R. J. Galley

Perennial pack ice in the southern Beaufort Sea was not as it appeared in the summer of 2009

[1] In September 2009 we observed a much different sea icescape in the Southern Beaufort Sea than anticipated, based on remotely sensed products. Radarsat derived ice charts predicted 7 to 9 tenths multi-year (MY) or thick first-year (FY) sea ice throughout most of the Southern Beaufort Sea in the deep water of the Canada Basin. In situ observations found heavily decayed, very small remnant MY and FY floes interspersed with new ice between floes, in melt ponds, thaw holes and growing over negative freeboard older ice. This icescape contained approximately 25% open water, predominantly distributed in between floes or in thaw holes connected to the ocean below. Although this rotten ice regime was quite different that the expected MY regime in terms of ice volume and strength, their near-surface physical properties were found to be sufficiently alike that their radiometric and scattering characteristics were almost identical.

Frost flowers on young Arctic sea ice: The climatic, chemical, and microbial significance of an emerging ice type

Ongoing changes in Arctic sea ice are increasing the spatial and temporal range of young sea ice types over which frost flowers can occur, yet the significance of frost flowers to ocean-sea ice-atmosphere exchange processes remains poorly understood. Frost flowers form when moisture from seawater becomes available to a cold atmosphere and surface winds are low, allowing for supersaturation of the near-surface boundary layer. Ice grown in a pond cut in young ice at the mouth of Young Sound, NE Greenland, in March 2012, showed that expanding frost flower clusters began forming as soon as the ice formed. The new ice and frost flowers dramatically changed the radiative and thermal environment. The frost flowers were about 5°C colder than the brine surface, with an approximately linear temperature gradient from their base to their upper tips. Salinity and δ18O values indicated that frost flowers primarily originated from the surface brine skim. Ikaite crystals were observed to form within an hour in both frost flowers and the thin pond ice. Average ikaite concentrations were 1013 µmol kg−1 in frost flowers and 1061 µmol kg−1 in the surface slush layer. Chamber flux measurements confirmed an efflux of CO2 at the brine-wetted sea ice surface, in line with expectations from the brine chemistry. Bacteria concentrations generally increased with salinity in frost flowers and the surface slush layer. Bacterial densities and taxa indicated that a selective process occurred at the ice surface and confirmed the general pattern of primary oceanic origin versus negligible atmospheric deposition.

Change and variability in sea ice during the 2007–2008 Canadian International Polar Year program

In this paper we describe sea ice change and variability during the Canadian International Polar Year (IPY) program and examine several regional and hemispheric causes of this change. In a companion paper (Barber et al., Climate Change2012) we present an overview of the consequences of this observed change and variability on ecosystem function, climatically relevant gas exchange, habitats of primary and apex predators, and impacts on northern peoples. Sea ice-themed research projects within the fourth IPY were designed to be among the most diverse international science programs. They greatly enhanced the exchange of Inuit knowledge and scientific ideas across nations and disciplines. This interdisciplinary and cultural exchange helped to explain and communicate the impacts of a transition of the Arctic Ocean and ecosystem to a seasonally ice-free state, the commensurate replacement of perennial with annual sea ice types and the causes and consequences of this globally significant metamorphosis. This paper presents a synthesis of scientific sea ice research and traditional knowledge results from Canadian-led IPY projects between 2007 and 2009. In particular, a summary of sea ice trends, basin-wide and regional, is presented in conjunction with Inuit knowledge of sea ice, gathered from communities in northern Canada. We focus on the recent observed changes in sea ice and discuss some of the causes of this change including atmospheric and oceanic forcing of both dynamic and thermodynamic forcing on the ice. Pertinent results include: 1) In the Amundsen Gulf, at the western end of the Northwest Passage, open water persists longer than normal and winter sea ice is thinner and more mobile. 2) Large areas of summer sea ice are becoming heavily decayed during summer and can be broken up by long-period waves being generated in the now extensive open water areas of the Chukchi Sea. 3) Cyclones play an important role in flaw leads—regions of open water between pack ice and land-fast ice. They delay the formation of new ice and the growth of multi-year ice. 4) Feedbacks involving the increased period of open water, long-period wave generation, increased open-ocean roughness, and the precipitation of autumn snow are all partially responsible for the observed reduction in multiyear sea ice. 5) The atmosphere is observed as remaining generally stable throughout the winter, preventing vertical entrainment of moisture above the surface.

A Study on the C-Band Polarimetric Scattering and Physical Characteristics of Frost Flowers on Experimental Sea Ice

A focused study on the C-band polarimetric scattering and physical characteristics of frost-flower-covered sea ice was conducted at the Sea-Ice Environmental Research Facility over a three day period. Sea ice was grown in an outdoor pool outfitted with automated sensors to monitor environmental conditions. C-band polarimetric scattering measurements were conducted continuously at a range of incidence angles, and surface roughness statistics were obtained at discrete times using a laser scanner system LiDAR. Four stages of development were identified that exhibited notably different physical and scattering characteristics: 1) initial formation; 2) surface brine expulsion; 3) frost flower growth; and 4) decimation. An optimal polarization and incidence angle is not readily apparent for the purposes of identifying the frost flower development Stages I-III; however, the lower incidence angles (25° and 35°) appear to be most sensitive to the surface brine expulsion. Only the dual-polarization measurements at low incidence angles (e.g., 25°) could be used to identify the onset of the decimation stage. Backscatter increased rapidly during the initial formation, with a local maximum corresponding to ~ 80% areal coverage of frost flowers, followed by a local minimum when the surface was covered by a brine-rich surface layer, connoting that surface brine expulsion may be identified using polarimetric scatterometry.

Surface albedo observations of Hudson Bay (Canada) landfast sea ice during the spring melt

Abstract The shortwave albedo is a major component in determining the surface energy balance and thus the evolution of the spring melt cycle. As the melt commences, the ice is partitioned into multiple surface types ranging from highly reflective white ice to absorptive blue ice. The reflectance from these surfaces shows significant spatial and temporal variability. Spectral albedo measurements were made at six different sites encompassing these two surface types, from 19 March to 3 May 2005, on 1.5 m thick landfast sea ice in southwestern Hudson Bay, Canada (58˚ N). Furthermore, the broadband albedo and the surface energy balance were continuously recorded at a nearby site during the 1 month period. Rapid changes in the albedo were found to relate to typical subarctic climate conditions, i.e. frequent incursions of southerly air, resulting snow and rain events and the generally high maximum solar insolation levels. Subsequently, diurnal variations in snow surface temperature were evident, often causing daytime melting and night-time refreezing resulting in the formation of ice lenses and superimposed ice. After rain events and extensive melting, the snowpack was transformed throughout into melt/freeze metamorphosed snow and superimposed ice. The integrated (350–1050 nm) albedo varied between 0.52 and 0.95 at the blue-ice sites, while it varied between 0.73 and 0.91 at white-ice sites. Variability on the order of ±10% in the white-ice broadband albedo resulted from the diurnal freeze–thaw cycle, but also synoptic weather events, such as snowfall and rain events, could rapidly change the surface conditions.

Replacement of multiyear sea ice and changes in the open water season duration in the Beaufort Sea since 2004

The last decade has witnessed the nine lowest Arctic September sea ice extents in the observational record. It also forms the most recent third of the long-term trend in that record, which reached -13.4% decade-1 in 2015. While hemispheric analyses paint a compelling picture of sea ice loss across the Arctic, the situation with multiyear ice in the Beaufort Sea is particularly dire. This study was undertaken in light of substantial changes that have occurred in the extent of summer multiyear sea ice in the Arctic inferred from the passive microwave record. To better elucidate these changes at a sub-regional scale, we use data from the Canadian Ice Service archive, the most direct observations of sea ice stage-of-development available. We also build upon the only previous sea ice climatological analysis for Canadas western Arctic region by sea ice stage-of-development that ended in 2004. The annual evolution of sea ice by stage of development in Canadas western Arctic changed dramatically between 1983 and 2014. The rate of these changes and their spatial prevalence were most prominent in the last decade. In summer, total sea ice loss occurred via reductions in old and first-year sea ice over increasingly large areas and over more months per year. Resultant delay of thermodynamic freeze up has increased the annual open water duration in the study region. The winter sea ice cover was increasingly composed of first-year sea ice at the expense of old ice. Breakup timing has not significantly changed in the region.

Western Arctic Cyclones and Equilibrium between the Atmospheric Boundary Layer and the Sea Surface

Abstract The data-collection campaign for the 2008 International Polar Year–Circumpolar Flaw Lead System Study saw the Canadian Coast Guard Ship (CCGS) Amundsen, a research icebreaker, overwinter in high-concentration unconsolidated sea ice in Amundsen Gulf. Environmental monitoring continued into the open-water season. During this period, the Amundsen registered five relatively deep mean sea-level pressure minima (less than 100 kPa). Three were selected for further analysis based on season and the nature of the underlying ocean or sea-ice surface: (1) a winter pressure minimum over unconsolidated sea ice, (2) a spring pressure minimum which likely contributed to the break-up of the sea-ice cover on Amundsen Gulf, and (3) a summer pressure minimum over open water. The characteristics of these pressure minima and the impact of their passage on the atmospheric boundary layer and on the sea-ice cover as they crossed Amundsen Gulf were examined. Several features were revealed by the analysis. (1) The winter and summer pressure minima were migratory cyclones accompanied by Arctic frontal waves with characteristics very similar to the polar frontal waves associated with the migratory cyclones found at more southerly latitudes, whereas the spring pressure minimum was attributed to an Arctic frontal trough of low pressure with the cyclonic centre remaining south of the Gulf. (2) The passage of the frontal-wave cyclone in winter and the frontal trough of low pressure in spring disrupted the equilibrium that had been established during more settled periods between the atmospheric boundary layer and the mosaic surface (leads, polynyas, and sea ice); however, equilibrium was quickly re-established. (3) In summer, the thermal structure of the lower atmospheric boundary layer persisted through the passage of the frontal-wave cyclone over the open-water surface. (4) The passage of the frontal-wave cyclone in winter and the frontal trough of low pressure in spring modified the mesoscale sea-icescape.

Investigations into Frost Flower Physical Characteristics and the C-Band Scattering Response

A dedicated study on the physical characteristics and C-band scattering response of frost-flower-covered sea ice was performed in an artificial sea ice mesocosm over a 36-h period in January 2017. Meteorological conditions were observed and recorded automatically at the facility when the sea ice grew and frost flowers formed while the C-band scattering measurements were conducted continuously over a range of incidence angles. Surface roughness was characterized using a LiDAR. During the experiment, frost flowers did not initially form on the extremely smooth ice surface even though suitable meteorological conditions prevailed during their development (low air temperature, low near-surface wind speed, and high near-surface relative humidity). This provides evidence that both the presence of (i) liquid brine at the surface and (ii) raised nodules as nucleation points are required to enable frost flower initiation. As the ice thickened, we observed that raised nodules gradually appeared, frost flowers formed, and flowers subsequently spread to cover the surface over a six-hour period. In contrast to previous experiments, the frost flower layer did not become visibly saturated with liquid brine. The C-band scattering measurements exhibited increases as high as 14.8 dB (vertical polarization) in response to the frost flower formation with low incidence angles (i.e., 25°) showing the largest dynamic range. Co-polarization ratios responded to the physical and thermodynamic changes associated with the frost flower formation process. Our results indicate that brine expulsion at the sea ice surface and frost flower salination can have substantial temporal variability, which can be detected by scatterometer time-series measurements. This work contributes towards the operational satellite image interpretation for Arctic waters by improving our understanding of the highly variable C-band microwave scattering properties of young sea ice types.

Polarimetric scatterometer measurements at the Sea-ice Environmental Research Facility

A focused study on the C-band polarimetric scattering and physical characteristics of experimental sea ice was conducted at the Sea-ice Environmental Research Facility. Sea ice was grown in an outdoor pool outfitted with automated sensors to monitor environmental conditions. Radar measurements were sensitive to four distinct stages of development: (I) initial formation, (II) surface brine expulsion, (III) frost flower growth, and (IV) decimation. An optimal polarization and incidence angle was not readily apparent for the purposes of identifying the frost flower development stages I-III; however, low incidence angles appear to be most sensitive to the surface brine expulsion. Only the dual-polarization measurements at low incidence angles could be used to identify the onset of the decimation stage (IV). Backscatter increased rapidly during the initial formation, with a local maximum corresponding to ca. 80% areal coverage of frost flowers, followed by a local minimum when the surface was covered by a brine-rich surface layer, showing that surface brine expulsion may be identified using polarimetric scatterometry.

All-Sky Surface Radiation and Clear-Sky Surface Energy Budgets: Summer to Freeze-Up in the Western Maritime Arctic

The 2009 ArcticNet expedition was a field campaign in the Amundsen Gulf–eastern Beaufort Sea region from mid-July to the beginning of November aboard the CCGS Amundsen that provided an opportunity to describe the all-sky surface radiation and the clear-sky surface energy budgets from summer to freeze-up in the data sparse western maritime Arctic. Because the fractional area of open water was generally larger than the fractional area of ice floes, the net radiation at the water surface controlled the radiation budget. Because the water albedo is much less than the albedo of the ice floes, the extent and duration of open water in summer is an important albedo feedback mechanism. From summer to freeze-up, the net all-sky shortwave radiation declined steadily as the solar angle lowered, while coincidently the net all-sky longwave radiation became increasingly negative. The all-sky net surface radiation switched from positive in summer to negative during the freeze-up period. From summer to freeze-up, both upward and downward turbulent heat fluxes occurred. In summer, a positive surface energy budget residual contributed to the melting of ice floes and/or to the warming of the Arctic Oceans mixed layer. During the freeze-up period, with temperatures below approximately −5°C, the residuals were mainly negative suggesting that heat loss from the oceans mixed layer and heat released by the phase change of water were significant components of the energy budgets residual.