Landfast Sea Ice at Utquiagvik (Barrow), Alaska, 2015

• Main Authors: Rachel Obbard, Scott Pauls, Ross Lieb-Lappen
• Format: Dataset
• Language: unknown
• Published: Arctic Data Center 2019
• Subjects: Sea Ice; Ice Depth/Thickness; Ice Growth/Melt; Ice Types; Arctic; Chukchi Sea; Lappen; Barrow; Beaufort Sea; Chukchi; ice core; Point Barrow; Sea ice; Alaska
• Online Access: https://search.dataone.org/view/urn:uuid:60a51293-43c4-470b-9c7f-f03d929fc4be

This project focused on analyzing brine network structure in first year Arctic sea ice (samples collected during a 2015 field campaign), to collect data which could be used to develop applied mathematical methods to describe brine network structure in first year Arctic Sea Ice. We designed a Temperature Gradient Ice Core Transport System (TGICTS), named the ICE-MITT (Ice Core Extraction while Maintaining In-situ Temperature Transitions), with which we could transport cores from the field back to our lab at in-situ temperature gradients. It was only partially successful. We discovered that improvements needed to be made to the design of the device if it is to work for large cores (ours were 1 m x 14 cm diameter) and at non-freezing ambient temperatures. A later freezer failure at Dartmouth resulted in the loss of the cores that were transported with this device, leaving us with only cores that had been shipped back the traditional (isothermal) method (at a uniform -20C). Samples from the "isothermal" cores were taken every 10 cm and analyzed using X-ray micro computed tomography in a -14C cold room. We used a Bruker Skyscan 1172 desktop micro computed tomography system and the associated proprietary reconstruction and postprocessing software. MicroCT data began as raw tiff X-ray images taken at a number of rotation steps (0.7 deg apart) between 0 and 180 deg. These were reconstructed into bitmap (bmp) slices of the sample. A volume of interest was selected and the data within it binarized by the use of thresholds to distinguish ice from air and brine. Binarized images of the slices of the VOI are also saved as bmp files. We identified a set of metrics that can be gleaned from X-ray micro-computed tomography and are useful for interpreting the microstructure of sea ice (Lieb-Lappen et al., 2017). We have used these to quantify some differences in brine channel topology with depth, and some differences between granular and frazil ice. Finally, we tested the Notz wire harp by cutting a hole in the ice cover in late February 2015 (Feb 14-19, 2015) and freezing the harp into it. Based on the principle that pure solid ice is a good insulator whereas interstitial saltwater brine is a good conductor, the device developed by Notz, Worster and Wettlaufer (Notz et al., 2005; Notz and Worster, 2008) records temperature and resistivity at different depths as ice grows around it. Salinity of the interstitial brine is then inferred from the liquidus relationship (Cox and Weeks, 1986) and can be combined with the measured solid mass fraction to give the bulk salinity profile of the growing sea ice. This was a preliminary test for later use of the harp on another project. Notz, D., Wettlaufer, J. & Worster, M. (2005). A non-destructive method for measuring the salinity and solid fraction of growing sea ice in situ. Journal of Glaciology, 51(172), 159-166. Notz, D., and M. G. Worster (2008), In situ measurements of the evolution of young sea ice, J. Geophys. Res., 113, C03001, doi:10.1029/2007JC004333.