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Vanishing High Mountain Glacial Archives: Challenges and Perspectives Qianggong Zhang,*,†,‡,∇ Shichang Kang,*,‡,§ Paolo Gabrielli,∥,⊥ Mark Loewen,# and Margit Schwikowski∇ †
Key Laboratory of Tibetan Environment Changes and Land Surface Processes, Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing 100101, P.R. China ‡ CAS Center for Excellence in Tibetan Plateau Earth Sciences, Beijing 100101, P.R. China § State Key Laboratory of Cryospheric Sciences, Cold and Arid Regions Environmental and Engineering Research Institute, Chinese Academy of Sciences, Lanzhou, 730000, P.R. China ∥ School of Earth Sciences, 275 Mendenhall Laboratory, The Ohio State University, 125 South Oval Mall, Columbus, Ohio 43210, United States ⊥ Byrd Polar and Climate Research Center, The Ohio State University, 108 Scott Hall, 1090 Carmack Road, Columbus, Ohio 43210-1002, United States # Department of Chemistry, University of Manitoba, Winnipeg, MB R3T 2N2, Canada ∇ PSI, Paul Scherrer Institute, CH-5232 Villigen PSI, Switzerland and can preserve multiple proxies of various environments (air temperature, precipitation, atmospheric chemistry, volcanic depositions, etc.). The conservation and reliability of these glacial records is often attributed to the permanent freezing state of snow/ice, which entraps atmospheric depositions. In addition, the relatively high snow accumulation in middle- and low-latitude mountain glaciers (in the order of m/yr water equivalent compared to cm/yr for the polar ice caps) allows for the identification of decadal, interannual and seasonal variation of climatic and environmental parameters. Furthermore, being often adjacent to densely inhabited regions, mountain glaciers are more susceptible to the influence exerted by human activities and thus serve as excellent indicators of past anthropogenic activities. Continuous instrumental monitoring, by means of automatic weather stations and online measurements of atmospheric constituents is relatively recent, rare, expensive and difficult to maintain. In contrast, ice cores drilled in high-altitude glaciers yield continuous high-resolution paleoenvironmental records and thus provide a unique set of long-term complementary observations at high-altitudes. For example, ice cores have depicted consistent histories of vastly altered atmospheric composition due to anthropogenic emissions, while a decline of laciers in most mountain regions of the world have been atmospheric pollutants (e.g., heavy metals) in some high retreating, thinning, and disappearing at an accelerated mountain glacier records since around the 1970s has proven the rate in recent decades. Such trends are predicted to continue.1 success of various air quality measures implemented in North This widespread glacier decline has resulted in numerous America and Europe. environmental consequences such as freshwater supply crises, Noticeably, under the context of accelerating mountain natural calamities, and sea level rise. Other than these glacier decline worldwide, not only the glacier terminus but also important issues, a challenge that the scientific community is the upper parts of the glaciers (typically accumulating zones facing is that glacial-archived information, one of the best where intact ice core records could be obtained) have now been libraries of the past climatic and environmental changes, is subject to ablation. For example, plateau ice fields at the top of vanishing with rapid glacier reduction. Particularly, the recent Kilimanjaro (5893 m asl, the summit of Africa), have been widespread thinning of mountain glaciers’ summit globally, is observed to thin remarkably during the recent two decades. An erasing the histories of the most recent and intensive ice core drilled in 2003 on the Quelccaya ice cap (5670 m asl) interactions between humans and the environment. in the Peruvian Andes showed the irreversible obliteration of Owing to their strong coupling with climatic conditions, mountain glaciers are considered one of the most sensitive indicators of climatic and environmental changes, as they can Received: June 30, 2015 respond to different climate forcings by adjusting their shape Published: July 31, 2015
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© 2015 American Chemical Society
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DOI: 10.1021/acs.est.5b03066 Environ. Sci. Technol. 2015, 49, 9499−9500
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Environmental Science & Technology various environmental proxies in its top due to unprecedented meltwater percolation through the uppermost firn portion during the last two decades.2 Similarly, ice cores drilled in 2011 on Mt.Ortles (3905 m asl, Eastern European Alps) can provide full environmental information only from the pre-1980 cold portion of this glacier.3 In the Himalaya and the Tibetan Plateau, remarkable surface ablation of glaciers at extremely high elevations were discovered.4 Ice cores drilled at Mt.Naimona’nyi (6050 m asl) in 2006, at Mt.Nyainqentanglha (5850 masl) in 2002 showed absence of some critical reference chemical peaks (e.g., tritium), suggestive of mass loss at these drilling sites since the 1950s; an ice core retrieved at Mt.Geladaindong (5750 masl) in 2005 suggested the topmost of the core reached to the 1980s. Overall the widespread glacier ablation at high altitudes, either by meltwater percolation through their still existing temperate firn portion or direct “decapitation” of their top cold surface, is greatly reducing the possibility of obtaining past environmental records. Most problematic is that the apparent thinning of cold glaciers’ summits, although has not been well explained, is actually eroding glacial records over the period of instrumental observation which is a fundamental prerequisite for calibrating subsequent ice core reconstructions. These vanishing records represent unique memories of the most recent and intensive human impact on the earth’s system. Therefore, they are invaluable for probing the interplay between humans and the environment and provide the fundamental reference for the introduction of new environmental policies, and to test their efficacy in the future. Facing the challenge of fast diminishing glacial archives, we should identify a set of still potentially valuable drilling sites, accelerate the rate at which ice cores are being recovered, adopt new advanced techniques for interpreting partially obliterated ice core records and store additional core sections that may be analyzed in the future when more advanced techniques will become available. But, retrieving glacier archives may not be sufficient because ice fields are ablating faster than any possible extended salvage action. Ice samples are often destroyed when they are analyzed. Therefore, we also propose a holistic assessment of nearby environmental compartments linked to glaciers to attain integrated environmental information. Glaciers can be considered transitional environments between the high troposphere and high altitude terrestrial ecosystems. Contaminants conserved for a long time within glaciers can be released in meltwater and subsequently reintegrated in the global biogeochemical cycles through glacial-fed ecosystems. For instance, the recent increase of persistent organic pollutants recorded in glacial-fed lake sediments in the Swiss Alps was primarily attributed to the release of these substances from the melting glacier.5 This indicated a possibly more general pattern that glaciers wane while glacier-fed lakes wax. The recent glacier decline implies the erosion of the most recent glacial records, representing “the missing link” for the reconstruction of environmental histories. The dynamic exchange of substances between melting glaciers and the related nearby ecosystems (Figure 1) is ongoing and warrants a systemic study. In conclusion, rescued information from declining glaciers should be coupled with records extracted from the linked environmental compartments that can offer complementary information, to fully investigate regional and global environmental changes.
Figure 1. Scheme of the interaction between glacial and lake sediment archives. Until recently mountain ice cores used to provide environmental time series until present; today glacier ablation is eroding the most recent environmental ice core records while glacierfed lakes may entrap contaminants released by glaciers.
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AUTHOR INFORMATION
Corresponding Authors
*E-mail:
[email protected]. *E-mail:
[email protected]. Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS This work was supported by the National Natural Science Foundation of China (41371088 & 41225002), the “Strategic Priority Research Program (B)” of the Chinese Academy of Sciences (XDB03030504). P.G. acknowledges financial support from NSF awards nos. 1461422 and 1149239. This is also publication 1540 from the Byrd Polar and Climate Research Center.
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REFERENCES
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DOI: 10.1021/acs.est.5b03066 Environ. Sci. Technol. 2015, 49, 9499−9500
