Brine Network Structure in Sea Ice
The Arctic is losing thick multiyear sea ice cover at a rate of as much as 15% per decade, and it is being replaced by thinner, more porous, annual sea ice that forms in winter and melts in summer. The shrinking ice cover has implications for climate change (it's a positive feedback), as well as for wildlife, commerce, and even geopolitics in the Arctic.
As the interface between the ocean and the atmosphere in the Polar Regions, sea ice plays an enormous role in ocean circulation and global climate. While from a distance the ice may look solid, it is riddled with channels containing super salty brine. This complex pore network plays a key role in the exchange of heat, fluid, gases, and chemical species between the ocean and the boundary layer atmosphere, and in the habitat of photosynthetic marine biota.
Our work involves engineering, field and laboratory measurements, and the use of applied mathematics to characterize the topology, or detailed 3D geometry, of brine networks in sea ice. The results of our work will help climate modelers, oceanographers, and biologists understand the shape and connectivity of pore networks in sea ice.
We conduct our field work from Barrow, Alaska, the northernmost point in the United States and the place where the Chukchi and Beaufort Seas meet. There, we study sea ice freeze up, and collect sea ice cores that are shipped to Dartmouth for analysis.
X-Ray Micro Computed Tomography (X-ray microCT)
X-ray microCT, essentially a small scale CAT scan system, provides a non-destructive, high resolution means of three-dimensional analysis of the brine channel network in sea ice. X-ray attenuation images collected as the sample is rotated between a source and a detector are reconstructed into a 3D model of the interior features of the sample. Through postprocessing techniques, we gather data on the brine channel network which we use to measure porosity and connectivity and to model flow through the sample.
Ion Chromatography (IC)
Ion chromatography enables us to measure the concentration of different salts in sea ice: including chloride, bromide, nitrate, phosphate, sulfate, sodium, potassium, and calcium. Salt concentrations in sea ice and its snow cover have helped us explain the transport of bromide from the ocean into the atmosphere.
Synchrotron X-Ray MicroFluorescence
We take samples of sea ice to the Argonne National Laboratory, where we use x-ray micro-fluorescence on Advanced Photon Source (APS) beamline 13-DE to map the microstructural location of salts in the ice. This produces a de facto image of the brine channel network and the distribution of salts in it. Click here for a link to a short video describing our work at Argonne.
Stable Isotope Analysis
Analysis of the relative concentrations of stable isotopes is used to identify contributions to sea ice from fresh water sources, such as rivers and glacial melt.
Ignatius Rigor, University of Washington - co-PI - Buoy development
Xiahong Feng, Dartmouth College - co-PI - Ion chromatography and stable isotope analysis
Inga Smith, University of Otago, New Zealand - Sea ice modeling
This research has been supported by US National Science Foundation (NSF) grants PLR-1304134 and NSF-1603683. The views and conclusions contained herein are those of the authors and should not be interpreted as representing official policies, either expressed or implied, of the NSF or the United States Government.