Gas transport processes in sea ice: How convection and diffusion processes might affect biological imprints, a challenge for modellers

• Main Authors: Tison, J.-L., Zhou, Shaola J. G., Thomas, D. N., Rysgaard, Søren, Eicken, H., Crabeck, O., Deleu, F., Delille, B.
• Format: Conference Object
• Language: English
• Published: 2012
• Subjects: Greenland; Barrow; East Greenland; ice core; Sea ice; Alaska
• Online Access: https://pure.au.dk/portal/da/publications/gas-transport-processes-in-sea-ice-how-convection-and-diffusion-processes-might-affect-biological-imprints-a-challenge-for-modellers(a9f15bb1-8ad3-4c23-91b2-0aa63322d6aa).html; http://adsabs.harvard.edu/abs/2012EGUGA.1411390T

Recent data from a year-round survey of landfast sea ice growth in Barrow (Alaska) have shown how O2/N2 and O2/Ar ratios could be used to pinpoint primary production in sea ice and derive net productivity rates from the temporal evolution of the oxygen concentration at a given depth within the sea ice cover. These rates were however obtained surmising that neither convection, nor diffusion had affected the gas concentration profiles in the ice between discrete ice core collections. This paper discusses examples from three different field surveys (the above-mentioned Barrow experiment, the INTERICE IV tank experiment in Hamburg and a short field survey close to the Kapisilit locality in the South-East Greenland fjords) where convection or diffusion processes have clearly affected the temporal evolution of the gas profiles in the ice, therefore potentially affecting biological signatures. The INTERICE IV and Barrow experiment show that the initial equilibrium dissolved gas entrapment within the skeletal layer basically governs most of the profiles higher up in the sea ice cover during the active sea ice growth. However, as the ice layers age and cool down under the temperature gradient, bubble nucleation occurs while the concentration in the ice goes well above the theoretical one, calculated from brine equilibrium under temperature and salinity changes and observed brine volumes. This phase change locks the gases within the sea ice structure, preventing "degassing" of the ice, as is observed for salts under the mushy layer brine convection process. In some cases, mainly in the early stages of the freezing process (first 10-20 cm) where temperature gradients are strong and the ice still permeable on its whole thickness, repeated convection and bubble nucleation can actually increase the gas concentration in the ice above the one initially acquired within the skeletal layer. Convective processes will also occur on ice decay, when ice permeability is restored and the Rayleigh number reaches a critical value. The ...