Mesozoic palaeomagnetism in Vestfjella, Dronning Maud Land, East Antarctica

Summary. Thermal and alternating field demagnetization of oriented samples of Mesozoic lava flows (200–230 Myr) and dykes (154–172Myr) collected from seven nunataks within the Vestfjella region, Dronning Maud Land, revealed stable directions of magnetization of normal and reverse polarity. Directional distributions of both polarities define tight groups along the same palaeomagnetic axis. Depending on whether the regional westward dip of the lava flows originated prior to, or after the intrusive igneous phase, two or one, respectively, palaeomagnetic pole(s) can be estimated. Both poles, however, are in general accord with previous Mesozoic poles from East Antarctica.     

New records of terrestrial arthropods from Dronning Maud Land, Antarctica

Data on the occurrence of Eupodes angardi Strandtmann & Sømme, Tydeus erebus Strandtmann (Acari, Prostigmata), and Cryptopygus sverdrupi Lawrence (Collerabola) in Gjelsvikfjella and Muhlig-Hofmannfjella, as well as of Maudheimia wilsoni Dalenius (Acari, Cryptostigmata) in H.U. Sverdrupfjella and Gjelsvikfjella are presented. The four species differ in their distribution. While E. angardi, C. sverdrupi and M. wilsoni may be limited to central mountain ranges in Dronning Maud Land, T. erebus has been reported from 55°W to 80°E on the Antarctic Continent.     

Solar radiation transfer in the surface snow layer in Dronning Maud Land,Antarctica

Spectroradiometer measurements of solar radiation (the broadest band used 400–900 nm) were performed above and inside the surface snow layer in western Dronning Maud Land, Antarctica, during the austral summer of 2009–2010. The vertical distributions of transmittance and the extinction coefficient were examined from the surface to a depth of 30 cm. Physical characterization of the snowpack included measurements of thickness, density, hardness (hand test), liquid-water content, and grain size and shape (from photographs of grains). The transmittance was <1% in the upper 20 cm and <27% in the upper 10 cm. The mean spectral diffuse extinction coefficient varied between 0.04 and 0.31 cm^-1 (10–20-cm layer). Using the spectral extinction coefficients of the 0–10-cm and 10–20-cm layers, the depth, where broadband (400–700-nm band) irradiance was 1% of the downwelling irradiance at the surface, was 50 cm. The density of the snow in the upper part of the snowpack (depth of 0–55 cm) varied from 300 to 440 kg m^?3. The predominant grain type was large rounded particles (RGlr) and the predominant grain size was 1 mm.     

Physical properties and stratigraphy of surface snow in western Dronning Maud Land, Antarctica

Information about the spatial variations of snow properties and of annual accumulation on ice sheets is important if we are to understand the results obtained from ice cores, satellite remote sensing data and changes in climate patterns. The layer structure and spatial variations of physical properties of surface snow in western Dronning Maud Land were analysed during the austral summers 1999/2000, 2000/01 and 2003/04 in five different snow zones. The measurements were performed in shallow (1–2 m) snow pits along a transect extending 350 km from the seaward edge of the ice shelf to the polar plateau. These pits covered at least the last annual accumulation and ranged in elevation from near sea level to 2500 m a.s.l. The ع⁸O values and accumulation rates had a good linear correlation with the distance from the coast. The mean accumulation on the ice shelf was 312±28 mm water equivalent (w.e.); in the coastal region it was 215±43 mm w.e. and on the polar plateau it was 92±25 mm w.e. The mean annual conductivity and grain size values decreased exponentially with increasing distance from the ice edge, by 48%/100 km and 18%/100 km respectively. The mean grain size varied between 1.5 and 1.8 mm. Depth hoar layers were a common phenomenon, especially under thin ice crusts, and were associated with low dielectric constant values.     

Seismic anisotropy beneath Dronning Maud Land, Antarctica, revealed by shear wave splitting

Shear wave splitting analyses have been carried out using teleseismic data from broad-band seismograph stations deployed at temporary and permanent locations in Dronning Maud Land (DML), Antarctica. In most cases, the observed anisotropy can be related to major tectonic events that formed the present-day Antarctic continent. We rule out an anisotropic contribution from recent asthenospheric flow. At the Russian base Novolazarevskaya near the coast in central DML, waveform inversion suggests a two-layer model where the fast direction of the upper layer is oriented parallel to Archean fabrics in the lithosphere, whereas the anisotropy of the lower layer is interpreted to have been created during the Jurassic Gondwana break-up. Recordings at the South African base Sanae IV, however, show enigmatic results. For narrow backazimuthal segments, splitting parameters show strong variations together with a multitude of isotropic measurements, indicative of complex scattering that cannot be explained by simple one- or two-layer anisotropic models. In the interior of the continent, the data are consistent with single-layer anisotropy, but show significant spatial variations in splitting parameters. A set of temporary stations across the Heimefront shear zone in western DML yield splitting directions that we interpret as frozen anisotropy from Proterozoic assembly of the craton. An abrupt change in fast axis direction appears to mark a suture between the Grunehogna craton, a fragment of the Kalahari–Kaapvaal craton in southern Africa and the Mesoproterozoic Maudheim Province.     

Geology of Gjelsvikfjella and western Mühlig-Hofmannfjella, Dronning Maud Land, east Antarctica

As a part of the Norwegian Antarctic Research Expedition 1984/85, geological mapping was performed in Gjelsvikfjella and western Mühlig-Hofmannfjella, Dronning Maud Land. The northern part of Gjelsvikfjella is dominated by the Jutulsessen metasupracrustals which have been intruded by a major gabbroic body and several generations of dykes. To the south the metasupracrustals gradually transform into the Risemedet migmatites. In western Mühlig-Hofmannfjella the bedrock is dominated by the large Svarthamaren Charnockite batholith. The batholith is bordered by the Snøtoa metamorphic complex outcropping to the south and west in Mühlig-Hofmannfjella and it is characterized by a high content of partly assimilated country rock inclusions. Mineral paragenesis and geothermometry/geobarometry suggest a two-stage tectonothermal-igneous history with an initial intermediate pressure, upper amphibolite to granulite facies metamorphism followed by high temperature transformations related to the charnockite intrusion. The age of the initial tectonothermal event is probably about 1,100 Ma. Geochronological work in the present study (Rb/Sr whole rock) gave an age of 500 ± 24 Ma for the Svarthamaren Charnockite, interpreted to record the age of crystallization. Late brittle faulting and undeformed dolerite dykes outcropping in Jutulsessen are believed to be related to Mesozoic crustal stretching in the Jutulstraumen-Pencksøkket Rift Zone to the west.     

Discovery of an ice cave in the Yatude Valley, Langhovde, Dronning Maud Land, East Antarctica

A circular hole was discovered on the downstream side of a glacier dam in the Yatude Valley, Langhovde, East Antarctica, during the 2005–2006 austral summer. The opening of this hole is the first opportunity enabling us to observe the interior of the dam. The opening led to a large cave in the dam, raising the possibility of meltwater drainage through the dam. The Yatude Valley is an approximately U-shaped fluvial valley. The valley floor has been incised to form a box-shaped inner valley that contains fluvial terraces and large boulders upon the valley floor. The origin of these features can be explained by a large amount of running water; however, we consider it unlikely that a regular current has flowed through this site for a long period. Instead, it is more likely that large quantities of lake water have been periodically discharged due to collapse of the glacier dam or spilling out through a tunnel channel within the cave. The discovered hole and the ice cave are key features in understanding the historical development of the Yatude Valley in relation to the melting history of the Antarctic ice sheet.     

Combined use of field observations and SAR interferometry to study ice dynamics and mass balance in Dronning Maud Land, Antarctica

In the region of the Schirmacheroase (71 °S, 12°E) various geodetic and glaciological research activities have been carried out in the last decade. Several times three geodetic-glaciological traverses were undertaken to study ice velocity, accumulation and ablation, and ice surface height changes. Repeated ground surveys show a significant decrease in surface heights by about 15 cm/y for a large blue-ice area. This paper presents the first interferometrically derived ice velocity field of the inland ice close to the Schirmacheroase. The interferometric analysis of the synthetic aperture radar (SAR) data is performed in combination with ground-based information. Since only ERS-1&2 tandem mission image couples are available for this region a digital elevation model (DEM) is used to remove the effect of topography. Ice velocities up to 100 m/y are proved interferometrically for this part of the inland ice.     

Botany of two Antarctic mountain ranges: Gjelsvikfjella and Muhlig-Hofmannfjella, Dronning Maud Land

The investigated area is located between 71°45' and 72°20'S and between 1°35' and 5°33'E, from 1, 080 to 2, 695 m above sea level. An outline of climate, soil chemistry and main units of vegetation is provided. Of particular importance is the wet oasis area of Jutulsessen in Gjelsvikfjella which supports cyanophyceans, green algae, lichens and the mosses Grimmia lawiana and Sarconeurum glaciate , which have developed a series of distinctive communities. The nunataks fringing the Polar plateau harbour an impoverished cyanophycean and lichen vegetation up to approximately 2, 500 m a.s.l., which is the highest elevation that macroscopic plant life has hitherto been reported in Antarctica. The thermal relations of the vegetation are discussed, based on the climatological record and on local measurements during the Norwegian Antarctic Research Expedition 1984/85. Some zonal and vertical belt subdivisions are indicated for this part of Greater Antarctica.     

Spatial variability of chemical tracers in surface snow along the traverse route from the coast to 1000 km inland at east Dronning Maud Land, Antarctica

We measured the spatial variability of Cl -, Na +, SO 2- 4, NO - 3 and 7Be concentrations in snow cover along the traverse route from S16 to Dome Fuji station in east Dronning Maud Land, Antarctica. The concentrations of Cl - and Na + at the coast exponentially decreased with distance from the coast up to 200 km inland. Between 200 1000 km inland, the concentrations of Na + were nearly constant. On the other hand, the concentrations of Cl - increased with distance beyond 750 km inland. Furthermore, the contribution factors between Cl - and Na + decreased and the Cl -/Na + ratio and the nssCl -/Cl - ratio increased toward the interior of the continent. These results indicate that sea salt aerosols are transported from the coastal region toward the inland region of the Antarctic continent, and that a source of Cl - other than sea salt exists in the inland plateau of Antarctica. The concentrations of SO 2- 4, NO - 3 and 7Be in snow were relatively high in the coastal region and the inland plateau region compared with those in the katabatic wind region.     

Magnetostratigraphic reinvestigation of the Palaeocene/Eocene boundary interval in Hole 690B, Maud Rise, Antarctica

Hole 690B, drilled on Maud Rise near Antarctica, provides one of the most important Palaeocene/Eocene boundary interval sections. Magnetostratigraphy plays a key role in dating Palaeocene/Eocene boundary events, but there are two problems with the published scheme in Hole 690B. The first concerns major mismatches of several magnetozones and biozones in the succession. The second is an unexplained pervasive declination cluster, which should not be present in these azimuthally unoriented piston cores. To resolve these issues, a palaeomagnetic reinvestigation was carried out on 98 specimens from 12 cores through the upper Palaeocene–middle Eocene section in Hole 690B.
The bulk of the samples carry an approximately uniformly directed magnetically hard component resulting in a declination cluster effectively identical to that of the earlier study. The spurious magnetization can be explained either as an 'inward-radial magnetization' or as a 'core-split overprint'. By estimating the extent of the overprint within each sample, it has been possible to construct a filtered magnetostratigraphy for the section. The result is that many of the magnetozone–biozone mismatches are eliminated, and the record of the 2.5 Myr Chron C24r, which brackets the various events associated with the Palaeocene/Eocene boundary, is considerably cleaner. It is not possible to define the upper and lower boundaries of this magnetochron, so we recommend that the dating of the events within this section be based on the biostratigraphy only.     

Interpretation of the GRACE-derived mass trend in Enderby Land, Antarctica

Monthly gravity solutions of the Gravity Recovery and Climate Experiment (GRACE) reveal three areas in Antarctica with striking interannual mass trends. The positive mass trend in Enderby Land, East Antarctica, is poorly understood because of uncertainties in the surface ice-sheet mass balance, post-glacial rebound (PGR), and processing of GRACE data. In this study, we compare the GRACE mass trends with values estimated from in situ snow-stake measurements, and Ice Cloud and land Elevation Satellite (ICESat) data. The mass trends estimated from ICESat data show a strong correlation with GRACE mass trends. In contrast, the snow-stake data show discrepancies with temporal variations in GRACE mass, especially in 2006. The discrepancies are probably associated with basal ice-sheet outflow, which is difficult to observe using snow stakes. We conclude that the bulk of the GRACE mass trend can be explained by snow accumulation and basal ice-sheet outflow.     

毛乌素沙地风沙土粒径分布特征及其影响因素

为揭示毛乌素沙地风沙土粒径分布特征,推测其影响因素,以毛乌素沙地流动、半固定和固定沙丘风沙土为研究对象,利用激光衍射技术分析其粒度组成,并计算粒度参数,解析粒配曲线,研究结果表明：（1） 毛乌素沙地风沙土优势粒径组为细砂,其平均体积含量约为29.89%～32.46%,不同类型沙丘无显著差异（P>0.05）;少数粒径组分为粗砂、黏粒和极粗砂,其中流动沙丘与半固定、固定沙丘黏粒与粗砂含量均无显著差异（P>0.05）,从半固定到固定沙丘,黏粒含量显著增加（P<0.05）,粗砂含量显著减小（P<0.05）,从流动沙丘到固定沙丘,极粗砂含量显著减小（P<0.05）。（2） 毛乌素沙地风沙土平均粒径为3.35 Φ,粒度分布集中,分选性较差,偏度状况为正偏,尖窄峰态。在沙丘固定的过程中,平均粒径与标准偏差无显著变化（P>0.05）,峰态显著变宽平（P<0.05）,半固定沙丘偏态值与其他2种沙丘相比显著偏负（P<0.05）。（3） 流动、半固定与固定沙丘跃移组分的粒径区间分别为44～435 μm、63～500 μm和31～354 μm,风沙运动在半固定沙丘中最为强烈。毛乌素沙地风沙土优势粒径组分含量主要受物源影响,少数粒径组分含量主要受沙丘流动性影响,风沙运动强度随沙丘的固定呈先增大后减小的规律。     

南极樊尚湾大陆架mCDW入侵影响下的水体结构演变特征分析

利用象海豹CTD观测到的2012年3—10月南极樊尚湾海域的温盐剖面数据,研究结冰期该海域陆架区变性绕极深层水(mCDW)入侵影响下的水体结构演变过程.结果显示,从湾口到湾最内侧的深层都存在显著的mCDW入侵.结冰过程中来自海表的冷却和析盐作用从上方向海洋内部延伸,而到6月中旬湾最内侧的400 dbar以深层结依然没被...     

Assessing changes in nutrient status in the Richmond River estuary,Australia, using paleolimnological methods

Eutrophication from nutrient over-enrichment is a serious problem for the coastal zone and the estuarine environment globally. Australian estuaries are generally oligotrophic, but assessing whether they are becoming more eutrophic over time is inhibited by a lack of long-term monitoring data. The Richmond River, Australia, provided an ideal example of an estuary under anthropogenic pressure where the use of paleoecological techniques may potentially be used to reconstruct changes in nutrient status over time. Five cores were extracted from depositional areas in the Richmond River, and subjected to paleo-magnetic profiling and loss-on-ignition testing to ensure the core of greatest integrity was selected for further analytical work. Results from diatom and stable isotope analyses combined with ²¹⁰Pb and AMS ¹⁴C dating show a strong indication that the total phosphorus levels in the Richmond River have fluctuated since 1940. Evidence also suggests that these fluctuations are most likely a function of climate. This study has successfully applied paleolimnological techniques to the estuarine environment to produce information that can be used by environmental managers to aid decision making in relation to nutrient control for the Richmond River. Further work using paleolimnological techniques should be aimed at the extraction of a core containing diatoms that pre-date European settlement and include analyses of specific lipids and fatty acid biomarkers.     

The chemical characteristics of seawater in the Prydz Bay,Antarctica

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Seasonal variations of the near surfacelayer parameters over the Antarctic ice sheet in Princess Elizabeth Land,East Antarctica

Analysis of sensible heat flux(Qh),latent heat flux(Qe),Richardson number(Ri),bulk transport coefficient(Cd) and katabatic winds are presented by using the meteorological data in the near surface layer from an automatic weather station(AWS) in Princess Elizabeth Land,East Antarctica ice sheet and the data of corresponding period at Zhongshan station in 2002.It shows that annual mean air temperature at LGB69 is-25.6°C,which is 16.4°C lower than that at Zhongshan,where the elevation is lower and located on the coast.The temperature lapse rate is about 1.0°C/110 m for the initial from coast to inland.The turbulence heat flux at LGB69 displays obvious seasonal variations with the average sensible heat flux-17.9 W/m2 and latent heat flux-0.9 W/m2.The intensity(Qh+Qe) of coolling source is-18.8 W/m2 meaning the snow surface layer obtains heat from atmosphere.The near surface atmosphere is near-neutral stratified with bulk transport coefficients(Cd) around 2.8×10-3,and it is near constant when the wind speed higher than 8 m/s.The speed and the frequency of easterly Katabatic winds at LGB69 were higher than that at Zhongshan Station.