Prey composition and feeding rate of Sagitta elegans var. arctica (chaetognatha) in the Barents Sea in early summer

Sagitta elegans var. arctica , the dominant and locally abundant chaetognath in the Barents sea, was collected from the upper 50 m in Arctic water masses during an ice edge bloom in early summer 1983. In situ sampling was made along a transect at discrete depths with a 375 μm mesh net mounted on a plankton pump. Prey composition and feeding rate were estimated from gut content analyses on preserved specimens combined with data on digestion times from previous studies. No diel variations were found in feeding activity. The diet reflected the composition of available prey in the zooplankton and consisted mainly of nauplii, small copepods (early stages of Calanus, Pseudocalanus, Oithona ) and appendicularians. Prey usually occurred as a single item in the gut.
Mean prey body width related to chaetognath head width yielded a power curve, with a large amount of scatter, showing that chaetognaths in the Barents Sea can use a wide spectrum of prey sizes. Similarly, maximum prey body width was related to chaetognath head width as a power curve, reflecting the existence of an upper prey size limitation due to the chaetognath mouth size. The highest abundance of S. elegans (5 specimens m⁻³), and the most intense feeding activity, were found within or beneath the maximum zooplankton biomass. Further, distribution and feeding were affected by light intensity, salinity, and the population structure of 5. elegans var. arctica.
Estimated feeding rates ranged between 0.30 and 1.05 prey items per chaetognath day⁻¹. This corresponds to an ingestion of 8-54 μg AFDW day⁻¹, and a consumption of 0.08–0.22% of the zooplankton standing stock day⁻¹. From these rates, the calculated yearly ingestion by S. elegans var. arctica was 3% of the annually secondary production.     

Ctenophora in the Arctic: the abundance, distribution and predatory impact of the cydippid ctenophore Mertensia ovum (Fabricius) in the Barents Sea

The Ctenophora Mertensia ovum and Beroe cucumis , collected using both conventional sampling gear and scuba divers, were studied in the Barents Sea east of Bjørnøya and North Norway in spring 1987 and summer 1988. Among the gelatinous zooplankton, Mertensia ovum was the most consistently abundant copepod predator.
Feeding experiments were conducted to evaluate the predation rate of M. ovum in various trophic regimes. This ctenophore can take prey varying in size from small copepods to amphipods and krill, but gut-content analyses from field-collected specimens as well as experimental results showed that the main food source for adults was large-sized copepods (e.g. Calanus finmarchicus, C. glacialis, C. hyperboreus, Metridia longa ). The robust tentacle arrray of M. ovum makes this species effective as a predator on large prey. The high potential predation rate of this ctenophore relative to its estimated metabolic cost of only 1.7% of the body energy content d⁻¹ suggests that M. ovum may be able to maintain a positive energy balance even in conditions of low prey abundance. It is suggested that a single exploitation of a zooplankton patch may provide energy for survival for a very long time.
The potential impact of M. ovum on Barents Sea copepod populations is estimated on the basis of the minimal observed average daily ration in experiments and from field data on gut contents. Using abundances of copepods for the area, and the actual predator biomass collected, it was estimated that an average of 0.7% of the copepod fauna per day could fall prey to this predator.     

Seasonal and spatial changes in the zooplankton community of Kongsfjorden, Svalbard

Seasonal changes in the zooplankton composition of the glacially influenced Kongsfjorden, Svalbard (79°N, 12°E), and its adjacent shelf were studied in 2002. Samples were collected in the spring, summer and autumn in stratified hauls (according to hydrographic characteristics), by means of a 0.180-mm Multi Plankton Sampler. A strong front between the open sea and the fjord waters was observed during the spring, preventing water mass exchange, but was not observed later in the season. The considerable seasonal changes in zooplankton abundance were related to the seasonal variation in hydrographical regime. The total zooplankton abundance during the spring (40–2010 individuals m⁻³) was much lower than in the summer and autumn (410–10 560 individuals m⁻³). The main factors shaping the zooplankton community in the fjord include: the presence of a local front, advection, the flow pattern and the decreasing depth of the basin in the inner fjord. Presumably these factors regulate the gross pattern of zooplankton density and distribution, and override the importance of biological processes. This study increased our understanding of seasonal processes in fjords, particularly with regard to the strong seasonal variability in the Arctic.     

2012年马卡诺夫海盆与楚科奇深海平原浮游动物夏季的垂直分布及地理差异

利用2012年9月1—6日采自马卡诺夫海盆3个站位和楚科奇深海平原1个站位的分层浮游动物样品,研究了浮游动物在0—1 000 m水层的垂直分布以及地理差异。结果表明,浮游动物在上层分布密集而在深层比较稀少。4个站位在0—50 m、50—100 m和100—200 m水层的平均丰度分别为265.0、360.7和231.2 ind·m^-3,而在200—500 m和500—1 000 m的丰度只有64.4和36.9 ind·m^-3。在数量上占优势的种类中,植食性为主的拟长腹剑水蚤(Oithona similis)、北极哲水蚤(Calanus glacialis)和极北哲水蚤(Calanus hyperboreus)集中在200 m以浅的水层。虽然在200m以下杂食性种类矮小微哲水蚤(Microcalanus pygmaeus)、隆剑水蚤(Oncaea spp.)和细长长腹水蚤(Metridia longa)的丰度明显降低,但是占浮游动物总丰度的比例却明显更高。两个调查海区浮游动物种类组成相似,但是楚科奇深海平原大型桡足类极北哲水蚤的丰度较高,而小型桡足类丰度较低?垂直分布上差异主要在于500—1 000 m水层,马卡诺夫海盆站位丰度为22.7—92.6 ind·m^-3,而楚科奇深海平原只有1.6 ind·m^-3。深海区浮游动物丰度的地理差异说明生物泵的作用存在空间异质性。类似地理差异产生的原因在于楚科奇深海平原存在数量较多的极北哲水蚤,它们在春季融冰前就上升到表层摄食冰藻,显著降低了有机物的垂直通量。     

南极夏季南设得兰岛海域浮游动物群落垂直分布

浮游动物群落结构的垂直分布研究可以更好地了解其在海洋食物网物质能量循环中的作用。基于2012年1月中国第28次南极考察期间在西南极南设得兰岛海域4个站位Multinet网(200μm,0.5 m2)采集的浮游动物样品资料,运用多元统计方法对浮游动物群落垂直结构及与环境因子关系进行了分析,结果显示:浮游动物可划分为3个群落,群落1由采自上层水体(0—200 m)的样品组成,此群落平均丰度为31 782.02个·1 000 m-3,优势种为桡足类Oithona similis,Ctenocalanus citer,Oncaea curvata,Calanoides acutus,Calanus propinquus及南极大磷虾原蚤状幼体CⅠ-Ⅲ期个体;群落2主要由采自中层水(200—1 000 m)的样品构成,群落平均丰度为22 325.59个·1 000 m-3,其指示物种主要包括桡足类O.curvata,O.similis,Oithona frigida,C.citer,Aetideopsis minor,Bathycalanus bradyi,C.acutus,C.propinquus,Metridia gerlachei,介形类Alacia spp.及箭虫Eukrohnia hamata;群落3由采自较深层水(1 000—2 000 m)的样品组成,群落平均丰度为989.27个·1 000 m-3,其指示种为深水桡足类Bathycalanus bradyi。Bio-Env分析显示叶绿素a和盐度分别是对群落聚类起关键影响的单因子,水深、盐度和叶绿素a的组合则最好地解释了群落的划分。     

Glacier surge at Usherbreen, Svalbard

Usherbreen started to surge in 1978, and the front has advanced 1.5 km and covered an area of 4.5 km². During the first two years the front advanced more than 1 m/d, and the front was still advancing 0.15– 0.20m/d in 1985, seven years after the start. The mean gradient of the lower 7 km decreased from 3.3 grad. to 1.8 grad. during the surge. The volume of ice transported down the glacier from higher to lower parts during the surge was 815 x lO'm³. which is almost 20% of the total glacier volume. Old icecored ridges in front of the glacier were reactivated, and the whole ridge system was pushed forward, in the summer of 1985 at a speed of about 0.05 m/d. Parts of the ridge system were moved 200 m during this surge. New ridges were developed on the flat sandur in front of the old ridge system. This demonstrates that the glacier advanced further than in any previous surge.     

Dynamics of plankton growth in the Barents Sea: model studies

1-D and 3-D models of plankton production in the Barents Sea are described and a few simulations presented. The 1-D model has two compartments for phytoplankton (diatoms and P. pouchelii) , three for limiting nutrients (nitrate, ammonia and silicic acid), and one compartment called "sinking phytoplankton". This model is coupled to a submodel of the important herbivores in the area and calculates the vertical distribution in a water column. Simulations with the 3-D model indicate a total annual primary production of 90-120g C m⁻² yr⁻¹ in Atlantic Water and 20-50g C m⁻² yr⁻¹ in Arctic Water, depending on the persistence of the ice cover during the summer.
The 3-D model takes current velocities, vertical mixing, ice cover, and temperature from a 3-D hydrodynamical model. Input data are atmospheric wind, solar radiation, and sensible as well as latent heat flux for the year 1983. The model produces a dynamic picture of the spatial distribution of phytoplankton throughout the spring and summer. Integrated primary production from March to July indicates that the most productive area is Spitsbcrgenbanken and the western entrance to the Barents Sea. i.e. on the northern slope of Tromsøflaket.     

天山雪岭云杉个体生物量分配及其变化规律的研究

为了探讨天山雪岭云杉林生物量在个体组织中的分配情况及其变化规律,在研究区进行了大量的野外测量,利用已有的雪岭云杉林估算方程,分析了天山雪岭云杉林生物量在各器官（干、枝、叶、皮、根）中的分配及其变化规律。结果表明：（1） 研究区雪岭云杉林的平均生物量为388.74 t·hm^-2,树木各器官中,干、枝、根、叶和皮分别占生物量的43.65%、28.60%、13.49%、11.08%和3.18%。（2）各径级生物量所占百分比为：33.53%（40~50 cm）、20.13%（20~30 cm）、19.59%（30~40 cm）、18.19%（50~60 cm）和2.05%（10~20 cm）;树木生物量在不同树高中的分配表现为：48.78%（20~30 m）＞35.27%（10~20 m）＞14.70%（30~40 m）＞1.25%（0~10 m）;地上和地下生物量的分配比例为：87.54%和12.46%,分别为340.30 t·hm^-2和48.44 t·hm^-2。（3） 随海拔升高,天山雪岭云杉林生物量呈“单峰”变化,在海拔2 100~2 400 m处达到最大值611.58 t·hm^-2;干、皮生物量所占比例随海拔升高而减小,枝生物量逐渐增加,叶、根生物量呈先减小后增加的趋势;径级20~30 cm、30~40 cm和50~60 cm的生物量随海拔升高均呈“单峰型”变化趋势,都在海拔2 100~2 400 m处达到最大;雪岭云杉林不同树高生物量随海拔的升高呈现的趋势不同。天山雪岭云杉林生物量和年均降水量随经纬度的升高均呈降低变化,研究区林分生物量自西向东总体呈现逐渐降低的趋势;林分密度、海拔和降水共同决定了森林生物量的大小及其变化规律,海拔2 100~2 400 m是本研究区雪岭云杉林生长的最适宜场所。结果可为雪岭云杉林生态系统的恢复和重建提供基础资料,对研究区进行综合管理与生态健康分析具有重要意义。     

民勤绿洲青土湖植被优势种地上生物量估算

青土湖区域属于绿洲—荒漠过渡带,生态系统脆弱,极易发展为荒漠。梭梭、白刺和芦苇为青土湖区域的植被优势种,对其生态系统稳定与健康发展起着关键作用。以青土湖区域梭梭、白刺和芦苇为研究对象,利用空间分辨率为0.5 m的高分辨率遥感影像Worldview-2,采用辅以纹理特征的面向对象分类方法,提取梭梭和白刺的冠幅面积以及芦苇的分布面积;根据野外试验数据,建立梭梭和白刺地上生物量与冠幅面积、芦苇地上生物量与分布面积关系模型。利用关系模型、冠幅面积以及分布面积对青土湖区域植被优势种地上生物量进行了估算,实现了植被优势种地上生物量估算由“点”到“面”的转换。结果表明：（1） 采取辅以纹理特征的面向对象分类方法取得了较高的分类精度,总体Kappa系数为87.9%,总体精度达到91.3%。（2） 研究区植被优势种地上生物量总量为3.17×10³ t,其中梭梭地上生物量为0.54×10³ t,白刺地上生物量为0.90×10³ t,芦苇地上生物量为1.73×10³ t,地上生物量芦苇>白刺>梭梭。该研究可以为深入研究青土湖区域生态恢复与碳储量提供参考。     

Phytoplankton dynamics in the Barents Sea estimated from chlorophyll budget models

Pigment budgets use chlorophyll a and phaeopigment standing stock in combination with their photo-oxidation and sedimentation rates in the euphotic zone to estimate phytoplankton growth and grazing by micro- and macrozooplankton. Using this approach, average phytoplankton growth in the euphotic zone of the Barents Sea was estimated at 0.17 and 0.14 d⁻¹ during spring of 1987 and 0.018 and 0.036 d⁻¹ during late- and postbloom conditions in summer of 1988. Spring growth was 65% lower than the estimates from radiocarbon incorporation, supporting a 33% pigment loss during grazing. Macrozooplankton grazing and cell sinking were the main loss terms for phytoplankton during spring while microzooplankton grazing was dominant in summer.
In contrast to tropical and temperate waters, Arctic waters are characterized by a high phaeopigment: chlorophyll a ratio in the seston. Photooxidation rates of phaeopigments at in situ temperatures (0 ± 1°C) are lower than in temperate waters and vary by a factor of 2 for individual forms (0.009 to 0.018 m⁻²mol⁻¹). The phaeopigment fraction in both the suspended and sedimenting material was composed of seven main compounds that were isolated using high-performance liquid chromatography and characterized by spectral analysis. The most abundant phaeopigment in the sediment traps, a phaeo-phorbide-like molecule of intermediate polarity (phaeophorbide a₃), peaked in abundance in the water column below the 1% isolume for PAR (60-80 m) and showed the highest rate of photooxidation. This phaeopigment was least abundant in the seston when phytoplankton was dominated by prymnesiophytcs but increased its abundance in plankton dominated by diatoms. This distribution suggests that larger grazers feeding on diatoms are the main producers of this phaeopigment.     

Distribution of Chemical Constituents in Superimposed Ice from Austre Brøggerbreen, Spitsbergen

10 m and 2.3 m ice cores were obtained on Austre Brøggerbreen, Spitsbergen in Svalbard (78°53 ' N, 11°56 ' E, 450 m a.s.l.) in September 1994 and in March 1995, respectively. Stratigraphy, bulk density, pH, electrical conductivity, and major ions were obtained from the core samples.
The chemical effect of meltwater percolation through snow/ice is examined. Good correlation between Cl⁻ and Na⁺ was obtained. The ratio of Cl⁻ to Na⁺ was 1.14 which was nearly the same value as in bulk sea water. However, the variation of Cl⁻/Na⁺ shows that higher ratio occured in the bubble-free ice. Furthermore the Cl⁻ ions remain in higher concentration than SO ₄ ²⁻ or Na⁺ ions.     

A surge of Perseibreen, Svalbard, examined using aerial photography and ASTER high resolution satellite imagery

The identification of surge activity is important in assessing the duration of the active and quiescent phases of the surge cycle of Svalbard glaciers. Satellite and aerial photographic images are used to identify and describe the form and flow of Perseibreen, a valley glacier of 59 km² on the east coast of Spitsbergen. Heavy surface crevassing and a steep ice front, indicative of surge activity, were first observed on Perseibreen in April 2002. Examination of high resolution (15 m) Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) satellite imagery confirmed this surge activity. Perseibreen retreated by almost 750 m between 1961 and 1990. Between 1990 and the summer of 2000, Perseibreen switched from retreat and its front began to advance. Rapid advance was underway during the period June 2000 to May 2001, with terminus advance at over 400 m yr⁻¹. Between May and August 2001 the rate increased to over 750 m yr⁻¹. The observed crevasse orientation indicates that ice was in longitudinal tension, suggesting the down-glacier transfer of mass. Ice surface velocities, derived from image correlation between ASTER images, were 2-2.5 m d⁻¹ between May and August 2001. The glacier was flowing at a relatively uniform speed with sharp velocity gradients located close to its lateral margins, a velocity structure typical of ice masses in the active phase of the surge cycle. The stress regime is extensional throughout and the surge appears to be initiated low on the glacier. This is similar to the active-phase dynamics of other Svalbard tidewater glaciers. Perseibreen has probably been inactive since at least 1870, a period of about 130 years to the present surge which defines a minimum length for the quiescent phase.     

Correlations between pelagic distribution of Common and Brünnich's Guillemots and their prey in the Barents Sea

Correlations between guillemots (including Common Guillemots Uria aalge and Brünnich's Guillemots U. lomvia) and their prey (divided into five prey categories, capelin Mallotus villosus , herring Clupea harengus , polar cod Boreogadus saida , plankton, and a mixture of other prey species) at two depths (10-100 m and 100-200m) were estimated along an extended transect of 3,060 nautical miles (5,667 km) in the Barents Sea in April/May 1986. Spatial concordance was highest during daylight hours when the largest number of birds were seen on water (presumably feeding birds). Capelin was the single prey category which was most often associated with birds but no single prey category could alone explain the distribution of birds. Although only a small fraction of guillemots could be identified to species, there was some evidence that capelin were of greater importance to Common than to Brünnich's Guillemots. Overall correlation between birds and total prey density was statistically significant at the smallest scale of 5 nautical miles (n.m.). The removal of herring from the calculations increased the strength of the correlation. The depth at which prey was located had little effect on the distribution of birds. The correlation between birds and prey was scale dependent, and reached a maximum at 90 n.m., although there seemed to be some upper threshold in the coefficient at c. 40 n.m. Numerical concordance (including only 5 n.m. periods where both prey and birds were present) was significant at the 5 n.m. scale but was higher for high density than for low density prey patches. The results are discussed in relation to the few similar studies in other oceans and in relation to the severe reduction of important prey species in the Barents Sea.     

2010年夏季白令海小型底栖动物丰度与生物量初步研究

2010年7月12—18日, 中国第4次北极科考队在白令海以箱式或多管取样器采集7站位10 cm长度的表层沉积物芯样, 并在现场进行了分层处理。室内分析时共检出14个小型底栖动物类群：自由生活海洋线虫(free-living Nematoda)、底栖桡足类(Copepoda)、多毛类(Polycheata)、动吻类(Kinorhyncha)、端足类(Amphipoda)、双壳类(Bivalvia)、涟虫(Cumacea)、介形类(Ostracoda)、原足类(Tanaidacea)、腹足类(Gastropoda)、等足类(Isopoda)、海蛇尾(Ophiura)、缓步类(Tardigrada)以及其它类(Others)。平均丰度和平均生物量分别为2 658.89±2 452.86 ind/10 cm²和1 587.56±1 452.65 μg?dwt/10 cm², 最高值皆出现在白令海北部陆架浅水区, 分别为7 135.12±429.43 ind/10 cm²和4 056.42±721.33 μg?dwt/10 cm², 最低值皆出现在白令海盆西部深水区, 分别仅为56.04±39.38 ind/10 cm²和87.91±85.60 μg?dwt/10 cm²。线虫为丰度的最优势类群, 占平均丰度比例的94.81％, 桡足类为第二优势类群, 占3.60％。表层0—6 cm芯样的取样效率为93.44％。基于各站丰度的类群相似性分析, 浅水区与深水区的小型底栖动物群落的相似性系数仅为30.72%, 最大的差别在于深水区的丰度比浅水区小了一个数量级。白令海陆架浅水区比白令海盆深水区和中国海域具有明显更高的小型底栖动物丰度和生物量。Pearson相关性分析显示, 白令海小型底栖动物丰度和生物量与水深、营养盐及多个粒径参数呈负相关, 其中生物量对环境变化的响应可能比丰度更敏感。     

Storsteinsfjellbreen: Variations in Mass Balance from the 1960s to the 1990s

When the Norwegian State Power Board decided to plan an extensive water power development in the mountainous areas southeast of Narvik in northern Norway, a large mapping project was started. Detailed maps were constructed at a scale of 1:10 000 from aerial photographs taken in 1960. Several hydrometric stations were installed, and three glaciers were selected for mass balance observations. Storsteinsfjellbreen was the largest of these, and a special glacier map with 10 m contours was printed in four colours, to be used in the field work. Mass balance studies were carried out initially during one 5-year period (1964–68), and also later during another 5-year period (1991–95).
Results from these periods are compared with similar data from the Swedish glacier Storglaciären, about 45 km to the southeast. For all the years except one (1968), the net balance of these glaciers shows a similar pattern: positive years and negative years are synchronous.
A new glacier map was made from a special aerial survey in 1993 at the same scale and of similar accuracy as the first map, so a comparison could be made to calculate the change in glacier volume from 1960 to 1993. From digital terrain models it could be shown that the glacier surface had dropped more than 60 m vertically on the tongue, while the thickness increased above the equilibrium line by up to 20 m. The overall mass loss amounted to 16.8×10⁶ m³ water during 33 years, which corresponds to an extra 2.6 l·s⁻¹·km⁻² (litres per sec. per sq. km) delivered to the river, in addition to the "normal" discharge
due to annual precipitation, which is 36 l·s⁻¹·km⁻² in the area.
A copy of the new glacier map is enclosed with this article.     

黑河下游绿洲植被优势种生物量空间分布及蒸腾耗水估算

基于典型样点试验,建立了研究区植被优势种柽柳、胡杨与苦豆子地上生物量与其生态参数关系模型;利用高分辨率遥感影像Geoeye-1对植被优势种进行分类得到生态参数,实现了其地上部分生物量空间分布估算;最后利用生物量与蒸腾系数关系,估算植被优势种蒸腾耗水。结果显示：植被优势种总生物量为2.53×10⁶t,河流距离对生物量影响显著。根据试验测得的植被优势种蒸腾系数估算出总蒸腾耗水量为10.89×10⁸t,柽柳、胡杨与苦豆子所占比例分别为12.94%,82.93%与4.13%。     

Seismic moment release during slab rupture beneath the Banda Sea

The highest intermediate depth moment release rates in Indonesia occur in the slab beneath the largely submerged segment of the Banda arc in the Banda Sea to the east of Roma, termed the Damar Zone. The most active, western-part of this zone is characterized by downdip extension, with moment release rates (∼10¹⁸ Nm yr^–1 per 50 km strike length) implying the slab is stretching at ∼10⁻¹⁴ s⁻¹ consistent with near complete slab decoupling across the 100–200 km depth range. Differential vertical stretching along the length of the Damar Zone is consistent with a slab rupture front at ∼100–200 km depth beneath Roma propagating eastwards at ∼100 km Myr^–1. Complexities in the slab deformation field are revealed by a narrow zone of anomalous in-plane P -axis trends beneath Damar, where subhorizontal constriction suggests extreme stress concentrations ∼100 km ahead of the slab rupture front. Such stress concentrations may explain the anomalously deep ocean gateways in this region, in which case ongoing slab rupture may have played a key role in modulating the Indonesian throughflow in the Banda Sea over the last few million years.     

祁连山干旱山地草地生物量对水分条件的响应

以祁连山排露沟流域干旱山地为研究对象,对海拔2 700~3 000 m典型草地群落的草本种类、高度和生物量等进行调查,并同步测定样地内的土壤水分,分析草地生物量随海拔高度的季节性变化特征以及草本生物量和土壤水分的关系。结果表明：（1）草地地上生物量平均值为135.36 g·m^-2,并随海拔升高呈先增加后降低的"单峰"变化模式,在海拔2 900 m时最高,为176.79±28.37 g·m^-2。地下生物量平均值为946.13 g·m^-2,并随海拔升高生物量呈递增趋势,在海拔3 000 m时最高,为1 301.19 ±68.24 g·m^-2。（2）草地地上、地下生物量在不同海拔高度间差异性显著（P<0.05）;该流域干旱山地草地根冠比在4.14~11.95之间变化。（3）在生长季5~9月份,干旱山地草地土壤含水量在9.23%~31.31%之间波动,平均值为14.94%。（4）草本地上、地下生物量与土壤平均含水量均呈显著正相关（P<0.05）,相关性系数分别为0.7784和0.7843。在不同海拔草地群落中,不同土层含水量对草地生物量的贡献不尽相同,但60 cm以上根系主要分布层内的水分对草地生物量具有重要的意义。     

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 μm algae in the middle and lower part of the ice core were very high: up to 6.1 ± 10⁸ cells I⁻¹ and 194 μg C I⁻¹. Heterotrophic algae made up the largest proportion of the nanoplankton (2-20 μm) and microplankton (20-200 μm) 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.     

Carbon dioxide and methane dynamics in a sub-Arctic peatland in northern Finland

We studied carbon dynamics on various surface parts of a highly patterned fen, typical in northern Finland, to examine the importance of different microsites to the areal carbon fluxes. The studies were carried out in June-September 1995 on a mesotrophic flark fen (an aapa mire) in Kaamanen (69°08'N, 27° 17'E). Wet flarks, moist lawns and dry strings accounted for 60%, 10% and 30% of the surface area, respectively. A static chamber technique was applied to measure the CH₄ exchange, the instantaneous net ecosystem exchange (NEE, transparent chamber) and the ecosystem respiration (R_tot' opaque chamber) in several microsites. The static chamber results were compared with those obtained by the eddy covariance technique. The mean daytime areal net ecosystem CO₂ exchange rate measurement in conditions where photosynthesis was light saturated (PAR>400 μmol m_-2 s_-1) varied during the measurement period from −59 mg CO₂-C m⁻²h⁻¹ (release) to 250 (uptake). The mean CH₄ emission during the measuring period was 78 mg CH_4-Cm⁻² d⁻¹ on the flarks, 68 mg on the lawn and 6.0 mg on the strings. The strings without shrubs (mainly Betula nana ) were in general net sources of CO₂, even during the middle of the growing season, whereas the lawns, flarks and also strings growing B. nana showed a daytime net uptake of CO₂. Areally integrated chamber results showed lower CO₂ and higher CH₄ fluxes than predicted from the eddy covariance measurements.