凹型加肋锥-环-柱结合壳强度的模型试验研究

为考察凹型加肋锥-环-柱结合壳的力学行为,设计制作了3个凹型加肋锥-柱/锥-环-柱结合壳系列精车模型,采用分区样条等参元方法对它们进行了应力计算.分别对3个模型进行了静水外压试验,测量其应力,计算应力与实测应力吻合较好.模型试验和计算结果表明,凹型加肋锥-环-柱结合壳能有效降低锥、柱壳结合部的应力峰值.通过对模型试验结果的分析,得出了一些对指导凹型加肋锥-环-柱结合壳结构设计有实用价值的结论.     

加肋锥—环—柱组合壳强度及稳定性模型实验研究

本文进行了加肋锥－环－柱组合壳应力、稳定性模型实验，并运用分区样条等参元法进行了数值计算，计算结果与实验结果吻合良好。还将加肋锥－环－柱组合壳与相应加肋锥－柱组合壳应力、稳定性特性进行比较。研究结果表明，加肋锥－环－柱组合壳是锥壳与柱壳间一种优越的连接形式。     

加肋锥—环—柱结合壳初始几何缺陷形态分析

根据加肋锥—环—柱结合壳加工建造过程,分析其中可能产生初始几何缺陷的环节和关键因素。同时参考现行规范,根据大量环肋薄壳结构的建造经验,分别对肋骨与壳板初始几何缺陷的形态进行分析,并与已建模型存在的初始几何缺陷测量值进行对比,进一步验证建造经验的可靠性。结果表明:锥—环—柱结合壳初始几何缺陷主要因肋骨与壳板的角焊缝及壳板之间的环焊缝产生;具有不同半波数的肋骨初挠度以及壳板凹凸度等为典型的初始几何缺陷形态。所得结果可为后续探寻初始几何缺陷对锥—环—柱结合壳力学性能的影响提供参考。     

潜艇耐压艇体纵筋加强锥—柱结合壳结构行为的分析

为考察"纵筋加强锥—柱结合壳"的力学行为,设计了"纵筋加强锥—柱结合壳"作为计算模型,运用有限元方法分析了该模型凸/凹结合部母线方向和圆周方向应力分布。纵筋在纵向和环向均破坏了结构的连续性,在环向还破坏了结构的轴对称性,在纵筋端部(纵向)和纵筋与纵筋之间(环向)的壳板上产生了应力突变和很多应力集中点;此外,在锥—柱结合部增加了许多纵向焊缝,锥—柱结合部应力环境十分恶劣。这种结构形式增大了艇体出现疲劳破坏的危险性。在采用高强度钢(屈强比接近1)的大潜深潜艇的锥—柱结合部不能采用"纵筋加强"结构形式。     

加肋凹型锥环柱破坏机理研究

采用Ansys有限元软件分析静水压力作用下加肋凹型锥环柱结合壳的受力特点;运用弧长法对其破坏过程进行仿真分析。通过分析锥、环、柱三部分各自位移最大点及环壳两端肋骨的载荷-应力和载荷-位移关系。对加肋凹型锥环柱结合壳的破坏模式和破坏机理进行研究,并对破坏过程中出现环壳中面应力在破坏前卸载和环壳两端肋骨的高应力的现象做出合理的解释。     

加肋凹型锥环柱破坏机理研究

采用Ansys有限元软件分析静水压力作用下加肋凹型锥环柱结合壳的受力特点;运用弧长法对其破坏过程进行仿真分析.通过分析锥、环、柱三部分各自位移最大点及环壳两端肋骨的载荷-应力和载荷-位移关系.对加肋凹型锥环柱结合壳的破坏模式和破坏机理进行研究,并对破坏过程中出现环壳中面应力在破坏前卸载和环壳两端肋骨的高应力的现象做出合理的解释.     

基于舱壁设置的加肋凸、凹锥-环-柱结合壳强度分析

运用分区样条等参元法对舱壁不同布置位置的潜艇加肋凸、凹锥-环-柱结合壳进行强度分析,得出了一些对指导凸、凹型锥-环-柱结合壳结构设计和舱壁布置有实用价值的结论.     

加肋锥-环-柱结合壳应力峰值的计算方法

提出加肋锥-环-柱结合壳环壳块应力峰值的计算公式,并通过数值计算,拟合出公式中参数的计算曲线,为潜艇加肋锥-环-柱结合壳结构的初步设计提供方便快捷的计算方法。公式的计算结果与分区样条等参元方法的计算结果相对误差较小,可以在工程中应用。     

厚板削斜和纵筋加强非轴对称锥柱结合壳优化

对于在凹结合壳处采用厚板削斜加强、凸结合壳处采用纵筋加强的非轴对称锥柱结合壳的结构优化设计建立了数学模型。选取凹结合壳处的厚板长度、厚板厚度、厚板削斜长度,凸结合壳处的纵筋剖面参数、纵筋数目、纵筋间距,以及凸凹处的环肋剖面参数等作为设计变量,考虑锥柱结合壳段的内外表面周向应力、内外表面纵向应力、其它部位应力以及工艺性要求等约束,以锥柱结合壳处可变结构的总质量为目标函数。采用APDL语言建立结构的参数化模型,用ANSYS计算结构应力,然后用遗传算法求解优化设计数学模型,解决了非轴对称锥柱结合壳复杂结构的参数化建模和离散变量优化问题。优化的非轴对称锥柱结合壳结构的质量减轻了10.52%。还分析了主要的强度约束条件对优化设计结果的影响。     

几何参数对加肋凹型锥环柱极限承载能力影响

利用ANSYS有限元软件分析大尺寸加肋凹型锥环柱在静水压力作用下的破坏机理,采用单一变量法,分析几何参数对加肋凹型锥环柱结合壳的极限承载能力和破坏模式的影响。减小半锥角、适当增加环壳厚度及环壳两端肋骨尺寸有利于提高环壳的稳定性和结构整体的极限承载能力,提高环壳肋骨腹板尺寸,能更有效提高整体结构的极限承载能力;增加肋骨的水平方向尺寸能更好地提高环壳的稳定性。     

Seasonal study of dissolved CH4, CO2 and N2O in a shallow tidal system of the bay of Cádiz (SW Spain)

During 2004, 10 samplings were performed in order to measure dissolved methane (CH₄), carbon dioxide (CO₂) and nitrous oxide (N₂O) in the surface waters of Río San Pedro, a tidal creek in the salt marsh area of the Bay of Cádiz (SW Spain). The inner partvs of the creek is affected by the inputs coming from an intensive fish farm and the drainage of an extensive salt marsh area.Dissolved CH₄, CO₂ and N₂O concentrations ranged from 11 to 88 nM, 36 to 108 μM and 14 to 50 nM, respectively. Surface waters were in all cases oversaturated with respect to the atmosphere, reaching values of up to 5000% for CH₄, 1240% for CO₂ and 840% for N₂O. Dissolved CH₄, CO₂ and N₂O showed a significant tidal and seasonal variability. Over a tidal cycle, concentrations were always highest during low tide, which points to the influence of the inputs from the fish farm effluent and the drainage of the adjacent salt marsh area, as well as in situ production within the system. Dissolved CH₄, CO₂ and N₂O seasonal patterns were similar and showed maximum concentrations in summer conditions. Using four different parameterizations to calculate the gas transfer coefficients [Liss, P.S. and Merlivat, L., 1986. Air-sea exchange rates: introduction and synthesis. In P. Buat-Ménard (Ed.), The Role of Air-Sea Exchanges in Geochemical Cycling. Reidel, Dordrecht, The Netherlands, p. 113–127.; Clark, J.F., Schlosser, P., Simpson, H.J., Stute, M., Wanninkhof, R., and Ho, D.T., 1995. Relationship between gas transfer velocities and wind speeds in the tidal Hudson River determined by the dual tracer technique. In: B. Jähne and E. Monahan (Eds.), Air-Water Gas Transfer: AEON Verlag and Studio, Hanau, Germany, pp. 785–800.; Carini, S., Weston, N., Hopkinson, G., Tucker, J., Giblin, A. and Vallino, J., 1996. Gas exchanges rates in the Parker River estuary, Massachusetts. Biol. Bull., 191: 333–334.; Kremer, J.N., Reischauer, A. and D'Avanzo, C., 2003. Estuary-specific variation in the air-water gas exchange coefficient for oxygen. Estuaries, 26: 829–836.], the averaged air–water fluxes of CH₄, CO₂ and N₂O from the creek to the atmosphere ranged between 34 and 150 μmol CH₄ m^− 2 day^− 1, 73 and 177 mmol CO₂ m^− 2 day^− 1 and 24 and 62 μmol N₂O m⁻² day⁻¹, respectively.     

A dense water outflow from the Ross Sea, Antarctica: Mixing and the contribution of tides

We use hydrographic, current, and microstructure measurements, and tide-forced ocean models, to estimate benthic and interfacial mixing impacting the evolution of a bottom-trapped outflow of dense shelf water from the Drygalski Trough in the northwestern Ross Sea. During summer 2003 an energetic outflow was observed from the outer shelf ( 500 m isobath) to the  1600 m isobath on the continental slope. Outflow thickness was as great as  200 m, and mean speeds were  0.6 m s^− 1 relative to background currents exceeding  1 m s^− 1 that were primarily tidal in origin. No outflow was detected on the slope in winter 2004, although a thin layer of dense shelf water was present on the outer shelf. When the outflow was well-developed, the estimated benthic stress was of order one Pascal and the bulk Froude number over the upper slope exceeded one. Diapycnal scalar diffusivity (K_z) values in the transition region at the top of the outflow, estimated from Thorpe-scale analysis of potential density and measurements of microscale temperature gradient from sensors attached to the CTD rosette, were of order 10^− 3−10^− 2 m² s^− 1. For two cases where the upper outflow boundary was particularly sharply defined, entrainment rate w_e was estimated from K_z and bulk outflow parameters to be  10^− 3 m s^− 1 ( 100 m day^− 1). A tide-forced, three-dimensional primitive equation ocean model with Mellor-Yamada level 2.5 turbulence closure scheme for diapycnal mixing yields results consistent with a significant tidal role in mixing associated with benthic stress and shear within the stratified ocean interior.     

Mixing over the steep side of the Cycladic Plateau in the Aegean Sea

Intensive microstructure sampling over the southern slope of the Cycladic Plateau found very weak mixing in the pycnocline, centered on a thin minimum of diapycnal diffusivity with Kρ=1.5×¹⁰−6 m² s^− 1. Below the pycnocline, Kρ increased exponentially in the bottom 200 m, reaching 1 × 10^− 4 m² s^− 1 a few meters above the bottom. Near-bottom mixing was most intense where the bottom slope equaled the characteristic slope of the semi-diurnal internal tide. This suggests internal wave scattering and/or generation at the bottom, a conclusion supported by near-bottom dissipation rates increasing following rising winds and with intensifying internal waves. Several pinnacles on the slope were local mixing hotspots. Signatures included a vertical line of strong mixing in a pinnacle's wake, an hydraulic jump or lee wave over a downstream side of the summit, and a ‘beam’ sloping upward at the near-inertial characteristic slope. Because dissipation rate averages were dominated by strong turbulence, ?/νN² > 100, the effect on Kρ of alternate mixing efficiencies proposed for this range of turbulent intensity is explored.     

Microphytobenthos biomass at Kerguelen's Land (Subantarctic Indian Ocean): repartition and variability during austral summers

Microphytobenthos biomass has been measured at several coastal sites on the SE of the main island of the Kerguelen Archipelago (Indian Ocean), during several austral summers (1985–1992), using a conventional fluorometric method. Heterogeneity tests, conducted on two different intertidal sites (Port-Aux-Français, PAF; and Port-Raymond, PRA), showed low standard deviations, whereas the mean concentrations were highly different. Pigment concentrations showed a high variability related to the characteristics of the sediments: from low biomass in coarse intertidal sand, submitted to intense scouring (0.32±0.31 μg Chl a g⁻¹ dw, 0.29±0.14 μg Phaeo g⁻¹ dw) to high biomass in intertidal muddy sand in sheltered areas, particularly along estuaries (54 μg Chl a, 15 μg Phaeo g⁻¹ dw at Korrigan). The subtidal muddy sediments under a Macrocystis pyrifera (Linné) and Durvillaea antarctica (Chamisso in Choris) belt exhibited high concentrations in phaeopigment (Phaeo) (up to 136±83 μg g⁻¹ dw; PRA), while the concentration of chlorophyll a (Chl a) was relatively low. The dense macroalgal canopy supports an important epiphytic diatom biomass (mainly the genera Cocconeis Ehrenberg and Grammatophora Ehrenberg), which is sedimenting after degradation and is in part responsible of the high levels of Phaeo in all sediments. Macroalgal debris were observed, but diatom frustules were dominant in most surficial subtidal sediments. A circatidal mud, in the Morbihan Bay, made of a sponge spicule mat (50 m deep; 4.96 μg Chl a g⁻¹ dw), showed a very low Chl a/Phaeo ratio (0.1), while it reached up to 6 in intertidal sand. Surprisingly, a penguin rookery beach, at the east side of Courbet Peninsula, was characterized by a very low biomass (0.07±0.04 μg Chl a g⁻¹ dw), while it was nutrient enriched, particularly with nitrates.In comparison with the data at the similar latitude, but in temperate regions from the Northern Hemisphere, the microphytobenthos biomass, recorded at Kerguelen's Land, exhibited relatively high pigment concentrations, particularly the Phaeo, and supported a dense and diversified subtidal macrofauna composed of polychaetes (particularly Thelepus extensus Hutchings and Glasby), sea urchins, mytillids and gammarids. The exuberant macroalgal canopy, coastal indentations and low tidal amplitude must be in part responsible of these large benthic primary and secondary biomasses.     

The biogeochemical cycling of methane in Ria de Vigo, NW Spain: Sediment processing and sea–air exchange

Methane (CH₄) concentrations were measured in the water column, in sediment porewaters, and in atmospheric air, in the Ría de Vigo, NW Spain, during both the onset (April 2003) and at the end of (September 2004) seasonal upwelling. In addition, CH₄ concentration and stable isotopic signatures (δ¹³CH₄) were measured in porewaters, and sediment methanogenesis and aerobic oxidation of CH₄ were determined in sediment incubations. Surface water column CH₄ (2 m depth) was in the range 3–180 nmol l^− 1 (110–8500% saturation) and followed a generally landward increase but with localised maxima in both the inner and middle Ría. These maxima were consistent with CH₄ inputs from underlying porewaters in which CH₄ concentrations were up to 3 orders of magnitude higher (maximum 350 μmol l^− 1). Surface water CH₄ concentrations were approximately three times higher in September than in April, consistent with a significant benthic CH₄ flux driven by enhanced sediment methanogenesis following the summer productivity maximum. CH₄ and δ¹³CH₄ in sediment porewaters and in incubated sediment slurries (20 °C) revealed significant sediment CH₄ oxidation, with an apparent isotopic fractionation factor (r_c) of  1.004. Using turbulent diffusion models of air–sea exchange we estimate an annual emission of atmospheric CH₄ from the Ría de Vigo of 18–44 × 10⁶ g (1.1–2.7 × 10⁶ mol). This estimate is approximately 1–2 orders of magnitude lower than a previous estimate based on a bubble transport model.     

Turbulence in coastal fronts near the mouths of Block Island and Long Island Sounds

Measurements of turbulence were performed in four frontal locations near the mouths of Block Island Sound (BIS) and Long Island Sound (LIS). These measurements extend from the offshore front associated with BIS and Mid-Atlantic Bight Shelf water, to the onshore fronts near the Montauk Point (MK) headland, and the Connecticut River plume front. The latter feature is closely associated with the major fresh water input to LIS. Turbulent kinetic energy (TKE) dissipation rate, ε, was obtained using shear probes mounted on an autonomous underwater vehicle. Offshore, the BIS estuarine outflow front showed, during spring season and ebb tide, maximum TKE dissipation rate, ε, estimates of order 10^− 5 W/kg, with background values of order 10^− 6 to 10^− 9 W/kg. Edwards et al. [Edwards, C.A., Fake, T.A., and Bogden, P.S., 2004a. Spring–summer frontogenesis at the mouth of Block Island Sound: 1. A numerical investigation into tidal and buoyancy-forced motion. Journal of Geophysical Research 109 (C12021), doi:10.1029/2003JC002132.] model this front as the boundary of a tidally driven, baroclinically adjusted BIS flow around the MK headland eddy. At the entrance to BIS, near MK, two additional fronts are observed, one of which was over sand waves. For the headland site front east of MK, without sand waves, during ebb tide, ε estimates of 10^− 5 to 10^− 6 W/kg were observed. The model shows that this front is at the northern end of an anti-cyclonic headland eddy, and within a region of strong tidal mixing. For the headland site front further northeast over sand waves, maximum ε estimates were of order 10^− 4 W/kg within a background of order 10^− 7–10^− 6 W/kg. From the model, this front is at the northeastern edge of the anti-cyclonic headland eddy and within the tidal mixing zone. For the Connecticut River plume front, a surface trapped plume, during ebb tide, maximum ε estimates of 10^− 5 W/kg were obtained, within a background of 10^− 6 to 10^− 8 W/kg. Of all four fronts, the river plume front has the largest finescale mean-square shear, S² ~ 0.15 s^− 2. All of the frontal locations had local values of the buoyancy Reynolds number indicating strong isotropic turbulence at the dissipation scales. Local values of the Froude number indicated shear instability in all of the fronts.     

Pore water phosphate and ammonia below the permanent halocline in the south-eastern Baltic Sea and their benthic fluxes under anoxic conditions

In this paper the results of a study on the distribution of pore water phosphates and ammonia, and their fluxes under anoxic condition in a deep (> 70 m) accumulation-type bottom of the south-eastern Baltic Sea, namely in the Gdańsk Deep and the adjacent areas, are presented. All measurements were taken during the growth period, i.e. in September 2000, April 2001 and June 2002. Benthic phosphate and ammonia fluxes were estimated using Fick's First Law. Phosphate and ammonia concentrations ranged from 7.5 to 266.3 μmol dm^− 3 and from 53.6 to 1248.3 μmol dm^− 3, respectively. The values recorded in the central part of the Gdańsk Deep were lower than those found both on its slopes and on the SW slope of the Gotland Deep. The lowest phosphate contents were typical of the Oblique Sill which separates the Gdańsk and Gotland Deeps.In 1993–2002, as a result of anoxia the sediments in the Gdańsk Deep released about 5.1 × 10³ t P and 22.8 × 10³ t N. These loads supplied on average 1.5% and 0.9% of phytoplankton's demand for P and N, respectively. In comparison to the total external load of nutrients discharged to the Gulf of Gdańsk (i.e. 8.79 × 10³ t year^− 1 P_tot and 130.79 × 10³ t year^− 1 N_tot; [Witek, Z., Humborg, Ch., Savchuk, O., Grelowski, A. and Łysiak-Pastuszak, E., 2003. Nitrogen and phosphorus budgets of the Gulf of Gdańsk (Baltic Sea). Est. Coast. Shelf Sci., 57:239–248.]), the return flux of P and N from the anoxic sediments to the water column in the Gdańsk Deep was a minor source of these elements.     

Surf-riding and oscillations of a ship in quartering waves

The behavior of a ship encountering large regular waves from astern at low frequency is the object of investigation, with a parallel study of surf-riding and periodic motion paterns. First, the theoretical analysis of surf-riding is extended from purely following to quartering seas. Steady-state continuation is used to identify all possible surf-riding states for one wavelength. Examination of stability indicates the existence of stable and unstable states and predicts a new type of oscillatory surf-riding. Global analysis is also applied to determine the areas of state space which lead to surf-riding for a given ship and wave conditions. In the case of overtaking waves, the large rudder-yaw-surge oscillations of the vessel are examined, showing the mechanism and conditions responsible for loss of controllability at certain vessel headings.List of symbols c wave celerity (m/s) - C(p) roll damping moment (Ntm) - g acceleration of gravity (m/s²) - GM metacentric height (m) - H wave height (m) - I _x ,I _z roll and yaw ship moments of inertia (kg m²) - k wave number (m^–1) - K _H ,K _W ,K _R hull reaction, wave, rudder, and propeller - K _p forces in the roll direction (Ntm) - m ship mass (kg) - n propeller rate of rotation (rpm) - N _H ,N _W ,N _R hull reaction, wave, rudder, and propeller - N _P moments in the yaw direction (Ntm) - p roll angular velocity (rad/s) - r rate-of-turn (rad/s) - R(,x) restoring moment (Ntm) - Res(u) ship resistance (Nt) - t time (s) - u surge velocity (m/s) - U vessel speed (m/s) - v sway velocity (m/s) - W ship weight (Nt) - x longitudinal position of the ship measured from the wave system (m) - x _G ,z _G longitudinal and vertical center of gravity (m) - x _S longitudinal position of a ship section (S), in the ship-fixed system (m) - X _H ,X _W ,X _R hull reaction, wave, rudder, and propeller - X _P forces in the surge direction (Nt) - y transverse position of the ship, measured from the wave system (m) - Y _H ,Y _W ,Y _R hull reaction, wave, rudder, and propeller - Y _p forces in the sway direction (Nt) - z _Y vertical position of the point of action of the lateral reaction force during turn (m) - z _W vertical position of the point of action of the lateral wave force (m) Greek symbols angle of drift (rad) - rudder angle (rad) - wavelength (m) - position of the ship in the earth-fixed system (m) - water density (kg/m³) - angle of heel (rad) - heading angle (rad) - _e frequency of encounter (rad/s) Hydrodynamic coefficients K roll added mass - N _v ,N _r yaw acceleration coefficients - N _v N _r N _rr N _rrv ,N _vvr yaw velocity coefficients K. Spyrou: Ship behavior in quartering waves - X _u surge acceleration coefficient - X _u X _vr surge velocity coefficients - Y _v ,Y _r sway acceleration coefficients - Y _v ,Y _r ,Y _vv ,Y _rr ,Y _vr sway velocity coefficients European Union-nominated Fellow of the Science and Technology Agency of Japan, Visiting Researcher, National Research Institute of Fisheries Engineering of Japan     

Production of Acartia omorii (Copepoda: Calanoida) in Ilkwang Bay, southeastern coast of Korea

Production of the marine calanoid copepod Acartia omorii was measured from 2 October 1991 to 8 October 1992 at a station in Ilkwang Bay on the southeastern coast of Korea. A. omorii (nauplii + copepodites + adults) were present in the plankton throughout the year, with seasonal variation in abundance. Biomass of A. omorii was averaged at 0.44 mgC m^− 3, with peaks in February and July, and relatively low biomass in late summer and fall. Egg production rate ranged from 2.4 to 151.9 μgC m^− 3 day^− 1, which was equivalent to 95–6075 eggs m^− 3 day^− 1. Fecundity of an adult female was averaged at 38 eggs female^− 1 day^− 1. Instantaneous growth rates of copepodites were higher than those of nauplii stages. Annual production of A. omorii ranged from 33.5 mgC m^− 3 year^− 1 to 221 mgC m^− 2 year^− 1, showing a seasonal variation of daily production rate with peaks in February and July. The daily production rate of A. omorii was significantly correlated with chlorophyll a concentration. These results suggest that standing stocks and/or productivity of phytoplankton are the major influencing factors, rather than water temperature for the seasonal variation of production of A. omorii in Ilkwang Bay.     

Microbial food web responses to light and nutrients beneath the coastal Arctic Ocean sea ice during the winter–spring transition

We measured the abundance and biomass of phototrophic and heterotrophic microbes in the upper mixed layer of the water column in ice-covered Franklin Bay, Beaufort Sea, Canada, from December 2003 to May 2004, and evaluated the influence of light and nutrients on these communities by way of a shipboard enrichment experiment. Bacterial cell concentrations showed no consistent trends throughout the sampling period, averaging (± SD) 2.4 (0.9) × 10⁸ cells L^− 1; integrated bacterial biomass for the upper mixed layer ranged from 1.33 mg C m^− 3 to 3.60 mg C m^− 3. Small cells numerically dominated the heterotrophic protist community in both winter and spring, but in terms of biomass, protists with a diameter > 10 µm generally dominated the standing stocks. Heterotrophic protist biomass integrated over the upper mixed layer ranged from 1.23 mg C m^− 3 to 6.56 mg C m^− 3. Phytoplankton biomass was low and variable, but persisted during the winter period. The standing stock of pigment-containing protists ranged from a minimum value of 0.38 mg C m^− 3 in winter to a maximal value of 6.09 mg C m^− 3 in spring and the most abundant taxa were Micromonas-like cells. These picoprasinophytes began to increase under the ice in February and their population size was positively correlated with surface irradiance. Despite the continuing presence of sea ice, phytoplankton biomass rose by more than an order of magnitude in the upper mixed layer by May. The shipboard experiment in April showed that this phototrophic increase in the community was not responsive to pulsed nutrient enrichment, with all treatments showing a strong growth response to improved irradiance conditions. Molecular (DGGE) and microscopic analyses indicated that most components of the eukaryotic community responded positively to the light treatment. These results show the persistence of a phototrophic inoculum throughout winter darkness, and the strong seasonal response by arctic microbial food webs to sub-ice irradiance in early spring.