Soil characteristics of cryosols from two sites on King George Island, maritime Antarctica

This study presents soil temperature and moisture regimes from March 2008 to January 2009 for two active layer monitoring (CALM-S) sites at King George Island, Maritime Antarctica. The monitoring sites were installed during the summer of 2008 and consist of thermistors (accuracy of ±0.2 °C), arranged vertically with probes at different depths and one soil moisture probe placed at the bottommost layer at each site (accuracy of ± 2.5%), recording data at hourly intervals in a high capacity datalogger. The active layer thermal regime in the studied period for both soils was typical of periglacial environments, with extreme variation in surface temperature during summer resulting in frequent freeze and thaw cycles. The great majority of the soil temperature readings during the eleven month period was close to 0 °C, resulting in low values of freezing and thawing degree days. Both soils have poor thermal apparent diffusivity but values were higher for the soil from Fildes Peninsula. The different moisture regimes for the studied soils were attributed to soil texture, with the coarser soil presenting much lower water content during all seasons. Differences in water and ice contents may explain the contrasting patterns of freezing of the studied soils, being two-sided for the coarser soil and one-sided for the loamy soil. The temperature profile of the studied soils during the eleven month period indicates that the active layer reached a maximum depth of approximately 92 cm at Potter and 89 cm at Fildes. Longer data sets are needed for more conclusive analysis on active layer behaviour in this part of Antarctica.

Sedimentology on sediment cores from the eastern Weddell Sea, Antarctica

Sediment cores from nine sites along a profile on the Antarctic continental margin off Kapp Norvegia were analysed sedimentologicaly. The carbonate and organic carbon content, grain size distribution, composition of the coarse fraction and clay minerals were determined. d18O- and d13C-isotope ratios were also measured. The distribution of ice rafted debris was determined by a new method. Sedimentation-rates were obtained from 230Th- and 14C-analyses. A segregation into seven different sediment facies was made possible by different sedimentological parameters, which can be attributed to different sedimentation environments and conditions. Thr profile can be divided morphologicaly into shelf, upper continental slope, slope terrace and lower continental slope. The paratill facies is deposited on the shelf during an interglacial phase and consists mainly of ice rafted sediments. A portion of the fine fraction is being carried away by the antarctic coastel current. The sedimentation rate lies between 0 and 3 cm/1000 a. The coarse grained deposits of the upper, relatively steep continental slope, were specified as a rest sediment. Current and gravity sediment transport are responsible for the intensive sorting of ice rafted material coming from the shelf. The fine sediment is carried away by currents while sand and silt are deposited as small turbidites on the slope terrace. The morainic facies only appears at the base of the upper continental slope and defines ice advances, beyond the shelf margin. The facies mainly consists of transported shelf sediments. The interglacial facies, deposited during the interglacial phases on the continental slope, are characterized by high proportions of ice raft, coarse mean grain size, low content of montmorillonite and a carbonate content, which mainly originates from planktonic foraminifera (N. pachyderma). At the central part of the slope the sedimentation rate is at its lowest (2 cm/1000 a) and increases to 3-4 cm/1000 a towards the sea, due to high production of biogenic components and towards the continent due to an increasing input of terrigenous material. Sedimentary conditions during glacial times are depicted in the glacial facies by a low content of ice rafted debris, a lower mean grain size and a high content of montmorillonite. Biogeneous components are absent. The sedimentation rate is generally about 1 cm/1000a. A transition facies is deposited during the transition from glacial to interglacial conditions. Typical for this facies, with a terrigenous composition similar to the interglacial facies, is a high content of radiolaria. The reason for the change of plankton from a siliceous to a carbonacous fauna may have been the changing hydrography caused by the sea ice. The surge facies is deposited at the continental margin under the ice shelf and is a sediment exclusively delivered by currents. With the aid of this facies it was, for the first time possible to prove the existence of Antarctic ice surges, an aspect wh ich has been discussed for the past 20 years.

Topsoil properties and abundance of Acari and Collembola species in northern Victoria Land, Antarctica

Soil fauna in the extreme conditions of Antarctica consists of a few microinvertebrate species patchily distributed at different spatial scales. Populations of the prostigmatic mite Stereotydeus belli and the collembolan Gressittacantha terranova from northern Victoria Land (Antarctica) were used as models to study the effect of soil properties on microarthropod distributions. In agreement with the general assumption that the development and distribution of life in these ecosystems is mainly controlled by abiotic factors, we found that the probability of occurrence of S. belli depends on soil moisture and texture and on the sampling period (which affects the general availability of water); surprisingly, none of the analysed variables were significantly related to the G. terranova distribution. Based on our results and literature data, we propose a theoretical model that introduces biotic interactions among the major factors driving the local distribution of collembolans in Antarctic terrestrial ecosystems.

Density and stable oxygen isotope profiles of four snow pits from Berkner Island, Filchner-Ronne Ice Shelf, Antarctica

The ice cap on Berkner Island is grounded on bedrock within the Filchner-Ronne Ice Shelf and is, therefore, expected to be a well-suited place to retrieve long-term ice-core records reflecting the environmental situation of the Weddell Sea region. Shallow firn cores were drilled to 11 m at the two main summits of Berkner Island and analysed in high depth resolution for electrical d.c. conductivity (ECM), stable isotopes, chloride, sulphate, nitrate and methane-sulphonate (MSA). From the annual layering of dD and non-sea-salt (nss) sulphate, a mean annual snow accumulation of 26.6 cm water at the north dome and 17.4 cm water at the south dome are obtained. As a result of ineffective wind scouring indicated by a relatively low near-surface snow density, regular annual cycles are found for all species at least in the upper 4-5 m. Post depositional changes are responsible for a substantial decrease of the seasonal dD and nitrate amplitude as well as for considerable migration of the MSA signal operating below a depth of 3-4 m. The mean chemical and isotopic firn properties at the south dome correspond to the situation on the Filchner-Ronne Ice shelf at a comparable distance to the coast, whereas the north dome is found to be more influenced by maritime air masses. Persistent high sea-salt levels in winter snow at Berkner Island heavily obscure the determination of nss sulphate probably due to sulphate fractionation in the Antartic sea-salt aerosols. Estimated time-scales predict ages at 400 m depth to be ca. 2000 years for the north and ca. 3000 years for the south dome. Pleistocene ice is expected in the bottom 200 and 300 m, respectively.

Conductivity and oxygen isotope measured on ice core FRI09C90_13 (B13) from the Filchner-Ronne ice shelf, Antarctica

The Filchner-Ronne ice shelf, which drains most of the marine-based portions of the West Antarctic ice sheet, is the largest ice shelf on Earth by volume. The origin and properties of the ice that constitutes this shelf are poorly understood, because a strong reflecting interface within the ice and the diffuse nature of the ice?ocean interface make seismic and radio echo sounding data difficult to interpret. Ice in the upper part of the shelf is of meteoric origin, but it has been proposed that a basal layer of saline ice accumulates from below. Here we present the results of an analysis of the physical and chemical characteristics of an ice core drilled almost to the bottom of the Ronne ice shelf. We observe a change in ice properties at about 150 m depth, which we ascribe to a change from meteoric ice to basal marine ice. The basal ice is very different from sea ice formed at the ocean surface and we propose a formation mechanism in which ice platelets in the water column accrete to the bottom of the ice shelf.

Geological map of VIKENEGGA, Heimefrontfjella, Antarctica (Scale 1:25,000)

Topographic data of this geological map were obtained through stereoscopic aerial photo interpretation. The photogrammetric photo flights were undertaken in 1986 by the Institut für Angewandte Geodäsie, Frankfurt. Horizontal ground control points required for aerial photo interpretation were determined by means of Doppler satellite observation during the 2nd German Neuschwabenland Expedition 1985/86. Vertical ground control points were taken from unpublished map drafts at 1:100 000 scale by Norsk Polarinstitutt, Oslo. The elevation above mean sea level was transferred to Heimefrontfjella barometrically. For this reason assertions concerning the absolute elevation (referred to sea level) are uncertain. Contours and spot heights presented on the map were obtained from the photogrammetric evaluation of the photography taken in 1986; relative elevation data (hight differences) are accurate to approximately ±10 m.

Geochemistry of metasedimentary units of the Cambro-Ordovician Ross Orogen in North Victoria Land and Oates Land, Antarctica

Metasediments in the three early Palaeozoic Ross orogenic terranes in northern Victoria Land and Oates Land (Antarctica) are geochemically classified as immature litharenites to wackes and moderately mature shales. Highly mature lithotypes with Chemical Index of Weathering values of >=95 are typically absent. Geochemical and Rb-Sr and Sm-Nd isotope results indicate that the turbiditic metasediments of the Cambro-Ordovician Robertson Bay Group in the eastern Robertson Bay Terrane represent a very homogeneous series lacking significant compositional variations. Major variations are only found in chemical parameters which reflect differences in degree of chemical weathering of their protoliths and in mechanical sorting of the detritus. Geochemical data, 87Sr/ 86Sr t=490 Ma ratios of 0.7120 - 0.7174, epsilonNd, t=490 Ma values of -7.6 to -10.3 and single-stage Nd-model ages of 1.7 - 1.9 Ga are indicative of an origin from a chemically evolved crustal source of on average late Palaeoproterozoic formation age. There is no evidence for significant sedimentary infill from primitive "ophiolitic" sources. Metasediments of the Middle Cambrian Molar Formation (Bowers Terrane) are compositionally strongly heterogeneous. Their major and trace element data and Sm-Nd isotope data (epsilonNd, t=500 Ma values of -14.3 to -1.2 and single-stage Nd-model ages of 1.7 - 2.1 Ga) can be explained by mixing of sedimentary input from an evolved crustal source of at least early Palaeoproterozoic formation age and from a primitive basaltic source. The chemical heterogeneity of metasediments from the Wilson Terrane is largely inherited from compositional variations of their precursor rocks as indicated by the Ni vs TiO2 diagram. Single-stage Nd-model ages of 1.6 -2.2 Ga for samples from more western inboard areas of the Wilson Terrane (epsilonNd, t=510 Ma -7.0 to -14.3) indicate a relatively high proportion of material derived from a crustal source with on average early Palaeoproterozoic formation age. Metasedimentary series in an eastern, more outboard position (epsilonNd, t=510 Ma -5.4 to -10.0; single-stage Nd model ages 1.4 - 1.9) on the contrary document stronger influence of a more primitive source with younger formation ages. The chemical and isotopic characteristics of metasediments from the Bowers and Wilson terranes can be explained by variable contributions from two contrasting sources: a cratonic continental crust similar to the Antarctic Shield exposed in Georg V Land and Terre Adélie some hundred kilometers west of the study area and a primitive basaltic source probably represented by the Cambrian island-arc of the Bowers Terrane. While the data for metasediments of the Robertson Bay Terrane are also compatible with an origin from an Antarctic-Shield-type source, there is no direct evidence from their geochemistry or isotope geochemistry for an island-arc component in these series.

Sea ice draft measured by upward looking sonars in the Weddell Sea (Antarctica)

The presented database contains time-referenced sea ice draft values from upward looking sonar (ULS) measurements in the Weddell Sea, Antarctica. The sea ice draft data can be used to infer the thickness of the ice. They were collected during the period 1990-2008. In total, the database includes measurements from 13 locations in the Weddell Sea and was generated from more than 3.7 million measurements of sea ice draft. The files contain uncorrected raw drafts, corrected drafts and the basic parameters measured by the ULS. The measurement principle, the data processing procedure and the quality control are described in detail. To account for the unknown speed of sound in the water column above the ULS, two correction methods were applied to the draft data. The first method is based on defining a reference level from the identification of open water leads. The second method uses a model of sound speed in the oceanic mixed layer and is applied to ice draft in austral winter. Both methods are discussed and their accuracy is estimated. Finally, selected results of the processing are presented.