The spatial variation of Asian dust and marine aerosol contributions to glaciochemical signals in central Asia

Short-term (6 months to 17 years) glaciochemical records have been collected from several glacier basins in the mountains of central Asia. The spatial distribution of snow chemistry in central Asia is controlled by the influx of dust from the large expanse of arid and semiarid regions in central Asia. Glaciers in the Northern and Western Tibetan Plateau show elevated concentrations and elevated annual fluxes of calcium, sodium, chloride, sulphate and nitrate due to the influx of desert dust from nearby arid and semi-arid regions. Glaciers in the Southeastern Tibetan Plateau show lower concentrations and lower annual fluxes of major ions due to longer transport distances of dust from the arid and semi-arid regions of Western China. Snow from the Karakoram and Western Himalaya show ion concentrations similar to those in Southeastern Tibetan Plateau, but much higher annual fluxes suggesting that much of the aerosol and moisture transported with the westerly jet stream is removed as it ascends the Southwest margin of the Tibetan Plateau. Snow from the Southern slopes of the Eastern Himalayas shows very low concentrations and very low annual fluxes of major ions, indicating that this region is relatively free from the chemical influence of Asian dust. The glaciochemical data suggest that glaciers which are removed from large source areas of mineral aerosol, such as those in the Himalaya, the Karakoram, and the Southeastern Tibetan Plateau, are the ones most likely to contain longer-term glaciochemical records which detail annual to decadal variation in the strength of the Asian monsoon and long-range transport of Asian dust

A review of Central Asian glaciochemical data

The glaciers of central Asia provide suitable locations from which to recover continuous, high-resolution glaciochemical records on a continental scale. Although the glaciochemical investigations undertaken to date in central Asia are few in number and limited in terms of spatial coverage and length of record, some preliminary observations can be made concerning regional and seasonal trends in snow chemistry in this region. The sodium chloride ratio for most snow samples collected in central Asia approaches the ratio found in sea water (0.86 in /Leq kg-I ), reflecting a marine source for these constituents. Sodium and chloride concentrations are, on average, 3-10 times higher in the Himalayas than in the Karakoram, demonstrating the greater influence of monsoonal sources of moisture in the Himalayas. Very high sodium concentrations from Khel Khod Glacier probably reflect a local crustal source from surrounding ice-free areas. Low nitrate concentrations were found in snow collected from the southern margin of the Himalayas and high concentrations in snow deposited on the north margin of the Himalayas. This strong regional trend in the spatial distribution of nitrate suggests the influx of continental aerosols, rich in nitrate, originating from the arid regions of central Asia. High calcium concentrations measured in snow from Mount Everest and the north-west corner of China are also indicative of dust derived from the arid regions of central Asia. Very high sulfate concentrations found in snow from the Tien Shan and the Bogda Shan most likely reflect local anthropogenic sources. The altitude effect on isotopic composition is not apparent from snow samples collected in central Asia. Understanding the processes which control the chemical content of snow, the local-to-regional scale complexities, and the seasonal variability are fundamental steps necessary to assess the potential for recovering representative long-term glaciochemical records from central Asia

S6E1: What happens if Mount Everest loses all of its snow and ice?

No place on earth can escape the effects of climate change, not even Mount Everest. The highest glacier on the world’s tallest mountain — the South Col Glacier — is rapidly disappearing. A new University of Maine-led study found that the glacier is losing several decades of ice and snow accumulation annually due to human-induced climate change. These findings are the latest from the 2019 National Geographic and Rolex Perpetual Planet Everest Expedition, led by UMaine Climate Change Institute director Paul Mayewski. In this episode of “The Maine Question,” Mayewski and UMaine Ph.D. candidate Mariusz Potocki, both co-authors of the new study, elaborate on the findings and their implications for mountaineering and the glacier stored water on which more than 1 billion people depend to provide melt for drinking water and irrigation. They also describe what it takes to conduct research on the rooftop of the world

Relationship between continuous aerosol measurements and firn core chemistry over a 10-year period at the South Pole

Before ice core chemistry can be used to estimate past atmospheric chemistry it is necessary to establish an unambiguous link between concentrations of chemical species in the air and snow. For the first time a continuous long-term record of aerosol properties (aerosol light scattering coefficient, σsp, and Ångström exponent, å) at the South Pole are compared with the chemical record from a high resolution firn core (∼10 samples per year) covering the period from 1981 to 1991. Seasonal signals in å, associated with winter minima due to coarse mode seasalt and summer maxima due to accumulation mode sulfate aerosol, are reflected in the firn core SO42−/Na+ concentration ratio. Summertime ratios of σsp and aerosol optical depth, τ to corresponding firn core sulfur concentrations are determined and the ‘calibrations’ are applied to sulfur concentrations in snowpits from a previous study. Results show that σsp estimates from snowpit sulfur concentrations are in agreement with atmospheric measurements while τ estimates are significantly different, which is likely due to the lack of understanding of the processes that mix surface air with air aloft

Examination of the 500,000-Year Climate Record in Ice at Mt. Moulton, West Antarctica

This project was a pilot project to determine if the ice on Mt. Moulton provides a reliable record of past climatic conditions. The area of study is a several hundred-meter section of blue ice (Trench A) that spans the time period from approximately the early Holocene to over 492k years ago. Dating control is obtained through radiometrically-dated tephra layers (i.e., air fall deposits) within the section (Figure 1) originating from the adjacent Mt. Berlin. Fieldwork during the 1999-2000 field season included the trenching of the complete section with electric chain saws mounted on a wheeled frame. Blocks were extracted and cut-down to sample a continuous section from the 50-cm depth. Several overlapping trenches, some completed to a depth of 1 meter, were sampled to test the validity of sampling at the 50-cm depth. Individuals from New Mexico Tech, collaborators in the project, developed a detailed map of visible tephra layers using a GPS and collected additional tephra samples with the goal of dating layers not presently dated and for refining existing ages. Once samples were brought back to the lab, a glaciochemistry time series was developed for comparison with other such records from Antarctica as well as from Greenland ice cores. Through the use of an ion chromatograph, concentrations of the major ions found in the atmosphere are determined. The suite of chemical species measured includes Na2+, Ca2+, Mg2+, K+, NH4+, Cl-, SO42-, and NO3-. One sample per 20 cm of ice was analyzed over the last ~150k to obtain a coarsely-resolved record to test the reliability of the record. Figure 1 shows the relationship between the Na2+ time series and the location of the dated tephra layers, thus the age model developed for Trench A. A similarity in broad trends would suggest that Mt. Moulton ice contains a valid paleoclimatic record thereby warranting more detailed (i.e., a much higher resolution) sampling and analyses than done in this study. As this was a pilot project the only presentations made were at meetings of the U.S. Ice Core Working Group and at meetings for the Siple Dome ice-coring project

Lichenometric Distribution of \u3cem\u3eRhizocarpon geographicum\u3c/em\u3e on Mt. Washington: A Relative Dating Tool.

Excerpt from summary, p. 83: In addition to marking the distribution of snowpatches and the relative age of patterned ground features, local departures from the regional lichenometric trend may also be used to define and relatively date: changes in the distribution of soils and vegetation, avalanche deposits, and abrasion of hiking trails. Lichenometric studies will be undertaken in the following year to date more precisely features and events on Mount Washington

Himalayan and Trans-Himalayan Glacier Fluctuations Since AD 1812

Historical records of the fluctuations of glaciers in the Himalayas and Trans-Himalayas date back to the early 19th century. Local and regional syntheses of 112 of these fluctuation records are presented in this study. The local syntheses deal with fluctuations of glaciers in Kanchenjunga-Everest, Garwhal, Lahaul-Spiti, Kolahoi, Nanga Parbat, Karakoram (north and south sides), Rakaposhi-Haramosh, Batura Mustagh, and Khunjerab-Ghujerab. Regional syntheses deal with the composite record and the differentiation of records by glacier type (longitudinal versus transverse) and regional setting (Himalayan versus Trans-Himalayan). In a gross regional sense Himalayan and Trans-Himalayan glaciers have been in a general state of retreat since AD 1850. Filtering of the fluctuation records with respect to glacier type and regional setting reveals that the period AD 1870 to 1940 was characterized by alternations in the dominancy of retreat, advance, and standstill regimes

Variability in Accumulation Rates from GPR Profiling on the West Antarctic Plateau

Isochronal layers in firn detected with ground-penetrating radar (GPR) and dated using results from ice-core analyses are used to calculate accumulation rates along a 100 km across-flow profile in West Antarctica. Accumulation rates are shown to be highly variable over short distances. Elevation measurements from global positioning system surveys show that accumulation rates derived from shallow horizons correlate well with surface undulations, which implies that wind redistribution of snow is the leading cause of this variability. Temporal changes in accumulation rate over 25-185 year intervals are smoothed to along-track length scales comparable to surface undulations in order to identify trends in accumulation that are likely related to changes in climate. Results show that accumulation rates along this profile have decreased in recent decades, which is consistent with core-derived time series of annual accumulation rates measured at the two ends of the radar profile. These results suggest that temporal variability observed in accumulation-rate records from ice cores and GPR profiles can be obscured by spatial influences, although it is possible to resolve temporal signals if the effects of local topography and ice flow are quantified and removed

A Science Management Office for the U. S. Component of the International Trans Antarctic Expedition (US ITASE SMO)ûA Collaborative Pgrm of Research from S. Pole to N. Victoria Land

This award supports a science management office for a pilot ice-core drilling and analysis program to test the feasibility of obtaining well-dated, high-resolution isotope and chemistry records from East Antarctica. Shallow ice cores will be obtained from two locations: 1) ~100 km from South Pole towards the Pole of Inaccessibility, as an extension of the Byrd Station-to-South Pole ITASE traverse [International Trans Antarctic Scientific Expedition]; 2) at Taylor Dome, near the original deep coring site, and (3) possibly at AGO 3 and AGO 4 as part of a logistics traverse to these sites. All of the cores collected will be sampled at very high resolution (~1/2 cm) and analyzed for major ions. Results from this calibration work, along with those from another project that is analyzing stable isotopes will be used to help plan a program of larger scope, with the objective of mapping the spatial expression of climate variability in East Antarctica. Funds are also provided to organize a community workshop for coordination of the second phase of US ITASE and for one workshop per year for two years dedicated to writing and preparation of scientific papers from phase one of US ITASE. In addition, route selection activities for the follow-on traverse activities in East Antarctica will be conducted using satellite image mapping. A summary document will be produced and made available to the community to help with planning of related field programs (e.g. deep ice radar, firn radar profiling, atmospheric chemistry, ice coring, snow surface properties for satellite observations, ice surface elevation and mass balance)

Limited migration of soluble ionic species in a Siple Dome, Antarctica, ice core

High-resolution (\u3e10 samples a−1) glaciochemical analyses covering the last 110 years from a Siplc Dome, Antarctica, ire core reveal limited migration of certain soluble ionic species (methane sulfonic acid, NO3 − and Mg2+). The observed chemical migration may be due in part to seasonal alternation between less acidic winter (from high sea-salt concentrations) and more acidic summer (from high marine biogenic acid concentrations) layers, common at coastal siles such as Siplc Dome. Exact mechanisms to expla in the migration are unclear, although simple diffusion and gravitational movement are unlikely since new peaks are formed where none previously existed in each case. Initial migration of each species is both shallower and earlier at Siple Dome than at other sites in Antarctica where similar phenomena have been observed, which may be related to the relatively low accumulation rate at Siple Dome (~13.3 cm ice a−1). Migration appears to be limited to either the preceding or following seasonal layer for each species, suggesting that paleoclimatic interpretations based on dala with lower than annual resolution are not likely to be affected