Suzanne Sleewaegen

Tank study of physico-chemical controls on gas content and composition during growth of young sea ice

During an ice tank experiment, samples were taken to study the processes of acquisition and alteration of the gas properties in young first-year sea ice during a complete growth-warming-cooling cycle. The goal was to obtain reference levels for total gas content and concentrations of atmospheric gases (O2, N2, CO2) in the absence of significant biological activity.The range of total gas content values obtained (3.5 to 18 ml of gas per kilo of ice) was similar to previous measurements or estimates. However, major differences occurred between the current and quiet basins, showing the role of water dynamics at the ice-water interface in controlling bubble nucleation processes.Extremely high CO2 concentrations were observed in all the experiments (up to 57% in volume parts). It is argued that these could have resulted from two unexpected biases in the experimental settings.Concentrations of bubbles nucleated at the interface are controlled by diffusion both from the ice-water interface towards the well-mixed reservoir, and between the interface water and the bubble itself. This double kinetic effect results in a transition of the gas composition in the bubbles from values close to solubility in sea water towards values close to atmospheric, as the ice cover builds up.

A kinetic isotope effect during ice formation by water freezing

A kinetic isotope effect is known to occur during ice formation from water vapour in a cloud ; it is due to the difference in molecular diffusivities in air of HDO and H218O molecules. A similar effect is likely during water freezing since diffusion coefficients of HDO and H218O are also different in liquid water. Their values are however less different from each other than those in air. Therefore, such a kinetic isotope effect during water freezing is less frequently observed in Nature. This paper describes a situation in Antarctica where this effect is conspicuous in icings (aufeis). In this type of ice indeed there is no relationship between δD (or δ18O) and deuterium excess whereas a clear inverse relationship between these parameters exists in ice formed by water freezing when equilibrium isotopic fractionation applies. This kinetic effect is potentially present in hail within clouds, in infiltration ice (formed during sea ice growth) and in some kinds of ground ice.

Equifinality of basal ice facies from an Antarctic cold-based glacier

Abstract Three debris-bearing ice facies were recognized at the base of Suess Glacier, a cold-based glacier damming a lake in Taylor Valley, South Victoria Land, Antarctica. These facies are termed “amber ice”,“solid facies” and “basal stratified facies”. This paper uses stable-isotope composition (δD and δ18O), gas content and gas composition (CO2, O2 and N2) to develop an understanding of the processes responsible for the formation of these facies. The basal ice is characterized by a striking difference in ice properties between the innermost end of a 25 m long tunnel dug 200 m upstream from the glacier front and the front itself. At the glacier front, co-isotopic data plot along a well-defined freezing slope (S = 5.6), whereas, inside the tunnel, the isotopic data offset from the freezing slope and from the local meteoric water-line (which has a slope of 8.2). CO2 concentrations rise from a minimum of about 1000 ppmv in the tunnel to about 220000ppmv at the front. Taken together, these characteristics strongly suggest an increasing contribution of liquid water in the formation of basal ice towards the glacier terminus. We therefore conclude that visually similar basal ice facies can have different origins.

Ice Formation in an Antarctic Glacier-dammed Lake and Implications for Glacier-Lake Interactions

Perennially frozen lakes are common features in the McMurdo Dry Valleys of South Victoria Land in Antarctica. Some of them, called wet based, contain liquid water capped by a permanent ice cover between 2.5 and 6 m in thickness. The others, called dry based, are ice-block lakes. The thickness of the latter may far exceed those of the former. Their level is rising from freezing of the surface flooding of summer meltwater. However, we show here for the first time, using isotopic analyses together with an ionic and gas content and composition study, that the ice of one of these dry-based lakes has been formed by complete freezing from top to bottom of a closed water reservoir and not by successive layers of icings (aufeis) piling on top of each other. We also show how this lake, dammed by a cold-based glacier, has contributed to the formation of the basal ice layer of this glacier.