Mean Annual Accumulation Rate Research Articles

A quantitative method of resolving annual precipitation for the past millennia from Tibetan ice cores

Abstract. Net accumulation records derived from alpine ice cores provide the most direct measurement of past precipitation. However, quantitative reconstruction of accumulation for past millennia remains challenging due to the difficulty in identifying annual layers in the deeper sections of ice cores. In this study, we propose a quantitative method to reconstruct annual accumulation from alpine ice cores for past millennia, using as an example an ice core drilled at the Chongce ice cap in the northwestern Tibetan Plateau (TP). First, we used laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) technology to develop ultra-high-resolution trace element records in three sections of the ice core and identified annual layers in each section based on seasonality of these elements. Second, based on nine 14C ages determined for this ice core, we applied a two-parameter flow model to established the thinning parameter of this ice core. Finally, we converted the thickness of annual layers in the three sample sections to past accumulation rates based on the thinning parameter derived from the ice flow model. Our results show that the mean annual accumulation rates for the three sample sections are 109 mm yr−1 (2511–2541 years BP), 74 mm yr−1 (1682–1697 years BP), and 68 mm yr−1 (781–789 years BP), respectively. For comparison, the Holocene mean precipitation is 103 mm yr−1. This method has the potential to reconstruct continuous high-resolution precipitation records covering millennia or even longer time periods.

Time-elapsed evolution of aerosol size distributions by snow particles after the passage of blizzards over the Maitri (Antarctica)

Measurements of the aerosol size distribution in the diameter range 0.003–20 μm were made by a scanning mobility particle sizer (SMPS) and an aerodynamic particle sizer (APS) at Maitri (70° 45′ 52′′ S, 11° 44′ 03′′ E, Antarctica) during the 24th Indian Antarctic Expedition, which took place in January and February 2005. Time-elapsed evolutions of the aerosol size distributions on 30 January and 17 and 20 February 2005, after the passage of blizzards, were selected for estimation of the scavenging coefficient by considering the aerosol size distribution changes with snowfall over Antarctica. Scavenging efficiencies of snow particles and ice crystals collecting aerosols are obtained from the observed scavenging coefficients for 0.002–10μm aerosols. Also, theoretical snow scavenging efficiencies of snow particles and ice crystals in the diameter range 0.02–10 mm for 0.002–10 μm aerosols are determined and, thereupon, scavenging coefficients are calculated by assuming snowfall rates of 0.25 and 4 mm h−1 (in view of the reported decadal mean annual Antarctica snowfall accumulation rate of 180 mm yr−1). Snow scavenging efficiencies based on the scavenging coefficients found by considering the aerosol size distribution changes with snowfall after the occurrences of blizzards are higher than theoretical scavenging efficiencies and those of laboratory experiments for planar and columnar ice crystals. Also, the scavenging coefficients found are higher by two to three orders of magnitude than theoretical scavenging coefficients. Scavenging coefficients found from aerosol size distribution changes by snowfall after the passage of blizzards on 30 January and 17 and 20 February 2005 over Antarctica suggest that the orders of magnitude of their best estimation and the corresponding scavenging efficiencies can be viewed as being on a par with the natural snow scavenging of aerosols over this remote region.

Spatial and temporal variability in snow accumulation at the West Antarctic Ice Sheet Divide over recent centuries

Ice cores collected in 2000 (ITASE 00‐1) and 2005 (WDC05A, WDC05Q) from the West Antarctic Ice Sheet Divide (WAIS Divide) project site were used to investigate the spatial and temporal variability in accumulation. The ice cores were dated based on annual layer counting of multiple glaciochemical measurements resulting in bottom depth ages for WDC05A, WDC05Q, and ITASE 00‐1 of 1775, 1521, and 1653 A.D., with mean annual accumulation rates of 0.200, 0.204, and 0.221 mweq a−1, respectively. Small‐scale spatial variability (SSV) was determined using an analysis of variance of accumulation in the ice core array, thereby quantifying the uncertainty in individual accumulation records. Results indicate that the spatial variability was 0.030 mweq a−1, or approximately 15% of the average annual accumulation. An accumulation record representative of the WAIS Divide local area over recent centuries was developed using a principal component analysis to identify the coherent accumulation signal. The WAIS Divide local record exhibited 14% interannual variability (1 standard deviation of the mean) with the SSV reduced to 0.017 mweq a−1. Correlations of the WAIS Divide local accumulation record with atmospheric indices (e.g., Antarctic Oscillation) exhibited periods when the records oscillate in and out of phase. Thus, reconstructing local and global atmospheric indices from WAIS Divide accumulation records over recent centuries may prove problematic.

Snow accumulation rate on Qomolangma (Mount Everest), Himalaya: synchroneity with sites across the Tibetan Plateau on 50–100 year timescales

AbstractAnnual-layer thickness data, spanning AD 1534–2001, from an ice core from East Rongbuk Col on Qomolangma (Mount Everest, Himalaya) yield an age–depth profile that deviates systematically from a constant accumulation-rate analytical model. The profile clearly shows that the mean accumulation rate has changed every 50–100 years. A numerical model was developed to determine the magnitude of these multi-decadal-scale rates. The model was used to obtain a time series of annual accumulation. The mean annual accumulation rate decreased from ∼0.8 m ice equivalent in the 1500s to ∼0.3 m in the mid-1800s. From ∼1880 to ∼1970 the rate increased. However, it has decreased since ∼1970. Comparison with six other records from the Himalaya and the Tibetan Plateau shows that the changes in accumulation in East Rongbuk Col are broadly consistent with a regional pattern over much of the Plateau. This suggests that there may be an overarching mechanism controlling precipitation and mass balance over this area. However, a record from Dasuopu, only 125 km northwest of Qomolangma and 700 m higher than East Rongbuk Col, shows a maximum in accumulation during the 1800s, a time during which the East Rongbuk Col and Tibetan Plateau ice-core and tree-ring records show a minimum. This asynchroneity may be due to altitudinal or seasonal differences in monsoon versus westerly moisture sources or complex mountain meteorology.

Annual accumulation over recent centuries at four sites in central Greenland

Accurate accumulation records are fundamental to understanding mass balance of the Greenland ice sheet. Ice cores can provide multicentury, high‐resolution ground‐based point estimates of water accumulation. In 2003 and 2004, four new ice cores were collected in the central western (D4 and D5) and Summit (Sandy and Katie) regions of Greenland. Annual layer counting based on multiple glaciochemical parameters (primarily hydrogen peroxide, sea salt, and dust proxies) was used to date the ice cores, resulting in annual dating. The bottom depth ages for D4, D5, Sandy, and Katie were estimated at 1738, 1673, 1844, and 1934 A.D., with mean annual accumulation rates of 41.4, 35.2, 22.4, and 22.4 cmweq yr−1, respectively. These new records were in good agreement with previous accumulation maps and four previously published records from nearby multicentury ice cores. Spatial variability was quantified through an analysis of variance, thereby allowing for more meaningful comparisons to atmospheric processes. More regionally representative accumulation records were constructed for the central western and Summit regions spanning recent centuries using a principle component analysis of both the new and previously reported ice core measurements. These regional records exhibited 6–7% interannual variability (1 standard deviation of the mean) and had lower spatial variability uncertainties than individual accumulation records. Correlations indicate that ∼20% of the variance in the central western region was explained by the North Atlantic Oscillation (NAO), and suggests that an array of more northern ice cores may correlate more closely with NAO.

Above-ground carbon stocks in tropical fallows, Sarawak, Malaysia

Assessment of biomass stocks and growth rates are essential for knowledge on carbon cycle dynamics. Being a part of an agricultural system, fallows provide two services: they contribute to food security and they store carbon. In this study, 3384 trees in Sarawak, Malaysia, were measured for diameter at breast height (DBH) along a chronosequence of fallow ages, and the biomass and carbon stocks of the fallows were estimated using published allometric equations. During the first 15 years following abandonment, the biomass of the shifting cultivation fallows accumulates following a logistic model reaching saturation after 6 years at 47 Mg dry matter (DM) per hectare. Using the differential equation of the logistic model to calculate biomass accumulation rates shows very high accumulation rates (up to 12.7 Mg carbon per hectare per year) when compared to standard calculations of mean annual accumulation rates.

Organic carbon storage and stable isotope composition of soils along a grassland to forest environmental gradient in Saskatchewan

Limited information is available about soil organic carbon accumulation rates and stable isotope composition in the boreal region of the Canadian prairies. The objectives of the study were to document soil development, measure carbon storage and accumulation rates, and determine the 13C/12C ratio of organic matter in native prairie soils in the major soil-climatic zones of Saskatchewan. The mean thickness of the Ah horizon increases from 5 cm in the Brown Chernozems to 14 cm in Black Chernozems, and this horizon is absent in Gray Luvisols. The thickness and degree of development of B horizons increase from Brown to Gray soils. Total organic C storage to 1.2 m depth in Brown, Dark Brown, Black Chernozems, and Gray Luvisols is 9.08, 11.72, 14.88, 9.63 kg C m-2, respectively. The long-term mean annual accumulation rates of organic C for Brown, Dark Brown, Black, and Gray soils are 0.57, 0.90, 1.18, and 0.84 g m-2 yr-1, respectively. For a Rego Black Chernozem the rate is 1.83 g m-2 yr-1. All these values are higher than those reported for temperate grasslands in the United States of America. The ỏ13C values of organic C (an average of all profiles in each soil zone to 1.2-m depth) range from -22.9 ‰ for Dry Brown soils, -24.3‰ for Brown soils, -24.8‰ for Dark Brown soils, -25.3‰ for Black soils, and -26.8‰ for Gray soils. The relative contribution of C4 plants to soil organic C decreases from the warm semiarid grassland to the moist Boreal region, where C4 plants have not influenced organic C at all. Considering the net primary production (NPP) estimated for the soil zones, average aboveground carbon sequestration is estimated to be about 0.46% of NPP. These data provides a realistic assessment of C balances in native prairie soils of Saskatchewan. Key words: Rate of carbon accumulation, stable isotope of soil carbon, soil zones of Saskatchewan, grassland soils, forest soils, Rego Black Chernozem soils

Records of climatic changes and volcanic events in an ice core from Central Dronning Maud Land (East Antarctica) during the past century

The depth profiles of electrical conductance, δ18O,210Pb and cosmogenic radio isotopes10Be and36Cl have been measured in a 30 m ice core from east Antarctica near the Indian station, Dakshin Gangotri. Using210Pb and δ18O, the mean annual accumulation rates have been calculated to be 20 and 21 cm of ice equivalent per year during the past ∼ 150 years. Using these acumulation rates, the volcanic event that occurred in 1815 AD, has been identified based on electrical conductance measurements. Based on δ18O measurements, the mean annual surface air temperatures (MASAT) data observed during the last 150 years indicates that the beginning of the 19th century was cooler by about 2‡ C than the recent past and the middle of 18th century. The fallout of cosmogenic radio isotope10Be compares reasonably well with those obtained on other stations (73‡ S to 90‡ S) from Antarctica and higher latitudes beyond 77‡N. The fallout of36Cl calculated based on the present work agrees well with the mean global production rate estimated earlier by Lal and Peters (1967). The bomb pulse of36Cl observed in Greenland is not observed in the present studies – a result which is puzzling and needs to be studied on neighbouring ice cores from the same region.

Reconstruction of the historical temperature trend from measurements in a medium-length borehole on the Lomonosovfonna plateau, Svalbard

AbstractA medium-length ice core was drilled at the ice divide on the Lomonosovfonna plateau (1230 m a.s.l.), Svalbard, in May 1997. As part of this project, temperature measurements were performed in the 120m deep borehole. At this site the ice thickness based on radar measurements is 126.5 m and the mean annual accumulation rate is 380 kg m–3. the measurements over the 15–120m depth interval show a nearly isothermal profile with a mean value of –2.8˚C and a standard deviation of 0.2˚C. the measurements reveal a temperature minimum at approximately 70m depth and a temperature gradient of 0.011 ±0.004˚Cm–1 near the bottom. the temperature minimum and relatively low temperature gradient cannot be explained in terms of a steady-state climate. Numerical calculations with a simple one-dimensional diffusion–advection model show that the temperature increased at a maximum rate of 0.02–0.025Ka–1 over the last 100 years, the total temperature increase amounting to 2.0–3.0K. Forcing the model with the observed record at Svalbard airport revealed that in the 19th century the surface temperature was at most 2.5 K lower, and that the instrumental observations started during a period with temperatures comparable to the end of the 19th century. the data are of particular interest for historical simulations since often no other temperature data are available in polar areas.

Accumulation rate changes in central Greenland from passive microwave data1

Numerical modeling based on radiative transfer theory and observations of grain growth with depth have indicated that passive microwave brightness temperatures over the polar ice sheets should be a function of accumulation rate. Using accumulation‐rate time series from nine shallow cores in the dry‐snow facies in central Greenland, we find that multi‐year averages of mean annual SMMR brightness temperatures and accumulation rates are highly correlated. The 18 GHz vertically polarized channel is found to be the best predictor of accumulation rate. If the 18V brightness temperatures and the measured annual accumulation rates are averaged over 1979–1986, a linear regression to these multi‐year average values reproduces the corresponding measured accumulation rates to within about ±5%. This regression also was used to compute annual accumulation rates at the nine core sites from the corresponding average annual SMMR brightness temperature. Measured and predicted annual accumulation rates agree to within ±10% if the mean annual passive microwave data is lagged by one year. Finally, we find that the predicted total annual accumulation over the 150 × 150 km study area agrees well with the corresponding value computed from the measured accumulation rate; both for an eight‐year average and for annual values.

Spatial gradients in snow layering and 10 m temperatures at two EPICA-Dronning Maud Land (Antarctica) pre-site-survey drill sites

AbstractDuring the 1997/98 field season, Sweden, Norway and The Netherlands performed a pre-site survey for EPICA in Dronning Maud Land, Antarctica. This paper summarizes the results and pays special attention to the high spatial gradients found in snow layering and temperatures. The sites were "Camp Victoria" (CV) on Amundsenisen (76° S, 8° W; 2400 m a.s.l.), approximately 550 km from the coast, and "Camp Maudheimvidda" (CM) on Maudheimvidda (74° S 13° W; 362 m a.s.L), some 140 km from the coast.The drilling programme included both medium-long firn/ice cores and shallow firn cores. These were analysed by means of δ18O, DEP, ECM,β activity, density, and ion content. The combined results suggests a mean annual accumulation rate of 60 mm. we. for CV and 220 mm. we. for CM.Variability measurements of spatial snow layering were performed at two scales; over tens of kilometres by radar and over a few metres by pits and high-resolution radar soundings. Results, as measured by relative standard deviation, were typically 10% on the polar plateau and as high as 50% near the coast.The 10 m temperature measurements were –38.5°C (std dev. = 0.5°) for CV and –17.6°C (std dev.=0.15°) for CM.Snow chemistry was sampled at each medium-long-core drill site. Comparison of δ18O profiles from snow pits and the uppermost part of the CV medium-long core showed large variations. Mean δ18O valuesover 2 m profiles varied between 41.6%, and 39.7%o within a horizontal distance of 50 m.

Marine Sediments and Snow from Ross Sea Region (Antarctica) Dating by 210Pb Method

210Pb is widely used to determine accumulation rates in order to obtain a time scale in environmental samples. The most accurate method uses the determination of 210Pb via its grand-daughter 210Po by alpha spectrometry. Unfortunately this method requires a complex wet-chemistry procedure to achieve the separation of 210Po from its matrix. In this work a simplified procedure for the chemical separation of 210Po is proposed and applied to three marine sediment cores and a 10 m snow core collected in Antarctica. The calculated sedimentation rates for marine sediments range from 0.053 to 0.071 cm y−1. The mean annual accumulation rate for the snow is 16.6 cm y−1 w.e. A comparison with literature data in the same region is given.

Radioactivity measurements applied to glaciers and lake sediments

The behaviour of glaciers, polar ice-caps and lakes can be studied by means of natural and artificial radioactivity measurements conducted on snow (Alps, Arctic and Antarctic) and sediments samples. The nuclear decay of elements ( 210Pb and 238U filiation products) and nuclear events (atmospheric thermonuclear tests: 1954 and 1962–1963; Chernobyl accident: 1986) allow an absolute dating of corresponding layers. These determinations need radiochemical separations (electro-plating, ion exchange filters), followed by ultra low level alpha and gamma spectrometries, or beta counting ( 137Cs, 90Sr). The high purity — N type — germanium detector (Compton-suppressed) allows the 210Pb analysis at 46.52 KeV, enabling a direct comparison with 210Po alpha spectrometry. Typical applications concern primarily dating, and the determination of mean annual accumulation rates of glaciers, sedimentation rate and mixing time in lakes, with their associated spatio-temporal variations. These measurements give access to the global fallouts of radionuclides and to meteorological parameters: air to snow (or sediment) transfer, deposition processes and atmospheric circulation.

Seasonal Trends and Chemical Composition of Snow at Terra Nova Bay (ANTARCTICA)

Abstract Snow samples from two snow-pits, located at different altitudes and distances from the sea, were analyzed to establish the H2O2, NO3 −, Cl−, SO4 2-, nss SO4 2- and MSA concentrations. The mean annual accumulation rates were calculated from the layer dating based on the H2O2 depth profile. The seasonal trends of the examined components' time series are discussed. The results obtained for the two stations are compared and found to be coherent. MSA appears to be the most promising seasonal tracer for the Terra Nova Bay region which is characterized by a strong marine contribution.

ENVIRONMENTS OF AEOLIAN DEPOSITION IN SOUTH-CENTRAL NEBRASKA DURING THE LAST GLACIAL MAXIMUM

The Peoria loess of south-central Nebraska, deposited approximately during the last Glacial Maximum, can be subdivided into three zones: an upper laminated loess and a lower massive loess, separated by a dark gley zone in which bison bones and spruce charcoal are found. The lower Peoria unit is characterized by high organic matter content, relatively high bulk density, and common root channels. The upper Peoria unit has rhythmic patterns of two orders: strongly gleyed and weakly gleyed zones alternating in couplets about 2-5 m thick, and coarse- and fine-grained laminae of second order, about 2-4 mm thick. The strongly gleyed zones are relatively low in magnetic susceptibility and contain lenses with abundant fossil plant debris. They may have formed in active zones on top of permafrost during relatively cold and probably moist intervals, with magnetic susceptibility secondarily lowered in the redox environment. Magnetic susceptibility also indicates the possible existence of first-order rhythmic patterns in the lower massive loess. Each of the ten susceptibility oscillations within Peoria loess has a mean duration of about 1000 years, assuming that the loess was deposited between approximately 20,000-22,000 and 10,000-10,500 yr BP. The second-order laminae, close to the expected mean annual accumulation rate of Peoria loess, may be due to seasonal variation in wind intensity or to secondary grain sorting of niveoeolian deposits.

Pattern of annual snow accumulation along a west Greenland flow line: no significant change observed during recent decades

At 10 positions on a traverse along a West Greenland flow line, shallow drillings and pit studies were performed in summer 1990. Continuous in situ hydrogen peroxide analyses on these samples allowed the seasonal firn stratigraphy to be established and thus to collect seasonally adjusted subsamples from the core in the field. The mean annual accumulation rate decreases from about 440 mm water equivalent at the western sites T9 and T13 to about 250 mm at the central positions T41 and Crete. Most of the prominent inter-annual changes of the surface mass balance appear to be well preserved over the area investigated. A comparison of the accumulation rates of the last decades with earlier measurements along the same Greenland flow line shows no significant change in accumulation rates during the last forty years. Further, there is no significant evidence for a pronounced increase in the Greenland surface mass balance as suggested by satellite altimetry. DOI: 10.1034/j.1600-0889.1994.t01-3-00005.x

Characteristics of the Initial Densification of Snow/Firn in Wilkes Land, East Antarctica (Abstract)

Fourteen shallow snow/firn cores were drilled with the Polar Ice Coring Office light-weight hand-coring auger in Wilkes Land, along a line approximately long. 111°E between lat. 66° and 74°S. Five of these cores, all between 20 and 30 m deep, are studied in detail in this paper: LJ, BJ, GC30, GC40 and GC46. The physical geographical conditions differ at these five stations, but the general trend is for mean annual accumulation rate and mean annual temperature to decrease farther south, with increasing elevation. At the southernmost station, GC46, the mean annual temperature is –52.5°C, and accumulation rate is 52 kg m−2 a−1. The density measurements of the snow/firn were made in a cold-room at temperatures from –14− to –18−C, by taking consecutive samples from the core and measuring the mass of each sample of known volume. The characteristics of the initial densification (to a density of 550 kg m−3) – variation in snow/firn density with depth, the densification rate of snow/firn, and the compactive viscosity coefficient of snow/firn – are studied, and the factors affecting this initial densification process are discussed. The following observations were made and conclusions reached: 1. Plots of all the measurements, from each core, of density against depth showed three different patterns. The first type, typical of the coastal areas, shows a very great variability of density at shallow depth, reducing with an increase in depth. The second, typical of the high inland stations, shows a smaller scatter of densities at shallow depth, again reducing with an increase in depth. The third type is a pattern intermediate between these two. So, the range of density fluctuation with a depth range in any core is greater at the top of the core than at the bottom, and at the same depth in different cores the variation in density is greater where the mean annual temperature is higher. 2. The snow/firn density increases with an increase in depth at all stations, and the densification rate is higher at stations with higher mean annual temperature. 3. The mean density of snow/firn in the top 1 m decreases farther inland, and this decrease appears to be closely related to the decrease in temperature. 4. The mean densification rate is compared with the mean annual temperature and the mean annual accumulation rate over the past 40 years in the most southerly cores. The mean annual temperature is found to be the more important factor affecting the densification rate in the surface snow/firn on the cold ice sheet. 5. At each station, for ρ = 550 kg m−3, a linear relationship is found between log compactive-viscosity coefficient of snow/firn and mean annual temperature for a constant density. If only stations with a mean annual temperature below –25°C (i.e. no melt features are present in the stratigraphy) are considered, then these results from Wilkes Land are very similar to the results obtained by Nishimura and others (1983) from Mizuho Plateau, East Antarctica.

Characteristics of the Initial Densification of Snow/Firn in Wilkes Land, East Antarctica (Abstract)

Fourteen shallow snow/firn cores were drilled with the Polar Ice Coring Office light-weight hand-coring auger in Wilkes Land, along a line approximately long. 111°E between lat. 66° and 74°S. Five of these cores, all between 20 and 30 m deep, are studied in detail in this paper: LJ, BJ, GC30, GC40 and GC46. The physical geographical conditions differ at these five stations, but the general trend is for mean annual accumulation rate and mean annual temperature to decrease farther south, with increasing elevation. At the southernmost station, GC46, the mean annual temperature is –52.5°C, and accumulation rate is 52 kg m−2 a−1.The density measurements of the snow/firn were made in a cold-room at temperatures from –14− to –18−C, by taking consecutive samples from the core and measuring the mass of each sample of known volume. The characteristics of the initial densification (to a density of 550 kg m−3) – variation in snow/firn density with depth, the densification rate of snow/firn, and the compactive viscosity coefficient of snow/firn – are studied, and the factors affecting this initial densification process are discussed.The following observations were made and conclusions reached:1.Plots of all the measurements, from each core, of density against depth showed three different patterns. The first type, typical of the coastal areas, shows a very great variability of density at shallow depth, reducing with an increase in depth. The second, typical of the high inland stations, shows a smaller scatter of densities at shallow depth, again reducing with an increase in depth. The third type is a pattern intermediate between these two. So, the range of density fluctuation with a depth range in any core is greater at the top of the core than at the bottom, and at the same depth in different cores the variation in density is greater where the mean annual temperature is higher.2.The snow/firn density increases with an increase in depth at all stations, and the densification rate is higher at stations with higher mean annual temperature.3.The mean density of snow/firn in the top 1 m decreases farther inland, and this decrease appears to be closely related to the decrease in temperature.4.The mean densification rate is compared with the mean annual temperature and the mean annual accumulation rate over the past 40 years in the most southerly cores. The mean annual temperature is found to be the more important factor affecting the densification rate in the surface snow/firn on the cold ice sheet.5.At each station, for ρ = 550 kg m−3, a linear relationship is found between log compactive-viscosity coefficient of snow/firn and mean annual temperature for a constant density. If only stations with a mean annual temperature below –25°C (i.e. no melt features are present in the stratigraphy) are considered, then these results from Wilkes Land are very similar to the results obtained by Nishimura and others (1983) from Mizuho Plateau, East Antarctica.

Investigations of the Oxygen-18 Content of Samples from Snow Pits and Ice Cores from the Filchner-Ronne Ice Shelves and Ekström Ice Shelf

Since 1979–80, isotope studies with oxygen-18 (18O) have been carried out at several snow pits and ice cores near the German Georg-von-Neumayer station (Ekström ice shelf, Atka Bay), as well as from the Filchner-Ronne ice shelves, in the framework of the German Antarctic research programme. The investigations of snow pits on the Filchner-Ronne ice shelves yield a standard deviation for the annual average δ18O values of approximately 1‰ over the last five years, and a decrease of δ18O with distance from the ice edge of about 1‰ per 50 km. The variation of δ18O for stratigraphically matching snow layers from snow pits at the same location in different years is about 0.3‰ on the Filchner-Ronne ice shelves, and 0.8‰ at Georg-von-Neumayer station. The mean annual accumulation rate in the surroundings of Georg-von-Neumayer station was determined to be 34 g cm-2 for the years 1977–81. On the Filchner-Ronne ice shelves the mean annual accumulation rate (1979–83) decreases from 22 g cm−2 at Filchner station to 15 g cm−2 at traverse point T340, located 200 km southeast of Filchner station.

Investigations of the Oxygen-18 Content of Samples from Snow Pits and Ice Cores from the Filchner-Ronne Ice Shelves and Ekström Ice Shelf

Since 1979–80, isotope studies with oxygen-18 (18O) have been carried out at several snow pits and ice cores near the German Georg-von-Neumayer station (Ekström ice shelf, Atka Bay), as well as from the Filchner-Ronne ice shelves, in the framework of the German Antarctic research programme. The investigations of snow pits on the Filchner-Ronne ice shelves yield a standard deviation for the annual average δ18O values of approximately 1‰ over the last five years, and a decrease of δ18O with distance from the ice edge of about 1‰ per 50 km. The variation of δ18O for stratigraphically matching snow layers from snow pits at the same location in different years is about 0.3‰ on the Filchner-Ronne ice shelves, and 0.8‰ at Georg-von-Neumayer station. The mean annual accumulation rate in the surroundings of Georg-von-Neumayer station was determined to be 34 g cm-2 for the years 1977–81. On the Filchner-Ronne ice shelves the mean annual accumulation rate (1979–83) decreases from 22 g cm−2 at Filchner station to 15 g cm−2 at traverse point T340, located 200 km southeast of Filchner station.