Upper Fremont Glacier is in the

Fitzpatrick Wilderness The Fitzpatrick Wilderness is located in Shoshone National Forest in the U.S. state of Wyoming. The wilderness was originally known as the Glacier Primitive Area, but was redesignated a wilderness in 1976. Overview U.S. Wilderness Areas do not all ...

Shoshone National Forest Shoshone National Forest ( ) is the first federally protected National Forest in the United States and covers nearly in the state of Wyoming. Originally a part of the Yellowstone Timberland Reserve, the forest is managed by the United States ...

in the U.S. state of

Wyoming Wyoming () is a state in the Mountain West subregion of the Western United States. It is bordered by Montana to the north and northwest, South Dakota and Nebraska to the east, Idaho to the west, Utah to the southwest, and Colorado to t ...

. This

Wind River Range The Wind River Range (or "Winds" for short) is a mountain range of the Rocky Mountains in western Wyoming in the United States. The range runs roughly NW–SE for approximately . The Continental Divide follows the crest of the range and in ...

alpine glacier A glacier (; ) is a persistent body of dense ice that is constantly moving under its own weight. A glacier forms where the accumulation of snow exceeds its ablation over many years, often centuries. It acquires distinguishing features, such as ...

is associated with the largest grouping of glaciers in the U.S.

Rocky Mountain The Rocky Mountains, also known as the Rockies, are a major mountain range and the largest mountain system in North America. The Rocky Mountains stretch in straight-line distance from the northernmost part of western Canada, to New Mexico in ...

s and lies on the north slope of Fremont Peak, the third tallest mountain in Wyoming. Upper Fremont Glacier is at an average altitude of and is one of the highest altitude glaciers in the American Rockies.

Ice core An ice core is a core sample that is typically removed from an ice sheet or a high mountain glacier. Since the ice forms from the incremental buildup of annual layers of snow, lower layers are older than upper ones, and an ice core contains ...

samples were taken from Upper Fremont Glacier in 1990-1991. These ice cores were analyzed for climatic changes as well as alterations of atmospheric chemicals. In 1998 an unbroken ice core sample of was taken from the glacier and subsequent analysis of the ice showed an abrupt change in the oxygen isotope ratio

oxygen-18 Oxygen-18 (, Ω) is a natural, stable isotope of oxygen and one of the environmental isotopes. is an important precursor for the production of fluorodeoxyglucose (FDG) used in positron emission tomography (PET). Generally, in the radiopharmaceu ...

to oxygen-16 in conjunction with what is widely regarded as the end of the

Little Ice Age The Little Ice Age (LIA) was a period of regional cooling, particularly pronounced in the North Atlantic region. It was not a true ice age of global extent. The term was introduced into scientific literature by François E. Matthes in 1939. Ma ...

, a period of cooler global temperatures between the years 1550 and 1850. A linkage was established with a similar ice core study which had been undertaken on the

Quelccaya Ice Cap The Quelccaya Ice Cap (also known as Quenamari Ice Cap) is the second largest glaciated area in the tropics, after Coropuna. Located in the Cordillera Oriental section of the Andes mountains in Peru, the cap covers an area of with ice up t ...

Peru , image_flag = Flag of Peru.svg , image_coat = Escudo nacional del Perú.svg , other_symbol = Great Seal of the State , other_symbol_type = National seal , national_motto = "Firm and Happy f ...

, which also demonstrated the same changes in the oxygen isotope ratio during the same period. The climatic implications from the ice cores taken from both sites support evidence of a sudden global climate change during the mid 19th century. Ice cores from the glacier also showed increased levels of

Tritium Tritium ( or , ) or hydrogen-3 (symbol T or H) is a rare and radioactive isotope of hydrogen with half-life about 12 years. The nucleus of tritium (t, sometimes called a ''triton'') contains one proton and two neutrons, whereas the nucleus of ...

(³H) and

chlorine Chlorine is a chemical element with the symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the periodic table and its properties are mostly intermediate between them. Chlorine i ...

-36 around the year 1963, which coincides with the peak period of above ground

nuclear testing Nuclear weapons tests are experiments carried out to determine nuclear weapons' effectiveness, yield, and explosive capability. Testing nuclear weapons offers practical information about how the weapons function, how detonations are affected by ...

. The same ice cores were also tested for mercury deposition from natural and human-induced activities. This is the first known instance in which ice cores have been used to determine mercury deposition from a mid-latitude glacier in

North America North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and th ...

, as all previous studies have been derived from other sources. The majority of mercury deposition is by way of the atmosphere and sources of the element may be from

volcanic A volcano is a rupture in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface. On Earth, volcanoes are most often found where tectonic plat ...

activity or from industrialization, but volcanoes are believed to contribute a small proportion of the mercury. The ice core samples from the Upper Fremont Glacier indicated that levels of mercury increased dramatically during the

industrial revolution The Industrial Revolution was the transition to new manufacturing processes in Great Britain, continental Europe, and the United States, that occurred during the period from around 1760 to about 1820–1840. This transition included going f ...

and have decreased significantly since the mid-1980s. It is believed that the decrease in mercury deposition since the 1980s coincides with the passage of the Clean Air Act.

References

See also