Glaciers of Asia—

THE PALEOENVIRONMENTAL RECORD 

PRESERVED IN MIDDLE LATITUDE, HIGHMOUNTAIN GLACIERS—AN OVERVIEW OF 

THE U.S. GEOLOGICAL SURVEY EXPERIENCE 

IN CENTRAL ASIA AND THE UNITED STATES

By L. DeWayne Cecil, David L. Naftz, Paul F. Schuster, David D. Susong, and

Jaromy R. Green

SATELLITE IMAGE ATLAS OF GLACIERS OF THE WORLD

Edited by RICHARD S. WILLIAMS, JR., and JANE G. FERRIGNO

U. S. G EO LO G I C A L SU RV EY P RO F E SSI O N A L PA P E R 1 3 8 6 –F– 8

CONTENTS III

CONTENTS

Abstract----------------------------------------------------------------------------------------------335

Introduction----------------------------------------------------------------------------------------335

Figure 1. Map showing locations of the Nangpai Gosum Glacier, Lednik 

 Engil’chek (Inylchek Glacier), Belukha Glacier, Upper 

 Fremont Glacier, and the Idaho National Laboratory----------------------338

Study Sites----------------------------------------------------------------------------------339

Nangpai Gosum Glacier................................................................................339

Lednik Engil’chek..........................................................................................339

Belukha Glacier...............................................................................................339

Upper Fremont Glacier................................................................................339

Selected Results and Discussion---------------------------------------------------------------340

Nangpai Gosum Glacier------------------------------------------------------------------340

Figure 2. Graph showing chlorine-36 and cesium-137 concentrations 

 in the ice core collected from the Nangpai Gosum Glacier in 1998 ------340

Figure 3. Graphs showing concentrations of tritium, delta oxygen-18, 

 and chlorine-36 in ice-core samples from the 1991 Upper 

 Fremont Glacier expedition ------------------------------------------------------341

Lednik Engil’chek ------------------------------------------------------------------------341

Upper Fremont Glacier -----------------------------------------------------------------342

Figure 4. Graph showing refined age-to-depth profile for the 1991 Upper

 Fremont Glacier ice core ----------------------------------------------------------344

Figure 5. Graph showing profile of historic concentrations of mercury

 measured in selected ice-core sections from the Upper 

 Fremont Glacier---------------------------------------------------------------------345

Applications----------------------------------------------------------------------------------------345

Paleoclimatic Records-------------------------------------------------------------------345

Environmental Concentrations of Mercury ----------------------------------------346

Summary--------------------------------------------------------------------------------------------347

References Cited ----------------------------------------------------------------------------------348

GLACIERS OF ASIA — PALEOENVIRONMENTAL RECORD F335

SATELLITE IMAGE ATLAS OF GLACIERS OF THE WORLD 

GLACIERS OF ASIA— 

The Paleoenvironmental Record Preserved in MiddleLatitude, High-Mountain Glaciers—An Overview of the 

U.S. Geological Survey Experience in Central Asia and the 

United States

By L. DeWayne Cecil,1 David L. Naftz,2 Paul F. Schuster,3

David D. Susong,2 and Jaromy R. Green4

Abstract

The U.S. Geological Survey (USGS) is conducting a research program to study the 

geochemical and isotopic content of precipitation, snow, ice, and runoff samples from highmountain glaciers in the middle latitudes of central Asia and the United States. Related topics 

of research, such as the reconstruction of paleoclimate records, the description of anthropogenic input of chemicals to the environment, and computer modeling of global climate change, 

are important to the well being of the Earth’s human population. The  collection and chemical 

analysis of snow and glacier ice cores can improve our knowledge of all of these topics. Nearly 

all of the chemical constituents that compose snow and ice-core samples contribute important 

scientific information. This research is made critical by the fact that middle-latitude, highmountain glaciers, and the environmental and other information preserved in them, are rapidly 

disappearing as a result of global warming. Information collected to date includes the documentation of fallout from nuclear-weapons testing conducted during the 1940s, 1950s, and 

1960s, quantification of pre-industrialization levels of mercury in the environment, evidence 

of rapid regional climate change, and identification of microbial communities entrained in the 

ice. Researchers from national and international academic institutions and from federal and 

provincial governmental agencies are collaborating on this project.

Introduction

Global environmental changes have occurred throughout the 4.5 

billion-year history of the Earth, and such changes will continue to take place 

throughout the Earth System in the future. The  changes are now recognized 

to have the potential for immediate as well as long-term consequences for the 

Earth’s varied ecosystems. As a result, the importance of understanding current 

and potential global environmental change has dramatically increased (Cecil 

and others, 2004).

Archives of past climatic and environmental conditions are preserved in 

the Earth’s alpine glaciers, ice caps, ice fields, and ice sheets. Ice cores from the 

polar regions have provided the scientific community with an unprecedented 

view of past environmental change through analysis of chemical, isotopic, and 

stratigraphic data. These records extend back in time for 110,000 years in ice 

1

U.S. Geological Survey, Boise, Idaho 83702 U.S.A.

 2U.S. Geological Survey, Salt Lake City, Utah 84104 U.S.A.

 3U.S. Geological Survey, Boulder, Colorado 80303 U.S.A.

 4Garden City Community College, Garden City, Kansas 67846 U.S.A., formerly with the 

U.S. Geological Survey
F336 SATELLITE IMAGE ATLAS OF GLACIERS OF THE WORLD

cores from the Greenland ice sheet (Alley, 2000) and for more than 800,000 

years (EPICA, 2004) in the Antarctic ice sheet. However, changes in weather 

and climate patterns affect high-latitude regions of the world differently than 

they do middle- to low-latitude regions because of latitudinal differences in 

global circulation. Because the majority of the Earth’s population, at least 85 

percent, lives between latitudes 50°N. and 50°S., it is of prime importance 

to understand potential environmental change in middle- and low-latitude 

regions; ice cores collected from selected high-mountain glaciers in temperate 

regions are valuable tools for this effort.

Although some middle-latitude, high-mountain regions of the Earth are 

glacierized, glaciers in these regions are generally considered to have unusable 

records of past environmental and climatic changes because of thawing and 

refreezing, and associated meltwater percolation. Recently, however, it has 

been shown that carefully selected middle-latitude, high-mountain glaciers 

accurately preserve isotopic and chemical records, thus providing information about climatic and environmental changes (Naftz and others, 1996, 2004; 

Cecil and Vogt, 1997; Cecil and others, 1998, 2004; Thompson, 2000, 2004, in 

press; Schuster and others, 2002, 2004; Green, Cecil, Synal, and others, 2004). 

Middle-latitude, high-mountain glaciers must have certain characteristics to 

preserve retrievable environmental records in glacier ice-cores. These include 

relatively simple ice-flow dynamics, flat to low-angle bedrock topography, 

limited redistribution of snow from wind and avalanches, minimal snowmelt 

during the summer season or minimal effects from the snow melt, and sufficiently thick glacier ice for maximum record length. To determine if a glacier 

has some of these characteristics, snow samples that fall on the glacier surface 

can be analyzed for lateral variability of chemical and particulate constituents 

across the glacier surface, caused by processes such as wind, temperature, and 

elevation gradients.

In addition to recording naturally occurring past environmental changes, 

middle-latitude, high-mountain glaciers also preserve a record of atmospheric 

input from human activities. Increased levels of many modern substances are 

archived in younger glacier ice (less than about 100 years old). Such substances 

include pollutants from refrigerants, sulfate from acid rain, mercury and other 

heavy metals from coal-burning power-plants and other industrial emissions, 

isotopic fallout from nuclear facilities including accidents such as at Chernobyl, 

Russia, in April 1986, and fallout from above-ground testing of nuclear 

weapons in the 1940s, 1950s and 1960s.5 Detonation of nuclear devices by 

the United States and Great Britain over the Pacific Ocean in the mid-1960s 

created a significant quantity of radioactive isotopes, many of which were 

incorporated or injected directly into the upper atmosphere.6 Chlorine-36 

(36Cl), tritium (3H), and cesium-137 (137Cs) with half-lives of 301,000, 12.26, 

and 30.2 years, respectively, are three isotopes that were spread throughout 

the atmosphere and deposited around the globe by means of both wet precipitation and dry deposition. During the nuclear-weapons-testing era, small 

amounts of these isotopes became trapped each year in the glacier ice, thus 

compiling an atmospheric-based record of the recent past.

5

Editors’ note: The first above-ground test of a nuclear weapon was on 16 July 1945; most above-ground 

tests of nuclear weapons ceased in 1963, after 711 tests in the atmosphere or the ocean. According to 

Greenpeace, the source of information in this footnote, “the last atmospheric nuclear weapons test occurred 

on 16 October 1980 in China.” http://archive.greenpeace.org/comms/nukes/ctbt/read9.html

6

Editors’ note: During 1962, five high-altitude atmospheric tests of nuclear weapons were conducted by 

the United States in the Pacific Ocean under Operation “Fishbowl.” Four of the tests were 10s of kilometers 

above the Earth. The  fifth test, “Starfish Prime,” detonated a 1.4  megaton nuclear device 400  km above 

Johnston Island (exoatmospheric) on 9  July 1962. The tests produced many fallout products that were 

distributed globally.
GLACIERS OF ASIA — PALEOENVIRONMENTAL RECORD F337

With the advent of ultra-sensitive analytical methods such as accelerator 

mass spectrometry (AMS) and the collaboration of expert scientists with 

diverse expertise and experience, glaciers worldwide are more accessible for 

study. The  USGS and other institutions (Thompson, in press) are currently 

conducting research on middle-latitude, high-mountain glaciers in central 

Asia and North America, applying new scientific methods to an understanding 

of human influence on global environmental processes. Sites in central 

Asia are located on the Nangpai Gosum Glacier, Nepal; Lednik Engil’chek,7

Kyrgyzstan/Kazakhstan/China; and Belukha Glacier,

8

 Russia/Kazakhstan. 

The  site in North America is on the Upper Freemont Glacier, Wyoming 

(fig.  1). The  studies described here are being carried out in collaboration 

with researchers from several domestic and foreign universities, U.S. national 

laboratories, and other federal and provincial governmental agencies. 

The scientific validity of results from analysis of glacier ice cores is 

dependent on the following precise protocols for each step: ice-core collection, storage, analysis, and interpretation (Green, Cecil, and Frape, 2004). 

Mechanical drills were utilized for ice-core collection at the central-Asia sites, 

and a thermal drill was used for ice-core collection at the site in North America. 

This difference in drilling technique is a result of the difference in elevation of the sites. The  site in North America is the lowest in elevation above 

sea level; therefore, a thermal drill was utilized to insure maximum ice-core 

recovery. The  mechanical and thermal drills were used to obtain continuous 

ice-core samples for chemical and physical analyses. At  each site, 1-m long 

ice-core sections were removed from an aluminum core barrel, quickly sealed 

in polyethylene bags, and placed in lexan core tubes by personnel wearing 

TyvekTM suits and powder-free latex gloves. The core tubes were stored at a 

maximum temperature of 0  °C in snow vaults constructed at each collection 

site. Immediately after drilling was completed, the ice-core containers were 

packed in dry ice and transported by yak, helicopter, jet aircraft, and/or freezer 

truck to cold storage in the United States. Temperature recorders were placed 

in the shipping containers to monitor any changes during the shipping phase. 

The  temperature inside the containers did not exceed 0  °C during shipping. 

The cores were equilibrated to exam-room temperature, 10 °C to 24 °C, for 24 

hours prior to processing for chemical and physical analyses.

Ice and meltwater samples from the glacier ice core were analyzed for their 

elemental and isotopic content using various laboratory methods and established protocols. After melting the ice in a controlled environment to ensure 

minimal or no contamination from ambient air, the resultant melt-water was 

prepared for analysis. 

Certain constituents present in ice cores can be used to reconstruct 

the timing and significance of past environmental and climatic events. 

For example, radionuclides are useful for establishing time lines in ice-core 

records. Direct-current electrical-conductivity measurements (ECM), in 

combination with concentrations of selected anions, are used to document 

historic volcanic events that also aid in establishing time lines. Changes in the 

isotopic composition of the oxygen atom in ice molecules can be used to reconstruct changes in air temperature and relative precipitation rates during long 

time periods. Initial research indicates that microbial populations preserved in 

glacier ice may have responded to changes in atmospheric circulation patterns, 

land use, and biogeographical conditions.

7

Although Lednik Engil’chek is the officially approved version of the glacier name, the more commonly 

known and used versions are Inyl’chek or Inilchek Glacier.

8

 U.S. Government publications require that official place-names for foreign countries be used to the 

greatest extent possible. In this section, the use of geographic place-names is based on the U.S. Board on 

Geographic Names (BGN) website, as listed on the GEOnet Names Server (GNS): http://earth-info.nga.

mil/gns/html/index.html. Names not listed on the BGN website are shown in italics.
F338 SATELLITE IMAGE ATLAS OF GLACIERS OF THE WORLD

For the research described here, the radionuclides chlorine-36 (36Cl), 

cesium-137 (137Cs), and carbon-14 (14C) were analyzed by accelerator mass 

spectrometry (AMS) methods (Currie and others, 1985; Elmore and Phillips, 

1987). Tritium  (3H) was analyzed by using electrolytic enrichment (Ostlund 

and Werner, 1962; Thatcher and others, 1977). Concentrations of chloride 

(Cl-), nitrate (NO3

-

), and sulfate (SO4

-2) are determined by ion exchange 

chromatography (Fishman and Friedman, 1989). Concentrations of sodium 

(Na+), magnesium (Mg++), and calcium (Ca++) can be determined by inductively-coupled, plasma-emission spectroscopy (Garbarino and Taylor, 1979); 

however, recent advances in ion-exchange-chromatography equipment have 

permitted the analyses of these constituents, along with ammonium (NH4

+

) 

and potassium (K+), at small environmental concentrations. Values for delta 

oxygen-18 (δ18O) were determined using a gas- or solid-source mass spectrometer (Kendall and Caldwell, 1998). The mercury (Hg) analyses presented 

here were performed by Dual Amalgamation Cold Vapor Atomic Fluorescence 

Spectrometry (USEPA Method 1631, 1999).

The electrical-conductivity measurements (ECM) were performed by 

drawing a pair of electrodes along the entire length of an ice core at a constant 

velocity (Schuster and others, 2000). For microbiological analyses, total 

numbers of microbial cells and organic matter were determined by acridineorange, direct-count microscopy at the U.S. Department of Energy’s Idaho 

National Laboratory (INL), Idaho, USA (M. Delwiche, oral commun., 2005). 

The  glacier ice cores were melted according to protocols described by Naftz 

(1993) that were modified for microbial analyses. Standard quality assurance 

and quality control protocols and guidelines were followed for all analyses 

presented in this paper.

Figure 1.—Locations of the Nangpai Gosum Glacier, Nepal; Lednik Engil’chek (Inylchek Glacier), Kyrgyzstan/Kazakhstan/China; 

Belukha Glacier, Russia/Kazakhstan; and the Upper Fremont Glacier, Wyoming, U.S.A.; and the Idaho National Laboratory, U.S.A.

Idaho National

Laboratory Upper

Fremont

Glacier

Inylchek

Glacier

Belukha Glacier

Nangpai

Gosum

Glacier

180° 150°W 120°W 90°W 60°W 30°W 0° 30°E 60°E 90°E 120°E 150°E 180°

60°N

30°N

60°N

30°N

0°

30°S

60°S

Idaho

Wyoming
GLACIERS OF ASIA — PALEOENVIRONMENTAL RECORD F339

Study Sites

Nangpai Gosum Glacier

Researchers from the University of New Hampshire are studying the 

Nangpai Gosum Glacier, located 25  km west northwest of Mount Everest in 

the Nepal Himalaya (fig. 1). It is located at lat 28°02′N., long 86°36′E. The icecore drilling site is situated at 5,700 m above mean sea level. In 1998, a 37-m 

ice core was extracted from the glacier by Cameron P. Wake of the University 

of New Hampshire and transported to the University of New Hampshire for 

analysis. At  the request of the USGS study team, radionuclide analyses were 

performed for 36Cl and 137Cs on selected sections of the ice core by Hans-Arno 

Synal at the Paul Scherrer Institut (PSI) in Villigen, Switzerland.

Lednik Engil’chek

The Lednik Engil’chek (fig.  1) is being studied in collaboration with 

researchers from several U.S. and foreign universities. It is located in the Tien 

Shan of central Asia at lat 42°10′N., long 80°15′E. It is located in parts of three 

countries: northern China, southern Kazakhstan, and eastern Kyrghyzstan. 

Altitudes exceed 6,000 m on many parts of the remote, 65-km-long glacier. Its 

maximum 300-m depth is estimated to contain 1,000 to 5,000 years of accumulation. The  elevation of our selected drilling site, 5,300  m, is high enough 

that minimal or no melting occurs (Aizen and others, 1997). In the summer of 

2000, two deep ice cores, 162 m and 165 m in length, fresh snow, snow pit, and 

crevasse-wall samples were also recovered from this site (Kreutz and others, 

2003, 2004; Green, Cecil, Synal, and others, 2004). Ice chips from the uppermost 100  m of one of the deep cores were shipped frozen to PSI where 36Cl 

analyses were performed with the AMS. The  cores provide a high-resolution 

isotopic and geochemical record that spans approximately the last 200 years. 

Belukha Glacier

The Belukha Glacier [also called the Belukha Firn Plateau] is situated at 

an elevation of about 4,000  m in the Altay mountains of southern Siberia, at 

lat 49°48'26"N., long 86°34'43"E. on the border of Kazakhstan and Russia 

(fig. 1). The glacier’s remote location makes it potentially an ideal site for environmental studies. A  team of scientists, including Americans, Russians, and 

Japanese, traveled to this remote glacier in the summer of 2001 to assess the 

feasibility of studying the glacier and extracting ice cores at the site. A SwissRussian team also worked on the glacier in 2001. Research was carried out 

from 2001 to 2003; glaciological observations were made, and both shallow 

cores and cores to bedrock were extracted and analyzed (Olivier and others, 

2003; Fujita and others, 2004). Based on tritium analysis to date, the deeper 

cores may contain as much as 3–5,000 years of climatic and environmental 

records (Aizen, oral commun., 2005) 

Upper Fremont Glacier

The Upper Fremont Glacier (fig.  1) is located at lat 43°07'52"N., long 

109°36'55"W., in the Wind River Range of Wyoming (figs. 18 and 19 on p. J360 

and J361, respectively, in Krimmel, 2002). It is a relatively large middle-latitude 

glacier with a surface area between 2.5 and 3 km2, a maximum altitude of 4,100 m 

above sea level, and an ice thickness greater than 150 m. It is located nearly 40 km 

inside the boundary of a designated wilderness area; access to the glacier requires 

a rigorous 2-day hike from the nearest road as well as the use of pack goats to 

transport scientific equipment and supplies. Continuous ice cores were collected 
F340 SATELLITE IMAGE ATLAS OF GLACIERS OF THE WORLD

from the glacier in 1991 and 1998. The  site contains an ice-core record that is 

representative of past climatic and environmental changes, and of precipitation 

falling in remote, high-altitude environments in this part of North America (Naftz, 

1993; Naftz and others 1993, 1996, 2004, 2009; Cecil and Vogt, 1997; Cecil and 

others, 1998, 1999, 2004; Schuster and others, 2000, 2004).

Selected Results and Discussion

Various constituents from archived inventories of snow-and-ice cores from 

middle-latitude glaciers have been identified. To date, ice cores from the Nangpai 

Gosum Glacier, Lednik Engil’chek, and the Belukha Glacier have only been analyzed 

for select constituents (for example, δ18O, 36Cl, and 137Cs). The  initial work 

involving researchers from the USGS began on these glaciers in 1998. For the 

Upper Fremont Glacier, the ice-core and snow dataset is the most comprehensive 

of its kind for a middle-latitude glacier in the contiguous United States, the result 

of more than a decade of work on this glacier (Naftz and Miller, 1992; Naftz, 1993; 

Naftz and others, 1993, 1996, 2004, 2009; Cecil and Vogt, 1997; Cecil and others, 

1998, 1999, 2004; Schuster and others, 2000, 2004).

Nangpai Gosum Glacier

Many radioactive isotopes were produced during the 35 years of above-ground 

nuclear-weapons testing, including 137Cs. As with 36Cl and 3H, a small amount 

of 137Cs (greater than background concentrations) became trapped in glacier ice 

during the 1940s, 1950s, and 1960s. Analysis of the 37-m ice core collected from 

the Nangpai Gosum Glacier in 1998 showed a distinct peak of anthropogenic 36Cl 

and 137Cs concentrations (fig. 2), just as for 36Cl in the Upper Fremont Glacier ice 

core (fig. 3C). It was determined that the peak nuclear-weapons-tests fallout of 36Cl 

and 137Cs occurs at a depth of about 31 m in this glacier.

Figure 2.—Chlorine-36 and cesium-137 

concentrations in the ice core collected 

from the Nangpai Gosum Glacier in 1998. 

BqL–1 (Becquerels per liter) is a measure 

of radioactivity.

CHLORINE-36 CONCENTRATION

CESIUM-137 ACTIVITY (Bq/L ) -1

1 10 100 1,000

40

30

20

10

0

CHLORINE-36, IN MILLIONS OF ATOMS

PER LITER WATER EQUIVALENT

0 0.3 0.6 0.9

CESIUM-137 ACTIVITY (Bq/L ) -1

DEPTH BELOW SURFACE OF GLACIER, IN METERS
GLACIERS OF ASIA — PALEOENVIRONMENTAL RECORD F341

Lednik Engil’chek

Kreutz and others (2004) documented the limited spatial and elevational 

dependence that exists in isotopic and major ion data from the fresh snow pack 

at the Lednik Engil’chek site. There was no apparent trend with increasing 

elevation for any of the isotopic or geochemical variables measured. These 

findings lead to the conclusion that snow formation occurs from a horizontal 

cloud base across the Lednik Engil’chek and vicinity. In  addition, based on 

the estimated accumulation rates at this site (1.6  m a–1), it was reported that 

the interannual-scale variability in the ice-core profiles is significantly greater 

than the spatial variability during individual snowfall events. The  conclusion 

from this analysis is that the majority of the down-core isotopic variability may 

be a reflection of climate changes rather than ice-flow effects or noise in the 

snow-deposition signal.

These conclusions have implications for further interpretation of the 

apparently high-resolution isotopic and geochemical records that will be developed from the two deep cores collected in 2000 (Kreutz and others, 2003). 

The implications are: (1) the high-resolution records may be used to evaluate 

the time-series, signal-to-noise ratio related to small-scale deposition processes, 

(2) given the relatively high accumulation rate at this site, it may be possible to 

reconstruct climate and environmental change on a snowfall-event basis, and 

(3) given the isotopic signals observed in the fresh snow events and the snow 

pits, it may be possible to investigate moisture sources and pathways to the 

Lednik Engil’chek through time on a subannual scale. 

For example, Green, Cecil, Synal, and others (2004) reported a high-resolution 

subannual record of nuclear-weapons-test era 36Cl from an ice core collected at 

the Lednik Engil’chek in 2000. In spite of the accumulation differences between 

the Upper Fremont Glacier and Lednik Engil’chek, 0.76  m a–1 and 1.6  m a–1, 

respectively, the peak 36Cl concentrations were remarkably similar in shape 

and magnitude. However, because of the greater accumulation rate calculated 

for the Lednik Engil’chek site, it is possible that the isotopic and geochemical 

record archived in this glacier will provide the opportunity for detailed study 

Grasshopper leg found 152 meters

below the surface of the glacier

1963 Tritium weapons-test peak

0 200 300

160

120

80

40

0

A

TRITIUM ( H), PER LITER

WATER EQUIVALENT

3

DEPTH BELOW SURFACE OF GLACIER, IN METERS

100 400 0 50 100

CHLORINE-36, IN MILLIONS

OF ATOMS PER LITER

WATER EQUIVALENT

C

-30 -20 -10

DELTA OXYGEN-18, IN PERMIL

PER LITER WATER EQUIVALENT

B

Figure 3.—Concentrations of A, Tritium (

3

H) (data from Naftz and others, 1996), 

B, delta oxygen-18 (δ18O) (data from Naftz and others, 1996) and C, chlorine-36 

(36Cl) (data from Cecil and others, 1999) in ice-core samples from the 1991 Upper 

Fremont Glacier expedition.
F342 SATELLITE IMAGE ATLAS OF GLACIERS OF THE WORLD

of environmental changes during the last 150 years. Each section of the 

Lednik Engil’chek ice core that was analyzed for 36Cl was representative of as 

little as one-third of the annual accumulation; the same volume of ice used 

for 36Cl analyses at the Upper Fremont Glacier may have been representative of more than one year’s accumulation. This high-resolution record from 

Lednik Engil’chek may aid in the study of the documented diminishing water 

resources that may be one of the results of global warming in heavily-populated 

central Asia. 

Upper Fremont Glacier

Chlorine-36 (36Cl) and 3H have been measured in a series of precipitation, 

snow, ice, and runoff samples collected in 1991 and 1998 from the Upper 

Fremont Glacier. The  ice core collected from the Upper Fremont Glacier in 

1991 shows a profile with depth for 3H and 36Cl that is expected from a minimally disturbed, temperate-glacier environment (fig. 3A, C) (Naftz and others, 

1996; Cecil and others, 1999). Tritium  (3H) and 36Cl concentrations near 

the surface of the glacier are similar to concentrations in recent precipitation 

measured in the Rocky Mountains. In deeper sections of the 1991 core, 3H and 36Cl concentrations are higher, reaching maximums at 29 m below the glacier 

surface for 3H and 32 m for 36Cl. These “markers” represent the 1963 and 1958 

peak productions from atmospheric weapons tests, respectively (Cecil and 

others, 1999). The  3H and 36Cl concentrations decrease below these depths. 

Below a depth of 40 m, 3H concentrations are essentially zero and 36Cl concentrations return to pre-nuclear weapons test levels of 106 atoms per liter (l–1) 

water equivalent or less. 

In glacier environments, any plant or animal material within the ice potentially can be dated by determining the amount of 14C in the sample (5,730 year 

half-life). Several assumptions apply when using this method of dating organic 

materials incorporated into the ice. The assumptions include: (1) the organic 

material was incorporated into the snow and ice at the actual time of death of 

the plant or organism; and (2) the initial concentration of 14C in the plant or 

animal material is well-known and is independent of time, geographic location 

of the sample, and species of plant or animal. Naftz and others (1996) dated 

a species of grasshopper contained in the ice core collected from the Upper 

Fremont Glacier in 1991. The  sample was taken from the ice core at a depth 

of 152 m below the surface (fig. 3A). The  14C content of the grasshopper was 

determined using AMS (Currie and others, 1985). The  14C age of the sample 

(A.D. 1,729 ±95 years) indicates that the grasshopper was deposited on the 

glacier surface sometime in the mid-1600s to the mid-1700s. To build confidence in this 14C age, additional grasshopper parts were extracted from a depth 

of 146  m in the ice core collected in 1998. The  14C model age for the grasshopper parts was determined to be A.D. 1,680 ±80 years. This information, 

coupled with the mercury (Hg) profile (discussed below) and the nuclear 

weapons-testing dates provided by the 3H and 36Cl profiles was instrumental in 

establishing a detailed glacial ice-core chronology and age-to-depth profiles for 

the Upper Fremont Glacier.

Major ion analyses of ice cores are essential components of ice-core 

interpretation. Changes in the concentrations of selected major ions can be 

used to identify specific events (natural or anthropogenic) that affect the 

chemistry of precipitation deposited on a glacier. For example, increases in Cl-, 

NO3

-

, and SO4

-2 concentrations can provide supporting evidence for volcanicevent horizons used as time markers to develop an ice-core chronology. Colder 

periods are typically windier and dryer thus facilitating increased deposition 

of dust layers (rich in Mg++ and Ca++ in western North America). Increased 
GLACIERS OF ASIA — PALEOENVIRONMENTAL RECORD F343

concentrations of these same constituents can be caused by anthropogenic 

influences, such as acid rain and bio-mass burning; Na+, K+, Mg++, and Ca++

can be enriched in seasonal dust layers deposited on the surface of a glacier. 

Increased concentrations of these cations not only provide a potential mechanism for development of an ice-core chronology through counting annual dust 

layers, but they also may serve as indicators of paleoclimatic change. 

Changes in the δ18O concentrations in ice cores can be used to reconstruct 

changes in air temperature from the water-vapor source region to the ice-core 

site (White and others, 1989). Values of δ18O change in relation to temperature of formation of and distance from source water, storm track, altitude, and 

evaporation. In  most ice cores, more negative δ18O values represent cooler 

air temperatures. Relative changes in air temperature at the Upper Fremont 

Glacier were reconstructed by determining the δ18O values from equally 

spaced samples along the entire length of the 1991 ice core (fig. 3B). Between 

the depths of 102  m and 150  m, numerous high-amplitude oscillations in 

the δ18O values were detected. The  mean δ18O value for this depth range 

abruptly shifted to more negative values, corresponding to the approximate 

time interval from the mid-A.D. 1700s to mid-A.D. 1800s. This period of time 

coincides with the latter part of the “Little Ice Age” (LIA) (Naftz and others, 

1996, 2004).

Atmospheric circulation can deposit microbial cells on snowfields and 

glacier-ice surfaces. Some of these windborne organisms may survive in a 

preserved state for extended times, and some types may colonize microhabitats 

within the accumulated snow layers. It is possible that preserved microbial ice 

populations contain a record of atmospheric circulation patterns, land use, and 

biogeographical conditions upwind from deposition sites. Upwind sources of 

heavy metals from mining and smelting operations may have an influence on 

the microbial communities that can survive and flourish at higher altitudes; 

where heavy metal fallout is significant at the glacier’s surface, metal-reducing 

microbial types may prevail. In  addition, because of the intensity of highaltitude sunlight (for example, more intense UV radiation), radiation-tolerant 

species may dominate in these middle-latitude glacier sites and may act as 

monitors to changes in ultraviolet radiation caused by thinning of the ozone 

layer. Scientists at the INL have begun investigations on microbial organisms 

found in ice cores from our study sites. The  ice samples, which have been in 

frozen storage since collection, are being used to determine total biomass 

content and to estimate viability of englacier populations.

The total number of microbial cells and organic matter from nine ice-core 

samples collected from the Upper Fremont Glacier have been determined 

(M. Delwiche, personal commun., 2005). After melting, 0.1  milliliter (mL) 

of core interior meltwater was immediately plated onto rich (R2A) and lean 

(1 percent PTYG) types of standard solid medium for growth of heterotrophic 

microorganisms (Gerhardt and others, 1994). Also, 5  mL of each inner core 

and of each “rinse” from the core exterior, and 10  mL of filtered DI water as 

a negative control were stained with 0.01 percent acridine orange fluorescent 

dye. Standard microscopy methods were used for preparation and counting 

of stained cells on black polycarbonate membrane filters (Hobbie and others, 

1977). In  all, 8 negative controls, 18 core, and 9 rinse slides were counted. 

In  addition to analyses performed immediately after melting, meltwater was 

stored and retested after time periods of 12 days and 2  months to test the 

effects of storage on culturability of contained microbial populations. All plates 

and meltwater were stored at 12 °C.

Significant numbers of “cell-like” objects were observed in most ice 

samples. Total numbers were as high as 2.1×105 cells mL–1 of melted ice with 

numerous discernable morphologies; clumps of brightly fluorescing rods 

associated with inorganic particles were common in at least one third of the 
F344 SATELLITE IMAGE ATLAS OF GLACIERS OF THE WORLD

samples and appeared to be more numerous in the shallower sections of the 

ice core. There was no perceptible correlation between depth in the core and 

microbial numbers. Samples also contained numerous arthropod parts and 

large cellular objects believed to be unicellular algae. The results are consistent 

with reports in the literature from polar ice cores (Priscu and others, 1998; 

Karl and others, 1999) and appear to correspond with expectations of subsurface microbial communities (Pedersen, 1993; Phelps and others, 1994).

Direct current electrical conductivity measurements (ECMs), used to 

determine the acidity of ice cores, can be used to assist in the determination of 

ice-core chronology. ECM application includes the identification of seasonal/

summer dust layers for layer counting and the identification of volcanic events 

to be used as time-line markers. Schuster and others (2000, 2004) used the 

1991 Upper Fremont Glacier ice core to produce an ECM log (fig. 4). Together 

with major ion analyses, 3H, 36Cl, and 14C data, two of the largest explosive 

volcanic eruptions during the last 10,000 years (fig.  5) (Krakatau, Indonesia, 

on 27 August 1883; and Tambora, Sumbawa, Indonesia, on 10-11 April 1815) 

(Simkin and Siebert, 1994) were identified in the ECM signal produced from 

REPORTED YEAR

AGE-DEPTH PROFILE

1958 Cl peak 36

1883 Krakatau

(1885)

1815 Tambora

(1811)

1963 H peak 3

14C date,

1729 +/- 95 years

1600 1700 1800 1900 2000

0

DEPTH, IN METERS

20

40

60

80

100

120

140

160

YEARS (A.D.)

Figure 4.—Refined age-to-depth profile for the 1991 

Upper Fremont Glacier ice core. Modified from Schuster and others (2004). Boxes are the reported year for 

historic events that are preserved in the ice.
GLACIERS OF ASIA — PALEOENVIRONMENTAL RECORD F345

the Upper Fremont Glacier ice core along with more than 30 lesser volcanic 

eruptions. The  refined ice-core chronology indicated that the transition 

from the LIA that was preserved in the ice core occurred around A.D. 1845. 

Additionally, the transition was abrupt, probably fewer than 10 years, in the 

alpine regions of the Wind River Range, Wyoming U.S.A. (Naftz and others, 

1996, 2004; Schuster and others, 2000, 2004).

Applications

Future information obtained from the study of these glaciers will add 

significantly to our understanding of atmospheric processes and possibly 

provide a linkage to other middle-latitude ice cores that record global environmental changes. Middle-latitude glacier research can potentially be applied to 

numerous climatic and environmental studies worldwide. Applications of the 

results from the Upper Fremont Glacier study site are discussed below and 

include reconstructing paleoclimatic records on a global scale and documentation of environmental mercury concentrations during the past 270 years. 

Similar interpretations and applications of the datasets from the central Asia 

glacier sites are underway.

Paleoclimatic Records

In addition to the documentation of an abrupt end to the LIA, Naftz 

and others (2004) developed a transfer function for estimating the change 

in ambient air temperature over time using the δ18O profile from the Upper 

Fremont Glacier ice core and on-site snow-depth sensor data. The  transfer 

1700 2000

40

35

30

25

20

15

10

5

0

YEARS (A.D.)

Mount St. Helens, WA

(1980)

World War II

manufacturing

(1940-45)

Krakatau, Indonesia

(1883)

Tambora, Indonesia

(1815)

1750 1800 1850 1900 1950

Pre-Industrialization

Gold Rush

(1850-84)

TOTAL MERCURY, IN NANOGRAMS PER LITER

Industrialization (1880-present)

Figure 5.—Profile of historic concentrations of mercury (Hg) measured 

in selected ice-core sections from the Upper Fremont Glacier. Modified 

from Schuster and others (2000).
F346 SATELLITE IMAGE ATLAS OF GLACIERS OF THE WORLD

function was then used to reconstruct trends in average air temperature during 

the last 300 years. Based on this transfer function, an increase in air temperature of about +2 °C has occurred at the Upper Fremont Glacier site from the 

end of the LIA to the present, a relatively rapid air-temperature change.

 A consequence of this apparent rapid change in climate was documented 

in the form of a glacier-outburst flood event (jökulhlaup) (GLOF) that 

occurred at Grasshopper Glacier in September 2003, 14 km north of the Upper 

Fremont Glacier (Naftz and others, 2009). A  12-hectare lake at the head of 

Grasshopper Glacier instantaneously burst releasing approximately 3.2×106 m3

of water, with an associated maximum stream flow of about 35.7  m3 s–1 on 

Dinwoody Creek downstream from the lake. Annual peak stream flows on this 

creek generally occur during middle- to late-June as a result of snowmelt runoff 

and average 26.7  m3 s–1 based on 38 years of record. As a result of the jökulhlaup, there may be an increased flood risk in the upper reaches of the drainage 

basin because of aggradation of the stream channels. Continued warming and 

melting of glaciers in the Wind River Range may result in future and perhaps 

more frequent jökulhlaups. 

Environmental Concentrations of Mercury

A record of atmospheric mercury (Hg) deposition has been documented 

in ice from the Upper Fremont Glacier (Schuster and others, 2000, 2004). 

Although some polar ice-core studies have provided a limited record of past Hg 

deposition, polar cores are, at best, proxy indicators of historic Hg deposition 

in the middle-latitudes, where 80 to 90 percent of the Earth’s human population resides. Two ice cores extracted from the Upper Fremont Glacier in 1991 

and 1998 (each totaling 160  meters in length) provided a chronology and 

paleoenvironmental framework that were essential to the interpretation of the 

Hg deposition record. A total of 97 ice core samples were selected using lowlevel processing methods and were analyzed to reconstruct a 270-year atmospheric Hg deposition record for this part of North America. Trends in Hg 

concentration measured in ice from the Upper Fremont Glacier record major 

releases to the atmosphere of both natural and anthropogenic Hg from regional 

and global sources (fig. 5). 

The record shows that Hg concentrations are significantly, but for 

relatively short-time intervals, elevated during periods corresponding to 

explosive volcanic eruptions, an indication that natural volcanic events “punctuate” the record. Anthropogenic activities, such as industrialization (globalscale), gold mining, and wartime manufacturing (regional scale), indicate 

that chronic levels of elevated Hg emissions have a greater influence on the 

historical atmospheric deposition record from the Upper Fremont Glacier. 

In  terms of total Hg deposition recorded by the Upper Fremont Glacier 

during approximately the past 270 years: anthropogenic inputs appeared to 

contribute 52 percent; volcanic events contributed 6 percent; and pre-industrialization (or background level) accounted for 42 percent of the total input. 

More significantly, during the last 100 years, anthropogenic sources contributed 70 percent of the total Hg input. A declining trend in Hg concentrations 

is obvious during the past 20 years. Declining Hg concentrations in the upper 

section of the ice-core profile (fig.  5) are corroborated by recent declining 

trends observed in sediment cores (Engstrom and Swain, 1997; Norton 

and others, 1997; Bindler and others, 2001). This is also verified by similar 

concentrations in Upper Fremont Glacier snow samples collected in 1999 

(P.F. Schuster, written commun., 2005). This decline may be in response to 

the United States Clean Air Act of 1970.
GLACIERS OF ASIA — PALEOENVIRONMENTAL RECORD F347

Summary

Precipitation, snow, ice, and runoff samples from four glaciers, widely 

distributed geographically in the middle latitudes of the Northern Hemisphere, 

are currently being analyzed utilizing a wide array of geochemical, physical, and 

isotopic-measurement techniques. Radioactive fallout from nuclear-weapons 

testing in the 1940s, 1950s, and 1960s, large explosive volcanic eruptions with 

regional and global fallout, and radiocarbon dating of bio-organic material, 

have been identified as time markers in selected ice cores from the Nangpai 

Gosum Glacier, Nepal; Lednik Engil’chek, Kazakhstan/Kyrghyzstan/China; 

Belukha Glacier, Kazakhstan/Russia; and Upper Fremont Glacier, Wyoming, 

U.S.A., ice cores. These time markers, in conjunction with other types of 

analyses such as the delta oxygen-18 (δ18O) and mercury (Hg), aid in refining 

the chronology of the ice cores. The  reconstruction of ice-core chronologies 

provides critical support to other areas of research being undertaken. Linking 

data from middle-latitude glaciers around the world will aid in the reconstruction of paleoclimatic and paleoenvironmental records on regional and 

global scales.
F348 SATELLITE IMAGE ATLAS OF GLACIERS OF THE WORLD

References Cited

Aizen, V.B., Aizen, E.M., Dozier, J., Melack, J.M., Sexton, D.D., and 

Nesterov, V.N., 1997, Glacial regime of the highest Tien Shan 

mountain, Pobeda-Khan Tengry massif: Journal of Glaciology, 

v. 43, no. 145, p. 503–512.

Alley, R.B., 2000, The two-mile time machine—Ice cores, abrupt 

climate change, and our future: Princeton, N.J., Princeton 

University Press, 229 p.

Bindler, R., Renberg, I., Appleby, P.G., Anderson, N.J., and Rose, 

N.L., 2001, Mercury accumulation rates and spatial patterns in 

lake sediments from West Greenland — A coast to ice margin 

transect: Environmental Science and Technology, v. 35, no. 9, 

p. 1736–1741.

Cecil, L.D., Green, J.R., and Thompson, L.G., eds., 2004, Earth 

paleoenvironments—Records preserved in mid- and lowlatitude glaciers: Dordrecht, Kluwer Academic Publishers [now 

Springer], 250 p.

Cecil, L.D., Green, J.R., Vogt, S., Frape, S.K., Davis, S.N., Cottrell, 

G.L., and Sharma, P., 1999, Chlorine-36 in water, snow, and 

mid-latitude glacial ice of North America — Meteoric and 

weapons-tests production in the vicinity of the Idaho National 

Engineering and Environmental Laboratory, Idaho: U.S. 

Geological Survey Water-Resources Investigations Report 

99–4037, 27 p.

Cecil, L.D., Green J.R., Vogt, S., Michel, R.L., and Cottrell, G., 

1998, Isotopic composition of ice cores and meltwater from 

Upper-Fremont Glacier, and Galena Creek rock glacier, 

Wyoming: Geografiska Annaler, v. 80, nos. 3–4, p. 287–292.

Cecil, L.D., and Vogt, S., 1997, Identification of bomb-produced 

chlorine-36 in mid-latitude glacial ice of North America: 

Nuclear Instruments and Methods in Physics Research, v. B123, 

nos. 1–4, p. 287–289.

Currie, L.A., Klouda, G.A., Elmore, D., and Gove, H.E., 1985, 

Radiocarbon dating of microgram samples — Accelerator mass 

spectrometry and electromagnetic isotope separation: Nuclear 

Instruments and Methods in Physics Research, v.  B12, no.  3, 

p. 396–401.

Elmore, D., and Phillips, F.M., 1987, Accelerator mass spectrometry for measurement of long-lived radioisotopes: Science, 

v. 236, no. 4801, p. 543–550.

Engstrom, D.R., and Swain, E.B., 1997, Recent declines in atmospheric mercury deposition in the upper midwest: Environmental Science and Technology, v. 31, no. 4, p. 960–967.

EPICA, 2004, Eight glacial cycles from an Antarctic ice core: 

Nature, v. 429, no. 6992, p. 623–628.

Fishman, M.J., and Friedman, L.C., 1989, Methods for determination of inorganic substances in water and fluvial sediments: U.S. 

Geological Survey Techniques of Water-Resources Investigations, 3d ed., book 5, chap. A1, 709 p.

Fujita, K., Takeuchi, N., Aizen, V., and Nikitin, S., 2004, Glaciological observations on the plateau of Belukha Glacier in the Altai 

Mountains, Russia from 2001 to 2003: Bulletin of Glaciological 

Research, no. 21, p. 57–64.

Garbarino, J.R., and Taylor, H.E., 1979, An inductive-coupled 

plasma atomic emission spectrometric method for routine water 

quality testing: Applied Spectroscopy, v. 33, no. 3, p. 220–225.

Gerhardt, P., and others, eds., 1994, Methods for general and 

molecular bacteriology: Washington, D.C., American Society 

for Microbiology, 791 p.

Green, J.R., Cecil, L.D., and Frape, S.K., 2004, Methods of mid- and 

low-latitude glacial record collection, analysis, and interpretation, in Cecil, L.D., Green, J.R., and Thompson, L.G., eds., Earth 

paleoenvironments — Records preserved in mid- and lowlatitude glaciers: Dordrecht, Kluwer Academic Publishers [now 

Springer], p. 17–36.

Green, J.R., Cecil, L.D., Synal, H.-A., Santos, J., Kreutz, K.J., and 

Wake, C.P., 2004, A high resolution record of chlorine-36 

nuclear-weapons-tests fallout from central Asia: Nuclear 

Instruments and Methods in Physics Research, v.  B223–224, 

p. 854–857.

Hobie, J.E., Daley, R.J., and Jasper, S., 1977, Use of nuclepore filters 

for counting bacteria by fluorescence microscopy: Applied and 

Environmental Microbiology, v. 33, no. 5, p. 1225–1228.

Karl, D.M., Bird, D.F., Bjorkman, K., Houlihan, T., Shackelford, R., 

and Tupas L., 1999, Microorganisms in the accreted ice of Lake 

Vostok, Antarctica: Science, v. 286, no. 5447, p. 2144–2147.

Kendall, C., and Caldwell, E.A., 1998, Fundamentals of isotope 

geochemistry, in Kendall, C., and McDonnell, J.J., eds., Isotope 

tracers in catchment hydrology: Amsterdam, Elsevier Science, 

p. 51–86.

Kreutz, K.J., Wake, C.P., Aizen, V.B., Cecil, L.D., Green, J.R., and 

Synal, H-A., 2004, Event to decadal-scale glaciochemical variability on the Inilchek Glacier, central Tien Shan, in Cecil, L.D., 

Green, J.R., and Thompson, L.G., eds., Earth Paleoenvironments — Records preserved in mid- and low-latitude glaciers: 

Dordrecht, Kluwer Academic Publishers [now Springer], 

p. 61–79.

Kreutz, K.J., Wake, C.P., Aizen, V.B., Cecil, L.D., and Synal, 

H.-A., 2003, Seasonal deuterium excess in a Tien Shan ice 

core — Influence of moisture transport and recycling in 

Central Asia: Geophysical Research Letters, v. 30, no. 18, 1922, 

doi:10.1029/2003 GLO 17896.

Krimmel, R.M., 2002, Glaciers of the western United States, with 

a section on Glacier retreat in Glacier National Park, Montana 

by Key, C.H., Fagre, D.B., and Menicke, R.K., Glaciers of the 

conterminous United States ( J–2), in Williams, R.S., Jr., and 

Ferrigno, J.G., eds., Satellite image atlas of glacier of the world: 

U.S. Geological Survey Professional Paper 1386–J (North 

America), p. J329–J381.

Naftz, D.L., 1993, Ice-core records of the chemical quality of atmospheric deposition and climate from mid-latitude glaciers, Wind 

River Range, Wyoming: Golden, Colorado School of Mines, 

Ph.D. dissertation, 204 p.

Naftz, D.L., Klusman, R.W., Michel, R.L, Schuster, P.F., Reddy, 

M.M., and others, 1996, Little Ice Age evidence from a southcentral North American ice core, U.S.A.: Arctic and Alpine 

Research, v. 28, no. 1, p. 35–41.

Naftz, D.L., Michel, R.L., and Miller, K.A., 1993, Isotopic indicators of climate in ice cores, Wind River Range, Wyoming, in 

Swart, P.K., Lohmann, K.C., McKenzie, J., and Savin, S., eds., 

Climate change in continental isotopic records: Geophysical 

Monograph 78, p. 55–66.

Naftz, D.L., and Miller, K.A., 1992, USGS collects ice core through 

alpine glacier: EOS (Transactions, American Geophysical 

Union), v. 73, no. 3, p. 27.

Naftz, D.L., Oswald, L., Schuster, P.F., and Miller, K., 2009, 

Ice-core and flood-flow evidence of rapid climate change, 

Fitzpatrick Wilderness Area, Wind River Range, Wyoming, 
GLACIERS OF ASIA — PALEOENVIRONMENTAL RECORD F349

in Wagner, F.H., ed., Climate warming in western North 

America—Evidence and environmental effects: Salt Lake City, 

Utah, University of Utah Press, p. 35–48.

Naftz, D.L., Susong, D.D., Cecil, L.D., and Schuster, P.F., 2004, 

Variations between 18O in recently deposited snow and on-site 

air temperature, Upper Fremont Glacier, Wyoming, in Cecil, 

L.D., Green, J.R., and Thompson, L.G., eds., Earth paleoenvironments—Records preserved in mid and low latitude glaciers: 

Dordrecht, Kluwer Academic Publishers [now Springer], 

p. 217–234.

Norton, S.A., Evans, G.C., and Kahl, J.S., 1997, Comparison of Hg 

and Pb fluxes to hummocks and hollows of ombrotrophic Big 

Heath bog and to nearby Sargent Mountain Pond, Maine, USA: 

Water, Air, and Soil Pollution, v. 100, no. 3–4, p. 271–286.

Olivier, Susanne, and others, 2003, Glaciochemical investigation of an ice core from Belukha Glacier, Siberian 

Altai: Geophysical Research Letters, v.  30, no.  19, 2019 p., 

doi:10.1029/2003GL018290.

Ostlund, H.G., and Werner, E., 1962, The electrolytic enrichment 

of tritium and deuterium for natural tritium measurements, in 

Tritium in the physical and biological sciences, Proceedings 

of the symposium on the detection and use of tritium in the 

physical and biological sciences: Vienna, International Atomic 

Energy Agency, v. 1, p. 95–104.

Pedersen, K., 1993, The deep subterranean biosphere: EarthScience Reviews, v. 34, no. 4, p. 243–260.

Phelps, T.J., Murphy, E.M., Pfiffner, S.M., and White, D.C., 1994, 

Comparison between geochemical and biological estimates of 

subsurface microbial activities: Microbial Ecology, v. 28, no. 3, 

p. 335–349.

Priscu, J.C., Fritsen, C.H., Adams, E.E., Giovannoni, S.J., Paerl, 

H.W., and others, 1998, Perennial Antarctic lake ice — An oasis 

for life in a polar desert: Science, v. 280, no. 5372, p. 2095–2098.

Schuster, P.F., Naftz, D.L., Cecil, L.D., and Green, J.R., 2004, 

Evidence of abrupt climate change and the development of an 

historic mercury deposition record using chronological refinement of ice cores at Upper Fremont Glacier, in Cecil, L.D., 

Green, J.R., and Thompson, L.G., eds., Earth paleoenvironments — Records preserved in mid- and low-latitude glaciers: 

Dordrecht, Kluwer Academic Publishers [now Springer], 

p. 181–216.

Schuster, P.F., White, D.E., Naftz, D.L., and Cecil, L.D., 2000, 

Chronological refinement of an ice core record at Upper 

Fremont Glacier in south central North America: Journal of 

Geophysical Research, v. 105, no. D4, p. 4657–4666.

Simkin, Tom, and Siebert, Lee, 1994, Volcanoes of the world 

— A regional directory, gazetteer, and chronology of volcanism during the last 10,000 years, 2d ed.: Tucson, Arizona, 

Geoscience Press, 349 p.

Thatcher, L.L., Janzer V.J., and Edwards, K.W., 1977, Methods for 

determination of radioactive substances in water and fluvial sediments: U.S. Geological Survey Techniques of Water-Resources 

Investigations, book 5, chap. A5, 95 p.

Thompson, L.G., 2000, Ice-core evidence for climate change in 

the Tropics—Implications for our future: Quaternary Science 

Reviews, v. 19, no. 1–5, p. 19–35.

Thompson, L.G., 2004, High altitude, mid- and low-latitude ice 

core records — Implications for our future, in Cecil, L.D., Green, 

J.R., and Thompson, L.G., eds., Earth paleoenvironments — 

Records preserved in mid- and low-latitude glaciers: Dordrecht, 

Kluwer Academic Publishers [now Springer], p. 3–15.

Thompson, L.G., in press, Ice cores, high-mountain glaciers, and 

climate, in Williams, R.S., Jr., and Ferrigno, J.G., eds., Satellite 

image atlas of glaciers of the world: U.S. Geological Survey 

Professional Paper 1386–A (State of the Earth’s cryosphere at 

the beginning of the 21st century: Glaciers, global snow cover, 

floating ice, and permafrost and periglacial environments).

U.S. Environmental Protection Agency, 1999, Method 1631-Revision B — Mercury in water by oxidation, purge and trap, and 

cold vapor atomic fluorescence spectrometry: Washington, 

D.C., U.S. Environmental Protection Agency, Office of Water, 

EPA 821-R-99-005, 40 p.

White, J.W.C., Brimblecombe, P., Brühl, C., Davidson, C.I., 

Delmas, R.J., and others, 1989, How do glaciers record environmental processes and preserve information?, in Oeschger, 

H., and Langway, C.C., Jr., eds., The environmental record in 

glaciers and ice sheets: Chichester, John Wiley, p. 85–98.