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

• Published in: Journal of geophysical research. Oceans 2024-01, Vol.129 (1), p.n/a
• Main Authors: Sun, Xiaole, Anderson, Leif G., Dessirier, Benoît, Geibel, Marc, Mörth, Carl‐Magnus, Humborg, Christoph
• Format: Article
• Language: English
• Subjects: Ablation; Air; Arctic sea ice; Brines; Calcium; Calcium carbonate; Calcium carbonates; Carbon cycle; Carbon dioxide; Carbon dioxide concentration; carbonate chemistry; Carbonates; Chemistry; Climate; CO uptake 2; CO2 uptake; Crystals; Dissolution; Dissolved inorganic carbon; Dissolving; Drawdown; Earth and Related Environmental Sciences; East Siberian Sea; Geovetenskap och relaterad miljövetenskap; Heterogeneity; Ice formation; Ice melting; ikaite dissolution; Oceans; Patchiness; Primary production; Sea ice; Sea ice formation; sea ice melting; Spatial heterogeneity; Summer; Variability; Water chemistry; Water circulation; Water column; Water masses
• ISSN: 2169-9275; 2169-9291; 2169-9291
• DOI: 10.1029/2023JC020600

Sea‐ice dynamics can affect carbon cycling in polar oceans, with sea‐ice ikaite acting as a potentially important carbon pump. However, there is no large‐scale direct field evidence to support this. Here we used a unique data set that combined continuous measurements of atmospheric and water CO2 concentrations with water chemistry data collected over 1,200 km along the East Siberian Sea, the widest Arctic shelf sea. Our results reveal large spatial heterogeneity of sea‐ice ikaite contents, which directly interact with carbonate chemistry in the water column. Our findings demonstrate that the CO2 drawdown by sea‐ice ikaite dissolution could be as important as that by primary production. We suggest that the role of ikaite in regulating the seasonal carbon cycle on a regional scale could be more important than we previously thought. Effects of the warmer climate on sea ice loss might also play a role in the ikaite inventory. Plain Language Summary The extent of sea ice in the Arctic Ocean has been known to be an active player in the carbon cycle. Recent studies have discovered that sea ice formation in winter leads to precipitation of calcium carbonate crystals (known as ikaite) and expels carbon dioxide (CO2) either to air or to deeper water with sinking of a heavy cold‐water mass (known as brine). In summer, ikaite in sea ice dissolves when the sea ice melts. This process takes CO2 away from air and convert it to dissolved inorganic carbon in surface ocean. Our study used non‐stop real‐time field measurements of air and water CO2 levels and water column data to investigate variability of carbonate chemistry across the East Siberian Sea. We observed that the distribution pattern of ikaite in sea ice varied largely with space. Ikaite dissolution in association with sea ice melting could take up similar amount of air CO2 as primary production does. Our findings suggest that more research efforts should be made to assess the effect of ikaite dynamics on the seasonal carbon cycle in a warmer climate. Key Points Strong spatial heterogeneity of ikaite distribution in sea ice across East Siberian Sea is revealed via carbonate variability in water column Sea‐ice ikaite dissolution together with primary production was responsible for pCO2 drawdown in summer in the East Siberian Sea The role of sea‐ice ikaite dynamics in the seasonal carbon cycle could be subject to change in a warmer climate