IntroductionHolocene and latest Pleistocene alpine glacier fluctuations: a global perspective
Introduction
The papers in this volume originate from a session titled, “Holocene and latest Pleistocene alpine glacier fluctuations: A global perspective” organized by us for the XVII INQUA Congress in Cairns, Australia, in August 2007. Much new information has become available on the ages of alpine glacier fluctuations throughout the world since a special session dedicated to Holocene glacier fluctuations was convened at the XII INQUA Congress during July 1987 in Ottawa (Davis and Osborn, 1988). Abrupt Younger Dryas cooling at the end of the Pleistocene, for example, is now recognized in many areas around the globe, and a cooling episode about 8200 years ago also caused glaciers to advance at several alpine sites. In addition, some studies indicate that Neoglaciation began earlier than previously believed, perhaps as far back as about 6.5 ka.
Alpine glaciers provide important paleoclimate proxies for comparison with recent climate changes that are likely anthropogenic (Oerlemans, 1994, Oerlemans, 2005, Lowell, 2000, Meier et al., 2007, Barry, 2006, Owen et al., 2009). Continued retreat of alpine glaciers throughout the world provides a valuable opportunity to recover organic material, such as in situ sheared tree trunks, for 14C dating. Advances in cosmogenic nuclide exposure dating now allow high-precision measurements of moraine boulders and glaciated bedrock surfaces of Holocene and latest Pleistocene age. Higher resolution records from glacial lake sediments and related proxies, such as ice cores, tree rings, varves, corals, and speleothems, suggest decadal to multi-centennial Holocene climatic fluctuations, culminating with the Little Ice Age (Mayewski et al., 2004). Given the sensitivity of alpine glaciers to climate forcing (Schmidt et al., 2004) and the probable human-induced global warming over the past few decades (Intergovernmental Panel on Climate Change, 2007a, Intergovernmental Panel on Climate Change, 2007b), an understanding of naturally occurring climatic forcing over the past 10 to 12 millennia is more important than ever.
In the preface to an earlier special volume of Quaternary Science Reviews titled “Holocene glacier fluctuations,” Davis and Osborn (1988) stated: “Studies of Holocene glacier fluctuations may have practical applications, with relevance to, for example, water resources, mining and engineering operations, and agricultural endeavors in high mountain regions, and to dwelling and shipping in coastal areas. However, the broadest and most valuable application of alpine glaciers concerns their use as a proxy indicator of climatic change, as small glaciers are very sensitive to slight fluctuations in summer temperature and mean annual precipitation. Alpine glaciers are also surprisingly widely distributed, from polar latitudes to equatorial regions; thus they allow climatic comparisons to be made between many different geographic settings. An understanding of Holocene glacier fluctuations and the prediction of future climate are of obvious value to society, with consequences for food and water supply, energy production and use, and sea level change.”
Our words in the paragraph above are as important today as they were over two decades ago. The vulnerability of water resources to warming climate and glacier retreat has become a critical, global issue (cf., Gleick, 2003, Gleick, 2008, Vörösmarty et al., 2000, Peterson et al., 2002, Mark and Seltzer, 2003, Barnett et al., 2005, Milly et al., 2005, Singh et al., 2005, Bradley et al., 2006). Reduced meltwater from glacier and winter snowpack is also predicted to have a significant impact on agriculture (Schindler and Donahue, 2006, Lobell et al., 2008). Glacier recession and thawing permafrost also create geotechnical hazards and engineering problems in the mountain environment (Haeberli, 1992, Harris et al., 2001, Oppikofer et al., 2008) and myriad other hazards (Grove, 1987). Besides a wide array of health hazards related to global warming and glacier recession (Ebi et al., 2007), perhaps the most catastrophic health risk is the danger from glacier outburst floods (Watanabe et al., 1994, Walder and Costa, 1996, Clague and Evans, 2000, Richardson and Reynolds, 2000, Kattelmann, 2003, Huggel et al., 2004, Cary, 2005, O'Connor and Costa, 2004, Harrison, 2006). Melting of alpine glaciers has significantly contributed to global sea-level rise over the past century, and it is projected that sea-level rise could potentially displace millions of people over the next few decades (Nicholls et al., 1995, Nicholls et al., 1999, Titus and Narayanan, 1996, Gregory and Oerlemans, 1998, Nicholls and Mimura, 1998, Klein and Nicholls, 1999, Dyurgerov, 2003, Walsh et al., 2004, Meier et al., 2007, Edwards, 2008, Bahr et al., 2009). Although rapidly shrinking alpine glaciers reveal archeological treasures (Spindler, 1994, Fowler, 2001, Dixon et al., 2005), their demise is also a major aesthetic loss (Wilson, 2003, Kennedy and Hanson, 2006, Cary, 2007).
Our objective for this special volume of Quaternary Science Reviews is provision of the most up-to-date datasets on alpine glacier moraine ages for paleoclimate reconstruction and modeling. The data provided in a previous special volume on Holocene glacier fluctuations organized by Davis and Osborn (1988), for example, led Nesje and Johannessen (1992) to suggest that a combined effect of volcanic aerosols and summer insolation variations forced climate over the past 10 ka. A better understanding of the spatial distribution of lateglacial moraines may also allow more meaningful testing of hypotheses concerning the cause of Younger Dryas cooling (Taylor et al., 1997, Alley, 2000, Broecker, 2003, Broecker, 2006, Firestone et al., 2007, Lowell and Kelly, 2008, Bakke et al., 2009, Kennett et al., 2009). More precise and robust dating of Little Ice Age and Neoglacial moraines throughout the world may allow testing of hypotheses for Holocene climate variability (Bond et al., 1997, Bond et al., 2001, Broecker, 2000, Denton and Broecker, 2008).
Section snippets
Methods
Radiocarbon dating remains the primary method for constructing Holocene and latest Pleistocene alpine glacier chronologies. Over the past couple of decades, lichenometric dating of pre-Little Ice Age glacial chronologies (Benedict, 1973: Denton and Karlén, 1973) is less common than it was in the 1970s and 1980s, although lichens are still useful for distinguishing advances of the past few hundred years. Dendrochonology, especially using fossil wood, has continued to contribute many
Global regions
In this volume, 10 papers cover five of the same areas summarized in the 1988 Quaternary Science Reviews special volume (Davis and Osborn, 1988), along with five new regions. Barclay et al. (2009) provide an update on Calkin (1988) for Alaska, and Menounos et al. (2009) expand upon Osborn and Luckman (1988) by including the Yukon previously covered by Calkin (1988). A follow-up paper on Davis (1988) for the American Cordillera (lower 48 states) by D.H. Clark and P.T. Davis could not be
Discussion
Historical and geologic records of alpine glacier fluctuations were among the first proxy records used to establish the history of Holocene climate change, and these records continue to be valuable to assess current and future changes induced by human activities (Alley et al., 2003, Mayewski et al., 2004, Intergovernmental Panel on Climate Change, 2007a, Intergovernmental Panel on Climate Change, 2007b). The spatial coverage of these records is now global with firm dating constraints for many
Acknowledgments
We thank all of the authors and reviewers of papers for this special volume on Holocene and latest Pleistocene glacier fluctuations. We especially thank Debbie Barrett, Colin Murray-Wallace, and Jim Rose for their support. Also, we acknowledge the useful comments of Jeffrey Munroe and Thomas Lowell on this preface paper.
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