Polar Plateau Research Articles

Spatial and temporal variations in the thermodynamics since the Last Glacial Maximum at Jutulstraumen drainage basin, East Antarctica

A flow-line model is coupled to a 2D temperature model to simulate the thermodynamic changes of Jutulstraumen drainage basin due to grounding line retreat and increased surface temperature since the Last Glacial Maximum (LGM). The basin consists of a plateau drained by an outlet glacier, and the simulated ice volume reductions are 1% and 2% respectively of the current grounded volume. The mountain ranges H.U. Sverdrupfjella and Neumayerskarvet fringing the plateau were not overridden by ice at the LGM, while the Nashornet nunataks closer to the grounding line were. Today the glacier is almost in balance with the current climate, with the highest thinning rate < 5.0×10−3 ma−1 at the plateau. The simulated present-day thermal regime of the outlet glacier shows a basal layer at the pressure melting point and negative temperature gradients with depth due to horizontal advection of cold ice from the plateau. Sensitivity studies show that strain heating and horizontal advection are important for the basal temperatures in the fast flowing outlet glacier and for about half of the wide basin at the polar plateau. Increased strain heating and horizontal advection since the LGM control the response time required to readjust to the new conditions, and it controls the present-day volume.

Dominant bacteria in soils of Marble Point and Wright Valley, Victoria Land, Antarctica

A combination of culture-independent and culturing methods was used to assess the diversity of soil bacterial communities from four locations along 77 °S in Victoria Land, Antarctica. Soil samples were from the coast at Marble Point, in the Wright Valley from Bull Pass and near Lake Vanda, and from Mt. Fleming near the polar plateau. Total carbon and nitrogen, and water content of the soils were low, whereas total P was very high. The pH of the soils varied from extremely alkaline to slightly acid and electrical conductivity was medium to high on the coast and very high in inland soils from Bull Pass and Mt. Fleming. The average monthly air temperature was similar (−18 °C to −24 °C) at all the sites; however, in summer surface soil temperatures were >0 °C at Marble Point and in the Wright Valley for a total of 1100 and 1700 h, respectively. Marble Point soil had the most potential to support bacterial growth and activity with a mean total of 310 h per year when surface soils had a liquid volumetric soil moisture content >5%. Highest counts of culturable heterotrophs occurred in soil from Marble Point, whereas Mt. Fleming soil contained few organisms and had no liquid soil moisture recorded. Seven hundred and twenty-eight clones and 71 bacterial isolates were screened by restriction fragment length polymorphisms, and representatives of those dominant ribotypes that occurred more than 3 times were sequenced. The dominant ribotypes grouped within the bacterial divisions Bacteroidetes, Actinobacteria, Proteobacteria, Thermus-Deinococcus, Acidobacteria, Firmicutes and Cyanobacteria. The closest relatives of the amplicon library clones or cultured bacteria include the genera Hymenobacter, Gillisia, Arthrobacter, Rubrobacter, Friedmanniella, Deinococcus and Leptolyngbya. Many of the clones and bacteria were most similar to others from Antarctic sources, in particular a cyanobacterium-dominated cryptoendolithic community in Beacon sandstone. Some ribotypes were more prevalent in drier soils of the Wright Valley, including relatives of Deinococcus, Rubrobacter and clone FBP460 from Beacon sandstone. Bacterial communities from Marble Point soils were more diverse than those of the Wright Valley. Very few bacteria were isolated from Mt. Fleming soil.

Accumulation and erosion of south polar layered deposits in the Promethei Lingula region, Planum Australe, Mars

Background: Promethei Lingula, a part of Mars’ south polar plateau, Planum Australe, is made up of south polar layered deposits (SPLD) and includes three broad, deep canyons trending perpendicular to the plateau margin and several spiral troughs concentric to the plateau. Two of the canyons, Promethei and Ultimum Chasmata, expose substrate beneath SPLD, and the other canyon displays a variety of erosional landforms within SPLD, including curvilinear, longitudinal grooves (Australe

Antarctic polar plateau vertical electric field variations across heliocentric current sheet crossings

A superposed epoch analysis of variations of the vertical electric field measured at Vostok (78.5°S, 107°E; magnetic latitude 83.6°S) during 1998–2002 heliocentric current sheet (HCS) crossings yields no significant variation other than an association imposed by polar-cap potential differences above the site. This result contradicts published reports of a reduction ∼15% in electric field 1–3 days after HCS crossings, an observation initially made ∼30 years ago. If such a reduction had been caused by reductions in stratospheric ionising radiation, the presence of polar stratospheric clouds (PSC) would seem necessary for the occurrence of this effect. PSCs would increase the resistance of the stratosphere thus making ionisation in that region significant in the context of the ionosphere–ground current flow, in a manner analogous to the role of volcanic aerosols in the stratosphere in the explanation of the weakening of northern hemisphere winter cyclones associated with HCS crossings, the so-called ‘Wilcox effect’. However, separating the present data to correspond to the likely presence of PSC above Vostok also does not yield the reported reduction. Significant increases or decreases of the vertical electric field emerge from the observations when the HCS crossings are separated into sets depending on whether the solar wind magnetic field changes from ‘toward-to-away’ (increase of ∼11%) and ‘away-to-toward’ (decrease of ∼8%). Polar-cap potential changes above the site, inferred from solar wind parameters using the Weimer model, also show such step functions that reverse with the sign of HCS transition and are broadly consistent with the measured electric field increases or decreases. Remaining differences between the measurements and the model are consistent with a somewhat stronger solar wind speed and/or magnetic activity influence on polar-cap convection above Vostok than is predicted by the model. Variations in ground-level neutron counts, a measure of cosmic ray influence on the atmospheric conductivity, demonstrate average variations of less than 1% around HCS crossings and at this level would not contribute significantly to the electric field variations. Magnetic activity (measured using the Kp index) and solar wind speed decrease around HCS crossings independent of whether the crossings are ‘toward-to-away’ or ‘away-to-toward’. These decreases are broadly similar in shape to the previously reported Vostok electric field responses. However, their effects on ionospheric potential are included in the Weimer model, and are small. In contrast to sub-auroral latitudes, where the precipitation of MeV electrons from the radiation belts has a characteristic decrease for both types of HCS crossing, there are no known sources of stratospheric ionising radiation in the polar caps that could explain the previously reported effect. Thus, observation and theory are now in agreement for the absence of this effect.

Sulfur isotopic signals in two shallow ice cores from Dronning Maud Land, Antarctica

Sulfate deposited onto the Antarctic ice sheet originates from a mixture of sulfur sources. Two 100 m long ice cores from Dronning Maud Land have been studied by means of sulfur isotopic analysis and detailed ion analysis to reveal temporal and spatial differences in the influencing sulfur source. The two ice cores represent the coastal area and the polar plateau, respectively. The isotopic signals were similar within each ice core, indicating no temporal change of influencing sources during the last 1100 yr. The mean values at the two different sites were also similar: 14.6 ± 0.3% o and 14.7 ± 0.3‰ , respectively. The similarity remains between calculated non-sea-salt values when a sulfate-depleted sea-salt aerosol is assumed in the costal core. When the influence of sporadic explosive volcanic eruptions is subtracted from the signal, the isotopic value from the polar plateau (15.4 ± 0.6‰) is significantly lower than prescribed values for marine biogenic sulfur. This suggests that one or more additional sources contribute to the sulfate budget. Several possible contributors are discussed in the context of former sulfur isotopic signals presented from Antarctica. DOI: 10.1111/j.1600-0889.2005.00157.x

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 fi ve 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 ?18O 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.

Sulfur isotopic signals in two shallow ice cores from Dronning Maud Land, Antarctica

Sulfate deposited onto the Antarctic ice sheet originates from a mixture of sulfur sources. Two 100 m long ice cores from Dronning Maud Land have been studied by means of sulfur isotopic analysis and detailed ion analysis to reveal temporal and spatial differences in the influencing sulfur source. The two ice cores represent the coastal area and the polar plateau, respectively. The isotopic signals were similar within each ice core, indicating no temporal change of influencing sources during the last 1100 yr. The mean values at the two different sites were also similar: 14.6 ± 0.3% and 14.7 ± 0.3‰, respectively.The similarity remains between calculated non-sea-salt values when a sulfate-depleted sea-salt aerosol is assumed in the costal core. When the influence of sporadic explosive volcanic eruptions is subtracted from the signal, the isotopic value from the polar plateau(15.4 ± 0.6‰) is significantly lower than prescribed values for marine biogenic sulfur. This suggests that one or more additional sources contribute to the sulfate budget. Several possible contributors are discussed in the context of former sulfur isotopic signals presented from Antarctica.

Geology and insolation-driven climatic history of Amazonian north polar materials on Mars

Mariner 9 and Viking spacecraft images revealed that the polar regions of Mars, like those of Earth, record the planet's climate history. However, fundamental uncertainties regarding the materials, features, ages and processes constituting the geologic record remained. Recently acquired Mars Orbiter Laser Altimeter data and Mars Orbiter Camera high-resolution images from the Mars Global Surveyor spacecraft and moderately high-resolution Thermal Emission Imaging System visible images from the Mars Odyssey spacecraft permit more comprehensive geologic and climatic analyses. Here I map and show the history of geologic materials and features in the north polar region that span the Amazonian period (approximately 3.0 Gyr ago to present). Erosion and redeposition of putative circumpolar mud volcano deposits (formed by eruption of liquefied, fine-grained material) led to the formation of an Early Amazonian polar plateau consisting of dark layered materials. Crater ejecta superposed on pedestals indicate that a thin mantle was present during most of the Amazonian, suggesting generally higher obliquity and insolation conditions at the poles than at present. Brighter polar layered deposits rest unconformably on the dark layers and formed mainly during lower obliquity over the past 4-5 Myr (ref. 20). Finally, the uppermost layers post-date the latest downtrend in obliquity <20,000 years ago.

Dust size evidence for opposite regional atmospheric circulation changes over east Antarctica during the last climatic transition

Three east Antarctic ice cores (Dome B, EPICA-Dome C and Komsomolskaia) give evidence for a uniform dust input to the polar plateau during the last glacial maximum (LGM)/Holocene transition (20 to 10 kyr BP) and the 87Sr/86Sr versus 143Nd/144Nd isotopic signature of the mineral particles highlights a common provenance from southern South America at that time. However, the size distribution of dust from the three ice cores highlights important differences within the east Antarctic during the LGM and shows clearly opposite regional trends during the climatic transition. Between Dome B and Dome C the timing of these changes is also different. A geographical diversity also arises from the different phasing of the short-term (multi-secular scale) dust size oscillations that are superposed at all sites on the main trends of glacial to interglacial changes. We hypothesize the dust grading is controlled by size fractionation inresponse to its atmospheric pathway, either in terms of horizontal trajectory or in altitude of transport. Such mechanism is supported also by the dust size changes observed during a volcanic event recorded in Vostok ice. Ice core dust size data suggest preferential upper air subsidence over the EDC-KMS region and easier penetration of relatively lower air masses to the DB area during the LGM. At the end of the last glacial period and during the climatic transition the region of relatively higher subsidence progressively moved southward. The scenario proposed, supported also by the LGM/Holocene regional changes of snow accumulation, likely operates even at sub-millennial time scale.

New Zealand maritime glaciation: millennial-scale southern climate change since 3.9 Ma.

Ocean Drilling Program Site 1119 is ideally located to intercept discharges of sediment from the mid-latitude glaciers of the New Zealand Southern Alps. The natural gamma ray signal from the site's sediment core contains a history of the South Island mountain ice cap since 3.9 million years ago (Ma). The younger record, to 0.37 Ma, resembles the climatic history of Antarctica as manifested by the Vostok ice core. Beyond, and back to the late Pliocene, the record may serve as a proxy for both mid-latitude and Antarctic polar plateau air temperature. The gamma ray signal, which is atmospheric, also resembles the ocean climate history represented by oxygen isotope time series.

Australia’s Antarctic Turf

Australia’s Antarctic Turf

Wave-vector filtering and spin filtering in a magnetic double-barrier and double-well structure

We investigate wave-vector filtering and spin filtering for electrons tunneling through a magnetic double-barrier and double-well quantum structure in the presence of an external electric field, where the double magnetic wells are within or outside the double magnetic barriers. It is shown that electronic resonant tunneling shows strong wave-vector-dependent enhancement and suppression as the applied bias increases. It is also shown that although the current density decreases with the strength of the inhomogeneous magnetic field increasing, the degree of spin polarization is generally enhanced and shows a more wider and nearly 100% spin polarization plateau in small external bias range. The general rules for relations between wave-vector filtering and the magnetic configuration as well as between spin filtering and the magnetic configuration are summarized and explained.

Monsoonal circulation of the McMurdo Dry Valleys, Ross Sea region, Antarctica: signal from the snow chemistry

AbstractMcMurdo Dry Valleys (MDV; Ross Sea region, Antarctica) precipitation exhibits extreme seasonality in ion concentration, 3–5 orders of magnitude between summer and winter precipitation. To identify aerosol sources and investigate causes for the observed amplitude in concentration variability, four snow pits were sampled along a coast–Polar Plateau transect across the MDV. The elevation of the sites ranges from 50 to 2400 m and the distance from the coast from 8 to 93 km. Average chemistry gradients along the transect indicate that most species have either a predominant marine or terrestrial source in the MDV. Empirical orthogonal function analysis on the snow-chemistry time series shows that at least 57% of aerosol deposition occurs concurrently. A conceptual climate model, based on meteorological observations, is used to explain the strong seasonality in the MDV. Our results suggest that radiative forcing of the ice-free valleys creates a surface low-pressure cell during summer which promotes air-mass flow from the Ross Sea. The associated precipitating air mass is relatively warm, humid and contains a high concentration of aerosols. During winter, the MDV are dominated by air masses draining off the East Antarctic ice sheet, that are characterized by cold, dry and low concentrations of aerosols. The strong differences between these two air-mass sources create in the MDV a polar version of the monsoonal flow, with humid, warm summers and dry, cold winters.

Production of cosmogenic Be nuclei in the Earth's atmosphere by cosmic rays: Its dependence on solar modulation and the interstellar cosmic ray spectrum

Recent work by McCracken [2001] shows that 10Be production rates by cosmic rays on the polar plateau are little affected by geomagnetic field changes in the last few hundred years. Also, the 10Be observed in ice cores on the polar plateau probably originated at high latitudes and precipitated to the Earth in about 1 year, according to McCracken. As a result of this assumption, ice core records of 10Be concentration extending back several hundred years, including the Maunder minimum, have the potential to study the solar modulation of cosmic rays on a time scale extending back several hundred years. These ice core records indicate that the 10Be concentration at the time of the Maunder minimum was ∼2.0 times what it was during recent sunspot minima in 1965 and 1976. We have examined 10Be production in the atmosphere using new data related to the interstellar cosmic ray spectrum and the effects of solar modulation as determined from Voyager spacecraft data in the outer heliosphere. We have used the FLUKA Monte Carlo program along with new cross‐section data to calculate the production of nucleons and 10Be nuclei in the atmosphere. These calculations show that 10Be temporal variations are sensitive indicators of low‐energy solar modulation. Our calculations of 10Be production are able to reproduce well the factor ∼1.5–2.0 change in 10Be observed in the ice core data as a result of the 11‐year solar modulation. We are also able to show that starting as recently as the sunspot minimum of 1954, the cosmic ray intensity at the Earth was higher than it was during more recent minima. The cosmic ray intensity during these minima time periods represents the residual modulation between the Earth and interstellar space. The 10Be measurements are consistant with the fact that given the interstellar cosmic ray spectrum used in this analysis, this residual modulation was small or zero at the time of the Maunder minimum.

Snow-Patch Influence on Soil Biogeochemical Processes and Invertebrate Distribution in the McMurdo Dry Valleys, Antarctica

The McMurdo Dry Valleys is the largest of the ice-free areas in Antarctica. Precipitation events in excess of 1 cm of snow accumulation are rare. During the winter, snow is transported by strong katabatic winds blowing from the polar plateau, and deposited into the lee of topographic features (e.g., stream channels and other topographic depressions). At the start of the austral summer (early October), as much as 10% of the valley soils may be covered by distributed snow patches. Because liquid water is the primary driver of biological, physical, and chemical processes in this polar desert, quantifying fluxes of water from snow patches is important to understanding the influence of hydrology on soil biology and nutrient cycling. During the austral summer of 1999–2000, four snow patches that had developed during the previous winter in Taylor Valley were studied. We measured snow-patch area, depth, and snow water equivalent, as well as subnivian (under snow) and nearby exposed (control) soil temperature, light intensity, soil moisture, invertebrate abundance, soil organic matter content, and 95-d labile pools of C and N. Subnivian soils differed from exposed soils being as much as 26.8°C colder than exposed soils; average soil moisture ranging from 6.9 to 13.6% compared to 0.4% in exposed soils; soil invertebrate populations exceeding 7900 individuals kg−1 dry soil versus less than 1200 individuals kg−1 dry soil in exposed soils; and soil invertebrate species richness values greater than 2 taxa, compared to 1.3 taxa in exposed soils. The results of this study show that these seasonal, sparse snow patches may be an important source of moisture and control habitat of soil ecosystems in this extreme environment.

The influence of polar-cap convection on the geoelectric field at Vostok, Antarctica

Vertical geoelectric field measurements at Vostok, Antarctica ( 78.5° S, 107° E ; corrected geomagnetic latitude, 83.4°S) made during 1998 are compared with both Weimer (1996) and IZMEM (1994) model calculations of the solar-wind-induced, polar-cap potential differences with respect to the station. By investigating the correlations between these parameters for individual UT hours, we confirm and extend the diurnal range over which significant correlations have been obtained. Nineteen individual UT hours are significantly correlated with the Weimer model predictions and nine with the IZMEM model predictions. Diurnal variation in the slopes of the linear regressions allows us to comment on each model, demonstrating that Antarctic polar plateau geoelectric field measurements can be used to investigate polar convection. Seasonal variations in the diurnal electric field variations at Vostok are compared with the Carnegie global electric circuit diurnal curves, after allowance is made for the solar-wind-induced, polar-cap potential difference patterns.

Valley floor climate observations from the McMurdo dry valleys, Antarctica, 1986–2000

Climate observations from the McMurdo dry valleys, East Antarctica are presented from a network of seven valley floor automatic meteorological stations during the period 1986 to 2000. Mean annual temperatures ranged from −14.8°C to −30.0°C, depending on the site and period of measurement. Mean annual relative humidity is generally highest near the coast. Mean annual wind speed increases with proximity to the polar plateau. Site‐to‐site variation in mean annual solar flux and PAR is due to exposure of each station and changes over time are likely related to changes in cloudiness. During the nonsummer months, strong katabatic winds are frequent at some sites and infrequent at others, creating large variation in mean annual temperature owing to the warming effect of the winds. Katabatic wind exposure appears to be controlled to a large degree by the presence of colder air in the region that collects at low points and keeps the warm less dense katabatic flow from the ground. The strong influence of katabatic winds makes prediction of relative mean annual temperature based on geographical position (elevation and distance from the coast) alone, not possible. During the summer months, onshore winds dominate and warm as they progress through the valleys creating a strong linear relationship (r2 = 0.992) of increasing potential temperature with distance from the coast (0.09°C km−1). In contrast to mean annual temperature, summer temperature lends itself quite well to model predictions, and is used to construct a statistical model for predicting summer dry valley temperatures at unmonitored sites.

Landform and Soil Development in the McMurdo Dry Valleys, Antarctica: A Regional Synthesis

The McMurdo Valleys Mapping Project (VALMAP) contains soils data collected from 473 sites in the McMurdo Dry Valleys (77°07.5–78°00'S; 160°-164°E), Antarctica. The database includes surface boulder lithology, frequency, and weathering features; observations of patterned ground, permafrost, and ground-ice forms; detailed soil profile descriptions; laboratory characterization; and classification of the soils. Each site was located on 1:50,000 topographic maps from aerial photographs and elevation measurements, digitized, and entered into an ArcInfo Geographic Information System. The sites are arrayed along an ecoclimatic gradient that includes 21 coastal sites (4.4% of total), 109 inland valley floor sites (23%), 196 inland valley side sites (41%), 136 upland valley sites (29%), and 11 plateau fringe sites (2.3% of total). Whereas ice-cemented permafrost was predominant at coastal sites and along the polar plateau, 42% of the sites had dry permafrost in the upper 1 m. Massive ice occurs to a limited extent as ice-wedge polygons, ice-cored drift, and rock glaciers. Sand-wedge casts in upland valleys attest to a recession of the ice-cemented permafrost to greater depths over time. The most strongly developed soils and weathering features are on valley floors and in upland valleys where older deposits and landforms occur. The distribution of anions in soil:water extracts is reflective of air mass movement, with most soils reflecting a coastal source. Seventy percent of the soils examined in the McMurdo Dry Valleys are classified as Anhyorthels reflecting the lack of cryoturbation in the cold desert Antarctic environment.

Landform and Soil Development in the McMurdo Dry Valleys, Antarctica: A Regional Synthesis

The McMurdo Valleys Mapping Project (VALMAP) contains soils data collected from 473 sites in the McMurdo Dry Valleys (77?07.5-78?00'S; 160?-164?E), Antarctica. The database includes surface boulder lithology, frequency, and weathering features; observations of patterned ground, permafrost, and ground-ice forms; detailed soil profile descriptions; laboratory characterization; and classification of the soils. Each site was located on 1:50,000 topographic maps from aerial photographs and elevation measurements, digitized, and entered into an ArcInfo Geographic Information System. The sites are arrayed along an ecoclimatic gradient that includes 21 coastal sites (4.4% of total), 109 inland valley floor sites (23%), 196 inland valley side sites (41%), 136 upland valley sites (29%), and 11 plateau fringe sites (2.3% of total). Whereas ice-cemented permafrost was predominant at coastal sites and along the polar plateau, 42% of the sites had dry permafrost in the upper 1 m. Massive ice occurs to a limited extent as ice-wedge polygons, ice-cored drift, and rock glaciers. Sand-wedge casts in upland valleys attest to a recession of the ice-cemented permafrost to greater depths over time. The most strongly developed soils and weathering features are on valley floors and in upland valleys where older deposits and landforms occur. The distribution of anions in soil:water extracts is reflective of air mass movement, with most soils reflecting a coastal source. Seventy percent of the soils examined in the McMurdo Dry Valleys are classified as Anhyorthels reflecting the lack of cryoturbation in the cold desert Antarctic environment.

Physical properties of the seasonal snow cover in Dronning Maud Land, East Antarctica

AbstractSnow stratigraphy was analyzed in the Maudheimvidda area of western Dronning Maud Land, East Antarctica, during austral summer 1999/2000 as a part of the Finnish Antarctic Research Programme (FINNARP). Measurements were made in shallow (1–2m) snow pits along a 350 km transect from the coast to the polar plateau, covering at least one annual cycle and an elevation range from sea level to about 2500 m. The aim of the study is to document spatial and temporal variations in snow-cover properties, with the further aim of relating these variations to environmental factors and to patterns observable by remote sensing. The measurements suggest five principal snow zones: (i) sea ice, (ii) the seaward edge zone of the ice shelf, (iii) the inner parts of the ice shelf, (iv) the snow cover above the grounding line and (v) the local topographic highs. Local topographic highs such as ice domes and ice rises differ from other snow environments: the snow is less densely packed, possibly an indication of locally reduced speed of the katabatic outflow. Fewer and thinner crusts on the topographic highs are consistent with RADARSAT backscatter variations.