Imaging air volume fraction in sea ice using non-destructive X-ray tomography

Odile Crabeck, Ryan Galley, Bruno Delille, Brent Else, Nicolas-Xavier Geilfus, Marcos Lemes, Mathieu Des Roches, Pierre Francus, Jean-Louis Tison, Søren Rysgaard
2016 The Cryosphere  
<p><strong>Abstract.</strong> Although the presence of a gas phase in sea ice creates the potential for gas exchange with the atmosphere, the distribution of gas bubbles and transport of gases within the sea ice are still poorly understood. Currently no straightforward technique exists to measure the vertical distribution of air volume fraction in sea ice. Here, we present a new fast and non-destructive X-ray computed tomography technique to quantify the air volume fraction and produce separate
more » ... nd produce separate images of air volume inclusions in sea ice. The technique was performed on relatively thin (4&amp;ndash;22<span class="thinspace"></span>cm) sea ice collected from an experimental ice tank. While most of the internal layers showed air volume fractions<span class="thinspace"></span> &amp;lt; <span class="thinspace"></span>2 %, the ice–air interface (top 2 cm) systematically showed values up to 5 %. We suggest that the air volume fraction is a function of both the bulk ice gas saturation factor and the brine volume fraction. We differentiate micro bubbles (Ø<span class="thinspace"></span> &amp;lt; <span class="thinspace"></span>1 mm), large bubbles (1 mm<span class="thinspace"></span> &amp;lt; <span class="thinspace"></span>Ø<span class="thinspace"></span> &amp;lt; <span class="thinspace"></span>5 mm) and macro bubbles (Ø<span class="thinspace"></span> &amp;gt; <span class="thinspace"></span>5 mm). While micro bubbles were the most abundant type of gas bubbles, most of the air porosity observed resulted from the presence of large and macro bubbles. The ice texture (granular and columnar) as well as the permeability state of ice are important factors controlling the air volume fraction. The technique developed is suited for studies related to gas transport and bubble migration.</p>
doi:10.5194/tc-10-1125-2016 fatcat:ik3jjonjgnftflzxbtbu2fnwny