Canadian Beaufort Sea Research Articles

Biogeochemistry of near-bottom suspended particulate matter of the Beaufort Sea shelf (Arctic Ocean): C, N, P, δ 13C and fatty acids

The influence of the Mackenzie River on the source, composition, and distribution of dissolved nutrients and suspended particulate matter (SPM) in near-bottom waters on the Beaufort Sea shelf was determined by measuring particulate organic carbon (POC), particulate nitrogen (PN), particulate phosphorus (PP), elemental ratios (C:N, C:P, N:P), chlorophyll a, bulk δ13C, and fatty acids. The Mackenzie River had a strong influence on the composition of SPM in near-bottom waters across the entire Canadian Beaufort Sea shelf, including the Amundsen Gulf. This influence was strongest at stations near the river mouth and decreased offshore and northeastward towards the Amundsen Gulf, as seen in SPM elemental concentrations, δ13C, and terrestrial plant fatty acid markers. Low C:N ratios and high relative levels of odd-numbered carbon and branched-chained fatty acids (bacterial fatty acid markers) indicated that bacteria were an important contributor to organic matter at stations near the river and on the Mackenzie shelf. Fatty acid analysis allowed detection of a phytoplankton sinking event in the Amundsen Gulf in which polyunsaturated fatty acid (PUFA) levels in near-bottom waters significantly increased from June to July. However, this change in PUFA was not associated with any observed temporal change in chlorophyll a, δ13C, or C:N ratios. These results show that a multiple biomarker approach is necessary in ecosystem studies of dynamic environments such as near-bottom waters or river-influenced shelves.

Distribution and diet of the bottom dwelling Arctic cod in the Canadian Beaufort Sea

Distribution and diet of bottom-dwelling Arctic cod were studied in the nearshore Canadian Beaufort Sea in summer of 2006–2009 using a 3m benthic beam trawl. In total, 82 stations were visited ranging in depth from 8 to 128m. Fish densities were generally low for benthic habitats; pelagic fish occurrence was not assessed. We observed a gradual increase in both the biomass of daily food rations and their energetic content over fish age. Overall, fish were able to obtain high food rations indicating that the Beaufort Sea Shelf has sufficient food resources for them. Demersal Arctic cod fed mainly on copepods (Pseudocalanus spp., Calanus glacialis, Calanus hyperboreus, Limnocalanus macrurus and Jaschnovia tolli), amphipods (Apherusa glacialis and Themisto libellula) and mysids (Mysis oculata). Further studies, particularly focused on combined pelagic/benthic sampling, are needed to fully assess ecology of the Arctic cod population in the Canadian Beaufort Sea.

Larval and early juvenile fish distribution and assemblage structure in the Canadian Beaufort Sea during July–August, 2005

The distribution and composition of marine larval and early juvenile fish were investigated during a multidisciplinary project conducted in the nearshore Canadian Beaufort Sea in July and August, 2005. Larvae were sampled using replicate bongo net (500μm) tows within 50m water depth. A total of 458 larval fish representing seven families were captured.Multivariate statistical analyses revealed two distinct larval assemblages that were closely correlated to water mass category. The two larval fish assemblages were defined as coastal and estuarine. The coastal assemblage was dominated by Pacific Herring (Clupea pallasii) and was found in the shallow intense plume water mass. This area is greatly influenced by the Mackenzie River outflow. The estuarine assemblage was dominated by Arctic Cod (Boreogadus saida) and was typically found within the diffuse plume and oceanic water masses. Other larval fish families that were represented in the estuarine assemblage were Cottidae, Stichaeidae, Liparidae and Agonidae. Species richness and abundance was greater along the Toker transect in Kugmallit Bay than the Paktoa transect northwest of Garry Island in the Mackenzie Bay.

Fall Migration of Ringed Seals (<i>Phoca hispida</i>) through the Beaufort and Chukchi Seas, 2001–02

In a study examining the range, distribution, and habitat use of the ringed seal, Phoca hispida , in Canada’s Western Arctic, eight ringed seals were live-captured, instrumented with satellite-linked (SLTDR-16) transmitters, and released at Cape Parry, Northwest Territories, Canada, on 17 – 19 September 2001 and 7 – 8 September 2002. Locations accepted by the filtering process were received from seven of the eight tagged seals (5 subadults, 1 adult female, 1 pup) over periods ranging from 35 to 207 days (mean 99 d, SD 66). Mean rates of travel were 0.91 m/s (SE 0.011, n = 7) in the Canadian Beaufort Sea, 0.92 m/s (SE 0.014, n = 7) offshore of Alaska’s North Slope, and 0.79 m/s (SE 0.008, n = 5) in the Chukchi Sea. On average, the seals took 32 days (range 19 – 56 d) to migrate between Cape Parry and Point Barrow, almost always remaining within 100 km of shore and over the continental shelf or slope, and covering an average migration distance of 2138 km. Dive depths for all groupings were mainly in the 4 – 80 m range (adult female: 63 – 73%; subadults: 54 – 73%; pup: 64 – 82%), with only the adult female diving deeper than 80 m on occasion, mainly in the Canadian Beaufort Sea (15.1% of her dives). The subadults and pup dove mainly for more than 1 to 5 min (60% and 55%, respectively), while a large proportion of the adult female’s dives were longer (34% for > 1 to 5 min; 31% for > 5 to 8 min; 5.4% for > 8 min). The tracks of the westward migrating seals revealed a routing through three political jurisdictions (including oil and gas industry lease areas in all three) over a period of about two months. This pattern highlights the importance of cooperation between the United States, Canada, and Russia in managing this species.

Two Configurations of the Western Arctic Shelfbreak Current in Summer

Abstract Data from a closely spaced array of moorings situated across the Beaufort Sea shelfbreak at 152°W are used to study the Western Arctic Shelfbreak Current, with emphasis on its configuration during the summer season. Two dynamically distinct states of the current are revealed in the absence of wind, with each lasting approximately one month. The first is a surface-intensified shelfbreak jet transporting warm and buoyant Alaskan Coastal Water in late summer. This is the eastward continuation of the Alaskan Coastal Current. It is both baroclinically and barotropically unstable and hence capable of forming the surface-intensified warm-core eddies observed in the southern Beaufort Sea. The second configuration, present during early summer, is a bottom-intensified shelfbreak current advecting weakly stratified Chukchi Summer Water. It is baroclinically unstable and likely forms the middepth warm-core eddies present in the interior basin. The mesoscale instabilities extract energy from the mean flow such that the surface-intensified jet should spin down over an e-folding distance of 300 km beyond the array site, whereas the bottom-intensified configuration should decay within 150 km. This implies that Pacific Summer Water does not extend far into the Canadian Beaufort Sea as a well-defined shelfbreak current. In contrast, the Pacific Winter Water configuration of the shelfbreak jet is estimated to decay over a much greater distance of approximately 1400 km, implying that it should reach the first entrance to the Canadian Arctic Archipelago.

Vertical distribution of mesozooplankton in the coastal Canadian Beaufort Sea in summer

This paper contributes to baseline knowledge of lower trophic levels that is necessary to monitor the impact of oil and gas development on the Canadian Beaufort Sea ecosystem. As part of the Nahidik Program, the vertical distribution of mesozooplankton was studied along two transects in the coastal Canadian Beaufort Sea in the summer of 2009. Mesozooplankton was collected with 153μm conical net in two hydrologically distinct layers – the upper layer which was fresher and warmer due to the Mackenzie River runoff, and the lower layer which was colder and more saline. Two separate mesozooplankton assemblages were distinguished in the individual layers. The average zooplankton abundance in the two layers was 3120±2860 ind. m−3 and 4200±5550 ind. m−3 in the upper and lower layer, respectively. The upper layer was largely inhabited by meroplanktonic Polychaeta (752±1038 ind. m−3) and Bivalvia larvae (228±307 ind. m−3) as well as by youngest stages of Pseudocalanus spp. (245±499 ind. m−3). Conversely, the lower layer was mainly occupied by typical marine taxa such as Calanus glacialis (95±76 ind. m−3), C. hyperboreus (27±12 ind. m−3) and Triconia borealis (111±81 ind. m−3). Oithona similis, a widely distributed eurytopic cyclopoid copepod, showed no consistent pattern of vertical distribution (280 and 291 ind. m−3, in the lower and upper layer, respectively).

Introduction to the special issue on the biology of the circumpolar flaw lead (CFL) in the Amundsen Gulf of the Beaufort Sea (Arctic Ocean)

The sea-ice cover of the Arctic Ocean is decreasing in areal extent and volume more rapidly than model predictions of its response to continued warming of earth’s lower atmosphere. Reflecting this decrease is the spatial and temporal widening of the circumpolar flaw lead, a zone of open water and unconsolidated ice along the coastlines of the shallow seas that surround the deep Arctic Ocean basins. As part of the International Polar Year, the Circumpolar Flaw Lead System Study deployed the research icebreaker Amundsen from October 2007 to August 2008 in the flaw lead segment bordering Banks Island in the Canadian Beaufort Sea. With participation from Canada, the USA, Spain, Germany, China, Russia, the UK, Norway, Belgium, the Netherlands, France, and Sweden, the multi-disciplinary overwintering expedition logged 9,812 scientist-days in an effort to decipher key aspects of the ecosystem of the flaw lead. Highlights of the scientific achievements documented in this special issue on the biology of the circumpolar flaw lead system help to capture the depth, breadth, and novelty of this remarkable exploration.

Vertical distribution of sympagic meiofauna in sea ice in the Canadian Beaufort Sea

This is the first study to determine vertical distribution patterns of sympagic meiofauna, including metazoans, protozoans and eggs >20 μm, in the Amundsen Gulf (southeastern Beaufort Sea, Arctic). Full sea-ice cores were sampled from mid of March to end of May 2008 (Circumpolar Flaw Lead system study). Investigations were performed on first-year ice from three pack- and three fast-ice stations. Additionally, 5-cm bottom-ice sections were sampled at 13 pack-ice and 5 fast-ice stations. The metazoan community was composed of nematodes, rotifers, copepods, copepod nauplii, platyhelminthes and a few rare taxa such as mollusks, cnidarians and nemerteans. High numbers of eggs, between 50 and 2,188 eggs L−1, particularly of nematodes and copepods, were present in the ice. Investigations revealed also eggs of the pelagic species Calanus hyperboreus and Sagitta spp. within the ice, so that further research is needed to clarify whether more organisms than expected might use this habitat as a reproduction ground. Many different morphotypes of protozoans were observed in the samples, especially ciliates of the order Euplotida. The highest abundance was always found in the lowermost 5 cm of the ice cores, nevertheless sympagic meiofauna was not restricted to that part of the ice. Integrated meiofauna abundance ranged between 41 and 4,738 × 102 Ind. m−2 and was highest in the fast ice in early May. Differences between pack and fast ice in terms of integrated meiofauna communities and vertical distribution were not significant, while the analysis of the bottom-ice sections indicated both a temporal development and ice-type-specific differences.

Protist assemblages in winter sea ice: setting the stage for the spring ice algal bloom

This study documents, for the first time, the abundance and species composition of protist assemblages in Arctic sea ice during the dark winter period. Lack of knowledge of sea-ice assemblages during the dark period has left questions about the retention and survival of protist species that initiate the ice algal bloom. Sea-ice and surface water samples were collected between December 27, 2007 and January 31, 2008 within the Cape Bathurst flaw lead, Canadian Beaufort Sea. Samples were analyzed for protist identification and counts, chlorophyll (chl) a, and total particulate carbon and nitrogen concentrations. Sea-ice chl a concentrations (max. 0.27 μg l−1) and total protist abundances (max. 4 × 103 cells l−1) were very low, indicating minimal retention of protists in the ice during winter. The diversity of winter ice protists (134 taxa) was comparable to spring ice assemblages. Pennate diatoms dominated the winter protist assemblage numerically (averaging 77% of total protist abundances), with Nitzschia frigida being the most abundant species. Only 56 taxa were identified in surface waters, where dinoflagellates were the dominant group. Our results indicate that differences in the timing of ice formation may have a greater impact on the abundance than structure of protist assemblages present in winter sea ice and at the onset of the spring ice algal bloom.

Temporal and vertical variations of lipid biomarkers during a bottom ice diatom bloom in the Canadian Beaufort Sea: further evidence for the use of the IP25 biomarker as a proxy for spring Arctic sea ice

Variations in the concentrations of the sea ice diatom biomarker, IP25 (Ice Proxy with 25 carbon atoms), were measured in the bottom 10 cm of sea ice collected from the eastern Beaufort Sea and Amundsen Gulf from January to June 2008, as part of the International Polar Year–Circumpolar Flaw Lead system study. Temporal and vertical changes in IP25 concentrations were compared against other biomarkers and indicators of ice algal production. IP25 was not detected in sea ice samples collected from mid-winter to early spring, likely as a result of light-limiting conditions for algal growth and accumulation. From early March to mid-June, IP25 concentrations correlated well with those of fatty acids (r = 0.79; P 5% which is consistent with the hypothesis that brine channel connectivity limits the internal colonisation of sea ice by diatoms. Maximum IP25 concentrations occurred at 1–3 cm from the ice–water interface providing further evidence for a selective sea ice diatom origin for this biomarker. In contrast, vertical concentration profiles for fatty acids and sterols indicated mixed sources for these biomarkers.

Distribution and diet of larval and juvenile Arctic cod ( Boreogadus saida) in the shallow Canadian Beaufort Sea

The distribution and diet of larval and juvenile Arctic cod ( Boreogadus saida) were studied during summer 2005 in the coastal Canadian Beaufort Sea. A total of 275 individuals were captured and the highest abundance was observed at station depths of 20–30 m. This corresponds well with the location of the frontal zone where the Mackenzie River plume water and open sea water meet. Diet examinations were performed on 220 Arctic cod, which were found undamaged from sampling. We observed a gradual decrease in prey number per fish and increase in prey size as larvae grew which corresponded to a shift from Rotifera and nauplii towards larger copepodid stages. However, at all sizes, the larvae remain generalists and feed on a broad range of organisms. Environmental changes due to climate warming could have a two-fold impact on fish larvae feeding in the studied region. First, the potential for increased primary production may lead to increased zooplankton production that may impact the feeding and nutrition positively. On the other hand, greater discharge of turbid water from the Mackenzie River may reduce light penetration in the water column that may negatively influence the ability of visual predators to successively forage.

Illegal, Unreported and Unregulated Fishing in the Circumpolar Arctic

Climate change has increased both marine access to much of the circumpolar Arctic and the migration of fish stocks into northern waters. As fish stocks become depleted in southern jurisdictions, Arctic fish stocks could become more attractive for illegal, unre ported, and unregulated (IUU) fishing. This situation has many parallels with the experiences of IUU fishing in the Southern Ocean around the Antarctic. However, unlike those in Antarctica, fish and marine mammal stocks in the circumpolar Arctic are subject to indigenous and local subsistence harvesting, which has priority over commercial harvesting. Arctic fish stocks are also characterized by lower growth rates, which increase their vulnerability to the impact of IUU fishing. In the Canadian Arctic, because of slow fish growth, limited seasonal fishing opportunities, and the high cost of shipping, extensive ecosystem and economic changes would be required to make commercial fisheries feasible. Fisheries have been very close to shore throughout the Canadian Arctic. Though attempts have been made to harvest Arctic char (Salvelinus alpinus) commercially, this species has been harvested primarily for subsistence and recreation. Arctic cisco (Coregonus autumnalis) or Pacific herring ( Clupea palasii) are potential commercial fishery targets in the Canadian Beaufort Sea, but these harvests would be subject to beluga whale feeding requirements. In this essay, I explore several northern fisheries to examine various IUU fishing scenarios for the Arctic: com mercial fishing in the Canadian and U.S. Beaufort Sea, the offshore halibut fishery adjacent to the Nunavut Territory of Canada, and the Irminger Sea redfish fishery in the Rey kjanes Ridge of the North Atlantic. I then consider current regulatory regimes for IUU fisheries in Antarctica and Europe, which provide potential models for Arctic fisheries.

Parasitic infection of the hyperiid amphipod Themisto libellula in the Canadian Beaufort Sea (Arctic Ocean), with a description of Ganymedes themistos sp. n. (Apicomplexa, Eugregarinorida)

Two parasites were found in the hyperiid amphipod Themisto libellula sampled with nets and collected by sediment traps over the annual cycle in the Canadian Beaufort Sea. The trophozoites of the newly described gregarine Ganymedes themistos sp. n. infected the digestive tract of 60.2% of the T. libellula analyzed from net collections. An unidentified ciliate infected the body cavity of 4.4% of amphipods. G. themistos possessed the ball-like structure at the anterior end and the cup-like invagination at the posterior end that are typical of the genus Ganymedes. The frequency and severity (number of parasites host−1) of infection by G. themistos increased with the length of T. libellula in the range 8–20 mm, and leveled off at ca. 94% and 186 trophozoites host−1 on average in the range 20–34 mm. Spatially, gregarine infection was less severe (63 ± 100 G. themistos host−1) on the Slope than on the Mackenzie Shelf (110 ± 160) and in the Amundsen Gulf (132 ± 157). No evidence of an impact of trophozoite infection on the feeding and sexual maturation of the host was found. For a given size of T. libellula, infection by both parasites was more frequent in the traps than in the nets (G. themistos: 91.0% vs. 82.7%; ciliates: 16.3% vs. 6%). The 2.7 times higher infection frequency in the traps suggested that the ciliate parasite may kill its host.

Contribution of under‐ice primary production to an ice‐edge upwelling phytoplankton bloom in the Canadian Beaufort Sea

The Canadian Beaufort Sea has been categorized as an oligotrophic system with the potential for enhanced production due to a nutrient‐rich intermediate layer of Pacific‐origin waters. Using under‐ice hydrographic data collected near the ice‐edge of a shallow Arctic bay, we documented an ice‐edge upwelling event that brought nutrient‐rich waters to the surface during June 2008. The event resulted in a 3‐week long phytoplankton bloom that produced an estimated 31 g C m−2 of new production. This value was approximately twice that of previous estimates for annual production in the region, demonstrating the importance of ice‐edge upwelling to the local marine ecosystem. Under‐ice primary production estimates of up to 0.31 g C m−2 d−1 showed that this production was not negligible, contributing up to 22% of the daily averaged production of the ice‐edge bloom. It is suggested that under‐ice blooms are a widespread yet under‐documented phenomenon in polar regions, which could increase in importance with the Arctic's thinning ice cover and subsequent increase in transmitted irradiance to the under‐ice environment.

Distribution, diversity and biomass of summer zooplankton from the coastal Canadian Beaufort Sea

Composition, abundance, biomass and distribution of zooplankton in the coastal Canadian Beaufort Sea were studied in the summer of 2005 and 2006. Data were collected from two cross-shelf transects (11 stations in each). Sampling was conducted with vertical hauls using a conical net of 153-μm mesh size. Our results revealed that there are three ecological zones, Intense Plume, Diffuse Plume and oceanic, which are primarily shaped by the highly variable Mackenzie River plume. The Intense Plume Grouping was located at stations influenced greatly by the Mackenzie River, where Podon leuckarti, Pseudocalanus spp., Copepoda nauplii and Limnocalanus macrurus were most abundant. The Diffuse Plume Grouping, that was located in the transitional zone between the river plume and the ocean, had the highest diversity. This grouping was characterised by high abundance of Copepoda nauplii, Polychaeta larvae, Pseudocalanus and L. macrurus. The Oceanic Grouping, located farthest from shore beyond the 85-m depth contour, was mainly inhabited by marine taxa—Calanusglacialis, C. hyperboreus, Triconia (Oncea) borealis and Microcalanus spp.—and had the greatest overall zooplankton abundance and biomass of all groupings.

Water and Ice-Related Phenomena in the Coastal Region of the Beaufort Sea: Some Parallels between Native Experience and Western Science

Information gained through Native experience is combined here with scientific measurements to describe aspects of the wintertime oceanography of the Eskimo Lakes and Mackenzie River delta regions of the Canadian Beaufort Sea. The experiences of Jimmy Jacobson, a Tuktoyaktuk elder who lived in this region for over 70 years, were used as the basis for scientific planning and measurement. We focus on phenomena of special relevance to winter travel and fishing in four specific examples of Native insight guiding scientific inquiry. First, we examine local knowledge of ice characteristics and fish abundance in terms of tidal dispersion and its effect on mixing patterns during winter. Second, we relate the maintenance of a small ice-free area, used by caribou as a salt lick, to the vertical heat flux associated with flow through narrow channels. Third, we look at potentially dangerous episodes of overflooding of snow and ice in the nearshore zone in midwinter, caused by strong westerly winds, through the analysis of oxygen isotope distributions in ice cores. Fourth, we discuss the important influence of wind direction on ice conditions, lead formation, and brine production in semi-enclosed coastal bays. Finally, we note certain circulation features of ecological significance relevant to concerns about development and the transport of pollutants. We conclude that by not requiring agreement between indigenous knowledge and Western science, or ranking one above the other, we can realize the values of each approach. Specifically, indigenous knowledge can provide direction to scientific inquiry, while Western science can be used to measure, model, and predict where development or change might have the most serious impact.

Influence of environmental factors on the development of bottom ice protist communities during the winter–spring transition

Seasonal changes in the abundance and taxonomic composition of bottom ice protists (i.e. diatoms, flagellates, and dinoflagellates) were assessed in the first-year landfast ice of Franklin Bay (Canadian Beaufort Sea) from 24 February to 20 June 2004. On each sampling day, bottom sea- ice protists were collected at sites of high (>10 cm) and low (<10 cm) snow cover. The net observed growth rates of diatoms and nanoflagellates were significantly higher during the pre-bloom (24 Feb- ruary to 25 March) than the bloom (ca. 3 April to 23 May) period under low snow cover but were not different under high snow cover. In contrast, dinoflagellates showed relatively constant net observed growth rate before and during the bloom period under both snow covers. These results indicate that the 3 protist groups responded differently to changes in the light regime during the growth period. The decline of the protist community after the bloom period was related to a combination of factors including nitrogen deficiency and melting processes. Prior to the bloom, flagellated cells, likely het- erotrophic, dominated numerically under high snow cover, whereas autotrophic protists, especially solitary diatoms, prevailed under low snow cover. During the bloom period, colonial diatoms such as Nitzschia frigida, N. promare, Navicula sp. 6, N. pelagica, and Fragilariopsis cylindrus dominated the bottom ice community irrespective of snow depth, although abundances were higher under low snow cover. The arborescent colonial N. frigida, a key species of landfast ice across circumarctic regions, was the most abundant bottom ice algal diatom throughout the entire season. During the post-bloom period, colonial and solitary diatoms declined more rapidly than nanoflagellates, suggesting that nanoflagellates, presumably heterotrophic, were better adapted to melting sea-ice conditions. Our results demonstrated that the availability of nitrate in the surface water limits the accumulation of algal biomass in the bottom horizon of Arctic landfast ice during the vernal growth season.

Primary productivity and export fluxes on the Canadian shelf of the Beaufort Sea: A modelling study

We present a coupled sea ice–ocean-biological (including ice algae) model in the Arctic Ocean. The 1D model was developed and implemented on the Canadian Beaufort Sea shelf to examine the importance of different physical processes in controlling the timing and magnitude of primary production and biogenic particle export over an annual cycle (1987). Our results show that the snow and sea ice cover melt and/or break-up controls the timing of the phytoplankton bloom but primary producers (ice algae and phytoplankton) on the outer shelf are essentially nutrient limited. The total annual primary production (22.7 to 27.7 g-C m − 2 ) is thus controlled by nutrient “pre-conditioning” in the previous fall and winter and by the depth of wind mixing that is controlled in part by the supply of fresh water at the end of spring (ice melt or runoff). The spring bloom represents about 40% of the total annual primary production and occurs in a period of the year when sampling is often lacking. Time interpolation of observed values to obtain total annual primary production, as done in many studies, was shown to lead to an underestimation of the actual production. Our simulated ratios of export to primary production vary between 0.42 and 0.44.

Protist entrapment in newly formed sea ice in the Coastal Arctic Ocean

Protist abundance and taxonomic composition were determined in four development stages of newly formed sea ice (new ice, nilas, young ice and thin first-year ice) and in the underlying surface waters of the Canadian Beaufort Sea from 30 September to 19 November 2003. Pico- and nanoalgae were counted by flow cytometry whereas photosynthetic and heterotrophic protists ≥ 4 µm were identified and counted by inverted microscopy. Protists were always present in sea ice and surface water samples throughout the study period. The most abundant protists in sea ice and surface waters were cells < 4 µm. They were less abundant in sea ice (418–3051 × 10 3 cells L − 1 ) than in surface waters (1393–5373 × 10 3 cells L − 1 ). In contrast, larger protists (≥ 4 µm) were more abundant in sea ice (59–821 × 10 3 cells L − 1 ) than in surface waters (22–256 × 10 3 cells L − 1 ). These results suggest a selective incorporation of larger cells into sea ice. The ≥ 4 µm protist assemblage was composed of a total number of 73 taxa, including 12 centric diatom species, 7 pennate diatoms, 11 dinoflagellates and 16 flagellates. The taxonomic composition in the early stage of ice formation (i.e., new ice) was very similar to that observed in surface waters and was composed of a mixed population of nanoflagellates (Prasinophyceae and Prymnesiophyceae), diatoms (mainly Chaetoceros species) and dinoflagellates. In older stages of sea ice (i.e., young ice and thin first-year ice), the taxonomic composition became markedly different from that of the surface waters. These older ice samples contained relatively fewer Prasinophyceae and more unidentified nanoflagellates than the younger ice. Diatom resting spores and dinoflagellate cysts were generally more abundant in sea ice than in surface waters. However, further studies are needed to determine the importance of this winter survival strategy in Arctic sea ice. This study clearly shows the selective incorporation of large cells (≥ 4 µm) in newly formed sea ice and the change in the taxonomic composition of protists between sea ice and surface waters as the fall season progresses.

Traversing grounded rubble fields by foot — Implications for evacuation

A field program was carried out in the Canadian Beaufort Sea to obtain quantitative details of the time required to traverse a variety of ice rubble conditions, typical of those that may surround an offshore structure in landfast ice. The results indicate that the time required to cross rubble fields increases rapidly with increasing rubble severity, determined by factors such as rubble height, ice block size and snow depth. The quantitative findings have implications for emergency evacuation from an offshore structure when an on-ice Evacuation Shelter is identified in the EER strategy for the structure. The results and analysis show that preparing and maintaining a suitable egress path across ice rubble is essential for safe evacuation from an offshore structure surrounded by landfast ice and a grounded rubble field. The implications for an offshore structure in a variety of ice conditions are presented.