Abundance and composition of the sea-ice meiofauna in off-shore pack ice of the Beaufort Gyre in summer 2002 and 2003

We studied the abundance, biomass and potential ingestion rates of meiofauna in multi-year sea ice (MYI) of the Beaufort Gyre during two icebreaker expeditions in summers 2002 and 2003. Ice cores were taken at a total of ten stations and analyzed for ice temperature, salinity, chlorophyll a (Chl a), and ice meiofauna abundances. In 2002, ice was free of snow and covered with melt ponds. In 2003, snow still covered the ice and a slush-layer was found in the ice-water interface. The vertical distribution of Chl a mostly followed C-shaped curves with elevated concentrations at the bottom and top of the ice. Ice meiofauna was mainly restricted to the bottom 10 cm of the ice and was dominated by turbellarians, harpacticoid copepods and nematodes. The meiofauna abundances (range: 8–3,000 individuals m^–2) and Chl a concentration (range: 0.1–1.7 mg Chl a m^–2) were similar to estimates for MYI of the Transpolar Drift, but about 2 orders of magnitude below coastal fast first-year ice estimates. Calculated potential meiofaunal ingestion rate, based on allometric equations and volume estimates from the literature, was about 1% of published daily algal production rates and was thus unlikely to constrain algal biomass accumulation.     

In situ spectroradiometric estimation of microalgal biomass in first-year sea ice

Summary First- and multi-year sea ice are colonized by microalgae, whose biomass modifies the spectral distribution of underice downwelling irradiance. It is proposed that an index of algal biomass in the first-year ice may be derived from the ratio of underice irradiance at a wavelength where absorption by chlorophyll a is high to a wavelength where absorption by the photosynthetic pigments is low and transmission through the ice is high. In southeastern Hudson Bay (Canadian Arctic), the irradiance ratio (671540 nm) accounts for 55% of the variance in chlorophyll a, indicating that the in situ biomass of algae in first-year ice can be estimated from spectral measurements of underice downwelling irradiance.Contribution to the programme of GIROQ (Groupe interuniversitaire de recherches océanographiques du Québec)     

Vertical distribution of bacteria in Arctic sea ice from the Barents and Laptev Seas

The vertical distribution of bacterial abundance and biomass was investigated in relation to algal biomass in ice cores taken from drifting ice floes in two Arctic shelf areas: the Barents Sea and the Laptev Sea. Bacteria were not homogeneously distributed throughout the cores but occurred in dense layers. Different types of distribution patterns were found: either a single maximum occurred inside or at the bottom of the ice floe or maxima were found in different parts of the floes. Bacterial concentrations ranged from 0.4 to 36.7 · 10⁵ cells ml⁻¹. The size spectra of sea-ice bacteria were determined by image analysis. Cell sizes showed considerable variation between the ice floes. In multi-year sea ice, the largest bacteria were observed in the area of an internal chlorophyll a maximum. No specific vertical distribution patterns were found in first-year ice floes. Bacterial biomass for the ice cores ranged from 19.2 to 79.2 mg C m⁻², and the ratio of bacterial:ice algal biomass ranged from 0.43 to 10.42. A comparison with data collected from fast ice revealed large differences in terms of cell size, abundance and biomass. Received: 7 September 1995 / Accepted: 10 September 1996     

Scales of horizontal patchiness in chlorophyll a, chemical and physical properties of landfast sea ice in the Gulf of Finland (Baltic Sea)

Horizontal variation of first-year landfast sea ice properties was studied in the Gulf of Finland, the Baltic Sea. Several scales of variation were considered; a number of arrays with core spacings of 0.2, 2 and 20 m were sampled at different stages of the ice season for small-scale patchiness. Spacing between these arrays was from hundreds of meters to kilometers to study mesoscale variability, and once an onshore–offshore 40-km transect was sampled to study regional scale variability. Measured variables included salinity, stable oxygen isotopes (¹⁸O), chlorophyll a (chl-a), nutrients and dissolved organic carbon. On a large scale, a combination of variations in the under-ice water salinity (ice porosity), nutrient supply and the stage of ice development control the build-up of ice algal biomass. At scales of hundreds of meters to kilometers, there was significant variability in several parameters (salinity, chl-a, snow depth and ice thickness). Analyses of the data from the arrays did not show evidence of significant patchiness at scales <20 m for algal biomass. The results imply that the sampling effort in Baltic Sea ice studies should be concentrated on scales of hundreds of meters to kilometers. Using the variations observed in the study area, the estimate for depth-integrated algal biomass in landfast sea ice in the Gulf of Finland (March 2003) is 5.5±4.4 mg chl-a m^–2.     

rRNA and rDNA based assessment of sea ice protist biodiversity from the central Arctic Ocean

Sea ice is a large and diverse ecosystem contributing significantly to primary production in ice-covered regions. In the Arctic Ocean, sea ice consists of mixed multi-year ice (MYI), often several metres thick, and thinner first-year ice (FYI). Current global warming is most severe in Arctic regions; as a consequence, summer sea ice cover is decreasing and MYI is disappearing at an alarming rate. Despite its apparent hostility, sea ice is inhabited by a diverse microbial community of bacteria and protists, many of which are photosynthetic. Here we present an assessment of eukaryotic biodiversity in MYI and FYI from the central Arctic Ocean using high-throughput 454 sequencing of 18S rRNA and rDNA amplicons. We compared the rDNA-based ‘total’ biodiversity with the ‘active’ biodiversity from rRNA amplicons and found differences between them including an over-representation of Ciliophora, Bicosoecida and Bacillariophyceae operational taxonomic units (OTUs) in the active part of the community. Differences between the two libraries are more pronounced at the lower taxonomic level: certain genera, such as Melosira, are more abundant in the rRNA library, indicating activity of these genera. Furthermore, we found that one FYI station showed a higher activity of potential grazers which was probably due to the advanced stage of melt evident by higher ice temperatures and highly porous ice compared with the other stations.     

Linking ice structure and microscale variability of algal biomass in Arctic first-year sea ice using an in situ photographic technique

Microscale photographs were taken of the ice bottom to examine linkages of algal chlorophyll a (chl a) biomass distribution with bottom ice features in thick Arctic first-year sea ice during a spring field program which took place from May 5 to 21, 2003. The photographic technique developed in this paper has resulted in the first in situ observations of microscale variability in bottom ice algae distribution in Arctic first-year sea ice in relation to ice morphology. Observations of brine channel diameter (1.65–2.68 mm) and number density (5.33–10.35 per 100 cm²) showed that the number of these channels at the bottom of thick first-year sea ice may be greater than previously measured on extracted ice samples. A variogram analysis showed that over areas of low chl a biomass (≤20.7 mg chl a m⁻²), patchiness in bottom ice chl a biomass was at the scale of brine layer spacing and small brine channels (∼1–3 mm). Over areas of high chl a biomass (≥34.6 mg chl a m⁻²), patchiness in biomass was related to the spacing of larger brine channels on the ice bottom (∼10–26 mm). Brine layers and channels are thought to provide microscale maxima of light, nutrient replenishment and space availability which would explain the small scale patchiness over areas of low algal biomass. However, ice melt and erosion near brine channels may play a more important role in areas with high algal biomass and low snow cover.     

High number of diatom species in first-year ice from the Chukchi Sea

Our study describes the species composition of microalgae, primarily diatoms, in two ice cores collected from the Chukchi Sea in early June 1998. At least 251 species were present in 2 cores collected 10 m apart in first-year ice. This is a greater number of algal species in ice from one locality than has been recorded from any other area of the Arctic. Microalgae were distributed throughout the 173-cm-long core, but abundance and species composition varied among different sections of the core, with maximum species richness (108 and 103 species in the 94- to 103- and 103- to 113-cm sections, respectively) occurring in the middle sections. More than 237 species were recorded from this core. Only the bottom 20 cm of the shorter (110 cm) core was analysed and it contained 135 algal species, still an extraordinarily high number of species. Marine species dominated both cores, but typical brackish and freshwater species were also present. None of these species, however, had more than 1% relative abundance. It should be noted, though, that there were several distinct, but unidentified, species of unknown origin. Characteristic ice algal species (e.g. Nitzschia frigida, Navicula pelagica, solitary Navicula spp., in addition to Cylindrotheca closterium) were the numerical dominants in most sections of the long core, but phytoplankton and benthic species were quite abundant in some sections. One section was dominated by a blue-green bacterium, presumably of the genus Anabaena. The species composition is consistent with several different mechanisms for algal incorporation into ice (i.e. seawater filtration ice, seeding from the sea floor, freshwater input). Over time, ice dynamics and sources of ice in the Chukchi Sea appear to result in high numbers of algal species in the ice. It is also likely that season of collection contributed to the high number of species observed. Determining the geographical area of origin for the different species is however difficult, due to the large-scale pattern of ice circulation.     

Note on sea-ice nematodes (Monhysteroidea) from Resolute Passage, Canadian High Arctic

Nematodes from the bottom section of first-year ice sampled every 4 days during April/May 1992 at two adjacent sites of an ice field station in Resolute Passage have been identified as members of the Monhysteroidea: Theristus melnikovi Tchesunov, 1986; Cryonema tenue Tchesunov and Riemann, 1995; and three unknown monhysterids that are similar to Cryonema. The maximum population density of nematodes was 23 810 m⁻². None of the ice nematodes has ever been reported from benthic samples and their occurrence in ephemeral sea ice is the subject of hypotheses. Since a drastic change of the community structure was noted to take place within a few days, it is assumed that the majority of ice-nematode species do not represent an autochthonous faunal element in the examined habitat and that the main site for their reproduction is elsewhere. The nematode community found near the undersurface of ephemeral ice is apparently influenced by particular import and export processes that are unknown as yet. Received: 2 October 1996 / Accepted: 15 December 1996     

Structure of the diatom community of the River Adige (North-Eastern Italy) along a hydrological gradient

Physical constrains such as water discharge, suspended solids and turbidity act as dominant factors in driving the planktonic diatom assemblages of the River Adige (North-Eastern Italy). Two sampling stations, characterised by different hydromorphological features (Cortina all’Adige and Boara Pisani, with torrential and more potamal characteristics, respectively) were sampled fortnightly following an integrated approach encompassing physical, chemical and biological measurements and aiming at identifying the dominant factors controlling the temporal development of the community. A morpho-functional approach was used to classify the diatom assemblages where Morpho-Functional Diatom Groups (MFDG) were defined for diatom genera, according to their morphology, habitat selection and modality of adhesion to river substrate. In the two sampling points, algal growth was never limited by nutrients or zooplankton. The irregular development of MFDG was determined by the stochastic hydrological events and changes in variables related to water discharge (suspended solids and light attenuation). Tychoplanktonic, benthic and drifted taxa (such as Diatoma spp., Encyonema spp., Navicula spp. and Nitzschia spp.) were dominant in the torrential station (Cortina all’Adige), while the contribution of euplanktonic unicellular centric taxa (such as Cyclotella spp., and Stephanodiscus spp.) was higher in the potamal station (Boara Pisani).     

Influence of sea ice on the composition of the spring phytoplankton bloom in the northern Baltic Sea

During the late winter and spring of 1994, the influence of sea ice on phytoplankton succession in the water was studied at a coastal station in the northern Baltic Sea. Ice cores were taken together with water samples from the underlying water and analysed for algal composition, chlorophyll a and nutrients. Sediment traps were placed under the ice and near the bottom, and the sedimented material was analysed for algal composition. The highest concentration of ice algae (4.1 mmol C m⁻²) was found shortly before ice break-up in the middle of April, coincidental with the onset of an under-ice phytoplankton bloom. The ice algae were dominated by the diatoms Chaetoceros wighamii Brightwell, Melosira arctica (Ehrenberg) Dickie and Nitzschia frigida Grunow. Under the ice the diatom Achnanthes taeniata Grunow and the dinoflagellate Peridiniella catenata (Levander) Balech were dominant. Calculations of sinking rates and residence times of the dominant ice algal species in the photic water column indicated that only one ice algal species (Chaetoceros wighamii) had a seeding effect on the water column: this diatom dominated the spring phytoplankton bloom in the water together with Achnanthes taeniata and Peridiniella catenata. Received: 9 May 1997 / Accepted: 15 February 1998     

Size,age and diet of polar cod,Boreogadus saida (Lepechin 1773), in ice covered waters

Summary Polar cod (Boreogadus saida) associated with drifting sea-ice were collected in the western Barents sea and north of Svalbard with dip-nets while SCUBA-diving in 1986 and 1987. Length-frequency measurements and otolith-readings suggested that the specimens were either one or two years old. The diet of fish from the western Barents sea (first-year ice) consisted mainly of copepods (Calanus finmarchicus, Calanus glacialis) and the hyperiid amphipod Parathemisto libellula. Fish collected north of the Svalbard archipelago (multi-year ice) had a more diverse diet, in which P. libellula and the sympagic amphipod Apherusa glacialis contributed more to the total diet biomass than copepods.     

Comparing Springtime Ice-Algal Chlorophyll a and Physical Properties of Multi-Year and First-Year Sea Ice from the Lincoln Sea

With near-complete replacement of Arctic multi-year ice (MYI) by first-year ice (FYI) predicted to occur within this century, it remains uncertain how the loss of MYI will impact the abundance and distribution of sea ice associated algae. In this study we compare the chlorophyll a (chl a) concentrations and physical properties of MYI and FYI from the Lincoln Sea during 3 spring seasons (2010-2012). Cores were analysed for texture, salinity, and chl a. We identified annual growth layers for 7 of 11 MYI cores and found no significant differences in chl a concentration between the bottom first-year-ice portions of MYI, upper old-ice portions of MYI, and FYI cores. Overall, the maximum chl a concentrations were observed at the bottom of young FYI. However, there were no significant differences in chl a concentrations between MYI and FYI. This suggests little or no change in algal biomass with a shift from MYI to FYI and that the spatial extent and regional variability of refrozen leads and younger FYI will likely be key factors governing future changes in Arctic sea ice algal biomass. Bottom-integrated chl a concentrations showed negative logistic relationships with snow depth and bulk (snow plus ice) integrated extinction coefficients; indicating a strong influence of snow cover in controlling bottom ice algal biomass. The maximum bottom MYI chl a concentration was observed in a hummock, representing the thickest ice with lowest snow depth of this study. Hence, in this and other studies MYI chl a biomass may be under-estimated due to an under-representation of thick MYI (e.g., hummocks), which typically have a relatively thin snowpack allowing for increased light transmission. Therefore, we suggest the on-going loss of MYI in the Arctic Ocean may have a larger impact on ice–associated production than generally assumed.     

Succession of sea-ice bacterial communities in the Baltic Sea fast ice

Coastal fast ice and underlying water of the northern Baltic Sea were sampled throughout the entire ice winter from January to late March in 2002 to study the succession of bacterial biomass, secondary production and community structure. Temperature gradient gel electrophoresis (TGGE) and sequencing of TGGE fragments were applied in the community structure analysis. Chlorophyll-a and composition of autotrophic and heterotrophic assemblages were also examined. Overall succession of ice organism assemblages consisted of a low-productive stage, the main algal bloom, and a heterotrophic post-bloom situation, as typical for the study area. The most important groups of organisms in ice in terms of biomass were dinoflagellates, plasticidic flagellates, rotifers and ciliates. Ice bacteria showed a specific succession not directly dependent on the overall succession events of ice organisms. Sequenced 16S rDNA fragments were mainly affiliated to α-, β-, and γ-proteobacterial phyla and Cytophaga–Flavobacterium–Bacteroides-group, and related to sequences from cold environments, also from the Baltic Sea. Temporal clustering of the TGGE fingerprints was stronger than spatial, although lower ice and underlying water communities always clustered together, pointing to the importance of ice maturity and ice–water interactions in shaping the bacterial communities.     

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

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

Development of ice biota in a temperate sea area (Gulf of Bothnia)

A study of sea ice biota was carried out in the Gulf of Bothnia (northern Baltic Sea) during the winter of 1989–1990. Samples (ice cores) were taken at a coastal station at regular time intervals during the ice season. Chlorophyll a concentration, algal species distribution, bacterial numbers, and primary and bacterial production were measured. Colonization of the ice began in January when daylight was low. As the available light increased, the algae started to grow exponentially. The vertical chlorophyll a distribution changed and algal species composition and biomass changed during the season. During the initial and middle phase of colonization, ice-specific diatoms, Nitzschia frigida and Navicula pelagica, dominated the algal biomass. Nutrients (PO₄ ^3– and NO_3j) were found to be depleted during the time of algal exponential growth. The maximum algal biomass exceeded 800 g C 1^–1. The primary production supplied food for heterotrophic organisms. The presence of heterotrophic organisms of different trophic levels (bacteria, flagellates, ciliates and rotifers) indicated an active microbial food web.     

Mesoscale spatial distribution of chaetognaths along hydrographic gradients in the South Scotia Sea (Antarctica)

Mesoscale distribution of chaetognaths in the South Scotia Sea was studied in January 1994. Three transects (ice margin to Elephant Island, ice margin to the Weddell-Scotia Confluence, and the Drake Passage) and a station grid in the East Bransfield Strait were laid out, seeking the greatest possible heterogeneity in hydrographic conditions. Six species were collected, with the most abundant species, Eukrohnia hamata, accounting for 83% of the total number of individuals, followed by Sagitta gazellae (9.7%). High spatial variability was observed both along the transects and over the mesoscale station grid. The station grid allowed two assemblages to be distinguished on the basis of species abundance and demographic population structure. Both assemblages were distributed through areas with distinct hydrographic characteristics. Use of a smaller sampling scale and a more detailed definition of development stages than in earlier studies revealed a higher level of spatial heterogeneity than previously suggested for chaetognaths in the Southern Ocean. Accepted: 11 April 1999     

ALGAL ASSEMBLAGES IN ANTARCTIC PACK ICE AND IN ICE-EDGE PLANKTON1

A significant amount of the primary production in the Southern Ocean and other ice-covered oceans takes place in localized ice edge plankton blooms. The dynamics of these blooms appear to be closely related to seasonal melting of sea ice. Algal cells released from the ice are a possible source of ice edge planktonic assemblages, but evidence for this “seeding” has been equivocal. We compared algal assemblages in ice and water in the Weddell Sea during the austral spring of 1983 at a receding ice edge with a well-developed ice edge bloom. The high degree of similarity between ice and water column assemblages, the spatial and temporal patterns in the distribution and abundances of species, and preliminary evidence for the viability and growth of ice-associated species provide evidence for seeding from sea ice of some species in Antarctica.     

Chlorophyll a biomass and growth of sea-ice microalgae along a salinity gradient (southeastern Hudson Bay,Canadian Arctic)

Summary The biomass of microalgae at the bottom of first-year sea ice, in southeastern Hudson Bay (Canadian Arctic), parallels an inshore-offshore salinity gradient caused by the under-ice plume of the Great Whale River. The present study was designed to test the hypothesis that the variation of ice-algal biomass (chlorophyll a) along the salinity gradient was mainly controlled by nutrient availability, with the alternative hypothesis of a direct control by ambient salinity. The approach was that of differential in situ bioassays, conducted at the ice-water interface of two stations, located in the plume of the Great Whale River (lower salinity) and in the offshore waters of Hudson Bay (higher salinity). The inoculum (collected at the higher salinity station) was diluted with three types of seawater, i.e. (1) from the higher salinity station, (2) from the lower salinity station, and (3) from the latter but with salinity artificially increased to the level of the higher salinity station. The three sets of cultures were differentially enriched. In situ incubations for the first set were at the higher salinity station and, for the other two, at the lower salinity station. Results indicate possible Si limitation of the algal biomass at the higher salinity station. First, concentrations of Si(OH)₄ observed at this station were lower than in the plume of the Great Whale River; in addition, the SiP molar ratios were lower than ca. 15; also, Si was the only nutrient whose addition (alone or combined with others) yielded biomasses higher than in the reference enrichment; finally, the highest growth rate for a singly added nutrient was with Si and subtraction of Si (single nutrient) was more detrimental to growth rate than that of N or P. In contrast, there was no strong indication of nutrient effects at the lower salinity station, so that nutrient limitation could not explain the lower ice-algal biomasses in lower salinity waters. At this same station, on the other hand, growth rates in water with artificially increased salinity were 2–3 times higher than those in unaltered water. These results are consistent with the hypothesis that salinity, and not nutrients, is the main factor that limits the development of ice algae in the lower salinity waters of southeastern Hudson Bay.Contribution to the programs of GIROQ (Groupe interuniversitaire de recherches océanographiques du Québec) and of the Maurice Lamontagne Institute (Biological Oceanography Division, Department of Fisheries and Oceans)     

Effect of ammonium load on the growth of attached microalgae in the northern Baltic Sea

The effect of ammonium discharge from a food factory on the growth of attached microalgae was monitored north of the Hanko peninsula, on the southwestern coast of Finland. The impact of the discharge was studied at twelve localities, at four stages of seasonal succession. The microalgae were sampled from glass slides exposed at 0.4 m depth for two weeks. The variables measured for the microalgal growth were chlorophylla, primary production and total organic carbon (TOC). These were compared with planktonic chlorophylla and nutrient concentrations. The growth of attached microalgae displayed a consistent pattern of spatial distribution. Depending on season, TOC and primary production values were 7 to 70 times higher and chlorophylla values up to 1000 times higher close to the effluent outlet than in undisturbed areas of the archipelago. The microalgal samples near the discharge were characterized by low TOC/chlorophylla and TOC/primary production ratios. The temporal consistency of microalgal distribution illustrates the advantages of using attached algal assemblages in monitoring programmes.     

Sub-ice algal assemblages of the Barents Sea: Species composition,chemical composition,and growth rates

Summary The ice algae of the Barents Sea were studied from 1986 to 1988. With a few exceptions, the ice algal assemblages were dominated by pennate diatoms. From March to early June there was a transition from a mixed population of both centric and pennate diatoms at the start into a well developed Nitzschia frigida assemblage. Nutrier ts in ice-covered regions were high in spring, and high N/C and protein/carbohydrate ratios indicated no nutrient deficiency in the ice algae. The N/P ratios were lower than 15, but comparable to ratios of three ice algae species grown in culture at -0.5 °C and various light conditions. The Si/N ratios were lower than corresponding ratios from the Canadian Arctic and the Antarctic. The chemical composition revealed that silicate limited growth cannot be excluded. The cells were heavily shade-adapted the entire spring season, with high Chl/C ratios (0.045–0.084), comparable to the cultures growing at low irradiances. The growth rates in the cultures peaked at 50 mol m^-2s^-1 with maximum rates of 0.6–0.8 div. day^-1, both for 12 and 24 h day lengths. The low growth rates for the May assemblages (max 0.20 div. day^-1) indicated strong light limitation by self-shading. Adaptation experiments showed that some ice algae are highly adaptable, while others are not able to adjust to new irradiances. Their growth rates are inhibited by high irradiances and this may affect the distribution in the field.