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Landfast Ice Dynamics and Stability

A fresh crack in young ice just seaward of
a grounded pressure ridge off Barrow

Over the past many years, various projects have addressed landfast ice stability in a variety of ways, often blending geophysical approaches with local knowledge.

Alaska Landfast Sea Ice Dynamics is the title of Andy Mahoney's PhD thesis, which was completed in 2007. By definition, landfast ice remains stationary and attached to the coast for most of the year. However, it is shaped by dynamic events throughout its seasonal existence between formation in late fall and break-up in spring. Using a combination of satellite and ground-based remote sensing, together with field observations, this work outlined the mechanisms by which the landfast ice responds to the forces of ocean currents, tides and winds. This study incorporated the different scales at which these processes act.

At the regional scale, 8 years of Radarsat Synthetic Aperture Radar (SAR) imagery was used to delineate the seaward landfast ice edge (SLIE) as it evolved through the different seasons (see Mapping and Characterization of Recurring Spring Leads and Landfast ice in the Beaufort and Chukchi Seas). At this scale, the SLIEs appear to resolve themselves into nodes of stability separating regions of greater variability.

At the local scale, a land-based side-looking X-band marine radar was employed to scan landfast ice within approximately 5 km of Barrow, Alaska every 5 minutes (see Barrow Sea Ice Observatory). This high temporal resolution captured ice dynamics during the creation of grounded ridges. These ridges can be built in less than an hour and remain for the entire season, before breaking up and drifting away as swiftly as they arrived. At the highest spatial resolution, field observations using a Differential Global Positioning System (DGPS) and an electromagnetic induction device were combined to measure sea ice elevation and thickness nearly continuously along transects within the land-based radar footprint from the beach at Barrow to the SLIE. These transects located and determined the size of grounded ridges, which surely play an important role in holding the ice cover fast to the coast.

In addition to examining processes across spatial scales, this project also looked at previous data collected on the landfast ice, mainly during the Outer Continental Shelf Environmental Assessment Program (OCSEAP) years in the 1970s, to examine evidence for changes in the landfast ice regime. By comparing the regimes of the landfast ice and the larger scale atmospheric circulation and sea ice distribution, this worked aimed to identify processes responsible for any change.

Relevant Publications:
  • Mahoney, A., H. Eicken, L. Shapiro, and A. Graves (2006) Defining and locating the seaward landfast ice edge in northern Alaska, paper presented at the 18th International Conference on Port and Ocean Engineering under Arctic Conditions, POAC ‘05, Potsdam, N.Y., June 26-30, 2005, vol. 3, 991-1001. (download this paper as an Adobe pdf file)
  • Mahoney, A., H. Eicken, L. Shapiro (2007) How fast is landfast ice? A study of the attachment and detachment of nearshore ice at Barrow, Alaska. Cold Reg. Sci. Technol., 47, 233-255 (download this paper as an Adobe pdf file)
  • Mahoney, A., H. Eicken, A. Graves, and L. Shapiro (2007) Alaska landfast sea ice: Links with bathymetry and atmospheric circulation, J. Geophys. Res., 112, C02001, doi:10.1029/2006JC003559 (download this paper as an Adobe pdf file)

Integrating Geophysical and Inupiat Knowledge of Landfast Ice Stability is the topic of Matt Druckenmiller’s current PhD thesis work. This work seeks to integrate geophysical methods of monitoring and studying Alaskan landfast sea ice (e.g., coastal radar, SAR satellite imagery, electromagnetic induction sounding, etc.) with Iñupiat local and traditional knowledge. He aims to improve upon monitoring capabilities and the accessibility of local-scale sea-ice information relevant in areas vulnerable to increases in climate variability. Much of this work is centered on the Barrow sea ice observatory. While geophysical monitoring of landfast ice has been carried out systematically here since the late 1990's, local indigenous knowledge has observed local and regional ice conditions for countless centuries as the Iñupiat people have pursued the traditional hunt of the bowhead whale and other marine mammals from the ice. These parallel observations are compared in the context of assessing ice stability throughout winter and spring. Differences in epistemology and in scales of observation are considered as this work attempts to identify areas where these seemingly disparate types of knowledge may interface to improve the range of information accessible to those concerned with personal and community safety on ice.

Relevant Publications:
  • Druckenmiller, M.L.; H. Eicken; M. Johnson; D. Pringle; C. Williams (2009) Towards an integrated coastal sea-ice observatory: System components and a case study at Barrow, Alaska. Cold Regions Science and Technology 2009, 56 (1-2), 61-72 . (pdf)
  • Druckenmiller, M.L.; H. Eicken; J.C. George; L. Brower (In Press, 2010) Assessing the Shorefast Ice: Iñupiat Whaling Trails off Barrow, Alaska. Book Chapter, Sea Ice Knowledge and Use, I. Krupnik (ed).
  • Druckenmiller, M.L., et al. (In Prep) Integrating Geophysical and Iñupiat Knowledge on Alaska Shorefast Ice Stability using Fault Tree Analysis.