Present status and variations in the Arctic energy balance

The total solar irradiance (TSI, or solar constant) acquired a new value: 1361 W m^?2 instead of 1365 W m^?2. However a long-term variation of TSI was not detected. The solar irradiance at the earth's surface is considerably smaller (170 W m^?2) than previously believed (e.g. 198 W m^?2 of IPCC AR4). The previous overestimation is due to the underestimation of the absorption of solar radiation in the atmosphere. The absorption of solar radiation in the atmosphere at about 90 W m^?2, or 25–28% of the primary solar radiation from space. The global mean atmospheric downward terrestrial radiation is much larger (345 W m^?2) than previously assumed (325 W m^?2 of IPCC AR4). The Arctic has regions of negative annual net radiation, a very rare phenomenon on the globe. These regions are the Central Arctic Ocean with its multi-year ice coverage and the accumulation area of the Greenland ice sheet. The energy balance of these regions is presented. Long-wave incoming radiation has been increasing in the Arctic at a rate of 4–5 W m^?2/Decade. The Greenland ice sheet exhibits a large vertical difference in net radiation from the ablation area to the dry snow zone in summer. It ranges from 80 W m^?2 in the ablation area to 20 W m^?2 at the equilibrium line and to 10 W m^?2 in the dry snow zone. This gradient determines the melt gradient on the ice sheet, and is mainly caused by the altitude variation in atmospheric long-wave radiation, seconded by the albedo variation. The effect of albedo in summer for various surfaces is discussed. Simulation capabilities of radiation for many GCMs are investigated.     

Ablation Rate Estimates over the Greenland Ice Sheet from Microwave Radiometric Data

Scanning Multichannel Microwave Radiometer (SMMR) data are used to estimate the annual melt duration (number of days with melt) for elevation transects over the Greenland ice sheet during the period from 1979-1986. The annual melt duration is used to estimate the number of positive degree days (PDDs), which are used in a degree-day mass balance model to determine ablation rates and the equilibrium line altitude (ELA). The annual melt duration along two transects estimated with SMMR data compares favorably, particularly above the ELA, to melt duration calculated from surface temperature data for the same locations. The mass balance estimates and ELA locations along eight transects agree reasonably well with measurements reported in previous studies using surface temperature data. ELAs were within 10m of published values along two transects, and the root mean square error of SMMR-derived versus surface mass balance measurements was 43mm yr^?1. The estimated error in SMMR-derived ablation is between ±15% and ±50%, but could be reduced substantially by using daily microwave data available from the Special Sensor Microwave/Imager (SSM/I). This research shows the feasibility of using passive microwave data to estimate the ablation rate in order to determine ELA, which can be used to monitor the mass balance of the ice sheet.     

Ablation Rate Estimates over the Greenland Ice Sheet from Microwave Radiometric Data

Scanning Multichannel Microwave Radiometer (SMMR) data are used to estimate the annual melt duration (number of days with melt) for elevation transects over the Greenland ice sheet during the period from 1979‐1986. The annual melt duration is used to estimate the number of positive degree days (PDDs), which are used in a degree‐day mass balance model to determine ablation rates and the equilibrium line altitude (ELA). The annual melt duration along two transects estimated with SMMR data compares favorably, particularly above the ELA, to melt duration calculated from surface temperature data for the same locations. The mass balance estimates and ELA locations along eight transects agree reasonably well with measurements reported in previous studies using surface temperature data. ELAs were within 10m of published values along two transects, and the root mean square error of SMMR‐derived versus surface mass balance measurements was 43mm yr^?1. The estimated error in SMMR‐derived ablation is between ±15% and ±50%, but could be reduced substantially by using daily microwave data available from the Special Sensor Microwave/Imager (SSM/I). This research shows the feasibility of using passive microwave data to estimate the ablation rate in order to determine ELA, which can be used to monitor the mass balance of the ice sheet.     

Sediment accumulation along a glacially impacted mountainous coastline: north-east Gulf of Alaska

Tectonically active coastal regions of the world recently have been suggested to supply the bulk of sediment from land to the oceans. Seabed sampling on the continental shelf and in coastal embayments of the north-east Gulf of Alaska (Alsek River to Prince William Sound) was performed to examine the temporal and spatial variability of sediment accumulation in a mountainous coastal setting. Cores of varying lengths (30–300 cm) were collected at 84 stations to provide information on sedimentary processes using radiochemical (²¹⁰Pb and ¹³⁷Cs) techniques. Four types of ²¹⁰Pb activity profiles were observed, dominantly reflecting steady-state sediment accumulation. However, nonsteady-state profiles also were measured, resulting in part from episodic deposition near glacier-fed rivers and on the Copper River Delta. Sediment accumulation rates in the eastern half of the study area are highest at midshelf depths (≈100 m) (≥10 mm yr^?1) and near rivers draining the Bering Glacier (≈20 mm yr^?1). On the Copper River Delta, sediment accumulation rates are highest for the delta front (> 20 mm yr^?1) and decrease westward along the sediment dispersal route. Total annual sediment accumulation is 90–140×10⁶ tons yr^?1 on the shelf in the study area. Annual sediment accumulation for the total marine environment in the study area (including Icy and Yakutat Bays) exceeds 250×10⁶ tons yr^?1, potentially making this region the largest sink for sediment in North America. Spatial patterns in sediment accumulation on the shelf are similar between centennial and Holocene time-scales, reflecting the dominance of the Copper River and Bering and Malaspina glaciers as sediment sources. Temporal variability in accumulation rates between centennial and Holocene time-scales exists for portions of the study area near fiords and demonstrates the considerable changes that occur in sediment supply during glacial advances and retreats.     

Snow,runoff, and mass balance modeling for the entire Mittivakkat Glacier (1998–2006), Ammassalik Island,SE Greenland

Geografisk Tidsskrift, Danish Journal of Geography 108(1):121–136, 2008

SnowModel, a physically-based snow evolution modeling system that includes four submodels—MicroMet, EnBal, SnowPack, and SnowTran-3D—was used to simulate eight full-year (1998/99 through 2005/06) evolutions of snow accumulation, blowing snow sublimation, evaporation, snow and ice surface melt, runoff, and mass changes on the entire Mittivakkat Glacier (31 km²) in southeast Greenland. Meteorological observations from two meteorological stations inside the glacier catchment were used as model input, and glaciological mass balance observations were used for model calibration (1998/99 through 2001/02) and validation (2002/03 through 2005/06) of winter snow simulations. As confirmed by observations, the spatially modeled end-of-winter snow water equivalent (SWE) accumulation increased with elevation up to 700–800 m a.s.l. in response to elevation, topography, and dominating wind direction, and maximum snow deposition occurred on the lee side of the ridge east and south of the glacier. Simulated end-of-summer cumulative runoff decreased with elevation and minimum runoff occurred on the shadowed side of the ridge east and south of the glacier. The modeled test period averaged annual mass balance was 65 mm w. eq. y^?1 or ～8% more than the observed. For the simulation period, the glacier net mass balance varies from -199 to -1,834 mm w.eq. y^?1, averaging -900 (±470) mm w.eq.y^?1. The glacier averaged annual modeled precipitation ranged from 1,299 to 1,613 mm w.eq. y^?1, evaporation and sublimation from 206 to 289 mm w.eq., and runoff from 1,531 to 2,869 mm w.eq. y^?1. The model simulated Mittivakkat Glacier net loss of900 mm w.eq. y^?1 contributes approximately 42% to the average simulated runoff of 2,140 mm w.eq. y^?1, indicating a mean specific runoff of 67.8 l s^?1 km^?2.     

Solifluction rates and environmental controls at local and regional scales in central Austria

Solifluction is a widespread periglacial phenomenon. Little is known about present solifluction rates in Austria. The author monitored five solifluction lobes during a four-year period. Annual rates of surface velocity, vertical velocity profiles, depths of movement, and volumetric velocities were quantified using near-surface markers and painted lines. Environmental conditions were assessed using air temperature, soil texture, and ground temperature-derived parameters. The latter were used to estimate the relevance of needle-ice creep, diurnal frost creep, annual frost creep, and gelifluction. The mean surface velocity rates were 3.5–6.1 cm yr^?1 (near-surface markers) and 6.2–8.9 cm yr^?1 (painted lines), respectively, indicating a high relevance of needle-ice creep. The mean depth of movement was 32.5–40 cm. The mean volumetric velocities were 71–102 cm³ cm^?1 yr^?1. Solifluction rates at the five sites did not correlate with each other due to site-specific controls. No statistically significant correlations were quantified between solifluction rates and different environmental parameters due to data gaps and short time series, thus highlighting the importance of long-term monitoring. Nevertheless, the results suggest that longer zero curtain periods, longer seasonal ground thawing periods, later start of the seasonal snow cover, more freeze-thaw cycles, and cooler early summer temperatures promote solifluction.     

Post‐1850 changes in Glacier Benito,North Patagonian Icefield,Chile

Glacier Benito is a temperate outlet glacier on the west side of the North Patagonian Icefield. Rates of thinning and ablation were obtained using data collected by the British Joint Services Expedition in 1972/73 and subsequent data collected in 2007 and 2011. Ice‐front recession rates were based on dendrochronological dating for the terminal moraines and aerial and satellite imagery of the ice front in 1944, 1998 and 2002. Between the first Benito survey in 1973 and 2007, the lower glacier thinned by nearly 150 m at an average rate of 4.3 m yr^?1 with the rate increasing to 6.1 m yr^?1 between 2007 and 2011, a 28.7% increase during the latter period. Increases in ice movement and ablation were negligible: ice movement for 1973 and 2007 averaged 0.45 m day^?1 and ablation averaged 0.05 m day^?1. Ice front recession along the glacier's centre line from 1886 to 2002 was approximately 1860 m. Retreat rates between 1886 and 1944 averaged 8.9 m yr^?1. Thereafter glacier asymmetry makes measurement along the glacier centre line unrepresentative of areal change until 1998 when symmetry was restored; retreat between 1944 and 1998 was 15.4 m yr^?1. From 1998 to 2002 the rate increased dramatically to 127.2 m yr^?1. Recession from the southern end of Benito's terminal moraine in the 1850s supports an early date for initial retreat of the Icefield's glaciers.     

COSMOGENIC 10BE-AGES FROM THE STORE KOLDEWEY ISLAND, NE GREENLAND

Earlier work in northeast Greenland has suggested a limited advance of the Greenland Ice Sheet during the Last Glacial Maximum (LGM). However, this concept has recently been challenged by marine geological studies, indicating grounded ice on the continental shelf at this time. New ¹⁰Be‐ages from the Store Koldewey island, northeast Greenland, suggest that unscoured mountain plateaus at the outer coast were covered at least partly by cold‐based ice during the LGM. It is, however, still inconclusive whether this ice was dynamically connected to the Greenland Ice Sheet or not. Regardless of the LGM ice sheet extent, the ¹⁰Be results from Store Koldewey add to a growing body of evidence suggesting considerable antiquity of crystalline unscoured terrain near present and Pleistocene ice sheet margins.     

Wisconsinan and Holocene Climate History from an Ice Core at Taylor Dome, Western Ross Embayment, Antarctica

Geochemical data and geophysical measurements from a 554-m ice-core from Taylor Dome, East Antarctica, provide the basis for climate reconstruction in the western Ross Embayment through the entire Wisconsinan and Holocene. In comparison with ice cores from central East and West Antarctica, Taylor Dome shows greater variance of temperature, snow accumulation, and aerosol concentrations, reflecting significant variability in atmospheric circulation and air mass moisture content. Extreme aridity during the last glacial maximum at Taylor Dome reflects both colder temperatures and a shift in atmospheric circulation patterns associated with the advance of the Ross Sea ice sheet and accounts for regional alpine glacier retreats and high lake levels in the Dry Valleys. Inferred relationships between spatial accumulation gradients and ice sheet configuration indicate that advance of the Ross Sea ice sheet began in late marine isotope stage 5 or early stage 4. Precise dating of the Taylor Dome core achieved by trace-gas correlation with central Greenland ice cores shows that abrupt deglacial warming at Taylor Dome was near-synchronous with the ∼14.6 ka warming in central Greenland and lags the general warming trend in other Antarctic ice cores by at least 3000 years. Deglacial warming was following by a warm interval and transient cooling between 14.6 and 11.7 ka, synchronous with the Bølling/Allerød warming and Younger Dryas cooling events in central Greenland, and out of phase with the Antarctic Cold Reversal recorded in the Byrd (West Antarctica) ice core. Rapid climate changes during marine isotope stages 4 and 3 at Taylor Dome are similar in character to, and may be in phase with, the Northern Hemisphere stadial–interstadial (Dansgaard–Oeschger) events. Results from Taylor Dome illustrate the importance of obtaining ice cores from multiple Antarctic sites, to provide wide spatial coverage of past climate and ice dynamics.     

积雪对南极冰盖自动气象站气温观测影响的研究

随着冰盖表面雪的累积或消融,自动气象站(AWS)传感器相对地表的高度随之发生变化,故所记录的观测资料不能直接反映相对地表固定高度上的气象参数。为了使南极冰盖上AWS所获取的气象资料具有可靠性,在积累率对AWS观测气温影响的基础上,将东南极冰盖上中山站至DomeA断面3个AWS的连续观测气温修正到相对于雪表面的某一真实高度上。结果表明:(1)DomeA,Eagle和LGB69年平均1m气温分别为-53.19℃,-41.33℃和-26.29℃,年平均积累率分别为0.11m、0.30m和0.49m,对应的1m气温年平均修正量分别为0.34℃、0.29℃和0.35℃,2m和4m气温的年平均修正量均小于0.1℃;(2)积累率变化对离地表最近层次上的气温影响最大,越往上层影响越小;(3)气温的修正量大小与积累率并非成简单的正比关系,它与气温本身的季节变化特征以及局地近地表逆温强度有很大的关系。气温的平均修正量冬季为正,夏季修正量的正负由局地是否存在逆温决定,修正量值的大小主要由逆温强度和积累率决定。     

Lake and catchment response to Holocene environmental change: spatial variability along a climate gradient in southwest Greenland

The Kangerlussuaq area of southwest Greenland is a lake-rich landscape that covers a climate gradient: a more maritime, cooler and wetter coastal zone contrasts with a dry, continental interior. Radiocarbon-dated sediment sequences (covering ~11,200?C8,300?cal?year) from paired lakes at the coast and the head of the fjord were analysed for lithostratigraphic variables (organic-matter content, bulk density, Ti, Ca). Minerogenic and carbon accumulation rates from the four lakes were compared to determine catchment and lake response to Holocene climatic variability. Catchment erosion at the coast was dominated by cryonival processes, with considerable sediment production due to the limited vegetation cover and exposed rock faces. Input of minerogenic sediment at one site (AT4) was high (>1?gDW?cm^?2?year^?1) during the period 5,800?C4,000?cal?year BP, perhaps reflecting intensification of cryogenic processes on northeast-facing slopes and rapid delivery to the lake. This period of erosional activity was not observed at the nearby, higher elevation site (AT1) due to the lower catchment relief; instead, there was an abrupt decline in carbon and minerogenic accumulation rates at ~5,800?cal?year BP. Sediment accumulation rates at the inland sites were much lower (<0.005?gDW?cm^?2?year^?1) reflecting greater catchment stability (more extensive vegetation cover), lower relief and substantially lower precipitation, but synchronous increases in mineral accumulation rates from ~1,200 to 1,000?cal?year BP may reflect wind erosion associated with regional cooling and local aridity. Carbon-accumulation-rate profiles were similar at the two inland sites, with higher-than-average accumulation (~6?C8?g?C?m^?2?year^?1) during the early Holocene and a subsequent decline after ~6,000?cal?year BP. At the inland lakes, both mineral and carbon accumulation rates exhibited a stronger link to climate, driven by trends in effective precipitation and regional aeolian activity. Catchment differences (relief, altitude) lead to more individualistic records in both erosion history and lake productivity at the coast.     

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.     

Use of the revised universal soil loss equation (RUSLE) for soil and nutrient loss estimation in long-used rainfed agricultural lands,North Ethiopia

This study was conducted to quantify agricultural land degradation in the Ruba Gered watershed, Ethiopia. The watershed was divided into 12 land mapping units (LMU) after superimposing maps of soil, slope, land use/cover, and elevation. Subsequently, cultivated land was delineated to assess degradation types and severity based on standard approaches. Sheet erosion was estimated using the revised universal soil loss equation. Composite soil samples were collected from each LMU to quantify key soil nutrients (OM, total nitrogen, available phosphorus, and available potassium) lost by sheet erosion. The annual average soil loss due to sheet erosion was estimated to be 17.4 t ha^?1 yr^?1, with average annual nutrient losses estimated as 246.5 kg ha^?1 organic matter, 12.4 kg ha^?1 total nitrogen, 0.1 kg ha^?1 available phosphorus, and 1.6 kg ha^?1 available potassium. The study revealed that substantial quantities of soil and nutrients are lost every year in the study area due to severe sheet erosion. This amount of nutrient loss severely degrades soil and reduces soil fertility.     

Recent sedimentary histories of shallow lakes in the guatemalan savannas

Shallow basins in the savannas of Peten, Guatemala filled with water after 305±55 BP (calibrated age+1430–1660 AD). Aguadas Chimaj and Chilonche possess dilute waters and iron-rich, clayey sediments that are poor in Ca and Mg, reflecting the highly weathered nature of riparian soils. Low ²¹⁰Pb flux rates to Chimaj (0.085 pCi cm^-2 yr^-1) and Chilonche (0.134 pCi cm^-2 yr^-1) are attributed to low ²²²Rn emission rates from the nearby Caribbean Sea. Mean sediment accumulation rates in Chimaj and Chilonche for the past 150 years are 0.015 g cm^-2 yr^-1 and 0.047 g cm^-2 yr^-1 respectively. Forest expansion after 305 BP is documented in pollen profiles from the small aguadas and larger Lake Oquevix. Regional reforestation postdates the 9th century Classic Maya collapse and coincides with indigenous depopulation that was a consequence of European intrusion that began in the early 1500s. The timing of forest regrowth indicates the importance of historical anthropogenic factors in controlling Peten's vegetation. Nevertheless, other sedimentological lines of evidence (e.g. lithology, algal remains and charcoal particles) suggest that changing climate and/or local hydrology may have played a role in the reforestation process.     

Spatial pattern of recent sediment and diatom accumulation in a small,monomictic, eutrophic lake

Spatial variability of sediment and diatom deposition was assessed in a small monomictic, eutrophic lake in Northern Ireland (Lough Augher, Co. Tyrone) using measurements from 17 sediment cores. Loss-onignition profiles in water depths >6 m showed good repeatability, while littoral cores were more variable with localised profiles. Dry mass accumulation rates, derived by biostratigraphic correlation to a ²¹⁰Pb dated master core, were variable and not correlated with water depth. Basin mean dry mass accumulation rate was 0.068 g cm^-2 yr^-1 (range 0.036–0.09) prior to 1900, and 0.19 g cm^-2 yr^-1 (range 0.11–0.3) after 1974. Post-1940 cumulative fluxes were estimated for dry mass (range 3.49–916 g cm^-2) and diatoms (range 16.9–113.8×10⁷ frustules cm^-2). Cumulative dry mass was inversely correlated (r=–0.64) with distance from the inflow, indicating its localised influence. No variable was correlated with water depth except frustules of planktonic diatoms (r=0.66). However, high cumulative fluxes of diatoms and dry mass away from the inflow suggest that the expansion of the littoral macrophyte community may be responsible for decreased resuspension in shallow water, and together with increased sediment trapping, has enhanced sediment accumulation in shallow water over recent time periods.     

A Holocene paleoenvironmental history of Lake Alexandria,South Australia

An investigation of Holocene sediments within Lake Alexandrina, a shallow coastal lake at the mouth of the Murray River, South Australia, is presented based on a multidisciplinary approach.¹⁴C and²¹⁰Pb radiometric dating methods are used to establish a geochronological framework for the last 7000 yr BP, and diatoms, sand-siltclay ratios, organic carbon, phosphorus and copper concentrations are used to infer paleoenvironmental changes.The diatom assemblages indicate a change from marine-brackish to oligosaline-freshwater conditions between 7000 and 6000 yr BP, with sea-level stabilisation and continuous barrier formation across the Murray mouth. Sand pulses after 2300 yr BP document sand spit formation in the lake and the commencement of extensive lacustrine sedimentation.In the past 100 years which include the advent of European settlement in the region, the short-term²¹⁰Pb-based mass accumulation rate of 0.063 g cm^–2 yr^–1 is greater than that of the longer-term mean¹⁴C-based rate (0.023 g cm^–2 yr^–1), and high concentrations of phosphorus and copper correspond to historical records of blue-green algal blooms.This is the fifth in a series of papers published in this issue on the paleolimnology of aric regions. These papers were presented at the Sixth International Paleolimnology Symposium held 19–21 April, 1993 at the Australian National University, Canberra, Australia. Dr A. R. Chivas served as guest editor for these papers.     

Mass Balance of the Greenland Ice Sheet: Can Modern Observation Methods Reduce the Uncertainty?

The future contribution to sea level change from the large ice sheets in Greenland and Antarctica is composed of two terms: (i) a background trend determined by the past climate and dynamic history of the ice sheets on a range of time scales (decadal, millennial or even longer); and (ii) a rise/fall related to future climate change, whether due to anthropogenic effects or natural climate variability. The accelerating development of remote sensing techniques for monitoring ice sheet behaviour, and the use of high-resolution general circulation models to estimate temperature and precipitation changes are likely to result in improved estimates of the sensitivity of ice sheet mass balance to climate change and thereby to narrow down the uncertainty of contribution (ii). Contribution (i) is much more difficult to assess, because the mass balance displays large temporal variability on year-to-year and even on decadal time scales that masks the long-term trend. So, although modern remote sensing techniques enable accurate measurement of ice sheet surface elevation change, the mass changes derived from such measurements, even if performed over a period of several years, might just reflect a statistical fluctuation around the long-term background trend, which we must know in order to assess the future ice sheet contribution to sea level change on century and longer time scales. The measured volume changes must therefore be evaluated on the background of short- and long-term accumulation rates (e.g. determined from ice cores and high-resolution ice radar) and dynamic model studies of ice sheet evolution on century, millennial and longer time scales. The problems are illustrated by using the Greenland ice sheet as an example.     

Snow accumulation, melt, mass loss, and the near-surface ice temperature structure of Irenebreen, Svalbard

This study examines the mass balance, accumulation, melt, and near-surface ice thermal structure of Irenebreen, a 4.1 km² glacier located in northwest Spitsbergen, Svalbard. Traditional glaciological mass balance measurements by stake readings and snow surveying have been conducted annually at the glacier since 2002, yielding a mean annual net mass balance of −65 cm w.e. for the period 2002–2009. In 2009, the annual mass balance of Irenebreen was −63 cm w.e. despite above-average snow accumulation in winter. The near-surface ice temperature in the accumulation area was investigated with automatic borehole thermistors. The mean annual surface ice temperatures (September–August) of the accumulation area were −3.7 °C at 1 m depth and −3.3 °C at 10 m depth. Irenebreen is potentially polythermal, with cold ice and a temperate surface layer during summer. This temperate surface layer is influenced by seasonal changes in temperature. In winter, the temperature of all the ice is below the melting point and temperate layers are probably present in basal sections of the glacier. This supposition is supported by the presence of icings in the forefield of Irenebreen.     

Mass Balance Methods on Kongsvegen, Svalbard

On the glacier Kongsvegen (102 km²) in northwest Spitsbergen, Svalbard, traditional mass balance measurements by stake readings and snow surveying have been conducted annually since 1987. In addition, repeated global positioning system (GPS) profiling, shallow core analysis and ground-penetrating radar (GPR) surveying have been applied. The purpose of this paper is to evaluate the input from the different methods, especially the GPS profiling, using the results from the traditional direct method as a reference. The annual flow rate on Kongsvegen is low (2 ? 3 m a^?1), and the emergence velocity is almost negligible. Thus the geometry changes of the glacier, i.e. the change in altitude per distance from the head of the glacier, should reflect the change in net balance of the glacier. The mean annual altitude change from the longitudinal, centreline GPS profiles was compared to the direct stake readings and showed a very good agreement. On Kongsvegen the measured actual ice flux is so low that the mass transfer down-glacier at the mean equlibrium line altitude is less than 10% of what is needed to maintain steady-state geometry. This is clearly shown in the changing altitude profiles. GPS profiling can be used on large glaciers in remote areas to monitor geometry changes, ice flow and net mass balance changes. However, it requires that the centreline profile changes are representative for the area/altitude intervals, i.e. that the accumulation and ablation pattern is evenly distributed. For this purpose the GPR surveying quickly gave the snow distribution variability over long distances. Shallow cores drilled in different altitudes in the accumulation area were analysed to detect radioactive reference layers from the fallout after the Chernobyl accident in 1986, and showed very good agreement to the direct measured net balance. Thus older reference horizons from bomb tests in 1962 could be used to extend the net balance series backwards.     

揭示气候变化的南极冰盖研究新进展

南极冰盖是气候的产物，对气候也有反馈作用，冰盖物质平衡变化与全球海平面升降息息相关，并引发地球系统内的一系列变化，南极冰盖是记录全球变化信息的良好载体，具有信息量大，时间序列长，保真性能强，分辨率高以及可进行现代过程定量研究等其他介质无法取代的独特优点，随着科学技术的发展和人类对全球问题的日益重视，南极冰盖与全球变化研究这一领域将会以高起点，多学科互相交叉，渗透为特色，成为未来南极研究的热点领域。