The outflow of polar water through the Arctic Archipelago and the oceanographic conditions in Baffin Bay

The transports of mass, heat, and salt through the Arctic Archipelago are estimated by two different approaches. First: A baroclinic, rotationally controlled flow is assumed through the Arctic Archipelago and the Davis Strait, with all passages transporting at maximum capacity. Second: Mass, salt, and energy balances are considered for the upper 'cold core' in Baffin Bay. The mass transport in the first case decreases and in the second case increases with increasing salinity in the Beaufort Sea. It is thus possible to determine a salinity at which both approaches give the same mass transport. The outflow in the upper layers is estimated at 0.7 · 10⁹ kg s⁻¹ with a salinity of 32.9. The amount of water from the Polar Ocean entering the deeper (Atlantic) layer in Baffin Bay is more difficult to assess. A tentative value of 0.3 10·kg s⁻¹ with a salinity cf 34.3 is proposed.     

Volume, heat and salt transport by the West Spitsbergen Current

During the summer of 2000 (June-July) 14 CTD and ADCP transects perpendicular to the West Spitsbergen Current and along the western border of the Barents Sea were made. The measurements covered the area between 69° 43'and 80° N and 01° and 20° E. The main purpose was to follow changes in volume, heat and salt content of Atlantic Water (AW) on its way north. The strongest and most stable flow of AW was located along the continental slope where northward flowing currents exceeding 40 cm/sec were measured. A few weaker northward branches were also found to the west of the slope. South-directed currents were recorded between them and eddy-like mesoscale structures were commonly observed. Measured by vessel-mounted acoustic Doppler current profiler (VM-ADCP), the net northward transport of AW volume in the upper 136 m layer decreased from nearly 6 Sv at the southernmost transect to below 1 Sv at a latitude of 78° 50'N. Similarly, heat transport drops from about 173 TW to about 9 TW and relative salt transport (over 34.92 psu) from 980 × 10³ kg/sec to 14 × 10³ kg/sec. Transport in the southern direction prevails at the transect located between 79° 07'and 79° 30'N. The calculated baroclinic geostrophic transport of AW volume, heat and salt in the upper 1000 m layer behaves similarly. East-directed transport dominates at the Barents Sea boundary while westward flow prevails on the western side of the West Spitsbergen Current.     

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.     

Micromonas pusilla (Prasinophyceae) as part of pico-and nanoplankton communities of the Barents Sea

Micromonas pusilla (Butcher) Manton & Parke appears to be a prominent member of the Barents Sea picoplankton community as revealed by the serial dilution culture method. Cell numbers frequently exceeded 10⁷ cells 1⁻¹, though they usually varied between 10³and 10⁶ cells l⁻¹. A number of other identified and unidentified taxa were recorded and quantified. Distribution relative to the marginal ice zone is reported.     

One-year records of current and bottom pressure in the strait between Nordaustlandet and Kvitøya, Svalbard, 1980-81

we have obtained one year of measurements from a subsurface instrumented mooring carrying two current meters and one bottom pressure recorder in the strait between Nordaustlandet and Kvitøya in the northeastern Svalbard archipelago. The observations show a mixed tide with typical amplitudes 0.4 db and 10cm sec⁻¹. The semidiurnal tide is characterized by a progressive wave propagating toward the south. together with a cross-channel baroclinic mode. The annual average (non-tidal) current is less than 2cm sec⁻¹ toward the north-east, suggesting that the transport into the Arctic Ocean is approximately 0.2 × 10⁶m³s⁻¹.     

Direct measurements of volume transports through Fram Strait

Heat and freshwater transports through Fram Strait are understood to have a significant influence on the hydrographic conditions in the Arctic Ocean and on water mass modifications in the Nordic seas. To determine these transports and their variability reliable estimates of the volume transport through the strait are required. Current meter moorings were deployed in Fram Strait from September 1997 to September 1999 in the framework of the EU MAST III Variability of Exchanges in the Northern Seas programme. The monthly mean velocity fields reveal marked velocity variations over seasonal and annual time scales, and the spatial structure of the northward flowing West Spitsbergen Current and the southward East Greenland Current with a maximum in spring and a minimum in summer. The volume transport obtained by averaging the monthly means over two years amounts to 9.5 ± 1.4 Sv to the north and 11.1 ± 1.7 Sv to the south (1 Sv = 10⁶ m³s⁻¹). The West Spitsbergen Current has a strong barotropic and a weaker baroclinic component; in the East Greenland Current barotropic and baroclinic components are of similar magnitude. The net transport through the strait is 4.2 ± 2.3 Sv to the south. The obtained northward and southward transports are significantly larger than earlier estimates in the literature; however, within its range of uncertainty the balance obtained from a two year average is consistent with earlier estimates.     

Glacier extent in a Novaya Zemlya fjord during the "Little Ice Age" inferred from glaciomarine sediment records

Glacier activity at Russkaya Gavan', north-west Novaya Zemlya (Arctic Russia), is reconstructed by particle size analysis of three fjord sediment cores in combination with ¹⁴C and ²¹⁰Pb dating. Down-core logging of particle size variation reveals at least two intervals with sediment coarsening during the past eight centuries. By comparing them with reconstructions of summer temperature and atmospheric circulation, these intervals are interpreted to represent two cycles of glacier advance and retreat sometime during ca. AD 1400–1700 and AD 1700–present. Sediment accumulation thus appears to be sensitive to century-scale fluctuations of the Barents Sea climate. The identification of two glacier cycles in the glaciomarine record from Russkaya Gavan' demonstrates that during the "Little Ice Age" major glacier fluctuations on Novaya Zemlya occurred in broad synchrony with those in other areas around the Barents Sea.     

南北极海冰变化及其影响因素的对比分析

海冰是海洋-大气交互系统的重要组成部分,与全球气候系统间存在灵敏的响应和反馈机制。本文选用欧洲空间局发布的1992—2008年海冰密集度数据分析了南北极海冰在时间和空间上的变化规律与趋势,并结合由美国环境预报中心(National Centers for Environmental Prediction,NCEP)和美国大气研究中心(National Center for Atmospheric Research, NCAR)联合制作的NCEP/NCAR气温数据和ENSO指数探讨了南北极海冰变化的影响因素。结果表明,北极海冰面积呈明显的减少趋势,其中夏季海冰最小月的减少更快。北冰洋中央海盆区、巴伦支海、喀拉海、巴芬湾和拉布拉多海的减少最明显。南极海冰面积呈微弱增加趋势,罗斯海、太平洋扇区和大西洋扇区的海冰增加。北极海冰面积与气温有显著的滞后1个月的负相关关系(P0.01)。北极升温显著,北冰洋中央海盆区、喀拉海、巴伦支海、巴芬湾和楚科奇海升温趋势最大,海冰减少很明显。南极在南大西洋、南太平洋呈降温趋势,海冰增加。北极海冰减少与39个月之后ONI的下降、40个月之后SOI的上升密切相关;南极海冰增加与7个月之后ONI的下降、6个月之后SOI的上升存在很好的响应关系。南北极海冰变化与三次ENSO的强暖与强冷事件有很好的对应关系。     

Deglacial land emergence and lateral upper-mantle heterogeneity in the Svalbard Archipelago—II. Extended results for high-resolution load models

In Paper I (Breuer & Wolf 1995), a preliminary interpretation of the postglacial land emergence observed at a restricted set of six locations in the Svalbard Archipelago was given. The study was based on a simple model of the Barents Sea ice sheet and suggested increases in lithosphere thickness and asthenosphere viscosity with increasing distance from the continental margin.
In the present paper, the newly developed high-resolution load model. BARENTS-2, and land-uplift observations from an extended set of 25 locations are used to study further the possibility of resolving lateral heterogeneity in the upper mantle below the northern Barents Sea. A comparison of the calculated and observed uplift values shows that the lithosphere thickness is not well resolved by the observations, although values above 110 km are most common for this parameter. In contrast to this, there are indications of a lateral variation of asthenosphere viscosity. Whereas values in the range 10¹⁸-10²⁰Pas are inferred for locations close to the continental margin, 10²⁰-10²¹ Pa s are suggested further away from the margin.
A study of the sensitivity of the values found for lithosphere thickness and asthenosphere viscosity to modifications of load model BARENTS-2 shows that such modifications can be largely accommodated by appropriate changes in lithosphere thickness, whereas the suggested lateral variation of asthenosphere viscosity is essentially unaffected. An estimate of the influence of the Fennoscandian. ice sheet leads to the conclusion that its neglect results in an underestimation of the thickness of the Barents Sea ice sheet by about 10 per cent.     

Ice draft and current measurements from the north-western Barents Sea, 1993–96

From 1993 to 1996, three oceanographic moorings were deployed in the north-western Barents Sea, each with a current meter and an upward-looking sonar for measuring ice drafts. These yielded three years of currents and two years of ice draft measurements. An interannual variability of almost I m was measured in the average ice draft. Causes for this variability are explored, particularly its possible connection to changes in atmospheric circulation patterns. We found that the flow of Northern Barents Atlantic-derived Water and the transport of ice from the Central Arctic into the Barents Sea appears to be controlled by winds between Nordaustlandet and Franz Josef Land, which in turn may be influenced by larger-scale variations such as the Arctic Oscillation/North Atlantic Oscillation.     

Deglaciation effects on the rotation of the Earth

Summary. The viscoelastic response of the Earth to the mass displacements caused by late Pleistocene deglaciation and concomitant sea level changes is shown to be capable of producing the secular motion of the Earth's rotation pole as deduced from astronomical observations. The calculations for a viscoelastic Earth yield a secular motion in the direction of 72° W meridian which is in excellent agreement with observed values. The average Newtonian viscosity and the relaxation time obtained from polar motion data are about (1.1 ± 0.6)10²³ poise (P) and 10⁴ (1 ± 0.5) yr. The non-tidal secular acceleration of the Earth can also be attributed to the viscoelastic response to deglaciation and results in an independent viscosity estimate of 1.6 × 10²³ P with upper and lower limits of 1.1 × 10²³ and 2.8 × 10²³ P. These values are in agreement with those based on the polar drift analysis and indicate an average mantle viscosity of 1–2 × 10²³ P.     

Slip rate on the Dead Sea transform fault in northern Araba valley (Jordan)

The Araba valley lies between the southern tip of the Dead Sea and the Gulf of Aqaba. This depression, blanketed with alluvial and lacustrine deposits, is cut along its entire length by the Dead Sea fault. In many places the fault is well defined by scarps, and evidence for left-lateral strike-slip faulting is abundant. The slip rate on the fault can be constrained from dated geomorphic features displaced by the fault. A large fan at the mouth of Wadi Dahal has been displaced by about 500 m since the bulk of the fanglomerates were deposited 77–140 kyr ago, as dated from cosmogenic isotope analysis (¹⁰Be in chert) of pebbles collected on the fan surface and from the age of transgressive lacustrine sediments capping the fan. Holocene alluvial surfaces are also clearly offset. By correlation with similar surfaces along the Dead Sea lake margin, we propose a chronology for their emplacement. Taken together, our observations suggest an average slip rate over the Late Pleistocene of between 2 and 6 mm yr⁻¹, with a preferred value of 4 mm yr⁻¹. This slip rate is shown to be consistent with other constraints on the kinematics of the Arabian plate, assuming a rotation rate of about 0.396° Myr⁻¹ around a pole at 31.1°N, 26.7°E relative to Africa.     

Nitrogen uptake rates in phytoplankton and ice algae in the Barents Sea

Uptake rates of NH₄⁺, NO₃⁻ and dissolved organic nitrogen (urea) were measured in phytoplankton and in ice algae in the Barents Sea using a ¹⁵N-technique. NO₃⁻ was the most important nitrogen source for the ice algae (f-ratio = 0.92). The in situ irradiances in the subsurface chlorophyll maximum and in the ice algal communities were low. The in situ NO₃⁻ uptake rate in the ice algal communities was light-limited The in situ NO₃⁻ and NH₄⁻ uptake rates in the subsurface chlorophyll maximum were at times light-limited. It is hypothesised that NH₄⁺ may accumulate in low light in the bottom of the euphotic zone and inhibit the in situ NO₃⁻ uptake rate.     

222Rn and 226Ra: indicators of sea-ice effects on air-sea gas exchange

²²² Rn and ²²⁶Ra distributions beneath the sea ice of the Barents Sea revealed that ice cover has varied effects on air-sea gas exchange. Twice, once in late summer and once in late winter, seawater samples from the top meter below drill holes had ²²²Rn activities that were not lower than their ^226,Ra activities, indicating the existence of secular equilibrium and a negligible net exchange of ²²²Rn and other gases with the atmosphere. However, seawater in the upper 20-85 m usually exhibited at least some ²²²Rn depletion; ²²²Rn-to-²²⁶Ra activity ratios tended to have 'ice-free' values (0.3-0.9) in the summer and values between 0.9 and 1.0 in the winter. Integrated ²²²Rn depletions and piston velocities in both seasons typically fell in the lower 25% of the ranges for ice-free seawater, suggesting that a moderate but far from total reduction in gas exchange is normally caused by ice cover and/or meltwater. The results demonstrate that sea-ice interference with the oceanic uptake of atmospheric gases such as CO, is not well understood and needs further investigation.     

Inference of mantle viscosity from GRACE and relative sea level data

Gravity Recovery And Climate Experiment (GRACE) satellite observations of secular changes in gravity near Hudson Bay, and geological measurements of relative sea level (RSL) changes over the last 10 000 yr in the same region, are used in a Monte Carlo inversion to infer-mantle viscosity structure. The GRACE secular change in gravity shows a significant positive anomaly over a broad region (>3000 km) near Hudson Bay with a maximum of ∼2.5 μGal yr⁻¹ slightly west of Hudson Bay. The pattern of this anomaly is remarkably consistent with that predicted for postglacial rebound using the ICE-5G deglaciation history, strongly suggesting a postglacial rebound origin for the gravity change. We find that the GRACE and RSL data are insensitive to mantle viscosity below 1800 km depth, a conclusion similar to that from previous studies that used only RSL data. For a mantle with homogeneous viscosity, the GRACE and RSL data require a viscosity between  1.4 × 10²¹  and  2.3 × 10²¹  Pa s. An inversion for two mantle viscosity layers separated at a depth of 670 km, shows an ensemble of viscosity structures compatible with the data. While the lowest misfit occurs for upper- and lower-mantle viscosities of  5.3 × 10²⁰  and  2.3 × 10²¹  Pa s, respectively, a weaker upper mantle may be compensated by a stronger lower mantle, such that there exist other models that also provide a reasonable fit to the data. We find that the GRACE and RSL data used in this study cannot resolve more than two layers in the upper 1800 km of the mantle.     

Interannual variability of dense shelf water salinities in the north-western Barents Sea

The maximum dense shelf water salinity formed during winter in the Svalbard Bank area of the north-western Barents Sea is reconstructed for the period 1952–2000 by analysing the transformation of summer remnants. The variability of 34.7 - 35.4, waters being at the freezing point, is mainly generated by interannual variations in the near surface salinity. On interannual time scales the latter is strongly linked to the sea ice import. In contrast, no correlation of the salinity of the Atlantic Water (AW) throughflow to the Arctic Ocean with the ice import is found. Salinities of both the dense shelf water site in the north-west Barents Sea and the north-eastward AW throughflow show a long term decrease, which can partly be explained by a less saline inflow of AW from the Norwegian Sea. The unusually low dense water salinities in the north-west Barents Sea during the 1990s appear to have a different origin, consistent with a response to oceanic heat advection and decreasing sea ice extent.     

Surface vertical displacements, potential perturbations andgravity changes of a viscoelastic earth model induced by internal point dislocations

Using the viscoelastic correspondence principle, we utilize the surface coseismic spheroidal deformation fields (i.e. vertical displacements, potential perturbations and gravity changes) of SNREI earth models caused by four typical types of point dislocation, derived by Sun & Okubo (1993 ), to deduce the fundamental formulas for spheroidal fields relevant to viscoelastic earth models. In computations, we employ a strike-slip dislocation on a vertical plane buried at the bottom of the lithosphere to estimate the maximal viscous relaxation responses to this kind of source that possibly exist on the surface of the earth. We take the seismic moment as 10²²  N  m, which is characteristic of an average large earthquake. The numerical results demonstrate that, if we take the viscosity as 10¹⁹  Pa  s in the asthenosphere, and 10²¹  Pa  s in the other mantle layers, the rates of surface vertical displacements and gravity changes within about 2.5° for the 10 postseismic years are respectively 1.5–8.1  cm  yr⁻¹ and 4.0–14.9  μgal  yr⁻¹ : the viscous relaxation for this mantle viscosity profile proceeds much faster than for a constant mantle viscosity of 10²¹  Pa  s.     

Uplift and heat flow following the injection of magmas into the lithosphere

Summary. The thermal effect of a rapid injection of hot magmas into the lower part of the lithosphere is modelled as an increase in heat production through the invaded region. The change in surface heat flow and the uplift resulting from the thermal expansion are determined in three-dimensional axially symmetric geometry: they are expressed as the space time convolutions of a Green's function with the anomalous heat production.
The anomalies with shorter wavelength (compared to the lithospheric thickness) are attenuated. This filtering affects the surface uplift more than the heat flow anomaly; the attenuation effect is larger when only the lower part of the lithosphere is invaded.
The uplift time constant is of the same order as the heat conduction time if the lower lithosphere is invaded by magmas at a moderate rate (i.e. the rate of injection does not exceed the equivalent of 0.1 per cent of the lithospheric volume in 10⁶yr). Fifty per cent of the total uplift takes place in about 80 × 10⁶yr for a lithosphere 100 km thick. The uplift is slightly faster when the whole lithosphere is invaded. The heat flow anomaly is delayed when the lower part of the lithosphere is invaded.
The spatial extent and the timing of the uplift and heat flow anomalies are critical in determining the mechanism's feasibility. Magma injections explain rapid uplifts [> 100 m (10⁶ yr)⁻¹] only if the magma is supplied at a very high rate (i.e. at least 10 per cent of the lithosphere volume per 10⁶yr). It is a feasible mechanism for uplifts that occur over longer periods of time (≊ 30 × 10⁶yr) such as those that seem to have occurred when the African plate came to rest with respect to the mantle.     

Distribution and life history of krill from the Barents Sea

Krill from the Barents Sea were studied on six cruises from 1985 to 1989. Thysanoessa inermis and T. longicaudata were the dominant species, while T. raschii and Meganyctiphanes norvegica were rarer in the studied areas. The two dominant species T. inermis and T. longicaudata are mainly found in the Atlantic. Water and they do not to a large extent penetrate into Arctic water masses in the northern Barents Sea. M. norvegica is a more strict boreal species that does not occur as extensively in the Barents Sea as do the Thysanoessa species. The mean population abundance ranged from 1 to 61 individuals m⁻² for T. inermis and from 2 to 52 ind. M⁻² for T. longicaudata . The mean dry weight biomass of these two species ranged from 14 to 616 and from 19 to 105 mg⁻². Length frequency distributions indicate a life span of just over two years for T. inermis and T. longicaudata . Growth took place from about April to autumn with no apparent growth during winter. Maturation and spawning seem to occur after two years for T. inermis and one year for T. longicaudata . Main spawning occurred from May to June coinciding with the spring phytoplankton bloom. Captive spawners of T. inermis (total length 17-22 mm) shed 30-110 eggs per female in a single batch.     

Early Holocene environment on Bjørnøya (Svalbard) inferred from multidisciplinary lake sediment studies

Bjørnøya, a small (178 km²) island situated between the mainland of Norway and southern Spitsbergen, provides the opportunity for the reconstruction of early Holocene terrestrial and limnic palaeoenvironments in the southwestern Barents Sea. The AMS ¹⁴C dating technique, geochemical, mineral magnetic, micro and macrofossil analyses were applied to sediments recovered from lake Stevatnet and the results are interpreted in terms of palaeoenvironmental conditions between 9800 and 8300 ¹⁴C bp. After the disappearance of local glaciers before ca 9800¹⁴C BP, the lake productivity increased rapidly at the same time as pioneer plant communities developed on soils which gradually became more stable. Insect data indicates that strong seasonal contrasts with mean July temperatures around 9°C and mean January temperatures around −12°C prevailed between 9500 and 8300 ¹⁴C BP. These high summer temperatures, possibly as much as 4-5°C higher than the present, favoured the development of a flora including Dryas and Angelica cf. archangelica . The enhanced freeze/thaw processes led to an increased erosion of minerogenic and organic material. After 8000 ¹⁴C BP the temperatures may have gradually declined. The environmental reconstruction derived from our data set supports the conceptual insolation model which proposes maximum Holocene seasonality for the Northern Hemisphere at ca 9000 ¹⁴C BP.