Jennifer V. Lukovich

Atmospheric forcing of the Beaufort Sea ice gyre: Surface pressure climatology and sea ice motion

[1] The Beaufort Gyre (BG) typically rotates anticyclonically and exerts an important control on Arctic Sea ice dynamics. Previous studies have shown reversals in the BG to rotate cyclonically during summer months and, in recent decades, throughout the annual cycle. In this investigation, we explore the synoptic climatology of atmospheric forcing and its relationship to sea ice motion and BG reversals. A catalog of daily synoptic weather types is generated for the Beaufort Sea Region covering the period 1979 to 2006 using NCEP/NCAR reanalysis mean sea level pressure data, principle components, and k-means cluster analyses. Mean synoptic type frequency, persistence, and duration values are calculated for each synoptic type and contrasted between the summer and winter seasons. Daily synoptic types are linked to changes in sea ice vorticity by using correlation analysis on lagged sea ice vorticity data. Lag correlations are found between synoptic types and sea ice vorticity smoothed over a 12-week running mean and show that cyclonic types, which promote southerly or easterly atmospheric circulation over the southern Beaufort Sea, commonly precede summer reversals. Furthermore, significant seasonal within-type variability in sea ice vorticity is detected within the synoptic types illustrating the importance of seasonal variability on these processes.

Changing Sea Ice Conditions in Hudson Bay, 1980–2005

We present an overview of changes in Hudson Bay sea ice in the context of thermodynamic forcing due to increased surface air temperatures and dynamic wind and current forcing mechanisms. Examined in particular is the correspondence between sea ice extent, surface air temperatures, and atmospheric indices during spring and fall from 1980 to 2005. Changes in the timing of freeze-up and break-up over the last several decades were significant. In the spring, temperature trends were consistently positive with temperature increases of 0.23°C/decade from 1950 to 2005. With increasing temperatures in the Hudson Bay region, sea ice concentrations and sea ice extents have decreased significantly as well. Warmer surface air temperatures have also shifted the mean freeze-up and break-up dates by 0.8–1.6 weeks in each of the seasons. Dynamic forcing of sea ice is further explored using the concept of relative vorticity, or the tendency for sea ice to rotate clockwise (or counterclockwise) within Hudson Bay in response to changes in atmospheric circulation. Surface air temperatures and hence ice extent showed cyclical patterns over the time period studied and appear to be driven by large scale atmospheric circulation patterns. This cyclical behaviour has been previously associated with various hemispheric indices including the North Atlantic Oscillation. The implications of changing ice conditions in Hudson Bay for marine mammal habitat are discussed.

Consequences of change and variability in sea ice on marine ecosystem and biogeochemical processes during the 2007–2008 Canadian International Polar Year program

Change and variability in the timing and magnitude of sea ice geophysical and thermodynamic state have consequences on many aspects of the arctic marine system. The changes in both the geophysical and thermodynamic state, and in particular the timing of the development of these states, have consequences throughout the marine system. In this paper we review the ‘consequences’ of change in sea ice state on primary productivity, marine mammal habitats, and sea ice as a medium for storage and transport of contaminants and carbon exchange across the ocean-sea-ice-atmosphere interface based upon results from the International Polar Year. Pertinent results include: 1) conditions along ice edges can bring deep nutrient-rich ‘pacific’ waters into nutrient-poor surface waters along the arctic coast, affecting local food webs; 2) both sea ice thermodynamic and dynamic processes ultimately affect ringed seal/polar bear habitats by controlling the timing, location and amount of surface deformation required for ringed seal and polar bear preferred habitat 3) the ice edges bordering open waters of flaw leads are areas of high biological production and are observed to be important beluga habitat. 4) exchange of climate-active gases, including CO2, is extremely active in sea ice environments, and the overall question of whether the Arctic Ocean is (or will be) a source or sink for CO2 will be dependent on the balance of competing climate-change feedbacks.

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.

Formation of winter water on the Canadian Beaufort shelf: New insight from observations during 2009–2011

The Arctic halocline forms a cold stratified barrier between the seasonally modified near-surface layers and deeper Atlantic-derived waters. Its low temperature is maintained by intrusions of cold water formed over Arctic shelves in winter. Surprisingly, cold salty (33) water capable of halocline ventilation (Beaufort Sea Winter Water: BSWW) has been observed in the Beaufort Sea during some winters despite the low salinity (20–25) of shelf waters there in summer. This study uses year-round data from moored instruments on the Beaufort shelf and slope during 2009–2011 to investigate the mechanisms involved. Our analysis reveals that four air-sea interaction processes contribute to the formation of BSWW—flushing of the low-salinity surface water from the shelf via Ekman transport in late summer and early fall, compensatory upwelling of more saline halocline water onto the shelf, net seaward ice drift that promotes ice production by maintaining a flaw lead, and entrainment of dense upwelled water into the freezing surface layer on the inner shelf. This work moves beyond earlier studies in revealing that while weather conditions were more favorable to BSWW formation in the winter of 2010–2011 than in 2009–2010, the difference was more strongly influenced by Ekman transport (offshore at the surface, onshore at the seabed) than by differences in cumulative brine injection from ice growth. The strength of the Ekman circulation over the Canadian Beaufort shelf in winter and its interannual variation have significance for surface nutrient renewal and for the cross-shelf transport of pollutants at the surface and the seabed.

Persistent artifacts in the NSIDC ice motion data set and their implications for analysis

In this study we evaluate weekly EASE-GRID sea-ice velocities released by the National Snow and Ice Data Centre (NSIDC). We identify persistent Eulerian and Lagrangian features, that arise solely as an artifact of the method used in the incorporation of buoy data. This, in turn, significantly impacts calculation of sea ice motion gradients, including divergence, convergence and shear. Our numerical experiments and comparison with observations further demonstrate the impact of these artificial features on climatological assessments, including age of ice studies. In particular, we find that age of ice studies using this dataset significantly underestimate multi-year ice extent by an average of 0.8 million km2 in the month of March.

Shelfbreak current over the Canadian Beaufort Sea continental slope: Wind‐driven events in January 2005

The shelfbreak current over the Beaufort Sea continental slope is known to be one of the most energetic features of the Beaufort Sea hydrography. In January 2005, three oceanographic moorings deployed over the Canadian (eastern) Beaufort Sea continental slope simultaneously recorded two consecutive shelfbreak current events with along-slope eastward bottom-intensified flow up to 120 cm s−1. Both events were generated by the local wind forcing associated with two Pacific-born cyclones passing north of the Beaufort Sea continental slope toward the Canadian Archipelago. Over the mooring array, the associated westerly wind exceeded 15 m s−1. These two cyclones generated storm surges along the Beaufort Sea coast with sea surface height (SSH) rising up to 1.4 m following the two westerly wind maxima. We suggest that the westerly along-slope wind generated a surface Ekman onshore transport. The associated SSH increase over the shelf produced a cross-slope pressure gradient that drove an along-slope eastward geostrophic current, in the same direction as the wind. This wind-driven barotropic flow was superimposed on the background baroclinic bottom-intensified shelfbreak current that consequently amplified. Summer-fall satellite altimetry data for 1992–2013 show that the SSH gradient in the southeastern Beaufort Sea is enhanced over the upper continental slope in response to frequent storm surge events. Because the local wind forcing and/or sea-ice drift could not explain the reduction of sea-ice concentration over the Beaufort Sea continental slope in January 2005, we speculate that wind-driven sea level fluctuations may impact the sea-ice cover in winter.

Projecting present and future habitat suitability of ship-mediated aquatic invasive species in the Canadian Arctic

A rise in Arctic shipping activity resulting from global warming and resource exploitation is expected to increase the likelihood of aquatic invasive species (AIS) introductions in the region. In this context, the potential threat of future AIS incursions at a Canadian Arctic regional scale was examined. Habitat suitability under current environmental conditions and future climate change scenarios was projected for a subset of eight potential invaders ranked as having a high risk of establishment in the Canadian Arctic based on dispersal pathways/donor regions, biological attributes and invasion history: (1) Amphibalanus improvisus, (2) Botrylloides violaceus, (3) Caprella mutica, (4) Carcinus maenas, (5) Littorina littorea, (6) Membranipora membranacea, (7) Mya arenaria and (8) Paralithodes camtschaticus. Habitat modelling was performed using MaxEnt based on globally known native and non-native occurrence records and environmental ranges for these species. Results showed that under current environmental conditions the habitat is suitable in certain regions of the Canadian Arctic such as the Hudson Complex and Beaufort Sea for L. littorea, M. arenaria and P. camtschaticus. Under a future climate change scenario, all species showed poleward gains in habitat suitability with at least some regions of the Canadian Arctic projected to be suitable for the complete suite of species modelled. The use of these models is helpful in understanding potential future AIS incursions as a result of climate change and shipping at large spatial scales. These approaches can aid in the identification of high risk regions and species to allow for more focused AIS monitoring and research efforts in response to climate change.

Lagrangian analysis of sea-ice dynamics in the Arctic Ocean

In this study, we present Lagrangian diagnostics to quantify changes in the dynamical characteristics of the Arctic sea-ice cover from 2006 to 2014. Examined in particular is the evolution in finite-time Lyapunov exponents (FTLEs), which monitor the rate at which neighbouring particle trajectories diverge, and stretching rates throughout the Arctic. In this analysis, we compute FTLEs for the Arctic ice-drift field using the 62.5 km daily sea-ice motion vector data from the European Organisation for the Exploitation of Meteorological Satellites Ocean and Sea Ice Satellite Application Facility. Results from the FTLE analysis highlight the existence of three distinct dynamical regions with strong stretching, captured by FTLE maxima or ridges. It is further shown that FTLE ridges are dominated by shear, with contributions from divergence in the Beaufort Sea. Localization of FTLE features following the 2012 record minimum in summertime sea-ice extent illustrates the emergence of an Arctic characterized by increased mixing. Results also demonstrate higher FTLEs in years when lower multi-year ice extent is observed.

Increasing Mobility of High Arctic Sea Ice Increases Marine Hazards Off the East Coast of Newfoundland

Heavy ice conditions along Canadas east coast during spring 2017 presented hazardous conditions for the maritime industry and required the Canadian Coast Guard to pull its research icebreaker, CCGS Amundsen, off its scientific cruise to provide ice escort services and conduct search and rescue operations along Newfoundlands northeast coast. Greater ice concentrations and a thicker ice pack than are typical of this area created the anomalous ice cover. Within this paper we present in situ observations of the ice cover, confirming that pieces of multiyear sea ice from the high Arctic were present within the ice cover, and subsequently examine the transport pathway that connects the export of thick multiyear sea ice from the Lincoln Sea and Canadian Arctic Archipelago to coastal communities in Newfoundland. We conclude with a discussion on how an increasingly mobile Arctic sea ice cover may increase these ice hazards in the south.