Impact of Sea Ice Melting on Summer Air-Sea CO2 Exchange in the East Siberian Sea

Abstract

The role of sea ice melting on the air-sea CO2 flux was investigated at two ice camps in the East Siberian Sea of the Arctic Ocean. On average, sea ice samples from the two ice camps had a total alkalinity (TA) of ∼108 and ∼31 μmol kg–1 and a corresponding salinity of 1.39 and 0.36, respectively. A portion (18–23% as an average) of these sea ice TA values was estimated to exist in the sea ice with zero salinity, which indicates the excess TA was likely attributed to chemical (CaCO3 formation and dissolution) and biological processes in the sea ice. The dilution by sea ice melting could increase the oceanic CO2 uptake to 11–12 mmol m–2 d–1 over the next 21 days if the mixed layer depth and sea ice thickness were assumed to be 18.5 and 1.5 m, respectively. This role can be further enhanced by adding TA (including excess TA) from sea ice melting, but a simultaneous release of dissolved inorganic carbon (DIC) counteracts the effect of TA supply. In our study region, the additional impact of sea ice melting with close to unity TA:DIC ratio on air-sea CO2 exchange was not significant.

Large‐Scale Summertime Variability of Carbonate Chemistry Across the East Siberian Sea: Primary Production Versus Ikaite Dissolution

“…These variations in TA and DIC were strongly related to salinity of an ice core sample. The largest variation of TA ice was so far reported from those sea ice cores taken near Svardbard, 306–1,239 μmol kg −1 (Nomura et al., 2013), while the lowest TA ice values of 3–220 μmol kg −1 and DIC ice values of 16–209 μmol kg −1 were from the boundary areas between the East Siberian and Chukchi Seas (Mo et al., 2022). It should be noted that these variation ranges of TA and DIC were exclusively derived from a vertical profile of sea ice cores, while our study attempted to provide a large‐scale horizontal distribution of TA ice and DIC ice of sea ice in the East Siberian Sea.…”

“… c δ 18 O values cited from Ekwurzel et al, 2001 and the range of TA and DIC of melted sea ice summarized from (Fischer et al, 2012; Geilfus et al, 2013; Mo et al, 2022; Nomura et al, 2013; Rysgaard et al, 2012). …”

“…When assuming conservative mixing only between river water and seawater, TA and DIC concentrations in surface water were written as: (Fischer et al, 2012;Geilfus et al, 2013;Mo et al, 2022;Nomura et al, 2013;Rysgaard et al, 2012).…”

Climate change drives rapid decadal acidification in the Arctic Ocean from 1994 to 2020

“…The black dots represent the observational conditions for pH T , Ω arag , and the Revelle factor (values calculated from decadal means; table S3). The gray dot represents the initial condition after sea ice melt [a two-endmember mixing model consisting of 1990s ice-covered seawater and ice-melt water was applied to calculate diluted TA and DIC and carbonate parameters; TA was used as a tracer, and the meltwater endmember was obtained from ( 40 )]. The arrows indicate the processes of warming (orange), dilution (I, dark cyan), dilution-induced CO 2 uptake (II, magenta), and ice melt–induced CO 2 uptake (III and IV, magenta).…”

“…The initial status of the ice-covered Canada Basin in the 1990s is set as salinity ( S ) = 31.3, temperature ( T ) = −1.6°C, TA = 2192 μmol kg −1 , DIC = 2059 μmol kg −1 , and P co 2 = 278 μatm (table S3). Dilution with a meltwater endmember of TA ≈ 70 μmol kg −1 ( 40 ) results in a lower TA of 1912 μmol kg −1 , DIC of 1792 μmol kg −1 , and P co 2 of 214 μatm (and simultaneously lower Ω arag owing to decreased salinity and carbonate ion concentration, but higher pH T owing to decreased hydrogen ion concentration) (dilution effect I). When P co 2 increases back to the initial P co 2 level before ice melting in the 1990s (dilution-induced CO 2 uptake, II), it causes a decrease in pH T of 0.10 and a decrease in Ω arag of 0.25.…”