Arctic sea ice volume export through the Fram Strait from combined satellite and model data: 1979–2012

By combing satellite-derived ice motion and concentration with ice thickness fields from a popular model PIOMAS we obtain the estimates of ice volume flux passing the Fram Strait over the 1979–2012 period. Since current satellite and field observations for sea ice thickness are limited in time and space, the use of PIOMAS is expected to fill the gap by providing temporally continued ice thickness fields. Calculated monthly volume flux exhibits a prominent annual cycle with the peak record in March(roughly 145 km3/month) and the trough in August(10 km~3/month). Annual ice volume flux(1 132 km~3) is primarily attributable to winter(October through May) outflow(approximately 92%). Uncertainty in annual ice volume export is estimated to be 55 km~3(or 5.7%). Our results also verified the extremely large volume flux appearing between late 1980 s and mid-1990 s. Nevertheless, no clear trend was found in our volume flux results. Ice motion is the primary factor in the determination of behavior of volume flux. Ice thickness presented a general decline trend may partly enhance or weaken the volume flux trend. Ice concentration exerted the least influences on modulating trends and variability in volume flux. Moreover, the linkage between winter ice volume flux and three established Arctic atmospheric schemes were examined. Compared to NAO, the DA and EOF3 mechanism explains a larger part of variations of ice volume flux across the strait.     

2017年夏季北冰洋浮冰区海雾特征分析

首先利用中国第八次北极考察队期间获取的走航观测数据分析了环北极考察的海雾特征。接下来利用在北冰洋密集浮冰区海雾加密观测实验期间获取的GPS探空观测数据和NCEP再分析资料,研究了北冰洋浮冰区海雾生成的气象要素特征、边界层特征和大气环流形势特征,发现浮冰区冰雪面之上的冷空气穹丘使得大气易于达到饱和,为北冰洋不同种类海雾的出现造了有利条件。平流雾、辐射雾和蒸汽雾生消的机理和影响期间边界层气象特征各不相同,并且根据特定环流形势对3种海雾进行预报是可行的。     

Recent satellite-derived sea ice volume flux through the Fram Strait: 2011–2015

The Fram Strait(FS) is the primary region of sea ice export from the Arctic Ocean and thus plays an important role in regulating the amount of sea ice and fresh water entering the North Atlantic seas. A 5 a(2011–2015) sea ice thickness record retrieved from Cryo Sat-2 observations is used to derive a sea ice volume flux via the FS. Over this period, a mean winter accumulative volume flux(WAVF) based on sea ice drift data derived from passivemicrowave measurements, which are provided by the National Snow and Ice Data Center(NSIDC) and the Institut Francais de Recherche pour d'Exploitation de la Mer(IFREMER), amounts to 1 029 km~3(NSIDC) and1 463 km~3(IFREMER), respectively. For this period, a mean monthly volume flux(area flux) difference between the estimates derived from the NSIDC and IFREMER drift data is –62 km~3 per month(–18×10~6 km~2 per month).Analysis reveals that this negative bias is mainly attributable to faster IFREMER drift speeds in comparison with slower NSIDC drift data. NSIDC-based sea ice volume flux estimates are compared with the results from the University of Bremen(UB), and the two products agree relatively well with a mean monthly bias of(5.7±45.9) km~3 per month for the period from January 2011 to August 2013. IFREMER-based volume flux is also in good agreement with previous results of the 1990 s. Compared with P1(1990/1991–1993/1994) and P2(2003/2004–2007/2008), the WAVF estimates indicate a decline of more than 600 km~3 in P3(2011/2012–2014/2015). Over the three periods, the variability and the decline in the sea ice volume flux are mainly attributable to sea ice motion changes, and second to sea ice thickness changes, and the least to sea ice concentration variations.     

Carbon flows in the benthic food web at the deep-sea observatory HAUSGARTEN (Fram Strait)

The HAUSGARTEN observatory is located in the eastern Fram Strait (Arctic Ocean) and used as long-term monitoring site to follow changes in the Arctic benthic ecosystem. Linear inverse modelling was applied to decipher carbon flows among the compartments of the benthic food web at the central HAUSGARTEN station (2500 m) based on an empirical data set consisting of data on biomass, prokaryote production, total carbon deposition and community respiration. The model resolved 99 carbon flows among 4 abiotic and 10 biotic compartments, ranging from prokaryotes up to megafauna. Total carbon input was 3.78±0.31 mmol C m⁻² d⁻¹, which is a comparatively small fraction of total primary production in the area. The community respiration of 3.26±0.20 mmol C m⁻² d⁻¹ is dominated by prokaryotes (93%) and has lower contributions from surface-deposit feeding macro- (1.7%) and suspension feeding megafauna (1.9%), whereas contributions from nematode and other macro- and megabenthic compartments were limited to <1%. The high prokaryotic contribution to carbon processing suggests that functioning of the benthic food web at the central HAUSGARTEN station is comparable to abyssal plain sediments that are characterised by strong energy limitation. Faunal diet compositions suggest that labile detritus is important for deposit-feeding nematodes (24% of their diet) and surface-deposit feeding macrofauna (∼44%), but that semi-labile detritus is more important in the diets of deposit-feeding macro- and megafauna. Dependency indices on these food sources were also calculated as these integrate direct (i.e. direct grazing and predator–prey interactions) and indirect (i.e. longer loops in the food web) pathways in the food web. Projected sea-ice retreats for the Arctic Ocean typically anticipate a decrease in the labile detritus flux to the already food-limited benthic food web. The dependency indices indicate that faunal compartments depend similarly on labile and semi-labile detritus, which suggests that the benthic biota may be more sensitive to changes in labile detritus inputs than when assessed from diet composition alone. Species-specific responses to different types of labile detritus inputs, e.g. pelagic algae versus sympagic algae, however, are presently unknown and are needed to assess the vulnerability of individual components of the benthic food web.     

An inverse modeling study in Fram Strait. Part I: dynamics and circulation

In order to reconstruct the circulation in the northern Greenland Sea, between 77°N and 81°N, and the exchanges with the Arctic Ocean through Fram Strait, a variational inverse model is applied to the density field observed in summer 1984 during the MIZEX 84 experiment. An estimate of the three-dimensional large-scale pressure field is obtained in which the solution is decomposed into a limited number of vertical modes and the mode amplitudes are described by piece-wise polynomials on a finite-element grid. The solution should be consistent with a frictional depth-integrated vorticity balance and with the density data. The global model parameters are tuned to ensure agreement between the retrieved geostrophic velocity and independent currentmeter data. In a companion paper (Schlichtholz and Houssais, 1999b), the same method, but without dynamical constraint, is applied to the same hydrographic dataset to perform a detailed water mass analysis and to estimate individual water mass transports.A comprehensive picture of the summer geostrophic circulation in Fram Strait is obtained in which northward recirculations in the East Greenland Current (EGC) and various recirculations from the West Spitsbergen Current (WSC) to the EGC are identified. It is suggested that the branch of the WSC following the upper western slope of the Yermak Plateau turns westward beyond 81°N and recirculates southward along the lower slope, then merging with a westward recirculating branch south of 79°N. At 79°N, a southward net transport of 6.5 Sv is found in the EGC which, combined with a northward net transport of only 1.5 Sv in the WSC, results in a fairly large outflow of 5 Sv from the Arctic Ocean to the Greenland Sea.The inverse solutions show that, in summer, the local induction of vorticity by the wind stress curl or by meridional advection of planetary vorticity should be small, so that, in the EGC and in the WSC, the vorticity balance is mainly achieved between the bottom pressure torque and dissipation of vorticity through bottom friction. A substantial barotropic flow associated with along-slope potential energy gradients is indeed identified on both sides of the strait.     

Particle sedimentation patterns in the eastern Fram Strait during 2000–2005: Results from the Arctic long-term observatory HAUSGARTEN

Since 2000 long-term measurements of vertical particle flux have been performed with moored sediment traps at the long-term observatory HAUSGARTEN in the eastern Fram Strait (79°N/4°E). The study area, which is seasonally covered with ice, is located in the confluence zone of the northward flowing warm saline Atlantic water with cold, low salinity water masses of Arctic origin. Current projections suggest that this area is particularly vulnerable to global warming. Total matter fluxes and components thereof (carbonate, particulate organic carbon and nitrogen, biogenic silica, biomarkers) revealed a bimodal seasonal pattern showing elevated sedimentation rates during May/June and August/September. Annual total matter flux (dry weight, DW) at ～300 m depth varied between 13 and 32 g m^?2 a^?1 during 2000 and 2005. Of this total flux 6–13% was due to CaCO₃, 4–21% to refractory particulate organic carbon (POC), and 3–8% to biogenic particulate silica (bPSi). The annual flux of all biogenic components together was almost constant during the period studied (8.5–8.8 g m^?2 a^?1), although this varied from 27% to 67% of the total annual flux. The fraction was lowest in a year characterized by the longest duration of ice coverage (91 and 70 days for the calendar year and summer season, May–September, respectively). Biomarker analyses revealed that organic matter originating from marine sources was present in excess of terrigenious material in the sedimented matter throughout most of the study period. Fluxes of recognizable phyto- and protozooplankton cells amounted up to 60×10⁶ m^?2 d^?1. Diatoms and coccolithophorids were the most abundant organisms. Diatoms, mainly pennate species, dominated during the first years of the investigation. A shift in the composition occurred during the last year when numbers of diatoms declined considerably, leading to a dominance of coccolithoporids. This was also reflected in a decrease in the sedimentation of bPSi. The sedimentation of biogenic matter, however, did not differ from the amount observed during the previous years. Among the larger organisms, pteropods at times contributed significantly to both the total matter and CaCO₃, fluxes.     

Transports of Nordic Seas water masses and excess SF6 through Fram Strait to the Arctic Ocean

To determine the exchanges between the Nordic Seas and the Arctic Ocean through Fram Strait is one of the most important aspects, and one of the major challenges, in describing the circulation in the Arctic Mediterranean Sea. Especially the northward transport of Arctic Intermediate Water (AIW) from the Nordic Seas into the Arctic Ocean is little known. In the two-ship study of the circulation in the Nordic Seas, Arctic Ocean - 2002, the Swedish icebreaker Oden operated in the ice-covered areas in and north of Fram Strait and in the western margins of Greenland and Iceland seas, while RV Knorr of Woods Hole worked in the ice free part of the Nordic Seas. Here two hydrographic sections obtained by Oden, augmented by tracer and velocity measurements with Lowered Acoustic Doppler Current Profiler (LADCP), are examined. The first section, reaching from the Svalbard shelf across the Yermak Plateau, covers the region north of Svalbard where inflow to the Arctic Ocean takes place. The second, western, section spans the outflow area extending from west of the Yermak Plateau onto the Greenland shelf. Geostrophic and LADCP derived velocities are both used to estimate the exchanges of water masses between the Nordic Seas and the Arctic Ocean. The geostrophic computations indicate a total flow of 3.6 Sv entering the Arctic on the eastern section. The southward flow on the western section is found to be 5.1 Sv. The total inflow to the Arctic Ocean obtained using the LADCP derived velocities is much larger, 13.6 Sv, and the southward transport on the western section is 13.7 Sv, equal to the northward transport north of Svalbard. Sulphur hexafluoride (SF₆) originating from a tracer release experiment in the Greenland Sea in 1996 has become a marker for the circulation of AIW. From the geostrophic velocities we obtain 0.5 Sv and from the LADCP derived velocities 2.8 Sv of AIW flowing into the Arctic. The annual transport of SF₆ into the Arctic Ocean derived from geostrophy is 5 kg/year, which is of the same magnitude as the observed total annual transport into the North Atlantic, while the LADCP measurements (19 kg/year) imply that it is substantially larger. Little SF₆ was found on the western section, confirming the dominance of the Arctic Ocean water masses and indicating that the major recirculation in Fram Strait takes place farther to the south.     

Arctic sea ice long-term dynamics according to the satellite microwave data

The main results of processing the long-term satellite data in different spectral ranges and with different spatial resolutions used to map Arctic sea ice parameters are presented. The advantages of the methods developed in order to estimate these parameters on the basis of microwave sensor measurements are indicated. The specific features of the long-term dynamics of the main sea ice geophysical parameters (the sea ice area and distribution during the summer minimum, ice age structure and thickness, multiyear ice concentration, times of ice melt and freeze onset, etc.) are presented. The effect of changes in sheet ice on the status of large Arctic mammals is estimated.     

Trophic structure of zooplankton in the Fram Strait in spring and autumn 2003

The trophic structure of zooplankton was investigated in Fram Strait (north western Svalbard) in spring and autumn of 2003. Depth-stratified zooplankton samples were collected at 12 stations on the shelf (200 m), across the shelf-slope (500 m) and over deep water (>750 m), using a Multiple Plankton Sampler equipped with 0.180-mm mesh size nets.Higher zooplankton abundance and estimated biomass were found in the shelf area. Abundance and biomass were two times higher in August, when sea-surface temperature was higher than in May. Herbivores dominated numerically in May, and omnivores in August, suggesting a seasonal sequence of domination by different trophic groups. Cirripedia nauplii and Fritillaria borealis prevailed in spring, whereas copepod nauplii and Calanus finmarchicus were numerically the most important herbivores in autumn. Small copepods, Oithona similis and Triconia borealis, were the most numerous omnivorous species in both seasons, but their abundances increased in autumn. Chaetognatha (mainly Eukrohnia hamata) accounted for the highest abundance and biomass among predatory taxa at all deep-water stations and during both seasons. Regarding vertical distribution, herbivores dominated numerically in the surface layer (0–20 m), and omnivores were concentrated somewhat deeper (20–50 m) during both seasons. Maximum abundance of predators was found in the surface layer (0–20 m) in spring, and generally in the 20–50 m layer in autumn. This paper presents the first comprehensive summary of the zooplankton trophic structure in the Fram Strait area. Our goals are to improve understanding of energy transfer through this ecosystem, and of potential climate-induced changes in Arctic marine food webs.     

北极气旋的季节、年际变化及其与北极海冰、大气遥相关的关系

The seasonal and inter-annual variations of Arctic cyclone are investigated. An automatic cyclone tracking algorithm developed by University of Reading was applied on the basis of European Center for Medium-range Weather Forecasts(ECMWF) ERA-interim mean sea level pressure field with 6 h interval for 34 a period. The maximum number of the Arctic cyclones is counted in winter, and the minimum is in spring not in summer.About 50% of Arctic cyclones in summer generated from south of 70°N, moving into the Arctic. The number of Arctic cyclones has large inter-annual and seasonal variabilities, but no significant linear trend is detected for the period 1979–2012. The spatial distribution and linear trends of the Arctic cyclones track density show that the cyclone activity extent is the widest in summer with significant increasing trend in CRU(central Russia)subregion, and the largest track density is in winter with decreasing trend in the same subregion. The linear regressions between the cyclone track density and large-scale indices for the same period and pre-period sea ice area indices show that Arctic cyclone activities are closely linked to large-scale atmospheric circulations, such as Arctic Oscillation(AO), North Atlantic Oscillation(NAO) and Pacific-North American Pattern(PNA). Moreover,the pre-period sea ice area is significantly associated with the cyclone activities in some regions.     

Bathymetric variations in vertical distribution patterns of meiofauna in the surface sediments of the deep Arctic ocean (HAUSGARTEN,Fram strait)

Deep-sea benthic communities and their structural and functional characteristics are regulated by surface water processes. Our study focused on the impact of changes in water depth and food supplies on small-sized metazoan bottom-fauna (meiobenthos) along a bathymetric transect (1200–5500 m) in the western Fram Strait. The samples were collected every summer season from 2005 to 2009 within the scope of the HAUSGARTEN monitoring program. In comparison to other polar regions, the large inflow of organic matter to the sea floor translates into relatively high meiofaunal densities in this region. Densities along the bathymetric gradient range from approximately 2400 ind. 10 cm^-2 at 1200 m to approximately 300 ind. 10 cm^-2 at 4000 m. Differences in meiofaunal distribution among sediment layers (i.e., vertical profile) were stronger than among stations (i.e., bathymetric gradient). At all the stations meiofaunal densities and number of taxa were the highest in the surface sediment layer (0–1 cm), and these decreased with increasing sediment depth (down to 4–5 cm). However, the shape of the decreasing pattern differed significantly among stations. Meiofaunal densities and taxonomic richness decreased gradually with increasing sediment depth at the shallower stations with higher food availability. At deeper stations, where the availability of organic matter is generally lower, meiofaunal densities decreased sharply to minor proportions at sediment depths already at 2–3 cm. Nematodes were the most abundant organisms (60–98%) in all the sediment layers. The environmental factors best correlated to the vertical patterns of the meiofaunal community were sediment-bound chloroplastic pigments that indicate phytodetrital matter.     

Physical and biological characteristics of the pelagic system across Fram Strait to Kongsfjorden

The Fram Strait is very important with regard to heat and mass exchange in the Arctic Ocean, and the large quantities of heat carried north by the West Spitsbergen Current (WSC) influence the climate in the Arctic region as a whole. A large volume of water and ice is transported through Fram Strait, with net water transport of 1.7–3.2 Sv southward in the East Greenland Current and a volume ice flux in the range of 0.06–0.11 Sv. The mean annual ice flux is about 866,000 km² yr⁻¹. The Kongsfjorden–Krossfjorden fjord system on the coast of Spitsbergen, or at the eastern extreme of Fram Strait, is mainly affected by the northbound transport of water in the WSC. Mixing processes on the shelf result in Transformed Atlantic Water in the fjords, and the advection of Atlantic water also carries boreal fauna into the fjords. The phytoplankton production is about 80 g C m⁻² yr⁻¹ in Fram Strait, and has been estimated both below and above this for Kongsfjorden. The zooplankton fauna is diverse, but dominated in terms of biomass by calanoid copepods, particularly Calanus glacialis and C. finmarchicus. Other important copepods include C. hyperboreus, Metridia longa and the smaller, more numerous Pseudocalanus (P. minutus and P. acuspes), Microcalanus (M. pusillus and M. pygmaeus) and Oithona similis. The most important species of other taxa appear to be the amphipods Themisto libellula and T. abyssorum, the euphausiids Thysanoessa inermis and T. longicaudata and the chaetognaths Sagitta elegans and Eukrohnia hamata. A comparison between the open ocean of Fram Strait and the restricted fjord system of Kongsfjorden–Krossfjorden can be made within limitations. The same species tend to dominate, but the Fram Strait zooplankton fauna differs by the presence of meso- and bathypelagic copepods. The seasonal and inter-annual variation in zooplankton is described for Kongsfjorden based on the record during July 1996–2002. The ice macrofauna is much less diverse, consisting of a handful of amphipod species and the polar cod. The ice-associated biomass transport of ice-amphipods was calculated, based on the ice area transport, at about 3.55 × 10⁶ ton wet weight per year or about 4.2 × 10⁵ t C yr⁻¹. This represents a large energy input to the Greenland Sea, but also a drain on the core population residing in the multi-year pack ice (MYI) in the Arctic Ocean. A continuous habitat loss of MYI due to climate warming will likely reduce dramatically the sympagic food source. The pelagic and sympagic food web structures were revealed by stable isotopes. The carbon sources of particulate organic matter (POM), being Ice-POM and Pelagic-POM, revealed different isotopic signals in the organisms of the food web, and also provided information about the sympagic–pelagic and pelagic–benthic couplings. The marine food web and energy pathways were further determined by fatty acid trophic markers, which to a large extent supported the stable isotope picture of the marine food web, although some discrepancies were noted, particularly with regard to predator–prey relationships of ctenophores and pteropods.     

极地低压对费拉姆海峡大西洋入流水天气尺度变化的影响

The Atlantic inflow in the Fram Strait(78°50′N) has synoptic scale variability based on an array of moorings over the period of 1998–2010. The synoptic scale variability of Atlantic inflow, whose significant cycle is 3–16 d, occurs mainly in winter and spring(from January to April) and is related with polar lows in the Barents Sea. On the synoptic scale, the enhancement(weakening) of Atlantic inflow in the Fram Strait is accompanied by less(more)polar lows in the Barents Sea. Wind stress curl induced by polar lows in the Barents Sea causes Ekman-transport,leads to decrease of sea surface height in the Barents Sea, due to geostrophic adjustment, further induces a cyclonic circulation anomaly around the Barents Sea, and causes the weakening of the Atlantic inflow in the Fram Strait. Our results highlight the importance of polar lows in forcing the Atlantic inflow in the Fram Strait and can help us to further understand the effect of Atlantic warm water on the change of the Arctic Ocean.     

Paleo-bathymetry of the northern North Atlantic and consequences for the opening of the Fram Strait

In the past decade, the geophysical database in the northern North Atlantic and central Arctic Ocean constantly grew. Though far from being complete, the information from new aeromagnetic and seismic data north of the Jan Mayen Fracture Zone and in the Arctic Ocean, in combination with existing compiled geological and geophysical data, is used to produce paleo-bathymetric maps for several Cenozoic time intervals. This paleo-bathymetric model provides evidence for an initial deep-water exchange through the Fram Strait starting around 17 Ma. Furthermore, the model suggests that crustal rifting prior to initial seafloor spreading might have facilitated an earlier deep-water connection. This confirms that the paleo-topography of the Yermak Plateau played an important role in allowing at least the exchange of shallow water between the northern North Atlantic and the Arctic Ocean before the opening of the deep-water Fram Strait gateway. In the south of the research area the paleo-bathymetric model indicates that the first possibility for a deep-water overflow from the Norwegian-Greenland Sea to the North Atlantic could have been between 15 and 20 Ma.     

Mean Dynamic Topography and Geostrophic Surface Currents in the Fram Strait Derived from Geodetic Data

Two mean dynamic topography (MDT) fields are determined in the Fram Strait between Svalbard and Greenland. New airborne gravity anomalies, older data, and two different mean sea surface (MSS) fields are combined using the least squares collocation (LSC) technique. The results are compared to an oceanographic MDT model and two synthetic MDT fields. The same main currents are seen in all fields. Additionally, smaller scale features are revealed in the new MDT fields. Geostrophic surface currents derived from the MDT models are compared to moorings and Lagrangian drifters. The agreement is desultory. The oceanographic data are an inadequate basis of comparison due to data gaps. Nevertheless, it is the only one available.     

北极地区不同冰龄的海冰厚度变化研究

In this study, changes in Arctic sea ice thickness for each ice age category were examined based on satellite observations and modelled results. Interannual changes obtained from Ice, Cloud, and Land Elevation Satellite(ICESat)-based results show a thickness reduction over perennial sea ice(ice that survives at least one melt season with an age of no less than 2 year) up to approximately 0.5–1.0 m and 0.6–0.8 m(depending on ice age) during the investigated winter and autumn ICESat periods, respectively. Pan-Arctic Ice Ocean Modeling and Assimilation System(PIOMAS)-based results provide a view of a continued thickness reduction over the past four decades. Compared to 1980 s, there is a clear thickness drop of roughly 0.50 m in 2010 s for perennial ice. This overall decrease in sea ice thickness can be in part attributed to the amplified warming climate in north latitudes. Besides, we figure out that strongly anomalous southerly summer surface winds may play an important role in prompting the thickness decline in perennial ice zone through transporting heat deposited in open water(primarily via albedo feedback) in Eurasian sector deep into a broader sea ice regime in central Arctic Ocean. This heat source is responsible for enhanced ice bottom melting, leading to further reduction in ice thickness.     

Studying changes of ice coasts in the European Arctic

The present extent of European ice coasts, their spatial changes in the past 50 years and the velocities of ice flow in marginal parts of tidewater glaciers were determined and mapped at a regional scale using space-borne image data, both optical and radar. The methods of satellite photogrammetry and radar interferometry provided efficient solutions to the integral estimation of ice-coast dynamics in the Franz Josef Land, Novaya Zemlya and Svalbard archipelagos. Studies revealed significant degradation of the ice coasts (–7.7% by length) compared to the situation represented in the available maps. The results obtained in the laboratory were verified during several field campaigns.     

Seasonal variations of the surface currents in the Tsushima Strait

Seasonal variations of the surface currents in the Tsushima Strait were investigated by analyzing the monthly mean surface currents measured with HF radar. Several new features of the surface currents have been found. One notable feature is the large, complicated seasonal variation in the current structure in the eastern channel of the strait. For example, in the southeastern and northwestern regions of the channel, southwestward countercurrents are found in summer while southeastward acrossshore currents are found in autumn and winter. The wind-driven flow (Ekman flow) as well as surface geostrophic currents are responsible for these complicated variations of the surface currents. To quantify each variation of the flow and current, the wind-driven flow was calculated from the monthly wind (more precisely, the friction velocity) using the monthly speed factor and deflection angle estimated in our previous study, and the surface geostrophic currents were then estimated by subtracting the wind-driven flow from the measured surface currents. It was found that the acrossshore currents are the wind-driven flow, and that the surface geostrophic currents flow almost in the along-shore direction, indicating the validity of the decomposition of the surface velocity into the wind-driven flow and the geostrophic currents using the speed factor and deflection angle. A real-vector empirical orthogonal function (EOF) analysis of the surface geostrophic currents shows a pair of eddies in the lee of Tsushima and Iki Islands as the first mode, which indicates that the southwestward countercurrents in the eastern channel are formed primarily by the incoming Tsushima Warm Current.     

Abundance,biomass and composition of the sea ice biota of the Greenland Sea pack ice

During two cruises to the Greenland Sea, we studied the abundance and biomass of the sea ice biota in summer and late autumn. The mean calculated biomass of the sympagic community was 0.2 g C m⁻² ice. Algae contributed on average 43% to total biomass, followed by bacteria (31%), heterotrophic flagellates (20%), and meiofauna (4%). Diatoms were the main primary producers (60% of total algal biomass), but flagellated cells contributed significantly to the algal biomass. Among the meiofauna, ciliates, nematodes, acoel turbellarians and crustaceans were dominant. Calculated potential ingestion rates of meiofauna (0.6 g C m⁻² (120 d)⁻¹) are on the same order of magnitude as annual primary production estimates for Arctic multi-year sea ice. We therefore assume that grazing can control biomass accumulation of primary producers inside the sea ice.