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Shallow firn cores, in addition to a near-basal ice core, were recovered in 2018 from the Quelccaya ice cap (5470 m a.s.l) in the Cordillera Vilcanota, Peru, and in 2017 from the Nevado Illimani glacier (6350 m a.s.l) in the Cordillera Real, Bolivia. The two sites are ~450 km apart. Despite meltwater percolation resulting from warming, particle-based trace element records (e.g. Fe, Mg, K) in the Quelccaya and Illimani shallow cores retain well-preserved signals. The firn core chronologies, established independently by annual layer counting, show a convincing overlap indicating the two records contain comparable signals and therefore capture similar regional scale climatology. Trace element records at a ~1–4 cm resolution provide past records of anthropogenic emissions, dust sources, volcanic emissions, evaporite salts and marine-sourced air masses. Using novel ultra-high-resolution (120 μm) laser technology, we identify annual layer thicknesses ranging from 0.3 to 0.8 cm in a section of 2000-year-old radiocarbon-dated near-basal ice which compared to the previous annual layer estimates suggests that Quelccaya ice cores drilled to bedrock may be older than previously suggested by depth-age models. With the information collected from this study in combination with past studies, we emphasize the importance of collecting new surface-to-bedrock ice cores from at least the Quelccaya ice cap, in particular, due to its projected disappearance as soon as the 2050s.
Stable isotope ratios (δ18O and δD) in Antarctic snow and ice are basic proxy indices of climate in ice core studies. The relation between the ratios has important indicative significance for moisture sources. In general, the fractionation characteristics of the two isotopes vary with different meteorological and topographical conditions. This paper presents the spatial and temporal distribution of meteoric water line (MWL) slopes along a traverse from the Zhongshan Station (ZSS) to Dome A in East Antarctica. It is found that the slopes decrease with the increasing distance inland from the coast and the lowest slope occurred at Dome A, where the long-range transported moisture dominates and clear sky snowing have an influence. The slopes in different layers of the snowpack showed a decreasing trend with depth and this is attributed to the fractionation during the interstitial sublimation and re-condensation processes of the water vapor. Frost flower development on the interior plateau surface can greatly alter the depth evolution of the MWL slope. The coastal snow pits also go through the post-depositional smoothing effect, but their influences are not so significant as the inland regions.
Despite a number of studies reporting glacier extent changes and their response to climate change over the eastern Tien Shan, glacier mass-balance changes over multiple decades are still not well reconstructed. Here, glacier mass budgets on the Karlik Range, easternmost Tien Shan during the time spans of 1972–2000 and 2000–2015 are quantified using digital elevation models reconstructed from topographic maps, SRTM X-band radar data and ASTER images. The results exhibit significant glacier mass loss in the Karlik Range for the two time spans, with a mean mass loss of −0.19 ± 0.08 m w.e. a−1 for the 1972–2000 period and −0.45 ± 0.17 m w.e. a−1 for the 2000–2015 period. The doubling of mass loss over the latter period suggests an acceleration of glacier mass loss in the early 21st century. The accelerated mass loss is associated with regional warming whereas the decline in annual precipitation is not significant.
Western Kunlun Mountain (WKM) glaciers show balanced or even slightly positive mass budgets in the early 21st century, and this is anomalous in a global context of glacier reduction. However, it is unknown whether the stability prevails at longer time scales because mass budgets have been unavailable before 2000. Here topographical maps, Shuttle Radar Topography Mission and Landsat data are used to examine the area and surface elevation changes of glaciers on the WKM since the 1970s. Heterogeneous glacier behaviors are observed not only in the changes of length and area, but also in the spatial distribution of surface elevation changes. However, on average, glacier area and elevation changes are not significant. Glaciers reduce in the area by 0.07 ± 0.1% a−1 from the 1970s to 2016. Averaged glacier mass loss is −0.06 ± 0.13 m w.e. a−1 from the 1970s to 1999. These findings show that the WKM glacier anomaly extends back at least to the 1970s.
Radioisotopes (239Pu, 240Pu, 236U) formed during atmospheric nuclear weapons testing (NWT) can be used for dating and therefore be applied as markers of the beginning of the Anthropocene Epoch. Moreover, 240Pu/239Pu ratios enable source identification (general fallout, local emission sources). Ice core segments from a 57.6 m ice core to bedrock from eastern Tien Shan, China were selected for 239,240Pu and 236U analyses by using compact low-energy accelerator mass spectrometry. The observed 240Pu/239Pu atom ratios were 0.18 ± 0.02, with one exception, indicating global fallout. No evidence for emissions from the nearby local sources Lop Nor was observed. The total deposition rates during NWT for 239Pu and 240Pu amount to 1.55 × 109 atoms·cm−2 and 3.1 × 108 atoms·cm−2, respectively. With the higher undisturbed fallout of 239Pu compared with values reported for glaciers from European Alps at Col du Dome and Colle Gnifetti as well as from the polar region, the eastern Tien Shan glacier would be an ideal site for defining the start of the Anthropocene. 236U is a rather new environmental tracer, while little is known about its global fallout from NWT. The observed deposition flux of 236U during NWT amounts to 3.5 × 108 atoms·cm−2 at the drill site. The average 236U/239Pu ratio of 0.27 ± 0.09 is in good agreement with literature values from global fallout.
The central Himalaya can be regarded as an ideal site for developing a long-term ice core dust record to reflect the environmental signals from regional to semi-hemispheric scales. Here we present a dust record from segments of a 108.83-m ice core recovered from the East Rongbuk (ER) Glacier (27°59â€²N, 86°55â€²E; 6518Â m a.s.l.) on the northeast slope of Mt. Qomolangma (Everest) in the central Himalaya, covering the period AD 600–1960. Due to rapidly layer thinning and coarse sampling, we primarily discuss the changes in the dust record since AD 1500 in this paper. Results show a significant positive relationship between the dust concentration and reconstructed air temperatures during this period, suggesting a likely cold–humid and warm–dry climatic pattern in the dust source regions, namely Central Asia. This is associated with the variability in the strength of the westerlies and its corresponding precipitation.
This study presents an arsenic concentration time series from 1964–2009 at Dome Argus, Antarctica. The data show a very large increase in arsenic concentration from the mid-1980s to the late-1990s (by a factor of~22) compared with the values before the mid-1980s. This increase is likely to be related to the increased copper smelting in South America. Arsenic concentration then decreased in the late-1990s, most probably as a result of environmental regulations in South America. The sudden increase in arsenic concentration observed at Dome Argus coincides with similar increases observed at Dome Fuji and in Antarctica Ice Core-6 (IC-6) at the same time, suggesting that arsenic pollution during the period from the mid-1980s to the late-1990s was a regional phenomenon in Antarctica. Investigations of arsenic concentrations at these three Antarctic locations show that, during this time, regional arsenic distribution followed dust transport pathways associated with general climate models with South America as a major source region for the half of Antarctica facing the Atlantic and Indian oceans.
Two ice cores drilled to the bottom were recovered from Miaoergou flat-topped glacier (43°03'19“N, 94°19'21“E; 4512 ma.s.l.), eastern Tien Shan, central Asia, in 2005. A high–resolution record of cadmium was established by applying inductively coupled plasma mass spectrometry to one of the ice cores (57.6 m), covering a 228 year period from AD 1776 to 2004. The results showed long-term variations of atmospheric transport and deposition of cadmium at high altitudes. Trend analysis based on the sequential Mann-Kendall test and the analysis of crustal enrichment factors of the cadmium shows that natural contribution, mainly from rock and mineral dust, dominated the atmospheric cycles of cadmium during the period AD 1776–1957, which was confirmed by the significant correlation between the winter North Atlantic Oscillation (NAO) index and annual cadmium concentration. The concentration of cadmium increased sharply from AD 1957 to 2004, suggesting increasing influence from human activities, such as metals production. The ice–core record indicated increasing atmospheric cadmium pollution in response to rapid economic growth after AD 1957 in the region.
Correlations between a 1000 year record of the major ions in a 108.83 m ice core from East Rongbuk Glacier (28°01’N, 86°58’E; 6518ma.s.l.) on the northeast slope of Qomolangma (Mount Everest) and the Southern Oscillation Index (SOI) were examined to investigate possible links between the ice-core records of the southern Tibetan Plateau (TP) and El Niño Southern Oscillation (ENSO). The results show that years with the highest crustal ion concentrations and lowest marine ion concentrations corresponded with a low SOI, and vice versa. Cross wavelet and wavelet coherence analysis between major ion time series and the SOI indicated that there were significant sections with high common power between the major ion time series and the SOI, suggesting a correlation between the ion records of the Qomolangma ice core and ENSO. Further investigation indicated that the higher SOI years corresponded with weaker continental air masses and stronger south Asian monsoons over the southern TP, leading to increased marine ions and decreased continental ions transported to the southern TP. The in-phase surface pressure anomalies of the southern TP and Darwin, Australia, link ENSO and ion transport over the southern TP, and thus suggest a link between aerosol transport over the southern TP and ENSO.
An ice core was extracted from the Zangser Kangri (ZK) ice field in the northern Tibetan Plateau (NTP), a location with limited instrumental and proxy records. In this paper, we present a continuous high–resolution dust concentration time series spanning the period AD 1951-2008 to investigate variations in atmospheric dust loading over the NTP. The results show that atmospheric dust loading exhibited significant decadal variations, with two periods of high dust loading (AD 1959–67 and AD 1979–89) and three periods of relatively low loading (AD 1951-58, AD 1968–78 and AD 1990–2008). The variability of atmospheric dust loading was related to wind speed at 500 hPa over the dust source regions. The winter Arctic Oscillation (AO) index showed a significant negative correlation with the annual dust concentration, implying a possible connection between the winter AO and the atmospheric dust loading over the NTP.
In 2005, two ice cores with lengths of 58.7 and 57.6 m respectively to bedrock were recovered from the Miaoergou flat-topped glacier (43°03′19″ N, 94°19′21″ E; 4512 m a.s.l.), eastern Tien Shan. 210Pb dating of one of the ice cores (57.6 m) was performed, and an age of AD 1851 ± 6 at a depth of 35.2 mw.e. was determined. For the period AD 1851-2005, a mean annual net accumulation of 229 ± 7 mm w.e. a–1 was calculated. At the nearby oasis city of Hami (~80 km from the Miaoergou flat-topped glacier) the annual precipitation rate is 38 mm w.e. a–1, hence glacial meltwater is a major water supply for local residents. The surface activity concentration of 210Pbex was found to be ~400 mBq kg–1, which is higher than observed at other continental sites such as Belukha, Russia, and Tsambagarav, Mongolia, which have surface activity concentrations of 280 mBq kg–1. The 210Pb dating agrees well with the chronological sequence deduced from the annual-layer counting resulting from the seasonalities of d18O and trace metals for the period AD 1953-2005, and ^-activity horizons resulting from atmospheric nuclear testing during the period AD 1962-63. We conclude that 210Pb analysis is a suitable method for obtaining a continuous dating of the Miaoergou ice core for ~160 years, which can also be applied to other ice cores recovered from the mountains of western China.
The Asian–Pacific Oscillation (APO) is a climate pattern related to the thermal differences between the Asian continent and the north Pacific. We present a 1000 year record of the major ions in a 108.83 m ice core from east Rongbuk glacier (28°01′ N, 86°58′ E; 6518ma.s.l.) on the northeast slope of Qomolangma (Mount Everest), and discuss its relationship with a 993 year time series of the summer APO index that has been reconstructed from Beijing’s summer temperature (recorded by a stalagmite) and the Pacific Decadal Oscillation (PDO) index. Empirical orthogonal function (EOF) analysis shows that crustal major ions (Mg2+, Ca2+, SO42– and NO3–) are highly loaded on EOF1, whereas marine major ions (Cl– and Na+) are highly loaded on EOF2. Higher EOF1 is associated with lower upper-troposphere temperature (UTT) over Mongolia, corresponding to a lower APO index and higher surface pressure. Higher EOF2 is associated with higher UTT over Mongolia, corresponding to a higher APO index and lower surface pressure. The higher burden of major ions and higher summer APO index during the period AD 1000–1323 may be due to drought and warm climate of the major-ion source regions. From AD1323 to 1900, EOF1 and EOF2 do not show a consistent correlation with summer APO index, indicating the complex mechanisms of ion transport over the southern Tibetan Plateau (TP) during this period. After AD 1900, the summer APO index is correlated negatively with EOF1 and positively with EOF2, indicating that ion transport over the southern TP during this period is influenced significantly by the APO. Our examinations of the PDO index and major-ion record show that higher PDO corresponds to higher EOF1 and lower EOF2. This suggests that the correlation between the recorded major-ion concentration and the APO index originates in the seesaw relationship in temperature between the Asian continent and the north Pacific.
In order to apportion the dust sources of mountain glaciers in western China, the Sr-Nd isotopic compositions of insoluble particles were determined in snow samples collected from 13 sites. The combined plot of 87Sr/86Sr and εNd(0) demonstrates a distinctive geographic pattern over western China, which can be classified into three regions from north to south. Samples from the Altai mountains show the lowest 87Sr/86Sr ratio and the highest εNd(0) value, similar to the data of deserts in the north of China such as the Gurbantunggut desert. Samples from the southern Tibetan Plateau (TP) and Himalaya show the highest 87Sr/86Sr and lowest εNd(0) values, resembling the local and regional dust sources found in the southern TP and Himalaya-India region. Samples from the Tien Shan and northern Tibetan Plateau exhibit intermediate 87Sr/86Sr and εNd(0) values, similar to the data reported for the northern margin of the TP (NM_TP). However, three sampling sites, JMYZ (Jiemayangzong) located in the Himalaya and ZD (Zadang) and YL (Yulong) located in the southeast TP, presented distinctive Sr-Nd isotopic signatures typical of the NM_TP, suggesting potential long-range and high-altitude dust transport across the TP.
Stakes at 2 km intervals were installed in January 1997 and remeasured in February 1998, January 1999, January 2005 and during the 2007/08 austral summer along a 1248 km traverse route from Zhongshan station to Dome A, East Antarctica. Based on topographical parameters, meteorological features and the records of ∼650 stakes and six stake arrays, the route is divided into five zones. We find that the snow accumulation rate decreases with increasing altitude as one progresses inland, except in the zone 800–1128 km from the coast, where the average annual accumulation rate is higher than in the zone 524–800 km from the coast. The Dome A zone (1128–1248 km) has the lowest accumulation rate (35 kg m−2 a−1, 2005–08) due to having the highest elevation and being furthest from the coast. The surface mass balance in the region 202–1128 km from the coast exhibits no temporal change from 1999–2005 to 2005–08, but there is a change in the accumulation distribution. The zone from 202 to 524 km shows a decrease in surface mass balance from 84 kg m−2 a−1 in 1999–2005 to 67 kg m−2 a−1 in 2005–08, while the zone between 800 and 1128 km shows an increase from 67 kg m−2 a−1 in 1999–2005 to 75 kg m−2 a−1 in 2005–08.
Glacier changes in the Karlik Shan, eastern Tien Shan, from 1971/72 to 2001/02 were monitored in this study. Topographic maps of 1 : 50 000 scale based on aerial photographs from 1971/72 and satellite images (Landsat TM, Landsat ETM+ and ASTER) from 1992, 2001 and 2002 were used to map glacier extent through a process of manual digitizing. The total glacier area decreased by 5.3% from 1971/72 to 2001/02. The rate of glacier area shrinkage was 0.13% a–1 between 1972 and 1992, but it was 0.27% a–1 from 1992 to 2001/02, suggesting accelerated glacier retreat in recent decades. Glacier changes in the region are a response to summer temperature increase. Annual precipitation also showed an upward trend, but this could not compensate for the mass loss due to ablation.
Annual-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.
An assessment of the glaciological and meteorological characteristics of Dome A, the summit of the East Antarctic ice sheet, is made based on field investigations during the austral summer of 2004/05. Knowledge of these characteristics is critical for future international studies such as deep ice-core drilling. The assessment shows that: (1) Dome A is characterized by a very low 10m depth firn temperature, –58.3˚C (nearly 3˚C lower than at EPICA Dome C and 1˚C lower than at Vostok). (2) Automatic weather station (AWS) measurements of snow surface height and reference layers in a snow pit indicate the present-day snow accumulation rate at Dome A is within the range 1–3cmw.e. a–1. Densification models suggest a range of 1–2cmw.e. a–1. This is lower than at other sites along the ice divide of East Antarctica (IDEA). Annual layers at Dome A are thus potentially thinner than at other sites, so that a longer record is preserved in a given ice thickness. (3) The average wind speed observed at Dome A (<4ms–1) is lower than at other sites along IDEA. Together, these parameters, combined with radio-echo sounding data and information on the subglacial drainage distribution beneath Dome A, suggest Dome A as a candidate site for obtaining the oldest ice core.
Stable oxygen isotope ratios (δ18O) of three shallow ice cores (extending back to 1963) from Urümqi glacier No. 1 at the headwater of Urümqi river, Tien Shan, northwest China, were used to test the relationship between δ18O and contemporaneous surface air temperature (Ta). The ice cores were dated using the seasonal stable-isotopic signals, and seven insoluble particulate β-activity horizons associated with known nuclear tests. Although a strong positive relationship exists between δ18O in precipitation and Ta at our study site, this relationship is not preserved between the annually averaged ice-core δ18O records and the local temperature due to post-depositional modification. These results indicate that the processes forming the ice-core chemical records in areas of high melt must be understood before the δ18O record can be confidently interpreted as a climatic indicator.