Christine Michel

Carbon budget of sea‐ice algae in spring: Evidence of a significant transfer to zooplankton grazers

The fate of ice-bottom algae, before and after release from the first-year sea ice into the water column, was assessed during the period of ice-algal growth and decline in Resolute Passage (Canadian Arctic). During spring 1992 (from April to June), algae in the bottom ice layer and those suspended and sinking in the upper water column (top 15 m) were sampled approximately every 4 days. Ice-bottom chlorophyll a reached a maximum concentration of 160 mg m−2 in mid-May, after which it decreased to lower values. In the water column, chlorophyll a concentrations were low until the period of ice-algal decline (∼0.1 mg m−3), with most biomass in the 65% of total export) and that ice-algae were ingested by under-ice grazers after release from the ice. These results stress the importance of ice algae for pelagic consumers during the early stages of ice melt and show that the transfer of ice algae to higher trophic levels extends beyond the period of maximum algal production in the ice bottom.

Ecological Implications of Changes in the Arctic Cryosphere

Snow, water, ice, and permafrost are showing evidence of substantial change in the Arctic, with large variations among different geographical areas. As a result of these changes, some habitats and their associated ecosystems are expanding, while others are undergoing rapid contraction. The warming of the Arctic cryosphere is limiting the range for cold-adapted biota, and less specialized taxa including invasive species from the south are likely to become increasingly common. Extreme climate events such as winter thawing are likely to become more frequent, and may accelerate shifts in community structure and processes. Many Arctic ecosystems are interdependent, and changes in the cryosphere are altering physical, biogeochemical, and biological linkages, as well as causing positive feedback effects on atmospheric warming. All of these climate-related effects are compounded by rapid socio-economic development in the North, creating additional challenges for northern communities and indigenous lifestyles that depend on Arctic ecosystem services.

Broad-scale predictability of carbohydrates and exopolymers in Antarctic and Arctic sea ice

Significance Many marine microalgae and bacteria secrete polysaccharide gels (exopolymers) in response to environmental stresses, such as the freezing temperatures and salt concentrations that organisms experience when in sea ice. This study of sea ice cores from both the Antarctic and Arctic identified compelling relationships between ice thickness and salinity, algal biomass, and the concentration of polysaccharides in the ice. Knowing the first three parameters, we were able to predict the polysaccharide concentrations of the ice. This predictability is the first step in estimating the importance of such secretions to the organic carbon content of the millions of square kilometers of the ice-covered Arctic and Southern Oceans. Sea ice can contain high concentrations of dissolved organic carbon (DOC), much of which is carbohydrate-rich extracellular polymeric substances (EPS) produced by microalgae and bacteria inhabiting the ice. Here we report the concentrations of dissolved carbohydrates (dCHO) and dissolved EPS (dEPS) in relation to algal standing stock [estimated by chlorophyll (Chl) a concentrations] in sea ice from six locations in the Southern and Arctic Oceans. Concentrations varied substantially within and between sampling sites, reflecting local ice conditions and biological content. However, combining all data revealed robust statistical relationships between dCHO concentrations and the concentrations of different dEPS fractions, Chl a, and DOC. These relationships were true for whole ice cores, bottom ice (biomass rich) sections, and colder surface ice. The distribution of dEPS was strongly correlated to algal biomass, with the highest concentrations of both dEPS and non-EPS carbohydrates in the bottom horizons of the ice. Complex EPS was more prevalent in colder surface sea ice horizons. Predictive models (validated against independent data) were derived to enable the estimation of dCHO concentrations from data on ice thickness, salinity, and vertical position in core. When Chl a data were included a higher level of prediction was obtained. The consistent patterns reflected in these relationships provide a strong basis for including estimates of regional and seasonal carbohydrate and dEPS carbon budgets in coupled physical-biogeochemical models, across different types of sea ice from both polar regions.

PARTICULATE DIMETHYLSULFOXIDE IN ARCTIC SEA-ICE ALGAL COMMUNITIES: THE CRYOPROTECTANT HYPOTHESIS REVISITED

The particulate‐phase concentrations of dimethyl sulfoxide (DMSOp) and dimethylsulfoniopropionate (DMSPp) in sea‐ice algal communities from the North Water, northern Baffin Bay, were examined from April to June 1998. The concentrations of these compounds were measured in the bottom 2 cm of the ice at 36 locations throughout this region and are compared with results from water‐column samples collected for a complementary study. In general, levels of DMSPp (8.66–987 nmol·L−1, average 126 nmol·L−1) in sea‐ice algal communities were slightly less than those found in bottom sea‐ice algal communities from other polar locations but greater than those found in phytoplankton in other polar environments or at more temperate latitudes. Furthermore, DMSPp  :chl a ratios (0.02–14.8 nmol·μg−1, average 1.91 nmol·μg−1) in the sea‐ice algal community were slightly less than those found in other polar environments. DMSOp was measured for the first time in sea‐ice algal communities. DMSOp concentrations varied from 1.35 to 102 nmol·L−1 (average 13.7 nmol·L−1). DMSOp:chl a ratios varied from 0.01 to 4.5 nmol·μg−1 (average 0.22 nmol·μg−1) and were significantly lower than the DMSPp:chl a ratios observed in this study. It has been hypothesized that DMSO can act as a cryoprotector in phytoplankton cells. However, the low concentrations of DMSO observed in the ice algae during this study indicate that intracellular concentrations of DMSO are unlikely to have a significant influence on the freezing point depression of intracellular fluids.

Mesoscale distribution and functional diversity of picoeukaryotes in the first-year sea ice of the Canadian Arctic

Sea ice, a characteristic feature of polar waters, is home to diverse microbial communities. Sea-ice picoeukaryotes (unicellular eukaryotes with cell size <3 μm) have received little attention compared with diatoms that dominate the spring bloom in Arctic first-year sea ice. Here, we investigated the abundance of all picoeukaryotes, and of 11 groups (chlorophytes, cryptophytes, bolidophytes, haptophytes, Pavlovaphyceae, Phaeocystis spp., pedinellales, stramenopiles groups MAST-1, MAST-2 and MAST-6 and Syndiniales Group II) at 13 first-year sea-ice stations localized in Barrow Strait and in the vicinity of Cornwallis Island, Canadian Arctic Archipelago. We applied Catalyzed Reporter Deposition–Fluorescence In Situ Hybridization to identify selected groups at a single cell level. Pavlovaphyceae and stramenopiles from groups MAST-2 and MAST-6 were for the first time reported from sea ice. Total numbers of picoeukaryotes were significantly higher in the vicinity of Cornwallis Island than in Barrow Strait. Similar trend was observed for all the groups except for haptophytes. Chlorophytes and cryptophytes were the dominant plastidic, and MAST-2 most numerous aplastidic of all the groups investigated. Numbers of total picoeukaryotes, chlorophytes and MAST-2 stramenopiles were positively correlated with the thickness of snow cover. All studied algal and MAST groups fed on bacteria. Presence of picoeukaryotes from various trophic groups (mixotrophs, phagotrophic and parasitic heterotrophs) indicates the diverse ecological roles picoeukaryotes have in sea ice. Yet, >50% of total sea-ice picoeukaryote cells remained unidentified, highlighting the need for further study of functional and phylogenetic sea-ice diversity, to elucidate the risks posed by ongoing Arctic changes.

Can ICT improve the quality of life of elderly adults living in residential home care units? From actual impacts to hidden artefacts

In a context of progressive loss of intellectual and interactional capacities for the elderly, the goal of this article is to examine to what extent a new technological environment can improve their quality of life. In this study, we examine the very elderly (mean age 87) who have experienced a loss in functional capacities and are dependent on managed care such as residential home care units. Using qualitative methods amongst a group of 17 residents (semi-structured interviews and longitudinal observations), we examine whether new social practices form and whether subjects feel more socially recognised. Our study shows that information and communications technologies may, to some extent, play an instrumental role in interconnectedness and social stimulation, and can also be seen as a ‘boundary object’ that communicates between the residents’ world (who are rather isolated) and their families’ world (including grandchildren).

Strong similarity measures for ordered sets of documents in information retrieval

A general method is presented to construct ordered similarity measures (OS-measures), i.e., similarity measures for ordered sets of documents (as, e.g., being the result of an IR-process), based on classical, well-known similarity measures for ordinary sets (measures such as Jaccard, Dice, Cosine or overlap measures). To this extent, we first present a review of these measures and their relationships.The method given here to construct OS-measures extends the one given by Michel in a previous paper so that it becomes applicable on any pair of ordered sets. Concrete expressions of this method, applied to the classical similarity measures, are given.Some of these measures are then tested in the IR-system Profil-Doc. The engine SPIRIT© extracts ranked document sets in three different contexts, each for 550 requests. The practical usability of the OS-measures is then discussed based on these experiments.

Construction of weak and strong similarity measures for ordered sets of documents using fuzzy set techniques

Ordered sets of documents are encountered more and more in information distribution systems, such as information retrieval systems. Classical similarity measures for ordinary sets of documents hence need to be extended to these ordered sets. This is done in this paper using fuzzy set techniques. First a general similarity measure is developed which contains the classical strong similarity measures such as Jaccard, Dice, Cosine and which contains the classical weak similarity measures such as Recall and Precision.Then these measures are extended to comparing fuzzy sets of documents. Measuring the similarity for ordered sets of documents is a special case of this, where, the higher the rank of a document, the lower its weight is in the fuzzy set. Concrete forms of these similarity measures are presented. All these measures are new and the ones for the weak similarity measures are the first of this kind (other strong similarity measures have been given in a previous paper by Egghe and Michel).Some of these measures are then tested in the IR-system Profil-Doc. The engine SPIRIT© extracts ranked documents sets in three different contexts, each for 600 request. The practical useability of the OS-measures is then discussed based on these experiments.

Impact of freshwater on a subarctic coastal ecosystem under seasonal sea ice (southeastern Hudson Bay, Canada) II. Production and export of microalgae *

Abstract In the under-ice plume of the Grande riviere de la Baleine (Great Whale River) and offshore waters of southeastern Hudson Bay (Canada), several environmental factors influence the distribution, growth, taxonomic composition and sedimentation of algae found in the sea ice, at the ice-water interface and in the underlying water column. During the spring and early summer, these factors include: salinity of bottom ice, water turbidity, nutrients and vertical stability of the water column. In the present study, relationships between three predictor variables (water salinity, river runoff and seasonal air temperature index) and biological variables are used to assess the impact of freshwater on production and export of microalgae. Relationships are derived from existing data, which were collected between 1978 and 1990. Correlations with water salinity are positive for some variables (salinity of bottom ice, phosphate, ammonium, Σ:Si, and algae in bottom ice and at the interface) and negative for others (coefficient of light attenuation, silicate, ΣN:P, ΣSi:P and water column phytoplankton). Using together salinity and the seasonal index leads to improved proportions of explained variance for nitrate, ammonium, ΣN:P and phytoplankton. The amount of sedimenting algae is positively correlated with runoff, and chemical composition (C/N) of the sedimenting material is negatively correlated with salinity. The empirical relationships are applied to the results of a model of river plume dynamics, for three runoff conditions. Seasonally averaged total Chl. a concentrations, derived from the model, are higher for maximum river runoff than for mean or minimum conditions. This is because, in the studied environment, areal concentrations of phytoplankton are higher than those of ice algae, especially under condition of maximum runoff.

Hydrocarbon biodegradation by Arctic sea-ice and sub-ice microbial communities during microcosm experiments, Northwest Passage (Nunavut, Canada)

The increasing accessibility to navigation and offshore oil exploration brings risks of hydrocarbon releases in Arctic waters. Bioremediation of hydrocarbons is a promising mitigation strategy but challenges remain, particularly due to low microbial metabolic rates in cold, ice-covered seas. Hydrocarbon degradation potential of ice-associated microbes collected from the Northwest Passage was investigated. Microcosm incubations were run for 15 days at -1.7°C with and without oil to determine the effects of hydrocarbon exposure on microbial abundance, diversity and activity, and to estimate component-specific hydrocarbon loss. Diversity was assessed with automated ribosomal intergenic spacer analysis and Ion Torrent 16S rRNA gene sequencing. Bacterial activity was measured by (3)H-leucine uptake rates. After incubation, sub-ice and sea-ice communities degraded 94% and 48% of the initial hydrocarbons, respectively. Hydrocarbon exposure changed the composition of sea-ice and sub-ice communities; in sea-ice microcosms, Bacteroidetes (mainly Polaribacter) dominated whereas in sub-ice microcosms, the contribution of Epsilonproteobacteria increased, and that of Alphaproteobacteria and Bacteroidetes decreased. Sequencing data revealed a decline in diversity and increases in Colwellia and Moritella in oil-treated microcosms. Low concentration of dissolved organic matter (DOM) in sub-ice seawater may explain higher hydrocarbon degradation when compared to sea ice, where DOM was abundant and composed of labile exopolysaccharides.