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Tergipes antarcticus (Gastropoda, Nudibranchia) has been reported from Antarctic sea ice twice (1903 and 2008). The extent of its distribution and life history remained unclear. We have evaluated data from several cruises, showing that T. antarcticus is widely distributed in sea ice throughout the Weddell Sea. Adults, juveniles, larvae and egg clutches of T. antarcticus were found in the ice indicating that the species reproduces within this habitat. We collected live material of T. antarcticus for a thorough description of all life stages and to investigate the developmental stages and physiological adaptations. Total developmental time from egg to veliger larvae was relatively short with 31 days (range 13–65 days) at 0°C. Liquid withdrawn from egg clutches and adult T. antarcticus showed clear signs of thermal hysteresis. This is the first report of thermal hysteresis from a sea ice metazoan. We conclude that T. antarcticus is an autochthonous species to Antarctic sea ice.

The Arctic sea ice is the habitat of an astonishing abundance of plant and animal life. These biocenoses have a momentous impact on the polar ecosystem

The concentration and size distribution of exopolymer particles were measured in and below pack ice in the Fram Strait area during autumn 1999. Vertical profiles of exopolymer particles were determined in young, first-year and multi-year sea ice. In addition, a variety of abiotic parameters (temperature, salinity, NO 2 , PO 4 , NO 3 , SiO 2 ) and biotic parameters (particulate organic carbon [POC] and nitrogen [PON], chlorophyll a [chl a], abundances of diatoms and bacteria) were measured. Median abundances and areas of exopolymer particles in the different ice types (3.17 x 10 6 to 4.90 x 10 6 particles 1 -1 and 4.6-6.9 cm 2 1 -1 , respectively) exceeded median concentrations in the under-ice water (0.56 x 10 6 particles 1 -1 ; 0.6 cm 2 1 -1 ) by 1 order of magnitude. Exopolymer particle concentrations in sea ice were highest in the interior of the sea ice and were significantly correlated with chl a as well as with the abundances of pennate diatoms, centric diatoms and bacteria. Our data indicate that pennate diatoms are the main producers of exopolymer particles in sea ice. The observed exopolymer particle-size spectra in both sea ice and under-ice water differed from those commonly reported for exopolymer particles in pelagic environments by a relatively large fraction of large particles. Crude estimates of integrated exopolymer particle carbon indicate that these particles can be important components in the context of food-web structure and organic carbon dynamics in the sea ice habitat. The high concentrations of exopolymer particles in the sea ice will also impact the fate of other particles during ice melt.

Physical, chemical and biological properties of sea ice and underlying brackish water (0–10 m water depth) were investigated in the Bothnian Bay and at a coastal station at the entrance of the Gulf of Finland in March 2000. Sea-ice texture was analysed and vertical profiles for δ18O, inorganic nutrient concentrations [NO3 –, NO2 –, NH4 +, PO4 3+, Si(OH)4] and chlorophyll a and pheopigment concentrations were obtained with a vertical resolution of 1–10 cm. Biomass estimates of bacteria, protists and metazoans were based on microscopical counts. Due to low ice bulk salinities, sea-ice brine volumes were small with a median value of only 3%. Ice thickness varied between 22 and 27 cm. Refrozen snow and granular ice dominated in the surface parts of the sea ice; columnar ice formed the bottom layers. The total biomass in the sea ice and under-ice water ranged from 2.7 mg C m–2 to 45.1 mg C m–2 and 36.8 mg C m–2 to 3,874.3 mg C m–2, respectively. Mean integrated ice values were dominated by pennate diatoms (33%), followed by centric diatoms (29%), autotrophic flagellates (23%), bacteria (8%) and heterotrophic flagellates (7%). The low integrated biomass of ice-associated metazoans (1%) consumed on average only 1.5% of the algal standing stock per day. The combined data suggest that abiotic factors (particularly nutrient availability as reflected by small brine volumes), rather than the heterotrophic component of the sympagic community, controlled autotrophic biomass in Baltic sea ice during March 2000.

Sea-ice meiofauna was studied during various cruises to the Weddell Sea. Foraminifers dominate (75%) the sea-ice community in terms of numerical abundance while turbellarians dominate (45%) in terms of biomass. Distribution of organisms is patchy and varies considerably between cruises but also between sampling sites within one cruise. The bulk of the meiofauna is concentrated in the lowest parts of the sea ice, especially during winter and autumn. However, in porous summer sea ice, sympagic organisms also occur in high densities in upper and intermediate layers of sea ice. Proto- and metazoans associated with Antarctic sea ice include organisms actually living in sea ice, as well as those on the underside of floes and in the underlying water. The sea-ice habitat serves as a feeding ground, as well as an important nursery for juveniles, providing energy-rich food resources. The ice also constitutes a shelter from predators.

Dynamic temporal and spatial changes of physical, chemical and spatial properties of sea ice pose many challenges to the sympagic community which inhabit a network of brine channels in its interior. Experiments were conducted to reveal the influence of the internal surface area and the structure of the network on species composition and distribution within sea ice. The surface of the brine channel walls was measured via a newly developed method using a fluorogenic tracer. These measurements allowed us to quantify the internal surface area accessible for predators of different sizes, at different ice temperatures and in different ice textures. Total internal surface area ranged from 0.6 to 4 m2 kg−1 ice and declined with decreasing ice temperature. Potentially, 6 to 41% of the area at −2°C is covered by micro-organisms. Cooling from −2 to −6°C drastically increases the coverage of organisms in brine channels due to a surface reduction. A combination of brine channel frequency measurements with an artificial brine network experiment suggests that brine channels ≤200 μm comprise a spatial refuge with microbial community concentrations one to two magnitudes higher than in the remaining channel network. The plasticity of predators to traverse narrow passages was experimentally tested for representative Arctic sympagic rotifers, turbellarians, and nematodes. By conforming to the osmotic pressure of the brine turbellaria match their body dimensions to the fluctuating dimensions of the brine channel system during freezing. Rotifers penetrate very narrow passages several times their body length and 57% their body diameter. In summary, ice texture, temperature, and bulk salinity influence the predatory–prey interactions by superimposing its structural component on the dynamic of the sympagic food web. Larger predators are excluded from brine channels depending on the architecture of the channel network. However, extreme body flexibility allows some predators to traverse structural impasses in the brine channel network.

During two cruises to the Greenland Sea, we studied the abundance and biomass of the sea ice biota in summer and late autumn. The mean calculated biomass of the sympagic community was 0.2 g C m −2 ice. Algae contributed on average 43% to total biomass, followed by bacteria (31%), heterotrophic flagellates (20%), and meiofauna (4%). Diatoms were the main primary producers (60% of total algal biomass), but flagellated cells contributed significantly to the algal biomass. Among the meiofauna, ciliates, nematodes, acoel turbellarians and crustaceans were dominant. Calculated potential ingestion rates of meiofauna (0.6 g C m −2 (120 d) −1 ) are on the same order of magnitude as annual primary production estimates for Arctic multi-year sea ice. We therefore assume that grazing can control biomass accumulation of primary producers inside the sea ice.

Studies on the life strategy of the small calanoid copepod Stephos longipes were carried out in the eastern Weddell Sea during four expeditions (January/February 1985, August 1986, October/December 1986 and April/May 1992). Samples were taken from the water column, the ice/water interface and the sea ice. In winter (August 1986) S. longipes copepodite stage CIV occurred mainly in the upper water layers of the ice covered eastern Weddell Sea, while only nauplii were found in the sea ice. In late winter/early spring (October-December 1986) very low numbers of S. longipes were found in the water column, mainly in the upper 50m, but high numbers occurred immediately below and within the sea ice. Adults dominated in the water column and in the under ice water layer while the sea ice contained nauplii and copepodite stage CI. During summer (January/February 1985) the eastern Weddell Sea was almost entirely free of ice with the exception of fast ice fields atthe ice shelf. During this time S. longipes was concentrated in the upper 50m of the water column and in the ice/water interface where an ice cover was present. Young copepodite stages (CI-CIII) comprised the largest fraction of the population. In autumn (April/May 1992) as new ice began to develop, S. longipes , dominated by copepodite stage CIV, occurred in greatest number within mid-water layers. The abundance of S. longipes in autumn was similar to late winter/early spring highest in the sea ice and lowest in the water column. During all periods of investigation the population structure differed between the various habitats with the youngest population occurring in the sea ice and the oldest in the water column. A younger generation of the S. longipes population appears to overwinter in the sea ice and ice/water interface and an older one in deeper water layers or near the bottom.

In 1988, the short-term response of sea-ice organisms to manipulated changes in snow cover (no snow cover, natural snow cover, natural snow cover + black foil) was investigated in one ice floe located in the East Greenland Current northwest of Svalbard over a period of three weeks. Autotrophic organisms (flagellates and diatoms) were concentrated in the lowermost 30 cm of the floe. In the field without snow cover, the highest diatom concentrations were observed, consisting nearly entirely of pennate forms, together with a maximum bacterial abundance. The community of larger protozoa and smaller metazoa was dominated by ciliates. Under natural conditions the flora consisted of both flagellates and diatoms, while turbellaria were the dominating animals. In the darkened field, the organism concentrations decreased with time. The results indicate that brine drainage, induced by changes in ice temperature, can reduce concentrations of ice organisms over short time scales.

The pelagic foraminifer Neogloboquadrina pachyderma (Ehrenberg, 1861) occurs in new ice, congelation ice, and the underlying water column of the Weddell Sea. Neogloboquadrina pachyderma is incorporated into the ice in large numbers at the time of its formation. The average number of foraminifers per liter of ice was 87 and numbers ranged between 0 and 1,075. Sea ice contained 70 times more foraminifers per unit volume than the underlying water column and on an areal basis the sea ice cover has approximately the same number of specimens as 60 m of underlying water column. The foraminifera are usually incorporated into the ice when it is being formed dynamically and are thus subsequently associated mainly with granular ice. Many foraminifers are able to survive and grow in the ice where algal biomass in winter is high compared to the water column, perhaps indicating an overwintering strategy. Arctic sea ice, on the other hand, is practically devoid of foraminifers. These observations may have implications for paleoceanographers who use N. pachyderma as a tool to reconstruct past surface water conditions.

The “Ice Station POLarstern” (ISPOL) drift experiment was an interdisciplinary study within the perennial sea ice of the western Weddell Sea that brought together scientists from 11 countries. The primary goal was the monitoring of physical and biogeochemical interactions between atmosphere, ice and ocean at the transition from austral winter to summer. Special emphasis was set on the processes controlling sea-ice melting and the onset of phytoplankton bloom. The ISPOL observations complement the study of the seasonal sea ice–ocean cycle in the western Weddell Sea, initiated by the summer to winter drift of Ice Station Weddell-1 (ISW-1) in 1992. This volume contains a collection of papers that range from the atmosphere to the deep ocean, from micro- to macro-scales, from physics to biology with their interactions investigated during the 36 days of the ISPOL experiment.

Russian and German scientists have investigated the extreme environmental system in and around the Laptev Sea in the Siberian Arctic. For the first time a major comprehensive research program combining the efforts of several projects addressed both oceanic and terrestrial processes, and their consequences for marine and terrestrial biota, landscape evolution as well as land-ocean interactions. The primary scientific goal of the multidisciplinary program was to decipher past climate variations and their impact on contemporary environmental changes. Extensive studies of the atmosphere, sea ice, water column, and sea-floor on the Laptev Sea Shelf, as well as of the vegetation, soil development, carbon cycle, permafrost behaviour and lake hydrology, and sedimentation on Taymyr Peninsula and Severnaya Zemlya Archipelago were performed during the past years under a framework of joint research activities. They included land and marine expeditions during spring (melting), summer (ice free), and autumn (freezing) seasons. The close bilateral cooperation between many institutions in Russia and Germany succeeded in drawing a picture of important processes shaping the marine and terrestrial environment in northern Central Siberia in Late Quaternary time. The success of the projects, which ended in late 1997, resulted in the definition and establishment of a new major research effort which will concentrate on establishing a better understanding of the paleoclimatic and paleoenvironmental record of the area. This is important because it allows to be able to judge rates and extremes of potential future environmental changes.

This contribution focuses on coupling processes between the three major Arctic marine realms, the sea ice, the pelagic and the benthic habitat. Physically and biologically mediated interactions cause specific Arctic growth regimes, which are—to a large extent — due to the seasonal changes of the Arctic sea ice cover. Based on the described interactions we recommend combined studies of ice extent and ocean colour together with field measurements of organic biomass, production and diversity for a better understanding of relevant biological processes in Arctic seas.

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.

The distribution of ice organisms was investigated in Fram Strait in May 1988 during the ARK V/1 expedition on RV Polarstern. Over a 3 week period the abundances of bacteria, diatoms, auto- and heterotrophic flagellates as well as various groups of meiofauna organisms were observed in the lowermost 30 cm of an ice floe. Data were obtained from three experimental fields under three different light regimes as a result of manipulations of the snow cover. The application of multivariate factor analysis on this time series data set resulted in the characterization of four succession stages of an Arctic sea ice community: 1) the diatom bottom assemblage, 2) the mixed autotrophic assemblage, 3) the mixed auto- and heterotrophic supra-bottom assemblage, and 4) the heterotrophic supra-bottom assemblage. The two most abundant meiofauna groups (Turbellaria, Ciliata) showed different preferences according to algal distribution. While turbellarians were most abundant in samples with mixed populations of diatoms and flagellates, ciliates reached their abundance maxima in samples dominated by diatoms, suggesting different prey selections. We have developed a model for the explanation of the spatial separation of auto- and heterotrophic organisms, highlighting the possible role of DOC production by ice algae and DOC transport with brine flow.

Polar regions are covered by extensive sea ice that is inhabited by a variety of plants and animals. The environments where the organisms live vary depending on the structure and age of the ice. Many terms have been used to describe the habitats and the organisms. We here characterize the habitats and communities and suggest some standard terms for them. We also suggest routine sampling methods and reporting units for measurements of biological and chemical variables. © 1992 Springer-Verlag GmbH & Co. KG.

The sea ice does not only determine the ecology of ice biota, but it also influences the pelagic systems under the ice cover and at ice edges. In this paper, new estimates of Arctic and Antarctic production of biogenic carbon are derived, and differences as well as similarities between the two oceans are examined. In ice-covered seas, high algal concentrations (blooms) occur in association with several types of conditions. Blooms often lead to high sedimentation of intact cells and faecal pellets. In addition to ice-related blooms, there is progressive accumulation of organic matter in Arctic multi-year ice, whose fate may potentially be similar to that of blooms. A fraction of the carbon fixed by microalgae that grow in sea ice or in relation to it is exported out of the production zone. This includes particulate material sinking out of the euphotic zone, and also material passed on to the food web. Pathways through which ice algal production does reach various components of the pelagic and benthic food webs, and through them such top predators as marine mammals and birds, are discussed. Concerning global climate change and biogeochemical fluxes of carbon, not all export pathways from the euphotic zone result in the sequestration of carbon for periods of hundreds of years or more. This is because various processes, that take place in both the ice and the water column, contribute to mineralize organic carbon into CO2before it becomes sequestered. Processes that favour the production and accumulation of biogenic carbon as well as its export to deep waters and sequestration are discussed, together with those that influence mineralization in the upper ice-covered ocean. © 1992 Springer-Verlag GmbH & Co. KG.

Seasonal and spatial variation in sea ice organisms were studied in the Weddell Sea region during the austral summer 1985 and winter and spring 1986. Sea ice cores were collected from 22 stations. Winter values for chlorophyll a measured per 10 cm segment of drilled ice core ranged between 0 and 49 μgl−1 (mean 3.4) during July to September and between 0 and 450 μgl−1 (mean 7.6) during October to December, while mean summer values were considerably higher (mean 34.5) with a maximum of 2220 μgl−1. Increasing numbers of sea ice organisms were also observed in sea ice cores from stations reoccupied after several weeks in spring. Samples taken later in season (November compared to October) revealed a higher biomass and more organisms. Algal biomass and absolute numbers of sea ice organisms including foraminifers, copepods and ciliates decreased along a transect from the ice edge towards the continent and along the eastern Weddell Sea coast from northeast to southwest. However, the distribution of organisms was patchy and replicate cores taken only a few centimeters apart contained numbers of organisms which differed considerably. This is partly due to different ice formation processes which show both small and mesoscale variation and may account for the observed abundances of ice organisms.

Sea ice cores were obtained from eleven fast ice stations and one floe in the Weddell Sea, Antarctica in January–February 1985. All cores from the north eastern part of the Weddell Sea contained numerous living and dead planktic foraminifers of the species Neogloboquadrina pachyderma (Ehrenberg), while cores drilled in southern parts were barren of foraminifers with one exception. Foraminiferal abundances were variable, with numbers up to 320 individuals per liter melted sea ice. Distribution of foraminifers appears to be patchy, parallel cores taken less than 30 cm apart contained numbers which varied considerably. On the other hand, three cores taken on a transect each more than 3 km apart showed striking similarities. In general, small dead tests were found in the upper parts of the sea ice cores while large living individuals mainly occurred in lower sections. Abundant diatoms probably serve as a food source for the foraminifers. Correlation of foraminiferal abundance with salinity, chlorophyll and nutrient profiles are inconsistent. The possible mechanism of incorporation of N. pachyderma into the ice is discussed.

On determine que la coloration vert foncee des icebergs antarctiques est due a des elements metalliques (fer, cuivre et autres) et non a des composes d'origine biologique