The dielectric profiling (DEP) technique is described and some of the differences between it and standard electrical tools used in ice core analysis are discussed. The results of DEP analysis on two cores from different regions of Antarctica, Dolleman Island and Mizuho Station are described. DEP measurements on the Dolleman core are related to the chemical composition of the core, showing that DEP can provide a high accuracy measure of total ionic content of the ice. The measurements on the Mizuho core are compared with earlier dielectric measurements on the same core which show dramatic changes over the 15 year period between the measurements. A mechanism which can explain the changes and other effects noted from d. c. conductivity (ECM) experiments, is suggested. The mechanism is based on the theory of d. c. conduction via liquid acid veins at triple junctions in the ice
Sublittoral epifaunal communities at Signy Island, Antarctica. I. The ice-foot zone
Photographs were taken every 0.5 m along three transects of 5.5 m length on shallow rock faces at Signy Island, Antarctica, during the austral summer of 1991/1992. The percentage cover of substratum ranged from 0 to 100% and the colonising communities included representatives of ten phyla. The zone from mean low-water neap level to 1.5 m depth was mostly devoid of organisms as a result of the seasonal formation of the encrusting ice foot. Coralline and macroalgae dominated from 2 to 3 m, and animal groups from 3.5 to 5.5 m. Bryozoans, and to a lesser extent sponges, were the most abundant animal phyla. Within the bryozoans a succession of colonisation of different species was observed, the most abundant two of which occupied >80% of substratum in places. Substratum type seemed to be the main factor influencing community development in the shallow sublittoral at Signy Island, although ice impact prevents community development in the top 1.5 m and limits it over the rest of the transect down to 5.5 m. Depth and profile of substratum also influenced communities within this depth range (particularly taxonomic composition).
Low summer temperatures: a potential mortality factor for high arctic soil microarthropods?
Throughout the summers of 1992–1994 the low temperature performance of soil microarthropods at Ny Ålesund, Spitsbergen (78 °56′N 10 °53′E), was investigated. Species studied were the Collembola Hypogastrura tullbergi (Schäffer), Onychiurus arcticus (Tullberg) and Onychiurus groenlandicus (Tullberg) and the mites Diapterobates notatus (Thorell), Hermannia reticulata (Thorell), Camisia anomia Colloff and Ceratoppia hoeli (Thor). The results show that: (i) The supercooling ability of these animals decreased rapidly on regaining activity in spring. For example, the supercooling point (scp) of H. tullbergi when heat extracted from frozen ground, decreased from −20 to −8 °C within 4 h. Population scp profiles of all species determined throughout the summer showed distinct bimodal distribution; (ii) starvation for 14 days, desiccation or a combination of both, resulted in little change in the mean scp of the collembolan O. arcticus; (iii) survival of the animals after a brief exposure to a sub-zero temperature was poor, in either humid or dry atmospheres. For example, 77% of H. tullbergi died after cooling to −5 °C at 1 °C min−1. Comparison with scp data indicates that animals died before they froze; (iv) all species examined showed some locomotory ability at temperatures approaching −3 °C; (v) polyols occurred in low concentrations, although elevated levels of glucose were observed in early spring and late autumn in O. arcticus; and (vi) soil temperature declined to −29.6 °C in the winter of 1992/93 and remained below zero for up to 289 days and the animals can be encased in ice for 75% of the year. Average daily soil temperatures for July and August rarely exceed 8 °C and were typically in the range 3–6 °C. Estimation of previous years soil temperatures from screen temperature records indicate that July /August ground surface temperatures < 0 °C occurred on 25 and 28 occasions between 1969–1993 at the polar semi-desert and tundra heath sites respectively; but, that soil temperatures at a depth of 3 cm are buffered against temperature extremes and temperatures below 0 °C are rarely encountered. The consequences for the soil microarthropod fauna of such extended periods of low temperature and the effects of climate change on these species are discussed.
Trends in the Southern Annular Mode from observations and reanalyses
Several papers have described a significant trend toward the positive phase of the Southern Hemisphere annular mode (SAM) in recent decades. The SAM is the dominant mode of atmospheric variability in the Southern Hemisphere (SH) so such a change implies a major shift in the broadscale climate of this hemisphere. However, the majority of these studies have used NCEP – NCAR reanalysis (NNR) data, which are known to have spurious negative trends in SH high-latitude pressure. Thus, given that the SAM describes the relative atmospheric anomalies at mid-and high southern latitudes, these errors in the NNR data have the potential to invalidate the published findings on changes in the SAM. Therefore, it is important that a “true” benchmark of trends in the SAM is available against which future climate scenarios as revealed through climate models can be examined. In this paper this issue is addressed by employing an empirical definition of the SAM so that station data can be utilized to evaluate true temporal changes: six stations are used to calculate a proxy zonal mean sea level pressure (MSLP) at both 408 and 658S during 1958 – 2000. The observed increase in the difference in zonal MSLP between 408 ( increasing) and 658S ( decreasing) is shown to be statistically significant, with the trend being most pronounced since the mid-1970s. However, it is demonstrated that calculated trends in the MSLP difference between 408 and 658S and the SAM itself are exaggerated by a factor of 3 and 2, respectively, in the NNR. The SH high-latitude errors in the early part of this reanalysis are greatest in winter as are subsequent improvements. As a result, the NNR shows the greatest seasonal trend in the SAM to be in the austral winter, in marked contrast to observational data, which reveal the largest real increase to be in summer. Equivalent data from two ECMWF reanalyses, including part of the new ERA-40 reanalysis, are also examined. It is demonstrated that ERA-40 provides an improved representation of SH high-latitude atmospheric circulation variability that can be used with high confidence at least as far back as 1973 – and is therefore ideal for examining the recent trend in the SAM – and with more confidence than the NNR right back to 1958.
The human exploration of the Martian poles Part 1 – from early expeditions to a permanent station
The establishment of a permanent human scientific presence at the Martian poles requires the identification of a strategy for growth, from localized field parties to a permanent polar infrastructure. Using terrestrial polar stations as a template and experiences from the terrestrial High Arctic, four phases of Martian polar exploration are suggested. The first phase provides for six people to operate at the edge of the north polar cap for a Martian summer period (similar to350 sol), with excursions limited to the immediate area <5 km distant from the station. With intermediate phases, this limited access phase expands to a final fourth phase that allows for the presence of 6 over-winterers and 20 summer personnel at a permanent polar station. This station will provide opportunities for scientists to investigate the geology, chemistry and organic chemical/exobiological potential of the Martian polar caps. The station will ultimately provide the means for unsupported overland assaults on the Martian geographical poles to be accomplished. The equipment and logistics required to support field parties from a permanent Martian polar station are considered. Preliminary concepts are provided for techniques of station maintenance (Martian polar regions engineering) in the light of data on the extent of seasonal snow and ice deposition at the Martian poles. Energy requirements for these methods are estimated.
Temporal variations in fatty acid composition of deep-sea holothurians: evidence of bentho-pelagic coupling
Fatty acid biomarkers were used to examine the diet of deep-sea holothurians. We collected 3 species from the Porcupine Seabight and Porcupine Abyssal Plain, NE Atlantic, between 800 and 4850 m in August 2001 (summer), March 2002 (pre-spring bloom), and October 2002 (autumn). Of these, 2 species, the abyssal Amperima rosea and the bathyal Bathyplotes natans, showed significant variations in fatty acid compositions. These are likely to be seasonal. Polyunsaturated fatty acids (PUFAs) were dominant within muscle tissue of both species during August 2001 and October 2002, in particular 20:4 (n-6), 20:5 (n-3) and 22:6 (n-3). During March 2002, prior to the spring bloom, there were substantially lower proportions of PUFAs in both species, and increased amounts of mono-unsaturated fatty acids (monoenes), particularly the bacterially-derived biomarkers 18:1 (n-7) and non-methyl uninterrupted dienes (NMIDs). In contrast, the fatty acid composition of the third species, the abyssal Deima validum, remained relatively stable, with muscle tissue containing a high proportion of PUFAs during pre- and post-spring-bloom periods. A further 6 species were sampled in March 2002 and October 2002. Across all these species, 3 patterns of fatty composition were evident: (1) Laetmogone violacea had higher proportions of PUFAs in October than in March; (2) Psychropotes longicauda and Benthogone rosea had lower proportions of PUFAs in October than in March; (3) Deima validum, Oneirophanta mutabilis, Paroriza pallens and P. prouhoi had unchanged fatty acid compositions during these contrasting periods. These differences may be related to the varying reproductive strategies of the species. The implications of changes in fatty acids for reproductive processes, and how these could be factors determining allocation of lipid resources in gonads, is discussed.
The future of ice core science
Cores drilled through the polar ice sheets provide information about past climate and environmental conditions on timescales from decades to hundreds of millennia, and direct records of changes in the composition of the atmosphere. As such, they are cornerstones of global change research. In the past 15 years, several major projects have increased our understanding of past climate change on a variety of timescales. These include the Greenland Ice Sheet Project 2 (GISP2), the Greenland Ice Core Project (GRIP), and North GRIP deep ice cores in Greenland. They also include the Taylor Dome, Siple Dome, Law Dome, Vostok, and European Programme for Ice Coring in Antarctica (EPICA) Dome C ice cores in Antarctica, the latter of which has pushed the record for the oldest ice core back to 720,000 years.
The surprising polar troposphere
Chemical processes in the troposphere are driven by acombination of factors. Emissions from the Earth’s surface, either natural or anthropogenic, are the primary source of trace gases in the troposphere. The energy driving many chemical reactions is derived from the Sun, hence the reactions are “photochemical”. Transport processes can distribute longerlived trace gases to locations remotefrom their origin. In this article, Dr Anna Jones, from the BritishAntarctic Survey, describes some of the highly surprising phenomena that have been discovered in thepolar troposphere over the past twenty years.
How accurate are estimates of glacier ice thickness? Results from ITMIX, the Ice Thickness Models Intercomparison eXperiment
Knowledge of the ice thickness distribution of glaciers and ice caps is an important prerequisite for many glaciological and hydrological investigations. A wealth of approaches has recently been presented for inferring ice thickness from characteristics of the surface. With the Ice Thickness Models Intercomparison eXperiment (ITMIX) we performed the first coordinated assessment quantifying individual model performance. A set of 17 different models showed that individual ice thickness estimates can differ considerably – locally by a spread comparable to the observed thickness. Averaging the results of multiple models, however, significantly improved the results: on average over the 21 considered test cases, comparison against direct ice thickness measurements revealed deviations on the order of 10 ± 24 % of the mean ice thickness (1σ estimate). Models relying on multiple data sets – such as surface ice velocity fields, surface mass balance, or rates of ice thickness change – showed high sensitivity to input data quality. Together with the requirement of being able to handle large regions in an automated fashion, the capacity of better accounting for uncertainties in the input data will be a key for an improved next generation of ice thickness estimation approaches.
Ice and firn heterogeneity within Larsen C Ice Shelf from borehole optical televiewing
We use borehole optical televiewing (OPTV) to explore the internal structure of Larsen C Ice Shelf (LCIS). We report a suite of five ~90 m long OPTV logs, recording a light-emitting diode-illuminated, geometrically correct image of the borehole wall, from the northern and central sectors of LCIS collected during austral spring 2014 and 2015. We use a thresholding-based technique to estimate the refrozen ice content of the ice column and exploit a recently calibrated density-luminosity relationship to reveal its structure. All sites are dense and strongly influenced by surface melt, with frequent refrozen ice layers and mean densities, between the depths of 1.87 and 90 m, ranging from 862 to 894 kg m−3. We define four distinct units that comprise LCIS and relate these to ice provenance, dynamic history, and past melt events. These units are in situ meteoric ice with infiltration ice (U1), meteoric ice which has undergone enhanced densification (U2), thick refrozen ice (U3), and advected continental ice (U4). We show that the OPTV-derived pattern of firn air content is consistent with previous estimates, but that a significant proportion of firn air is contained within U4, which we interpret to have been deposited inland of the grounding line. The structure of LCIS is strongly influenced by the E-W gradient in föhn-driven melting, with sites close to the Antarctic Peninsula being predominantly composed of refrozen ice. Melting is also substantial toward the ice shelf center with >40% of the overall imaged ice column being composed of refrozen ice.