Sub-ice Water Research Articles

Multimedia distribution, dynamics, and seasonal variation of PAHs in Songhua wetland: Implications for ice-influenced conditions

The knowledge of polycyclic aromatic hydrocarbons (PAHs) in wetlands remains limited. There is a research need for the dynamics between interfaces of multimedia when ice is present in this fragile ecosystem. In this study, sediment, open-water, sub-ice water, and ice samples were collected from the Songhua wetland to study the behaviors of PAHs with and without influences from ice. The concentration of all individual PAHs in sub-ice water (370–1100 ng/L) were higher than the open-water collected from non-ice-covered seasons (50–250 ng/L). Enrichment of PAHs in the ice of wetland was found, particularly for high-molecular-weight PAHs (HMW). This could be attributed to the relatively lower polarity of hydrocarbons compounds, making them more likely to remain in the ice layer during freezing. Source assessments reveal common sources for sub-ice water and ice, which differ from those in the open water in non-ice-covered seasons. This difference is primarily attributed to heating activities in the Harbin during winter. The average percentage contributions were 79% for sub-ice water and 36% for ice related to vehicle exhausts and coal combustion. Additionally, wood burning contributed 25% to sub-ice water and 62% to ice. Sediment in the wetland was found to serve as a final deposit particularly for heavier PAHs, especially those with 6 rings. Sediment also has the potential to act as a source for the secondary emission of low-molecular-weight PAHs (LMW) congeners into the water. PAHs in wetland displayed low ecological risk, while HMW PAHs with relative higher ecological risk is recommended to be further monitored.

Melting temperature of ice and total gas content of water at the ice-water interface above subglacial Lake Vostok

It is generally assumed that the gas composition and the total gas content of Lake Vostok’s water are, to a large extent, governed by the budget of atmospheric gases entering the lake together with glacier ice melt, mostly in its northern part. Since the ice accretion that prevails in the south of the lake leads to the exclusion of gases during the freezing process, these gases can build up in the lake water. Earlier theoretical works [2, 3] have demonstrated that about 30 water residence times are required to attain equilibrium between gases in solution and those in a hydrate phase, which sets the upper bounds of concentrations of nitrogen and oxygen dissolved in sub-ice water (~2.7 g N2 L–1 and ~0.8 g O2 L–1). Here we attempt to estimate the real gas content of the lake water based on the link between the pressure melting temperature of ice and the concentration of gases dissolved in the liquid phase [2]. We use the stacked borehole temperature profile extended to 3753 m depth and the measurements of temperature of sub-ice water that entered the borehole after the second unsealing of Lake Vostok to estimate the melting temperature of ice (–2.72 ± 0.1 °C) at the ice sheet-lake interface (depth 3758.6 ± 3 m, pressure 33.78 ± 0.05 MPa). The gas content of the near-surface layer of lake that corresponds to this melting temperature is calculated to be 2.23 g.L–1, meaning that the concentration of dissolved oxygen must be as high as 0.53 g.L–1, i. e. one-two orders of magnitude higher than in any other known water bodies on our planet. The inferred gas content of sub-ice water is, by a factor of 1.6, lower than the maximal solubility of air in water in equilibrium with air hydrate, though it is still higher, by a factor of 19, than the total air content of melting glacier ice. The relatively low concentration of dissolved air in the near-surface layer of the lake revealed in this study provides a new experimental constraint for understanding the gas distribution in Lake Vostok as affected by the circulation and mixing of water beneath the ice sheet.

Особенности временной изменчивости содержания кислорода в зарослях Zostera marina Linnaeus, 1753 в бухте Воевода (Амурский залив, Японское море)

В настоящее время мелководные бассейны с лугами Zostera marina L. рассматривают в качестве поглотителей атмосферного углекислого газа, способных сдерживать увеличение его концентрации. Благодаря своей высокой продуктивности взморник выделяет в среду большое количество кислорода. Для установления особенностей проявления продукционной активности мелководных бассейнов, покрытых лугами Z. marina, на примере бухты Воевода (Амурский залив, Японское море) проведён мониторинг гидрологических и продукционных параметров с различными интервалами измерений. Наблюдения продолжались 8,5 мес. (22.09.2012–07.06.2013). В зарослях Z. marina на глубине 4 м измеряли температуру, солёность, флуоресценцию хлорофилла и мутность с помощью гидрологической станции Water Quality Monitor с интервалом 3 часа. Малоинерционным оптическим кислородным датчиком ARO-USB определяли концентрацию растворённого кислорода с интервалом 1 час. Установлено два типа изменчивости содержания кислорода в среде: 1) долгопериодная изменчивость, обусловленная сезонными изменениями среды; 2) суточная в период ледостава, определяемая интенсивностью проникновения фотосинтетически активной радиации в подлёдную воду. В осенний сезон отмечены низкие концентрации кислорода, достигающие уровня гипоксии. Для зимнего и весеннего периодов содержание кислорода находилось, как правило, на уровне 100–130 % от насыщения. Высокую суточную изменчивость наблюдали в период ледостава, в отсутствие снега. В феврале амплитуда суточных колебаний концентрации кислорода достигала 730 мкмоль·кг−1, с трёхкратным пересыщением по отношению к атмосферному O2. Установлено, что максимальная скорость продукции кислорода, отнесённая к 1 г сырой массы Z. marina, составляет 6,5 мг O2·час−1·г−1. Суточная динамика кислорода в морской воде проанализирована в связи с физиологическими особенностями Z. marina (воздухоносные полости в побегах играют важную роль в динамике кислорода в среде), а также в связи с короткопериодными приливами.

Variability of chlorophyll and the influence factors during winter in seasonally ice-covered lakes

Lake ice is an essential and integral part of the cryosphere and freshwater systems. The formation of lake ice affects the physical, hydrological, and biological conditions of ecological systems. Global warming may contribute to even shorter periods of ice cover in the lakes of the Frigid Zone, which adversely affects the growth of phytoplankton and primary productivity. This study was conducted for the purpose of evaluating the growth of phytoplankton and factors involved, in 28 ice-covered lakes across the Songnen Plain, in the Northeast of China, to understand how they take part in the whole-ecosystem functioning. A total of 1026 water samples were collected in April, September, and January during the period 2014–2018. In the frozen period, the concentration levels of dissolved organic carbon (DOC), total nitrogen (TN), and total phosphorus (TP) were all comparable with the spring and autumn. Despite the limited light availability and low temperature, the phytoplankton survived in sub-ice waters during winter with a low concentration of chlorophyll a (Chla). Its average concentration was positively correlated with the concentration observed in the previous autumn (rp = 0.563, p < 0.01). According to the regression tree analysis, during the winter period, Chla was mainly related to the concentration of TN in sub-ice water (TNwater) and with the difference of concentration of TP between water and ice (TPcd). Furthermore, either in ice or in sub-ice water, the concentration of Chla was also significantly affected by total suspended matter (TSM) (p < 0.05). The levels of TNwater, TPcd, and TSM could explain the 77.8% of the variance in the concentration of Chla during winter with contributions in the ranges of 25.5%–35.0%, 9.2%–11.3%, and 21.5%–34.0%, respectively (p < 0.05). This research substantially contributes to comprehending how the existing conditions under-ice affect the whole ecosystem when the ice cover is reduced lakes or rivers.

Genomes of Novel Microbial Lineages Assembled from the Sub-Ice Waters of Lake Baikal.

We present a metagenomic study of Lake Baikal (East Siberia). Two samples obtained from the water column under the ice cover (5 and 20 m deep) in March 2016 have been deep sequenced and the reads assembled to generate metagenome-assembled genomes (MAGs) that are representative of the microbes living in this special environment. Compared with freshwater bodies studied around the world, Lake Baikal had an unusually high fraction of Verrucomicrobia Other groups, such as Actinobacteria and Proteobacteria, were in proportions similar to those found in other lakes. The genomes (and probably cells) tended to be small, presumably reflecting the extremely oligotrophic and cold prevalent conditions. Baikal microbes are novel lineages recruiting very little from other water bodies and are distantly related to other freshwater microbes. Despite their novelty, they showed the closest relationship to genomes discovered by similar approaches from other freshwater lakes and reservoirs. Some of them were particularly similar to MAGs from the Baltic Sea, which, although it is brackish, connected to the ocean, and much more eutrophic, has similar climatological conditions. Many of the microbes contained rhodopsin genes, indicating that, in spite of the decreased light penetration allowed by the thick ice/snow cover, photoheterotrophy could be widespread in the water column, either because enough light penetrates or because the microbes are already adapted to the summer ice-less conditions. We have found a freshwater SAR11 subtype I/II representative showing striking synteny with Pelagibacterubique strains, as well as a phage infecting the widespread freshwater bacterium PolynucleobacterIMPORTANCE Despite the increasing number of metagenomic studies on different freshwater bodies, there is still a missing component in oligotrophic cold lakes suffering from long seasonal frozen cycles. Here, we describe microbial genomes from metagenomic assemblies that appear in the upper water column of Lake Baikal, the largest and deepest freshwater body on Earth. This lake is frozen from January to May, which generates conditions that include an inverted temperature gradient (colder up), decrease in light penetration due to ice, and, especially, snow cover, and oligotrophic conditions more similar to the open-ocean and high-altitude lakes than to other freshwater or brackish systems. As could be expected, most reconstructed genomes are novel lineages distantly related to others in cold environments, like the Baltic Sea and other freshwater lakes. Among them, there was a broad set of streamlined microbes with small genomes/intergenic spacers, including a new nonmarine Pelagibacter-like (subtype I/II) genome.

Bloch–Siegert Effect in Magnetic-Resonance Sounding

The magnetic-resonance sounding (MRS) method is intended for groundwater prospecting. The Earth’s magnetic field used in MRS is of the order of 5 × 10−5 T. The radiofrequency (RF) field produced in MRS by the surface antenna is linearly polarized and may be comparable with the geomagnetic field. The use of RF pulses at Larmor frequency leads to the appearance of the mean resonance offset in rotating frame (Bloch–Siegert shift) which is caused by the influence of the off-resonance counter rotating component of the RF field. The solution of the inverse problem for ground water distribution must take account of the proton spin resonance frequency shift, because an inaccurate kernel of the respective integral equation may lead to significant errors in the estimation of aquifer characteristics. The value for Bloch–Siegert effect with one order of approximation higher than usual has been calculated. The MRS technique with 100-m-diameter antenna has been used at the frozen Ob reservoir near Novosibirsk, Russia, to detect subice water to prove the improved physical model of MRS. There is a good agreement between measured and calculated data taking into account the Bloch–Siegert and the next-order effects. New physical model accounting the Bloch–Siegert effect allowed a significant improvement of the reliability of the MRS data interpretation.

RESULTS AND CHARACTERISTICS OF 5G HOLE DRILLING AND THE FIRST TAPPING OF LAKE VOSTOK

We present here a brief description of the drilling operations in the deep 5G hole at the Russian Vostok Station with more detailed account of the final stage of this long-term project successfully ended on February 5, 2012 with the first Lake Vostok unsealing. Relevant information on the borehole design and the technical characteristics of the downhole and surface drilling equipment is given. The peculiarities of the drilling process are discussed in connection with changing properties of the penetrated ice. The data analysis allows defining the main factors that influence the efficiency of the electromechanical drill system at great depths. It is shown that the elevated temperature of ice and its coarse-crystalline texture are mainly responsible for the significant for the showing-down of ice coring in the bottom sections of ice sheets observed at Vostok and at other drilling sites in Antarctica and Greenland as well. Based on the large amount of experimental data obtained in the course of the deep drilling at Vostok, we discuss the processes which occur in the borehole during the ice drilling and unsealing the sub-ice water bodies. In particular, we investigate the conditions for occurrence of hydraulic fracturing in the hole and the possible effect of the hydrofrac on the height of the water column that have risen in hole 5G after the Lake Vostok unsealing. Finally we formulate the drill equipment requirements and process specifications that would ensure the best performance of an electromechanical drill and trouble-free drilling operations at different depths in a borehole up to the bottom of ice sheet.

Bathymetric and oceanic controls on Abbot Ice Shelf thickness and stability

Abstract. Ice shelves play key roles in stabilizing Antarctica's ice sheets, maintaining its high albedo and returning freshwater to the Southern Ocean. Improved data sets of ice shelf draft and underlying bathymetry are important for assessing ocean–ice interactions and modeling ice response to climate change. The long, narrow Abbot Ice Shelf south of Thurston Island produces a large volume of meltwater, but is close to being in overall mass balance. Here we invert NASA Operation IceBridge (OIB) airborne gravity data over the Abbot region to obtain sub-ice bathymetry, and combine OIB elevation and ice thickness measurements to estimate ice draft. A series of asymmetric fault-bounded basins formed during rifting of Zealandia from Antarctica underlie the Abbot Ice Shelf west of 94° W and the Cosgrove Ice Shelf to the south. Sub-ice water column depths along OIB flight lines are sufficiently deep to allow warm deep and thermocline waters observed near the western Abbot ice front to circulate through much of the ice shelf cavity. An average ice shelf draft of ~200 m, 15% less than the Bedmap2 compilation, coincides with the summer transition between the ocean surface mixed layer and upper thermocline. Thick ice streams feeding the Abbot cross relatively stable grounding lines and are rapidly thinned by the warmest inflow. While the ice shelf is presently in equilibrium, the overall correspondence between draft distribution and thermocline depth indicates sensitivity to changes in characteristics of the ocean surface and deep waters.

Total inorganic carbon in sea ice

The method proposed for determining the total inorganic carbon (TC) concentrations in sea ice (Arctic region, North Pole-35 expedition) based on the measurement of the total alkalinity (TA) and the pH in the melt waters without the CO2 exchange with the atmosphere is considered. It is shown that the TC/Sal and TA/TC values through the entire ice section remain similar to these parameters in the subice water. The surface snow and the uppermost ice layers are characterized by elevated TA/TC values, which indicate the reaction Ca2+ + 2HCO3− = ↓CaCO3 + ↑CO2 + H2O. The release of CO2 to the atmosphere due to the decomposition of calcium hydrocarbonate is as high as ∼20 mmol/m2. The meltwater of the examined ice is undersaturated with CO2, which may result in a sink of atmospheric CO2 (∼30 mmol/m2).

Brackish meltponds on Arctic sea ice—a new habitat for marine metazoans

Meltponds on Arctic sea ice have previously been reported to be devoid of marine metazoans due to fresh-water conditions. The predominantly dark frequently also green and brownish meltponds observed in the Central Arctic in summer 2007 hinted to brackish conditions and considerable amounts of algae, possibly making the habitat suitable for marine metazoans. Environmental conditions in meltponds as well as sympagic meiofauna in new ice covering pond surfaces and in rotten ice on the bottom of ponds were studied, applying modified techniques from sea-ice and under-ice research. Due to the very porous structure of the rotten ice, the meltponds were usually brackish to saline, providing living conditions very similar to sub-ice water. The new ice cover on the surface had similar characteristics as the bottom layer of level ice. The ponds were thus accessible to and inhabitable by metazoans. The new ice cover and the rotten ice were inhabited by various sympagic meiofauna taxa, predominantly ciliates, rotifers, acoels, nematodes and foraminiferans. Also, sympagic amphipods were found on the bottom of meltponds. We suggest that, in consequence of global warming, brackish and saline meltponds are becoming more frequent in the Arctic, providing a new habitat to marine metazoans.

Evaluation of the HUT modified snow emission model over lake ice using airborne passive microwave measurements

The algorithms designed to estimate snow water equivalent (SWE) using passive microwave measurements falter in lake-rich high-latitude environments due to the emission properties of ice covered lakes on low frequency measurements. Microwave emission models have been used to simulate brightness temperatures (Tbs) for snowpack characteristics in terrestrial environments but cannot be applied to snow on lakes because of the differing subsurface emissivities and scattering matrices present in ice. This paper examines the performance of a modified version of the Helsinki University of Technology (HUT) snow emission model that incorporates microwave emission from lake ice and sub-ice water. Inputs to the HUT model include measurements collected over brackish and freshwater lakes north of Inuvik, Northwest Territories, Canada in April 2008, consisting of snowpack (depth, density, and snow water equivalent) and lake ice (thickness and ice type). Coincident airborne radiometer measurements at a resolution of 80 × 100 m were used as ground-truth to evaluate the simulations. The results indicate that subsurface media are simulated best when utilizing a modeled effective grain size and a 1 mm RMS surface roughness at the ice/water interface compared to using measured grain size and a flat Fresnel reflective surface as input. Simulations at 37 GHz (vertical polarization) produce the best results compared to airborne Tbs, with a Root Mean Square Error (RMSE) of 6.2 K and 7.9 K, as well as Mean Bias Errors (MBEs) of −8.4 K and −8.8 K for brackish and freshwater sites respectively. Freshwater simulations at 6.9 and 19 GHz H exhibited low RMSE (10.53 and 6.15 K respectively) and MBE (−5.37 and 8.36 K respectively) but did not accurately simulate Tb variability (R = −0.15 and 0.01 respectively). Over brackish water, 6.9 GHz simulations had poor agreement with airborne Tbs, while 19 GHz V exhibited a low RMSE (6.15 K), MBE (−4.52 K) and improved relative agreement to airborne measurements (R = 0.47). Salinity considerations reduced 6.9 GHz errors substantially, with a drop in RMSE from 51.48 K and 57.18 K for H and V polarizations respectively, to 26.2 K and 31.6 K, although Tb variability was not well simulated. With best results at 37 GHz, HUT simulations exhibit the potential to track Tb evolution, and therefore SWE through the winter season.

Subglacial to emergent basaltic volcanism at Hlöðufell, south-west Iceland: A history of ice-confinement

Hlöðufell is a familiar 1186 m high landmark, located about 80 km northeast of Reykjavík, and 9 km south of the Langkjökull ice-cap in south-west Iceland. This is the first detailed study of this well-exposed and easily accessible subglacial to emergent basaltic volcano. Eight coherent and eleven volcaniclastic lithofacies are described and interpreted, and its evolution subdivided into four growth stages (I–IV) on the basis of facies architecture. Vents for stages I, II, and IV lie along the same fissure zone, which trends parallel to the dominant NNE–SSW volcano-tectonic axis of the Western Volcanic Zone in this part of Iceland, but the stage III vent lies to the north, and is probably responsible for the present N–S elongation of the volcano. The basal stage (I) is dominated by subglacially erupted lava mounds and ridges, which are of 240 m maximum thickness, were fed from short fissures and locally display lava tubes. Some of the stage I lavas preserve laterally extensive flat to bulbous, steep, glassy surfaces that are interpreted to have formed by direct contact with surrounding ice, and are termed ice-contact lava confinement surfaces. These surfaces preserve several distinctive structures, such as lava shelves, pillows that have one flat surface and mini-pillow (< 10 cm across) breakouts, which are interpreted to have formed by the interplay of lava chilling and confinement against ice, ice melting and ice fracture. The ice-contact lava confinement surfaces are also associated with zones of distinctive open cavities in the lavas that range from about 1 m to several metres across. The cavities are interpreted as having arisen by lava engulfing blocks of ice, that had become trapped in a narrow zone of meltwater between the lava and the surrounding ice, and are termed ice- block meltout cavities. The same areas of the lavas also display included and sometimes clearly rotated blocks of massive to planar to cross-stratified hyaloclastite lapilli tuffs and tuff–breccias, termed hyaloclastite inclusions, which are interpreted as engulfed blocks of hyaloclastite/pillow breccia carapace and talus, or their equivalents reworked by meltwater. Some of the stage I lavas are mantled at the southern end of the mountain by up to 35 m thickness of well-bedded vitric lapilli tuffs (stage II), of phreatomagmatic origin, which were erupted from a now dissected cone, preserved in this area. The tephra was deposited dominantly by subaqueous sediment gravity flows (density currents) in an ice-bound lake (or less likely a sub-ice water vault), and was also transported to the south by sub-ice meltwater traction currents. This cone is onlapped by a subaerial pahoehoe lava-fed delta sequence, formed during stage III, and which was most likely fed from a now buried vent(s), located somewhere in the north-central part of the mountain. A 150 m rise in lake level submerged the capping lavas, and was associated with progradation of a new pahoehoe lava-fed delta sequence, produced during stage IV, and which was fed from the present summit cone vent. The water level rise and onset of stage IV eruptions were not associated with any obviously exposed phreatomagmatic deposits, but they are most likely buried beneath stage IV delta deposits. Stage IV lava-fed deltas display steep benches, which do not appear to be due to syn- or post-depositional mass wasting, but were probably generated during later erosion by ice. The possibility that they are due to shorter progradation distances than the underlying stage III deltas, due to ice-confinement or lower volumes of supplied lava is also considered.

The content and composition of organic compounds in the snow-ice cover of the White Sea

This paper reports data on the concentrations of organic compounds (organic carbon, Corg; lipids; aliphatic hydrocarbons, AHCs; and polycyclic 0aromatic hydrocarbons, PAHs) in snow, ice, and subice waters from the mouth of the Severnaya Dvina River (2005–2007) and Kandalaksha Gulf (Chupa Bay, 2004) at the end of winter. It was established that organic compounds are accumulated in the snow and upper ice layer near the town of Archangelsk. The distribution of molecular markers indicates that pollution was mainly caused by local fallouts. In Chupa Bay, organic compounds are concentrated in the lower ice layers, which is typical of the Arctic snow-ice cover. The high contents of organic compounds in the snow-ice cover of the White Sea are caused by the pollution of its air and water during the winter season.

Northwest Territories and Nunavut Snow Characteristics from a Subarctic Traverse: Implications for Passive Microwave Remote Sensing

Abstract During April 2007, a coordinated series of snow measurements was made across the Northwest Territories and Nunavut, Canada, during a snowmobile traverse from Fairbanks, Alaska, to Baker Lake, Nunavut. The purpose of the measurements was to document the general nature of the snowpack across this region for the evaluation of satellite- and model-derived estimates of snow water equivalent (SWE). Although detailed, local snow measurements have been made as part of ongoing studies at tundra field sites (e.g., Daring Lake and Trail Valley Creek in the Northwest Territories; Toolik Lake and the Kuparak River basin in Alaska), systematic measurements at the regional scale have not been previously collected across this region of northern Canada. The snow cover consisted of depth hoar and wind slab with small and ephemeral fractions of new, recent, and icy snow. The snow was shallow (&amp;lt;40 cm deep), usually with fewer than six layers. Where snow was deposited on lake and river ice, it was shallower, denser, and more metamorphosed than where it was deposited on tundra. Although highly variable locally, no longitudinal gradients in snow distribution, magnitude, or structure were detected. This regional homogeneity allowed us to identify that the observed spatial variability in passive microwave brightness temperatures was related to subgrid fractional lake cover. Correlation analysis between lake fraction and Advanced Microwave Scanning Radiometer for Earth Observing System (AMSR-E) brightness temperature showed frequency dependent, seasonally evolving relationships consistent with lake ice drivers. Simulations of lake ice thickness and snow depth on lake ice produced from the Canadian Lake Ice Model (CLIMo) indicated that at low frequencies (6.9, 10.7 GHz), correlations with lake fraction were consistent through the winter season, whereas at higher frequencies (18.7, 36.5 GHz), the strength and direction of the correlations evolved consistently with the penetration depth as the influence of the subice water was replaced by emissions from the ice and snowpack. A regional rain-on-snow event created a surface ice lens that was detectable using the AMSR-E 36.5-GHz polarization gradient due to a strong response at the horizontal polarization. The appropriate polarization for remote sensing of the tundra snowpack depends on the application: horizontal measurements are suitable for ice lens detection; vertically polarized measurements are appropriate for deriving SWE estimates.

Living conditions, abundance and composition of the metazoan fauna in surface and sub-ice layers in pack ice of the western Weddell Sea during late spring

Abstract The surface and sub-ice layer habitats and their metazoan fauna were studied on a drifting pack-ice floe in the western Weddell Sea from 29 November 2004 to 1 January 2005 during the “Ice Station POLarstern” (ISPOL). Flooding of the floe occurred at some places, and the establishment of surface layers with a brownish colour due to growing algae was observed at several sampling sites. The average surface-layer temperature, brine salinity and brine volume were −1.4 °C, 25.3 and 54%, respectively. The temperature–salinity relationship in the surface layer was seldom at equilibrium conditions. Chlorophyll a (Chl a) concentrations in the brine varied between 1.0 and 53.5 μg L−1. Surface-layer thickness, salinity, Chl a concentration and copepod abundances were generally higher at the edge of the floe than in the inner part. The sympagic copepod species Drescheriella glacialis/racovitzai and Stephos longipes, with abundances ranging between 0 and 3830 ind. L−1 (median: 2 ind. L−1) and 0 and 1293 ind. L−1 (median: 4 ind. L−1), respectively, were the dominant members of the surface-layer meiofauna. Their populations consisted mainly of adults and early naupliar stages, which points to an active reproduction of these species within the surface layer. Other taxa found in the surface layer were undetermined turbellarians, the gastropod Tergipes antarcticus, and, for the first time, the ctenophore Callianira antarctica, and the amphipods Eusirus antarcticus and Eusirus tridentatus. During the course of our study, slight melting at the ice underside took place, releasing sympagic organisms to the water column. Chl a concentrations in the sub-ice water layer were very low (0.1–0.5 μg L−1), except for 25 December when the Chl a concentration at 0 m depth increased to 2.3 μg L−1. The most dominant sympagic copepod species found in the sub-ice layer was Ectinosoma sp., with abundances ranging between 1 and 599 ind. m−3 (median: 25 ind. m−3). Other sympagic copepod species occurring regularly in this habitat were D. glacialis/racovitzai, Diarthrodes cf. lilacinus, Idomene antarctica and S. longipes. All of these sympagic species were generally found in higher abundances at 0 m depth underneath the ice than at 5 m depth, in contrast to pelagic copepod species that occurred more frequently at 5 m depth. Niche separation and probable life-cycle strategies of dominant sympagic metazoans are discussed.

Seasonal dynamics of sub-ice fauna below pack ice in the Arctic (Fram Strait)

Pronounced seasonality is a characteristic feature of polar ecosystems, but seasonal studies in the high-Arctic pack-ice zone are still scarce because of logistical constraints. During six expeditions (1994–2003) to the Fram Strait area between Greenland and Svalbard in winter, spring, early summer, late summer and autumn, the sub-ice habitat and fauna below the pack ice (0–1 m depth) were analyzed for seasonal patterns. Both environmental variables such as ice cover, temperature, salinity and chlorophyll a (chl a), as well as species composition, abundance and biomass of the sub-ice fauna showed distinct seasonal dynamics. Most species of the sub-ice fauna were found in early summer, followed by autumn, spring and late summer; the lowest number occurred in winter. The sub-ice fauna was dominated by copepod nauplii during all seasons. Next numerous was the small pelagic copepod Oithona similis, followed by occassional swarms of Pseudocalanus minutus and Calanus spp. Abundances of the sympagic fauna in the sub-ice water layer were much lower, with ectinosomatid copepods being usually the most numerous sympagic group. In the course of the year, total abundances of the sub-ice fauna showed a steep increase from the earliest sampling dates towards the end of winter/beginning of spring reaching maximum numbers then, and a decrease to minimum numbers in early summer. A second peak occurred in late summer, followed by a decrease towards autumn. This significant trend was due to the abundances of copepod nauplii and Oithona similis. Sympagic species were virtually absent during winter, and increased significantly in spring and early and late summer. A factor analysis revealed the variables ice cover and thickness, water temperature and salinity, as well as chl a as the major controlling factors for the seasonal patterns in different groups and species of the sub-ice fauna. Because of the special environmental conditions in the sub-ice habitat, and the unique species composition characterized by small taxa, young stages, and sympagic species, the seasonal dynamics of the Arctic sub-ice fauna differ substantially from those of the epipelagic zooplankton community in the Arctic Ocean.

Phototrophic and heterotrophic nano- and microorganisms of sea ice and sub-ice water in Guba Chupa (Chupa Inlet), White Sea, in April 2002

Autotrophic and heterotrophic flagellates, microalgae and ciliates sampled at four stations in the White Sea in April 2002 were studied using epifluorescence microscopy. The concentrations of phototrophic 1.5 ?m algae in the middle and lower part of the ice core were very high: up to 6.1 ± 108 cells I?1 and 194 ?g C I?1. Heterotrophic algae made up the largest proportion of the nanoplankton (2-20 ?m) and microplankton (20-200 ?m) at depths 10-25 m below the ice. The proportion of ciliates ranged from about 0.01% to 18% at different stations and depths. Most of the ciliate biomass in the ice was made up of typical littoral zone species, whereas the water under the ice was dominated by phototrophic Myrionecta rubra. Ice algae, mainly flagellates in the upper ice layer and diatoms in the bottom ice layer, supported the proliferation of heterotrophs, algae and ciliates in early spring. Small heterotrophs and diatoms from the ice may provide food for early growth and development of pelagic copepods. Mass development of the ice algae in early spring appears typical for the seasonal ice of the White Sea. Ice algae differ in species composition from the spring pelagic community and develop independently in time and space from the spring phytoplankton bloom.

Phototrophic and heterotrophic nano- and microorganisms of sea ice and sub-ice water in Guba Chupa (Chupa Inlet), White Sea, in April 2002

Autotrophic and heterotrophic flagellates, microalgae and ciliates sampled at four stations in the White Sea in April 2002 were studied using epifluorescence microscopy. The concentrations of phototrophic 1.5 ?m algae in the middle and lower part of the ice core were very high: up to 6.1 ± 108 cells I?1 and 194 ?g C I?1. Heterotrophic algae made up the largest proportion of the nanoplankton (2-20 ?m) and microplankton (20-200 ?m) at depths 10-25 m below the ice. The proportion of ciliates ranged from about 0.01% to 18% at different stations and depths. Most of the ciliate biomass in the ice was made up of typical littoral zone species, whereas the water under the ice was dominated by phototrophic Myrionecta rubra. Ice algae, mainly flagellates in the upper ice layer and diatoms in the bottom ice layer, supported the proliferation of heterotrophs, algae and ciliates in early spring. Small heterotrophs and diatoms from the ice may provide food for early growth and development of pelagic copepods. Mass development of the ice algae in early spring appears typical for the seasonal ice of the White Sea. Ice algae differ in species composition from the spring pelagic community and develop independently in time and space from the spring phytoplankton bloom.

Lipid Content and fatty acid composition of algal communities in sea-ice and water from the Weddell Sea (Antarctica)

The lipid and fatty acid compositions of microalgae were investigated in sea-ice and water samples from six different habitats of the Weddell Sea (Antarctica). All sea-ice samples and ice-associated water contained high algal biomass dominated by centric and pennate diatoms. Cells partially filled with oil droplets and resting spores were found. In the cells from the ice platelet layer triacylglycerols formed the largest component of the lipids. The fatty acid composition of sea-ice microalgae was dominated by the 16:1(n-7), 16:0, 18:1(n-9) and 20:5 (n-3) fatty acids. Except 18:1, they are typical for diatom fatty acids. These fatty acids were most abundant in pieces of first year ice with a brown colouration (“brown-ice”) and in the water column directly below sea-ice (sub-ice water). The small amounts of non-diatom acids, as 22:6 (n-3) and 18:4 (n-3), clearly showed that the sea-ice communities were not purely composed of diatoms. The most striking difference, in comparison to the general fatty acid composition of diatoms, was the high proportion of the 18:1 fatty acid in all samples, which might be caused by detrital material or lipid accumulation within cells and resting spores. In general, no clear adaptation of the fatty acid composition to the Antarctic and sea-ice environment was found. The fatty acid composition of the particulate matter from the water column was totally different from all other samples dominated by the saturated fatty acids 16:0 and 18:0.

Diffusion of Light in Antarctic Sea Ice

ABSTRACTIt is important to understand the diffusion sun light in sea ice as this interaction exerts a strong influence over the weather in polar regions and over the growth of microbial communities in the sub-ice water column. Sea ice is a granular composite of ice, brine, air and at low temperatures precipitated salts, in which the proportion and disposition of these components vary with depth, with temperature and thermal history. It is demonstrated that by using a simple in situ technique, supported by Monto Carlo simulations, the diffusive transport of light through a weakly absorbing composite such as sea ice can be characterised. The radiation field both within and emergent from the ice is found to reflect the anisotropic structure of the ice, in particular, the scattering is found to be highly anisotropic so that the light is channelled predominantly vertically. The technique will be illustrated with experimental results collected in McMurdo Sound, Antarctica.