The objective of this 3-year project is to address gaps in knowledge of the development and evolution of some important macro- and microstructural features of first year sea ice by repeated measurements through the annual cycle from freezing to melting. Topics of study include:(1)the geometrical characteristics and spatial distribution of brine drainage networks and their relationship to the crystal structure of the ice, (2) the 3-dimensional characterization of brine and gas inclusions,(3)variations in permeability through the year and the resulting impact on heat and mass transfer through the ice, and (4)details of the relationship between c-axis fabrics and under-ice currents. Knowledge of these is important for studies of the optical and mechanical properties of sea ice, biological activity in sea ice, remote sensing applications, some aspects of climate modeling, and the entrainment and transport of contaminants.
The main activity of this project will be the acquisition and analysis of detailed observations relevant to the structural features listed, along with in-situ permeability measurements. The samples and data will be collected periodically through the year from a study site on first-year sea ice near Barrow, Alaska. The site will be instrumented to continuously monitor the thermal regime of the ice, and other relevant parameters will be measured periodically through the year. The scale of the features to be studied ranges from individual brine inclusions (approximately 10-4 m) to the full thickness of the ice sheet. Current information on these subjects comes mainly from short-term field studies (although there are some notable exceptions) which often involve relatively thin ice, or studies on laboratory-prepared specimens. To some extent, this reflects the difficulty of obtaining information on natural first year ice sheets as they evolve through the year from initial freezing to melting. The main problems in this regard are the remoteness of the field areas and the expense of getting to them, coupled with the lack of appropriate methodologies for collecting samples other than by relatively small-diameter corers. However, this project makes use of recent advances in techniques for sampling, measuring and testing for the relevant parameters, some of which the investigators helped to develop. In addition, the presence of the Barrow Arctic Science Consortium (BASC) as a reliable source of local personnel to assist in data gathering allows frequent visits to the site to be made for routine data collection or sampling. These data collection efforts will maintain continuity between and after 3 additional field programs of approximately 10 days each, during which extensive data sets will be acquired. These programs will be timed to conduct detailed studies of the ice at the site shortly after it forms, under cold, mid-winter conditions, and at the start of the melt season. In addition to the usual salinity, density, grain size and c-axis fabric measurements, specialized observations will include the permeability measurements and associated detailed measurement of drainage pathways, sets of orthogonal micrographs (which yield size distributions of small-scale inclusions in 3-dimensions), ocean current measurements, and vertical sections through the entire thickness of the ice sheet. The latter provide a unique view of larger-scale features such as brine drainage networks and horizontal banding. The data will be used to develop or evaluate and improve existing salt-flux/thermodynamic ice growth models.
