Ice diatom floras,Arthur Harbor,Antarctica

Summary Sea-ice microflora was collected from December 1971 to November 1972 from a variety of types of sea ice in the vicinity of Arthur Harbor, Anvers Island, Antarctic Peninsula. Sixty-seven identifiable species of diatoms, one silicoflagellate and several archaeomonads were recoverd from the ice. Of these, only 24 diatoms and the archaeomonads were considered to be truly cryophilic based on their occurrence and abundance. Qmode factor analysis revealed that four factors (species occurrences) account for 89% of the data. In a general way, these four factors are related to ice type-shore ice protected from turbulence, grounded pack ice, slush ice and sea ice. Shannon-Wiener species diversity functions range from 0.000 (monospecific) to 3.0515 (dominance divided among 9 species). Diversity also appeared to be related to ice type-protected shore ice was low, sea ice was intermediate, and grounded pack, exposed shore ice and slush were higherst. Short-term varibility in physical/biotic environment may control species diversity. Sea-ice assemblages may be useful in paleoclimatic interpretations of past ice distributions.     

The biota of Antarctic pack ice in the Weddell sea and Antarctic Peninsula regions

Summary Pack ice surrounding Antarctica supports rich and varied populations of microbial organisms. As part of the Antarctic Marine Ecosystem Research in the Ice Edge Zone (AMERIEZ) studies, we have examined this community during the late spring, autumn, and winter. Although organisms are found throughout the ice, the richest concentrations often occur in the surface layer. The ice flora consists of diatoms and flagellates. Chrysophyte cysts (archaeomonads) of unknown affinity and dinoflagellate cysts are abundant and may serve as overwintering stages in ice. The ice fauna includes a variety of heterotrophic flagellates, ciliates, and micrometazoa. The abundance of heterotrophs indicates an active food web within the ice community. Ice may serve as a temporary habitat or refuge for many of the microbial forms and some of these appear to provide an inoculum for planktonic populations when ice melts. Larger consumers, such as copepods and the Antarctic krill, Euphausia superba are often found on the underside of ice floes and within weathered floes. The importance of the ice biota as a food resource for these pelagic consumers is unknown.     

Notes on the biology of sea ice in the Arctic and Antarctic

The sea ice which covers large areas of the polar regions plays a major role in the marine ecosystem of both the Arctic and Southern Oceans. Not only do warmblooded animals depend on sea ice as a platform, but the sympagic organisms living internally within the sea ice or at the interfaces ice/snow and ice/water provide a substantial part of the total primary production of the ice covered regions. In addition sea ice organisms are an important food source for a variety of pelagic animals and may initiate phytoplankton spring blooms after ice melt by seeding effects.Sea ice organisms often are enriched by some orders of magnitude if the same volume of melted ice is compared to that of the underlying water column. Three hypotheses try to explain this discrepancy and are discussed. Investigations on the nutrient chemistry within the sea ice system and in-situ observations still are rare. Intense growth of sympagic organisms can result in nutrient deficiencies, at least in selected habitats. Advances in endoscopie methods may lead to a better understanding of the life within the sea ice.Paper presented at the Symposium on Polar regions: the challenge for biological and ecological research organised by the Swiss Committee for Polar Research, Basel on 2 October 1992     

Dynamics of ice algae and phytoplankton in Frobisher Bay

Summary Vertical and seasonal variations of ice algae and phytoplankton were studied in relation to their physico-chemical environments in Frobisher Bay from 1979 to 1986. The biomass, estimated by both chlorophyll a concentrations and cell counts, was greater in the ice algae than in the phytoplankton in the underlying sea-water during winter and spring. Algal distribution in the sea ice varied vertically and seasonally, while in the underlying water column the phytoplankton distribution was much less variable. The ice algal bloom occurred at the bottom of the ice, particularly in the lower 5 cm during late spring, while the phytoplankton bloom took place at depths between 1 and 10 m during early summer after the ice bloom was over. The community structure of the ice algae changed from pennate to centric diatoms as the ice melted. The centrics dominated through the fall, and then decreased as the pennates increased in dominance when the ice formed again in winter. Species diversity and number were greater in the sea ice than in the seawater, but they were similar vertically within each habitat. The evenness of the species distribution did not vary with ice thickness or water depth. Species composition, abundance and dominance of ice algae and phytoplankton continually change both vertically and seasonally. The differential abilities of the species to attain maximal growth rates under various environmental conditions may result in species succession. Evidence is given for the major role of environmental factors regulating the dynamics of ice algae and phytoplankton.     

Abundant dissolved genetic material in Arctic sea ice Part I: Extracellular DNA

The porous medium of sea ice, a surface-rich environment characterized by low temperature and high salinity, has been proposed as a favorable site for horizontal gene transfer, but few measurements are available to assess the possibility of this mode of evolution in ice. Here, we report the first measurements of dissolved DNA in sea ice, measured by fluorescent dye staining of centrifugal-filter-concentrated samples of melted ice. Newly formed landfast and pack ice on the Canadian Arctic Shelf (ca. 71°N, 125°W) contained higher concentrations (scaled to volume of brine) of the major components of dissolved DNA—extracellular DNA and viruses—than the underlying seawater. Dissolved DNA was dominated by extracellular DNA in surface seawater (up to 95%), with viruses making up relatively larger fractions at depths below 100 m (up to 27%) and in thick sea ice (66–78 cm; up to 100%). Extracellular DNA was heterogeneously distributed, with concentrations up to 135 μg DNA L⁻¹ brine detected in landfast sea ice, higher than previously reported from any marine environment. Additionally, extracellular DNA was significantly highly enriched at the base of ice of medium thickness (33–37 cm), suggestive of in situ production. Relative to underlying seawater, higher concentrations of extracellular DNA, viruses, and bacteria, and the availability of numerous surfaces for attachment within the ice matrix suggest that sea ice may be a hotspot for HGT in the marine environment.     

Gas Vacuolate Bacteria from the Sea Ice of Antarctica

Gas-vacuolate heterotrophic bacteria from marine habitats are reported here for the first time. They have been isolated from Antarctic sea ice microbial communities and the underlying water column. The predominant gas-vacuolate bacterium from the sea ice is filamentous and pigmented, whereas those of the water column are unicellular and nonpigmented. The highest concentrations of bacteria in sea ice were found in conjunction with the highest algal (chlorophyll a) concentrations.     

Contrasting population changes in sympatric penguin species in association with climate warming

Climate warming and associated sea ice reductions in Antarctica have modified habitat conditions for some species. These include the congeneric Adélie, chinstrap and gentoo penguins, which now demonstrate remarkable population responses to regional warming. However, inconsistencies in the direction of population changes between species at different study sites complicate the understanding of causal processes. Here, we show that at the South Orkney Islands where the three species breed sympatrically, the less ice‐adapted gentoo penguins increased significantly in numbers over the last 26 years, whereas chinstrap and Adélie penguins both declined. These trends occurred in parallel with regional long‐term warming and significant reduction in sea ice extent. Periodical warm events, with teleconnections to the tropical Pacific, caused cycles in sea ice leading to reduced prey biomass, and simultaneous interannual population decreases in the three penguin species. With the loss of sea ice, Adélie penguins were less buffered against the environment, their numbers fluctuated greatly and their population response was strong and linear. Chinstrap penguins, considered to be better adapted to ice‐free conditions, were affected by discrete events of locally increased ice cover, but showed less variable, nonlinear responses to sea ice loss. Gentoo penguins were temporarily affected by negative anomalies in regional sea ice, but persistent sea ice reductions were likely to increase their available niche, which is likely to be substantially segregated from that of their more abundant congeners. Thus, the regional consequences of global climate perturbations on the sea ice phenology affect the marine ecosystem, with repercussions for penguin food supply and competition for resources. Ultimately, variability in penguin populations with warming reflects the local balance between penguin adaptation to ice conditions and trophic‐mediated changes cascading from global climate forcing.     

Infiltration phyto- and protozooplankton assemblages in the annual sea ice of Disko Island, West Greenland, spring 1996

During the spring of 1996 we occupied a station on annual sea ice located several kilometers from Disko Island, West Greenland in water depths greater than 200 m. The goal of this 3-week field season was to characterize sea-ice communities and the underlying water column prior to, and during, ice break-up. A heavier than usual snow load depressed the sea ice below sea level and the snow-ice interface became flooded. Some of this flooded region subsequently refroze and the whole process repeated itself when additional snow accumulated. The infiltration phytoplankton and protozooplankton assemblages that developed in this region were abundant and diverse. Algal biomass in the infiltration layer was approximately an order of magnitude greater than in the underlying water column but an order of magnitude less than in the well-developed bottom ice community. The infiltration autotrophic assemblage resembled the bottom-ice assemblage while the protozooplankton assemblage was more similar to the water column assemblage. Received: 13 February 1998 / Accepted: 30 May 1998     

Variable sea‐ice conditions influence trophic dynamics in an Arctic community of marine top predators

Sea‐ice coverage is a key abiotic driver of annual environmental conditions in Arctic marine ecosystems and could be a major factor affecting seabird trophic dynamics. Using stable isotope ratios of carbon (δ¹³C) and nitrogen (δ¹⁵N) in eggs of thick‐billed murres (Uria lomvia), northern fulmars (Fulmarus glacialis), glaucous gulls (Larus hyperboreus), and black‐legged kittiwakes (Rissa tridactyla), we investigated the trophic ecology of prebreeding seabirds nesting at Prince Leopold Island, Nunavut, and its relationship with sea‐ice conditions. The seabird community of Prince Leopold Island had a broader isotopic niche during lower sea‐ice conditions, thus having a more divergent diet, while the opposite was observed during years with more extensive sea‐ice conditions. Species' trophic position was influenced by sea ice; in years of lower sea‐ice concentration, gulls and kittiwakes foraged at higher trophic levels while the opposite was observed for murres and fulmars. For murres and fulmars over a longer time series, there was no evidence of the effect of sea‐ice concentration on species' isotopic niche. Results suggest a high degree of adaptation in populations of high Arctic species that cope with harsh and unpredictable conditions. Such different responses of the community isotopic niche also show that the effect of variable sea‐ice conditions, despite being subtle at the species level, might have larger implications when considering the trophic ecology of the larger seabird community. Species‐specific responses in foraging patterns, in particular trophic position in relation to sea ice, are critical to understanding effects of ecosystem change predicted for a changing climate.     

Abundant dissolved genetic material in Arctic sea ice Part II: Viral dynamics during autumn freeze-up

Viruses play a significant role in nutrient cycling within the world’s oceans and are important agents of horizontal gene transfer, but little is know about their entrainment into sea ice or their temporal dynamics once entrained. Nilas, grease ice, pancake ice, first-year sea ice floes up to 78 cm in thickness, and under-ice seawater were sampled widely across Amundsen Gulf (ca. 71^° N, 125^° W71^\circ \hbox{N}, 125^\circ \hbox{W}) for concentrations of viruses and bacteria. Here, we report exceptionally high virus-to-bacteria ratios in seawater (45–340) and sea ice (93–2,820) during the autumn freeze-up. Virus concentrations ranged from 4.8 to 27 × 10⁶  ml⁻¹ in seawater and, scaled to brine volume, 5.5 to 170 × 10⁷ ml⁻¹ in sea ice. Large enrichment indices indicated processes of active entrainment from source seawater, or viral production within the ice, which was observed in 2 of 3 bottle incubations of sea ice brine at a temperature (-7^°C-7^\circ\hbox{C}) and salinity ( 110 \permille110 \permille) approximating that in situ. Median predicted virus-to-bacteria contact rates (relative to underlying seawater) were greatest in the top of thick sea ice (66–78 cm: 130×) and lowest in the bottom of medium-thickness ice (33–37 cm: 23×). The great abundance of viruses and more frequent interactions between bacteria and viruses predicted in sea ice relative to underlying seawater suggest that sea ice may be a hot spot for virally mediated horizontal gene transfer in the polar marine environment.     

Dynamics of antarctic penguin populations in relation to inter-annual variability in sea ice distribution

To investigate the role of sea ice cover on penguin populations we used principal component analysis to compare population variables of Adélie (Pygoscelis adeliae) and chinstrap (Pygoscelis antarctica) penguins breeding on Signy Island, South Orkney Islands with local (from direct observations) and regional (from remote sensing data) sea ice variables. Throughout the study period, the Adélie penguin population size remained stable, whereas that of chinstrap penguins decreased slightly. For neither species were there significant relationships between population size and breeding success, except for an apparent inverse density-dependent relationship between the number of Adélie breeding pairs and the number of eggs hatching. For both species, no general relationship was found between either population size or breeding success and the local sea ice conditions. However, the regional sea ice extent at a particular time prior to the start of the breeding season was related to the number of birds that arrived to breed. For both species, this period occurred before the sea ice reached its maximum extent and was slightly earlier for Adélie than for chinstrap penguins. These results suggest that sea ice conditions outside the breeding season may play an important role in penguin population processes.     

Diversity and association of psychrophilic bacteria in Antarctic sea ice.

The bacterial populations associated with sea ice sampled from Antarctic coastal areas were investigated by use of a phenotypic approach and a phylogenetic approach based on genes encoding 16S rRNA (16S rDNA). The diversity of bacteria associated with sea ice was also compared with the bacterial diversity of seawater underlying sea ice. Psychrophilic (optimal growth temperature, < or = 15 degrees C; no growth occurring at 20 degrees C) bacterial diversity was found to be significantly enriched in sea ice samples possessing platelet and bottom ice diatom assemblages, with 2 to 9 distinct (average, 5.6 +/- 1.8) psychrophilic taxa isolated per sample. Substantially fewer psychrophilic isolates were recovered from ice cores with a low or negligible population of ice diatoms or from under-ice seawater samples (less than one distinct taxon isolated per sample). In addition, psychrophilic taxa that were isolated from under-ice seawater samples were in general phylogenetically distinct from psychrophilic taxa isolated from sea ice cores. The taxonomic distributions of psychrotrophic bacterial isolates (optimal growth temperature, > 20 degrees C; growth can occur at approximately 4 degrees C) isolated from sea ice cores and under-ice seawater were quite similar. Overall, bacterial isolates from Antarctic sea ice were found to belong to four phylogenetic groups, the alpha and gamma subdivisions of the Proteobacteria, the gram-positive branch, and the Flexibacter-Bacteroides-Cytophaga phylum. Most of the sea ice strains examined appeared to be novel taxa based on phylogenetic comparisons, with 45% of the strains being psychrophilic. 16S rDNA sequence analysis revealed that psychrophilic strains belonged to the genera Colwellia, Shewanella, Marinobacter, Planococcus, and novel phylogenetic lineages adjacent to Colwellia and Alteromonas and within the Flexibacter-Bacteroides-Cytophaga phylum. Psychrotrophic strains were found to be members of the genera Pseudoalteromonas, Psychrobacter, Halomonas, Pseudomonas, Hyphomonas, Sphingomonas, Arthrobacter, Planococcus, and Halobacillus. From this survey, it is proposed that ice diatom assemblages provide niches conducive to the proliferation of a diverse array of psychrophilic bacterial species.     

Modelled and measured dynamics of viruses in Arctic winter sea-ice brines

We describe a model based on diffusion theory and the temperature-dependent mechanism of brine concentration in sea ice to argue that, if viruses partition with bacteria into sea-ice brine inclusions, contact rates between the two can be higher in winter sea ice than in seawater, increasing the probability of infection and possible virus production. To examine this hypothesis, we determined viral and bacterial concentrations in select winter sea-ice horizons using epifluorescence microscopy. Viral concentrations ranged from 1.6 to 82 x 10(6) ml(-1) of brine volume of the ice, with highest values in brines from coldest (-24 to -31 degrees C) ice horizons. Calculated virus-bacteria contact rates in underlying -1 degrees C seawater were similar to those in brines of -11 degrees C ice but up to 600 times lower than those in ice brines at or below -24 degrees C. We then incubated native bacterial and viral assemblages from winter sea ice for 8 days in brine at a temperature (-12 degrees C) and salinity ( approximately 160 psu) near expected in situ values, monitoring their concentrations microscopically. While different cores yielded different results, consistent with known spatial heterogeneity in sea ice, these experiments provided unambiguous evidence for viral persistence and production, as well as for bacterial growth, in -12 degrees C brine.     

Altered Sea Ice Thickness and Permanence Affects Benthic Ecosystem Functioning in Coastal Antarctica

Antarctic sea ice and the cold waters surrounding the continent are key elements of the global climate system, influencing heat redistribution, oceanic circulation and the absorption of carbon dioxide from the atmosphere. However, the Southern Ocean is predicted to warm by 1–6°C over the next century, altering sea ice extent, thickness and permanence. To better understand the connections between coastal sea ice conditions and the functioning of Antarctica’s unique marine benthic ecosystems, we performed manipulative experiments on the seafloor at two southwestern Ross Sea sites with contrasting sea ice conditions. Benthic systems at both study sites were net heterotrophic during the study period (early November), with primary production most likely limited by light availability rather than nutrients. There was five times more fresh algal detrital material in benthic sediments at the site with the thinner, snow-free, annually formed sea ice, relative to the site with thicker, multiyear sea ice. This elevated quantity and quality of algal detrital matter corresponded with a significantly greater rate of sediment oxygen utilization by the benthos and an altered pathway of nitrogen regeneration (tighter coupling between nitrification and denitrification). Large benthic animals (brittle stars, Ophionotus victoriae) enhanced the efflux of dissolved inorganic nutrients from the sediment to the water column and played a greater role in nutrient regeneration at the site with more food. Although changes in sea ice characteristics in the Western Ross Sea are difficult to predict at present, large benthic organisms can be expected to have an expanded role in mediating the effects of elevated coastal productivity and detritus supply on ecosystem dynamics in this part of Antarctica.     

Adaptation of Arctic and Antarctic ice metazoa to their habitat

Sea ice is a unique habitat in polar seas. A diverse assemblage of plants and animals lives in its interior parts and at the ice-water interface. Their distribution is to a large extent controlled by abiotic parameters such as light, salinity and space, as well as food availability. In both the Arctic and Antarctic, the highest metazoan concentrations occur mostly in the bottom centimetres of the sea ice. Dominant metazoans are nematodes, turbellarians, rotifers and crustaceans. The ice-water interface itself houses in addition to endemic amphipods migrants from both the ice and the pelagic realm. To survive with the environmental conditions of the sea ice habitat, the ice biota is adapted, specifically to seasonal salinity variations from below 5 to above 60 PSU. Sea ice metazoans feed mainly on the algae growing within the sea ice. The loss of habitat during ice melt periods can lead to substantial sedimentation of ice fauna to the sea floor, where it might act as food source for the benthos.     

The effects of climate change on harp seals (Pagophilus groenlandicus)

Harp seals (Pagophilus groenlandicus) have evolved life history strategies to exploit seasonal sea ice as a breeding platform. As such, individuals are prepared to deal with fluctuations in the quantity and quality of ice in their breeding areas. It remains unclear, however, how shifts in climate may affect seal populations. The present study assesses the effects of climate change on harp seals through three linked analyses. First, we tested the effects of short-term climate variability on young-of-the year harp seal mortality using a linear regression of sea ice cover in the Gulf of St. Lawrence against stranding rates of dead harp seals in the region during 1992 to 2010. A similar regression of stranding rates and North Atlantic Oscillation (NAO) index values was also conducted. These analyses revealed negative correlations between both ice cover and NAO conditions and seal mortality, indicating that lighter ice cover and lower NAO values result in higher mortality. A retrospective cross-correlation analysis of NAO conditions and sea ice cover from 1978 to 2011 revealed that NAO-related changes in sea ice may have contributed to the depletion of seals on the east coast of Canada during 1950 to 1972, and to their recovery during 1973 to 2000. This historical retrospective also reveals opposite links between neonatal mortality in harp seals in the Northeast Atlantic and NAO phase. Finally, an assessment of the long-term trends in sea ice cover in the breeding regions of harp seals across the entire North Atlantic during 1979 through 2011 using multiple linear regression models and mixed effects linear regression models revealed that sea ice cover in all harp seal breeding regions has been declining by as much as 6 percent per decade over the time series of available satellite data.     

Unusual narwhal sea ice entrapments and delayed autumn freeze-up trends

Sea ice entrapments of narwhals (Monodon monoceros) occur when rapid changes in weather and wind conditions create a formation of fast ice in bays or passages used by whales. Between 2008 and 2010, four entrapments of narwhals were reported in Canada and Greenland. In each case, large groups (40–600 individuals) succumbed in the sea ice at three separate summering localities, two of these where entrapments had never before been reported. We examined long-term trends in autumn freeze-up timing (date when sea ice concentration rises above some threshold) on the 6 largest narwhal summering areas using sea ice concentration from satellite passive microwave data (1979–2009). We found strongly positive and significant trends (P < 0.001) in progressively later dates of autumn freeze-up in all summering areas. Autumn freeze-up occurs between 0.5 and 1 day later per year, or roughly 2–4 weeks later, over the 31-year time series. This indicates that sea ice conditions on narwhal summering areas are changing rapidly. The question remains whether entrapment events on summering areas are random or whether narwhals are adapting to changes in sea ice freeze-up by prolonging their summer residence time.     

Denitrification activity and oxygen dynamics in Arctic sea ice

Denitrification and oxygen dynamics were investigated in the sea ice of Franklin Bay (70°N), Canada. These investigations were complemented with measurements of denitrification rates in sea ice from different parts of the Arctic (69°N–85°N). Potential for bacterial denitrification activity (5–194 μmol N m⁻² day⁻¹) and anammox activity (3–5 μmol N m⁻² day⁻¹) in melt water from both first-year and multi-year sea ice was found. These values correspond to 27 and 7%, respectively, of the benthic denitrification and anammox activities in Arctic sediments. Although we report only potential denitrification and anammox rates, we present several indications that active denitrification in sea ice may occur in Franklin Bay (and elsewhere): (1) despite sea ice-algal primary production in the lower sea ice layers, heterotrophic activity resulted in net oxygen consumption in the sea ice of 1–3 μmol l⁻¹ sea ice per day at in situ light conditions, suggesting that O₂ depletion may occur prior to the spring bloom. (2) The ample organic carbon (DOC) and NO₃ ⁻ present in sea ice may support an active denitrification population. (3) Measurements of O₂ conditions in melted sea ice cores showed very low bulk concentrations, and in some cases anoxic conditions prevailed. (4) Laboratory studies using planar optodes for measuring the high-resolution two-dimensional O₂ distributions in sea ice confirmed the very dynamic and heterogeneous O₂ distribution in sea ice, displaying a mosaic of microsites of high and low O₂ concentrations. Brine enclosures and channels were strongly O₂ depleted in actively melting sea ice, and anoxic conditions in parts of the brine system would favour anaerobic processes.     

Respiration and bacterial carbon dynamics in Arctic sea ice

Bacterial carbon demand, an important component of ecosystem dynamics in polar waters and sea ice, is a function of both bacterial production (BP) and respiration (BR). BP has been found to be generally higher in sea ice than underlying waters, but rates of BR and bacterial growth efficiency (BGE) are poorly characterized in sea ice. Using melted ice core incubations, community respiration (CR), BP, and bacterial abundance (BA) were studied in sea ice and at the ice–water interface (IWI) in the Western Canadian Arctic during the spring and summer 2008. CR was converted to BR empirically. BP increased over the season and was on average 22 times higher in sea ice as compared with the IWI. Rates in ice samples were highly variable ranging from 0.2 to 18.3 μg C l⁻¹ d⁻¹. BR was also higher in ice and on average ~10 times higher than BP but was less variable ranging from 2.39 to 22.5 μg C l⁻¹ d⁻¹. Given the high variability in BP and the relatively more stable rates of BR, BP was the main driver of estimated BGE (r ² = 0.97, P < 0.0001). We conclude that microbial respiration can consume a significant proportion of primary production in sea ice and may play an important role in biogenic CO₂ fluxes between the sea ice and atmosphere.