Deciphering the Properties of Different Arctic Ice Types During the Growth Phase of MOSAiC: Implications for Future Studies on Gas Pathways

Abstract

The increased fraction of first year ice (FYI) at the expense of old ice (second-year ice (SYI) and multi-year ice (MYI)) likely affects the permeability of the Arctic ice cover. This in turn influences the pathways of gases circulating therein and the exchange at interfaces with the atmosphere and ocean. We present sea ice temperature and salinity time series from different ice types relevant to temporal development of sea ice permeability and brine drainage efficiency from freeze-up in October to the onset of spring warming in May. Our study is based on a dataset collected during the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) Expedition in 2019 and 2020. These physical properties were used to derive sea ice permeability and Rayleigh numbers. The main sites included FYI and SYI. The latter was composed of an upper layer of residual ice that had desalinated but survived the previous summer melt and became SYI. Below this ice a layer of new first-year ice formed. As the layer of new first-year ice has no direct contact with the atmosphere, we call it insulated first-year ice (IFYI). The residual/SYI-layer also contained refrozen melt ponds in some areas. During the freezing season, the residual/SYI-layer was consistently impermeable, acting as barrier for gas exchange between the atmosphere and ocean. While both FYI and SYI temperatures responded similarly to atmospheric warming events, SYI was more resilient to brine volume fraction changes because of its low salinity (< 2). Furthermore, later bottom ice growth during spring warming was observed for SYI in comparison to FYI. The projected increase in the fraction of more permeable FYI in autumn and spring in the coming decades may favor gas exchange at the atmosphere-ice interface when sea ice acts as a source relative to the atmosphere. While the areal extent of old ice is decreasing, so is its thickness at the onset of freeze-up. Our study sets the foundation for studies on gas dynamics within the ice column and the gas exchange at both ice interfaces, i.e. with the atmosphere and the ocean.

Sea ice, argon and carbon dioxide

“…Degassing as sea water freezes drives argon from water into brine channels and inclusions in the ice, and bubble nucleation can occur (Zhou et al 2013). Bubbles may diffuse upwards but some reach impermeable layers of ice, and sea ice can have multiple layers with differing and low permeability to gases (Moreau et al 2014;Zhou et al 2014;Angelopoulos et al 2022). Field observations at Barrow (Alaska) and a tank experiment suggest bubbles rich in argon can escape sea ice as it melts, leading to the prediction that some bubbles are released to the atmosphere in an "intense and rapid" spring pulse (Moreau et al 2014).…”

Sea ice and oxygen

“…Gas dynamics in sea ice regions are very hard to sample, contributing to a serious deficit of data from this region and an urgent need for further research (Søgaard et al 2013;Hambler, C. (2022) Sea ice and oxygen Working Paper. Version 1 2 Vancoppenolle et al 2013;Moreau et al 2016;Vancoppenolle & Tedesco 2016;Tison et al 2016;Bushinsky et al 2017;MOSAiC 2019;Angelopoulos et al 2022).…”

Sea ice and argon

“…Degassing as sea water freezes drives argon from water into brine channels and inclusions in the ice, and bubble nucleation can occur (Zhou et al 2013). Bubbles may diffuse upwards but some reach impermeable layers of ice, and sea ice can have multiple layers with differing and low permeability to gases (Moreau et al 2014;Angelopoulos et al 2022). Field observations at Barrow (Alaska) and a tank experiment suggest bubbles rich in argon can escape sea ice as it melts, leading to the prediction that some bubbles are released to the atmosphere in an "intense and rapid" spring pulse (Moreau et al 2014).…”

“…However, Earth's abiotic seasonal processes involving sea ice (such as brine rejection, freeze degassing, temperature-dependent solubility and calcium carbonate crystallization) make a contribution to carbon dioxide fluxes, at least locally (Semiletov et al 2007;Nomura et al 2010;Geilfus et al 2013;Søgaard et al 2013;Vancoppenolle et al 2013;Moreau et al 2016;Brown et al 2015;Tison et al 2016;Bushinsky et al 2017Bushinsky et al , 2019MOSAiC 2019). The effect of sea ice on large-scale carbon dioxide fluxes, if any, remains unknown but is under investigation (Angelopoulos et al 2022). Due to data limitations and other constraints, the contribution of sea ice is arguably poorly quantified and incompletely represented in Earth System models (Vancoppenolle & Tedesco 2016).…”