss also has substantial impacts on OA as it experiences extended ice‐free periods during summers (as illustrated in Figure S1 in the Supporting Information ).…”

Early Wintertime CO2 Uptake in the Western Arctic Ocean

“…In addition, they have pointed out that the coupling of NCP and CO 2 fluxes in ice-free waters depends on nutrient supplies and has resulted in large amounts of CO 2 uptake on the Chukchi Shelf. Tu et al (2021) have used satellite data with a machine-learning-based approach to evaluate summertime CO 2 uptake capacity in the Chukchi Sea. They have attributed increased CO 2 uptake in recent decades to melting of sea ice followed by enhanced photosynthesis that leads to drawdown of surface seawater CO 2 .…”