Marine bacterioplankton at the Weddell Sea ice edge,distribution of psychrophilic and psychrotrophic populations

Summary In the eastern Weddell Sea on several transects from ice-covered, through ice melt, to open-ocean stations, total and heterotrophic bacteria were estimated to document an enhanced bacteriological biomass expected near the ice edge. The highest numbers of bacteria were found in melted ice cores, with 4.2·10³ CFUml^–1 and 1.1·10⁷ Cells ml^–1. Although brine from pore water samples average more than one order of magnitude less cells per ml, the highest bacterial production, 2.2·10⁷ cells l^–1 day^–1, was recorded in brine samples. All quantitatively studied bacterial parameters were lower under the ice than in the ice samples but there were no clear vertical gradients in the water column. In the studied spring situation, sea ice occurrence seems to play only a minor role in the general distribution of the seawater bacterioplankton. The bacterial community structure was investigated by carrying out 29 morphological and biochemical tests on 118 isolated strains. The bacterial communities inhabiting Antarctic pack ice differ from those found in underlying seawater. Although non fermentative Gram-negative rods were always dominant in seawater, Vibrio sp. represented more than 25% of the strains isolated from some ice samples. The results clearly indicated that a large majority of the bacteria isolated from seawater must be considered psychrotrophic but that truly psychrophilic strains occurred in melted ice and brine samples.Data presented here were collected during the European Polarstern Study (EPOS) sponsored by the European Science Foundation     

The Cell Wall of Fusarium oxysporum

Sugar analysis of isolated cell walls from three formae speciales of Fusarium oxysporum showed that they contained not only glucose and (N-acetyl)-glucosamine, but also mannose, galactose, and uronic acids, presumably originating from cell wall glycoproteins. Cell wall glycoproteins accounted for 50–60% of the total mass of the wall. X-ray diffraction studies showed the presence of α-1,3-glucan in the alkali-soluble cell wall fraction and of β-1,3-glucan and chitin in the alkali-insoluble fraction. Electron microscopy and lectin binding studies indicated that glycoproteins form an external layer covering an inner layer composed of chitin and glucan.     

A Comparative Analysis of the Ice Nucleation Activity of Pseudomonad Cells and Lipopolysaccharides

The paper deals with the study of the ice nucleation activity of the cells, extracellular lipopolysaccharides (ELPSs), lipopolysaccharides (LPSs), and LPS structural components (lipid A, core oligosaccharide, and O-specific polysaccharide) of Pseudomonas fluorescens, P. syringae, P. fragi, and P. pseudoalcaligenes. Aqueous suspensions of intact cells of P. syringae IMV 1951 and IMV 185 began to freeze at –1 and –4°C, respectively. This suggests that these cells possess ice nucleation activity. Aqueous cell suspensions of two other strains, P. fluorescens IMV 1433 and IMV 2125, began to freeze at lower temperatures than did distilled water (–9°C), which suggests that the cells of these strains possess antifreeze activity. The ice nucleation activity of the bacterial strains studied did not show any correlation with their taxonomic status. The ice nucleation activity of ELPSs depended little on their concentration (within a concentration range of 0.2–0.4%). In most cases, the ice nucleation activity of ELPSs, LPSs, and LPS structural components differed from that of the intact cells from which these biopolymers were obtained. This may indicate that the biopolymers under study play a role in ice nucleation but this role is not crucial. The relationship between the structure of LPSs and their effect on ice nucleation is discussed.     

Characterization of mucin glycoprotein-specific translation products from swine and human trachea,pancreas and colon

Summary RNA was isolated from cultured swine trachea epithelial cells and mucus-secreting tumor cell lines from human pancreas, lung and colon by extraction with guanidine isothiocyanate. Poly(A)⁺mRNA rich fractions were purified by repeated chromatography on oligo (dT)-cellulose columns and they were translated in a cell-free rabbit reticulocyte system. Translation products labelled with ³⁵S-methionine were isolated by immunoprecipitation with specific antibodies to the polypeptide chains of mucin glycoproteins and they were analyzed by SDS-PAGE and fluorography. A single principal polypeptide band of 67 kDa was found in all cases when the immunoprecipitates were washed with buffer containing bovine serum albumin and unlabeled deglycosylated mucin glycoprotein. The intensity of the 67 kDa band decreased when unlabeled deglycosylated mucin glycoprotein was added to the translation mixture before immunoprecipitation. Affinity purified monospecific antibodies elicited against chemically deglycosylated polypeptide chains of purified mucin glycoproteins from human and swine trachea and Cowper's gland were all equally effective in immunoprecipitating the 67 kDa translation product. Monospecific antibodies directed against the glycosylated and unglycosylated regions of the polypeptide chain yielded single bands with a molecular size of 67 kDa in each case. Peptide profiles obtained by digestion of the 67 kDa translation product with S. aureus V-8 protease were identical to those obtained with deglycosylated human and swine trachea mucin glycoproteins.These stydies clearly demonstrate that the translation product of swine trachea and human lung, colon and pancreatic mucin glycoprotein gene is a single polypeptide chain of 67 kDa. The relative size and properties of the translation products synthesized with poly (A)⁺RNA isolated from mucus-secreting cells derived from three different tissues are similar to those of mucin glycoproteins purified directly from mucus secretions of human and swine trachea epithelium.Abbreviations TFMS Trifluoromethanesulfonic acid - SDS Sodium Dodecyl Sulfate - PAGE Polyacrylamide Gel Electrophoresis - GalNAc N-Acetylgalactosamine - HTMG Human Trachea Mucin Glycoprotein - deHTMG deglycosylated Human Trachea Mucin Glycoprotein - STMG Swine Trachea Mucin Glycoprotein - deSTMG deglycosylated Swine Trachea Mucin Glycoprotein - CCMG Cowper's Gland Mucin Glycoprotein - deCGMG deglycosylated Cowper's Gland Mucin Glycoprotein - HPMG Pancreatic Mucin Glycoprotein from BxPC-3 cells - HCMG Colon Mucin Glycoprotein from SW 403 cells - HLMG Human Lung Mucin Glycoprotein from A-549 cells - STMG⁺deSTMG^– antibodies which bind to immobilized STMG but do not bind to immobilized deSTMG - deSTMG⁺STMG^– antibodies which bind to immobilized deSTMG but do not bind to immobilized STMG - STMG⁺deSTMG⁺ antibodies which bind to both STMG and deSTMG - HTMG⁺deHTMG^– antibodies which bind to immobilized HTMG but do not bind to immobilized deHTMG - deHTMG⁺HTMG^– antibodies which bind to immobilized deHTMG but do not bind to immobilized HTMG - HTMG⁺deHTMG⁺ Antibodies which bind to both HTMG and deHTMG     

The presence and quantification of splenic ice in the McMurdo Sound Notothenioid fish, Pagothenia borchgrevinki (Boulenger, 1902)

Survival of some polar fishes is associated with high levels of circulating antifreeze glycoproteins (AFGPs). AFGP prevent ice growth giving rise to thermal hysteresis. The inhibiting action of AFGPs implies that polar fish contain ice to which AFGPs adsorb. Cryopelagic Pagothenia borchgrevinki, inhabiting the ice-laden waters of McMurdo Sound, Antarctica, were assayed for ice and ice was found on skin, gills, in the intestine, and in the spleen. Two methods used to assess the number of ice crystals in spleens gave comparable results (12.1 +/− 1.9 and 22 +/− 3.8 per spleen). Attempts were made to measure the rate of uptake of ice by P. borchgrevinki held in cages immediately beneath the sub-ice platelet layer in McMurdo Sound; uptake was sporadic. Introduction of ice into fish by spray freezing a small patch of the integument resulted in detection of splenic ice after 1 h, illustrating that a mechanism exists for ice transport from the periphery to the spleen. Splenic ice did not seem to be eliminated from fish held in ice-free water at − 1.6 °C for approximately two months. The relatively small number of splenic ice crystals and the slow rate of ice uptake suggest efficient ice barriers exist in P. borchgrevinki.     

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.     

Purification,properties and comparison of invertase,exoinulinases and endoinulinases of Aspergillus ficuum

Summary One invertase (Inv), five exoinulinases (Exo I; II; III; IV; V) and three endoinulinases (Endo I; II; III) were isolated from a commercial inulinase preparation derived from Aspergillus ficuum using ammonium sulfate precipitation, ion exchange chromatography on DEAE-Sephacel and DEAE-Trisacryl, gel filtration on Ultrogel and Fast Protein Liquid Chromatography on a Mono Q column. The invertase (Inv) had a molecular weight of 84000 and was much more active on sucrose than on inulin: the ratio of activity on inulin and sucrose (I/S ratio) was 0.01. The five exoinulinases show the same molecular weight of 74000 and I/S ratios in the range 0.16–0.36. The three endoinulinases had molecular weight of 64000 and I/S ratios in the range 0.86–2.92. All the -fructofuranosidases were glycoproteins with a high sugar content (from 22 to 41% w/w). A. ficuum is the first described organism containing the three activities: invertase, exo and endoinulinase.     

Characterization of mucin isolated from rat tracheal transplants

Subcutaneous rat tracheal grafts yield several milligrams of secretions from which a homogeneous mucin fraction was isolated and purified. Histological evidence demonstrated that a normal mucociliary epithelium and mucous secretion were maintained for the 4–6 weeks of the experiment. The collected secretions were initially characterized by column chromatography on Sepharose CL-6B which separated the excluded high molecular weight mucins (unpurified mucin fraction) from most of the serum-type glycoproteins and proteins, including albumin. A reductive alkylation treatment of the unpurified mucin fraction followed by Sepharose CL-4B chromatography removed contaminating protein and most of the mannose-containing material from the mucin fraction. The void volume material from this column produced a single high molecular weight band upon sodium dodecyl sulfate agarose/acrylamide gel electrophoresis. The purified mucin fraction contained 16.5% protein and primarily galactose, N-acetylglucosamine, N-acetylgalactosamine, and sialic acid. This fraction also underwent β-elimination in the presence of alkaline borohydride, demonstrating the presence of O-glycosidic linkages.     

Size selectivity of aqueous pores in astomatous cuticular membranes isolated from<Emphasis Type="Italic"> Populus canescens</Emphasis> (Aiton) Sm. leaves

Little is known about the permeability of plant cuticles to ionic molecules with hydration shells that render them lipid insoluble and limit their diffusion to narrow aqueous pores. Therefore, the permeation of cuticular membranes to ionised calcium salts with anhydrous molecular weights ranging from 111 to 755 g mol^–1 was studied. Penetration was a first-order process and rate constants (k) (proportional to permeability) decreased exponentially with molecular weight. Plots of log k vs. molecular weight had slopes of –2.11×10^–3 and –2.80×10^–3, respectively, depending on the year in which the cuticular membranes were isolated. This corresponds to decreases in permeability by factors of about 7 to 13 when molecular weight increased from 100 to 500 g mol^–1. This size selectivity is small compared to the dependence on molecular weight of solute mobility in Populus cuticles. A decrease in mobility of neutral molecules by more than 3 orders of magnitude has been reported [A. Buchholz et al. (1998) Planta 206:322–328] for the same range of molecular weights. Hence, discrimination of large ionic species diffusing in aqueous pores (polar pathway) is much smaller than that for neutral solutes diffusing in cutin and waxes (lipophilic pathway). This indicates that formulating large solutes as ionic species would be advantageous.Abbreviation CM Cuticular membrane     

In-situ observations on the distribution and behavior of amphipods and Arctic cod (Boreogadus saida) under the sea ice of the High Arctic Canada Basin

The occurrence and behavior of sympagic amphipods and Arctic cod (Boreogadus saida) were studied in the High Arctic Canada Basin by diving under the ice at seven stations in summer 2002. Still images of video-transects were used to obtain animal abundances and information on the structure of the ice environment. Mean amphipod abundances for the stations varied between 1 and 23 individuals m^–2, with an increase towards the western part of the basin. The standard deviation within the 31–51 images analyzed per station was small (<1 individual m^–2). Gammarus wilkitzkii was found in low abundances, often hiding in small ice gaps. Small amphipods (Onisimus spp., Apherusa glacialis, and juveniles of all species) tended to move freely along the bottom of the floes. B. saida occurred in narrow wedges of seawater along the edges of melting ice floes at three stations in water depths of 10–50 cm and was never found under the ice. The fish occurred in schools of 1–28 per wedge. Fish were inactive and did not escape the approaching diver. Resting in the wedges may be a strategy to reduce energetic requirements and avoid predators.We dedicate this publication to Professor Dr. J. Lenz (Kiel University).     

The Effect of Antifreeze Glycoproteins on Survival of Fish Spermatozoa under the Conditions of Long-Term Storage at 4°C

It was already shown that antifreeze glycoproteins isolated from the blood of fish occurring in circumpolar regions inhibited the growth of ice crystals both in vitro and in vivo. When the spermatozoa were frozen to liquid nitrogen temperature, addition of antifreeze glycoproteins to cryoconserving media made it possible to decrease twofold the concentration of the synthetic cryoprotector dimethylsulfoxide without the loss and even with a certain increase in the number of viable spermatozoa. This effect was observed in the case of combined, rather than separate, addition of the fraction of weakly active (low molecular weight) and active (high molecular weight) antifreeze glycoproteins. Here, we studied the effect of antifreeze glycoproteins on the survival of carp spermatozoa under storage at 4°C for varying periods of time. In the presence of total fraction of low and high molecular weight antifreeze glycoproteins (2 and 10 mg/ml) added in a physiological proportion (3 : 1), the survival of spermatozoa increase but this increase did not depend linearly on the medium concentration of protein. Low and high molecular weight antifreeze glycoproteins added separately (10 mg/ml) either did not affect or slightly affected the preservation of cells. The hypothermic effect of antifreeze glycoproteins in water was significantly higher than in a medium with salt activator.     

Culturable Bacteria in Subglacial Sediments and Ice from Two Southern Hemisphere Glaciers

Viable prokaryotes have been detected in basal sediments beneath the few Northern Hemisphere glaciers that have been sampled for microbial communities. However, parallel studies have not previously been conducted in the Southern Hemisphere, and subglacial environments in general are a new and underexplored niche for microbes. Unfrozen subglacial sediments and overlying glacier ice samples collected aseptically from the Fox Glacier and Franz Josef Glacier in the Southern Alps of New Zealand now have been shown to harbor viable microbial populations. Total direct counts of 2–7 × 10⁶ cells g^–1 dry weight sediment were observed, whereas culturable aerobic heterotrophs ranged from 6–9 × 10⁵ colony-forming units g^–1 dry weight. Viable counts in the glacier ice typically were 3–4 orders of magnitude smaller than in sediment. Nitrate-reducing and ferric iron–reducing bacteria were detected in sediment samples from both glaciers, but were few or below detection limits in the ice samples. Nitrogen-fixing bacteria were detected only in the Fox Glacier sediment. Restriction fragment analysis of 16S rDNA amplified from 37 pure cultures of aerobic heterotrophs capable of growth at 4°C yielded 23 distinct groups, of which 11 were identified as -Proteobacteria. 16S rDNA sequences from representatives of these 11 groups were analyzed phylogenetically and shown to cluster with bacteria such as Polaromonas vacuolata and Rhodoferax antarcticus, or with clones obtained from permanently cold environments. Chemical analysis of sediment and ice samples revealed a dilute environment for microbial life. Nevertheless, both the sediment samples and one ice sample demonstrated substantial aerobic mineralization of ¹⁴C-acetate at 8°C, indicating that sufficient nutrients and viable psychrotolerant microbes were present to support metabolism. Unfrozen subglacial sediments may represent a significant global reservoir of biological activity with the potential to influence glacier meltwater chemistry.     

Aluminum-Induced Changes in Cell-Wall Glycoproteins in the Root Tips of Al-Tolerant and Al-Sensitive Wheat Lines

To investigate wheat (Triticum aestivumL.) responses to Al stress, KCl- and SDS-extracted glycoproteins (covalently bound proteins isolated by cell-wall digestion by cellulysine–pectolase mixture) and extensins (hydroxyproline-containing glycoproteins, HRGPs) were isolated from cell-wall preparations purified from the root apices of Al-sensitive and Al-tolerant near-isogenic lines ES8 and ET8. Under Al stress conditions, two lines differed mostly in their extensins. The untreated plants of two lines were low in covalently bound extensins, although the content of this protein fraction in ES8 was higher than in ET8. When the seedlings were treated with Al, the extensin content increased in both wheat lines and especially in the Al-tolerant ET8 plants. Using two-dimensional electrophoresis, the authors demonstrated the accumulation of polypeptides with mol wts of 22.2 kD (pI 5.5–6.5), 24.5 kD (pI 5.8–6.0), and 33.1 kD (pI 5.25) and polypeptides of 22.2 kD (pI 6.8–7.6) and 40.5 kD (pI 7.6) in the extensin fraction from the cell walls of the Al-sensitive plants. The regulation of cell responses to Al stress may involve extensin expression.     

Living conditions, abundance and biomass of under-ice fauna in the Storfjord area (western Barents Sea, Arctic) in late winter (March 2003)

The under-ice habitat and fauna were studied during a typical winter situation at three stations in the western Barents Sea. Dense pack ice (7–10/10) prevailed and ice thickness ranged over <0.1–1.6 m covered by <0.1–0.6 m of snow. Air temperatures ranged between –1.8 and –27.5°C. The ice undersides were level, white and smooth. Temperature and salinity profiles in the under-ice water (0–5 m depth) were not stratified (T=–1.9 to –2.0°C and S=34.2–34.7). Concentrations of inorganic nutrients were high and concentrations of algal pigments were very low (0.02 g chlorophyll a l^–1), indicating the state of biological winter. Contents of particulate organic carbon and nitrogen ranged over 84.2–241.3 and 5.3–16.4 g l^–1, respectively, the C/N ratio over 11.2–15.5 pointing to the dominance of detritus in the under-ice water. Abundances of amphipods at the ice underside were lower than in other seasons: 0–1.8 ind. m^–2 for Apherusa glacialis, 0–0.7 ind. m^–2 for Onisimus spp., and 0–0.8 ind. m^–2 for Gammarus wilkitzkii. A total of 22 metazoan taxa were found in the under-ice water, with copepods as the most diverse and numerous group. Total abundances ranged over 181–2,487 ind. m^–3 (biomass: 70–2,439 g C m^–3), showing lower values than in spring, summer and autumn. The dominant species was the calanoid copepod Pseudocalanus minutus (34–1,485 ind. m^–3), contributing 19–65% to total abundances, followed by copepod nauplii (85–548 ind. m^–3) and the cyclopoid copepod Oithona similis (44–262 ind. m^–3). Sympagic (ice-associated) organisms occurred only rarely in the under-ice water layer.     

Spatial and temporal photosynthetic compartments during summer in Antarctic Lake Kitiesh

Summary Four autotrophic compartments were recognised in Lake Kitiesh, King George Island (Southern Shetland) at the beginning of the summer in 1987: snow microalgae, ice bubble communities, phytoplankton in the water column and benthic communities of moss with epiphytes. Chlorophyll a concentration and pigment absorption spectra were obtained in these four compartments before and/or after the thawing of the ice cover. During the ice free period, carbon fixation and biomass was measured in the phytoplankton and in the benthic moss Campyliadelphus polygamus. From these measurements we conclude that the benthic moss is the most significant autotrophic component in this lake in terms of biomass, chlorophyll a content and primary productivity. The integral assimilation number (The ratio of carbon fixation per unit area to biomass per unit area) values were similar for both phytoplankton and the moss, ranging from 3.6 to 5.4 mg C (mg Chl a)^–1h^–1in phytoplankton and from 4.0 to 6.4 mgC (mg Chl a)^–1h^–1 in the benthic moss. This approach allows comparisons of carbon fixation efficiency of the chlorophyll a under a unit area between compartments in their different light environments.     

Purification, characterization, and relation to bikunin of rat urinary trypsin inhibitors

Two forms of urinary trypsin inhibitor (UTI-1 and UTI-2) were purified from pooled urine of normal male rats to apparent homogeneity by salting out, affinity chromatography, gel filtration, and reverse-phase HPLC. UTIs-1 and 2 were shown to be thermostable glycoproteins with the respective molecular weights of 22,000 and 18,000 estimated by SDS-PAGE. These inhibitors combined with bovine trypsin in a 1:1 molar ratio: the K _d values were 2.5 × 10^–10 and 2.3 × 10^–10 M, respectively. Amino acid composition and sequence analysis indicated that UTI-1 corresponded to rat bikunin of which the amino acid sequence was deduced from a rat liver cDNA clone encoding ₁-microglobulin [Lindqvist et al. (1992), Biochim. Biophys. Acta 1130, 63–67] except that the protein sequence seemed to lack C-terminal serine, and UTI-2 corresponded to UTI-1 lacking N-terminal 21 amino acid residues.     

Effects of Desmin Gene Knockout on Mice Heart Mitochondria

In heart tissue from mice lacking the intermediate filament (IF) desmin, mitochondria show an abnormal shape and distribution (Thornell et al., 1997). In the present study we have isolated heart mitochondria from desmin null (D–/–) and control (D+/+) mice, and analyzed their composition by SDS–PAGE, immunoblotting, and enzyme measurements. We found both in vitro and in situ that the conventional kinesin, the microtubule-associated plus-end directed motor, was frequently associated with D+/+ heart mitochondria, but not with D–/– heart mitochondria, suggesting that the positioning of mitochondria in heart is a dynamic event involving the IF desmin, the molecular motor kinesin, and, most likely, the microtubules (MT) network. Furthermore, an increased capacity in energy production was found, as indicated by a threefold higher creatine kinase activity in heart mitochondria from D–/– compared to D+/+ mice. We also observed a significantly lower amount of cytochrome c in heart mitochondria from D–/– mice, and a relocalization of Bcl-2, which may indicate an apoptotic condition in the cell leading to the earlier reported pathological events, such as cardiomyocytes degeneration and calcinosis of the heart (Thornell et al., 1997).     

Co-production of ice nuclei and xanthan gum by transformed Xanthomonas campestris grown in sugar beet molasses

Two recombinant plasmids, expressing ice nucleation activity, were constructed and named pCPP30inaZ and pCPP38inaZ. They were transferred to the ice-negative, xanthan-producing Xanthomonas campestris pv. campestris by electroporation. The transformants were used for co-production of xanthan gum and ice nuclei from sugar beet molasses. The highest values obtained were 20 g l^–1 and 10¹⁸ ice nuclei ml^–1, respectively. The above values fulfil the criteria for industrial manipulation. This is the first report on co-formation of two products by a transformed X. campestris strain.     

Photosynthesis-irradiance relationships and carbon metabolism of different ice algal assemblages collected from Weddell Sea pack ice during austral spring (EPOS 1)

Summary Photosynthesis-irradiance relationships and the carbon metabolism of different ice algal assemblages collected from Weddell Sea pack ice were investigated during the EPOS 1 cruise. Infiltration- and interstitial assemblages exhibited the photosynthetic characteristics of high-light adapted ice algae with a mean assimilation number of 1.81±0.93 mg C (mg Chl a)^–1 h^–1. A higher light harvesting efficiency under light limited conditions (alpha^B-value), as well as a lower light intensity for light saturation (I_K-value) was determined for the interstitial assemblage. An increase in light intensity from 3.5 to 106 mol m^–2s^–1 resulted in increased synthesis of polymeric carbohydrates (presumably reserve material) in a band assemblage. However, the absolute incorporation of radiolabel into lipid- and amino acid fractions remained essentially constant over this range of photon flux densities. Light-saturated rates of photosynthesis of three infiltration assemblages under hypersaline conditions (approx. 50 and 110%) decreased by 13–55% (controls: approx. 32–34%). The adverse effect of salinity treatment was much less pronounced under hyposaline conditions (approx. 20), where maximal photosynthetic rates were only slightly decreased (-9%) or even stimulated (14–22%). These observations suggest that sea ice microalgae in the ice edge region of the Weddell Sea during spring, being in a metabolically active stage, may have the potential to initiate or contribute to phytoplankton blooms upon release into the water column.Data presented here were collected during the European Polarstern Study (EPOS) sponsored by the European Science Foundation     

Respiratory electron transport activity of microplankton in the Weddell Sea during early spring: influence of the ice cover and the ice edge

Summary The activity of the respiratory electron transport system (ETS) of the microplankton (<240 m size) was measured in the Northern Weddell Sea during EPOS 1, in the Close Pack Ice (CPI), and in the ice edge (Outer and Inner Marginal Zones, OMIZ and IMIZ). During early spring the activity increased with time and in the pack ice-open water direction. The temporal trend was more obvious than the spatial one. ETS activity ranged from 0.01 to 1.25 ml O₂ m^–3 h^–1 under the ice and from 0.1 to 1.6 ml O₂ m^–3 h^–1 in the open water at the ice edge. Depth-integrated ETS activity in the upper 300 m ranged from 13 to 130 ml O₂ m^–2h^–1. 60% to 80% of the activity took place above 100 m in the OMIZ in the prebloom conditions at the end of the cruise. ETS/Chl a ratios showed the importance of microheterotrophs under the ice, versus a greater phytoplankton dominance in the ice edge-open water zone. The carbon-specific activity reached a maximum (0.43 day^–1) in the innermost zone of the CPI where bacteria dominated. Respiratory activity under the ice is important in producing the oxygen deficit observed, due to the negative balance between photosynthesis and respiration. The ETS activity was at the lower range of that found in the region in summer and is comparable to that measured in other oligotrophic, stratified systems in oceanic areas.Data presented here were collected during the European Polarstern Study (EPOS) sponsored by the European Science Foundation