Melt pond CO2 dynamics and fluxes with the atmosphere in the central Arctic Ocean during the summer-to-autumn transition

19 pages, 10 figures, 6 tables, supplemental material https://doi.org/10.1525/elementa.2024.00023.-- Data accessibility statement: The data analyzed in this study were retrieved from links below: RINKO profiler-derived variables: https://doi.pangaea.de/10.1594/PANGAEA.966749, thermistor probe derived variables: https://doi.pangaea.de/10.1594/PANGAEA.966770, water sampler derived variables: https://doi.pangaea.de/10.1594/PANGAEA.966787, CO2 chamber-derived variables: https://doi.pangaea.de/10.1594/PANGAEA.966833, and meteorological variables: https://doi.org/10.1594/PANGAEA.935267

Melt ponds are a common feature of the Arctic sea-ice environment during summer, and they play an important role in the exchange of heat and water vapor between the ocean and the atmosphere. We report the results of a time-series study of the CO2 dynamics within melt ponds (and nearby lead) and related fluxes with the atmosphere during the summer-to-autumn transition in the central Arctic Ocean during the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition. In late summer 2020, low-salinity meltwater was distributed throughout the melt ponds, and undersaturation of pCO2 in the meltwater drove a net influx of CO2 from the atmosphere. The meltwater layer subsequently thinned due to seawater influx, and a strong gradient in salinity and low-pCO2 water was observed at the interface between meltwater and seawater at the beginning of September. Mixing between meltwater and underlying seawater drives a significant drawdown of pCO2 as a result of the non-linearities in carbonate chemistry. By the middle of September, the strong stratification within the meltwater had dissipated. Subsequent freezing then began, and cooling and wind-induced drifting of ice floes caused mixing and an influx of seawater through the bottom of the melt pond. The pCO2 in the melt pond reached 300 µatm as a result of exchanging melt pond water with the underlying seawater. However, gas exchange was impeded by the formation of impermeable freshwater ice on the surface of the melt pond, and the net flux of CO2 was nearly zero into the pond, which was no longer a sink for atmospheric CO2. Overall, the melt ponds in this Arctic sea-ice area (both melt ponds and lead water) act as moderate sinks for atmospheric CO2

This study was supported by the Japan Society for the Promotion of Science (grant numbers: JP18H03745; JP18KK0292; JP17H04715; JP20H04345; 23KJ0017) and by a grant from the Joint Research Program of the Japan Arctic Research Network Center (MY, DN, MT, JI). ALW and KS were funded through the U.K. Natural Environment Research Council (NERC) (Grants Nos NE/S002596/1 and NE/S002502/1, respectively). ESD was supported by NERC through the EnvEast Doctoral Training Partnership (NE/L002582/1), as well as NERC and the Department for Business, Energy & Industrial Strategy (BEIS) through the U.K. Arctic Office. EJC was supported by the National Science Foundation (USA) NSF OPP 1821911 and NSF Graduate Research Fellowship. HM is supported through the German Federal Ministry of Education and Research (grant number 03FO869A). KMP, HA, and BB were supported by the U.S. National Science Foundation (awards OPP 1807496, 1914781, and 1807163). BD is a research associate of the FRS-FNRS and was supported by the research credit J.0051.20

With the institutional support of the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S)

Peer reviewed