Glaciers cover nearly half of Kenai Fjords National Park, serving an important role in ecosystem dynamics and attracting hundreds of thousands of visitors to the park each year. Glacial melt is important to park managers as it impacts visitor experience, infrastructure (e.g., trails and roads), and downstream habitats. Glacier mass balance is the annual gain and loss of ice calculated as a sum of seasonal measurements of accumulation and ablation (the loss of ice through melt, sublimation, and calving). Long-term glacier mass balance studies provide an established method for monitoring the status of glaciers and can be used to estimate rates of change and to predict thresholds and trigger points that could result in major changes to glacier extent and downstream systems. This report summarizes field efforts and results of eight years of stake-based mass balance measurements on the northern Harding Icefield, for water years 2010–2017. From 2010–2017, seasonal measurements were conducted at six sites on the northern Harding Icefield to quantify seasonal and annual point mass balances along an elevation gradient from 532 m to 1290 m. Cumulative winter mass balances range from 0.47 to 1.81 meters water equivalent (m w.e.) at the lowest site (532 m a.s.l), and 2.11 m w.e. to 3.43 m w.e. at the highest site with continuous annual data (1230 m a.s.l). Summer mass balances range from −5.85 m w.e. to −8.35 m w.e. at the lowest site (532 m a.s.l.) and −0.54 to −2.24 at the site located

or 210 gigatons per yr. The mass balance, or difference between accumulation and ablation (melting and sublimation), of a glacier is crucial to its survival The retreat of glaciers since 1850 is a well-documented effect of climate change. The retreat of mountain glaciers provides evidence for the rise in global temperatures since the late 19th century. Examples include mountain glaciers in western North America, Asia, the Alps in central Europe, and tropical and subtropical regions of South America and Africa. Since glacial mass is affected by long-te The mass balance, or difference between accumulation and ablation (melting and sublimation), of a glacier is crucial to its survival. Climate change may cause variations in both temperature and snowfall, resulting in changes in mass balance. A glacier with a sustained negative balance loses equilibrium and retreats. A sustained positive balance is also out of equilibrium and will advance to reestablish equilibrium. Currently, nearly all glaciers have a negative mass balance and are retreating. Glacier retreat results in the loss of the low-elevation region of the glacier. Since higher elevations are cooler, the disappearance of the lowest portion decreases overall ablation, thereby increasing mass balance and potentially reestablishing equilibrium. If the mass balance of a significant portion of the accumulation zone of the glacier is negative, it is in disequilibrium with the climate and will melt away without a colder climate and/or an increase in frozen precipitation. For example, Easton Glacier in Washington state, U.S. will likely shrink to half its size but at a slowing rate of reduction and stabilize at that size despite the warmer temperature over a few decades. However, the Grinnell Glacier in Montana, U.S. will shrink at an increasing rate until it disappears. The difference is that the upper section of Easton Glacier remains healthy and snow-covered, while even the upper section of the Grinnell Glacier is But the current glacier retreat is accelerated by global warming due to human-caused greenhouse gas emissions. Human activities since the start of the industrial era have increased the concentration of carbon dioxide and other heat-trapping greenhouse gases in the air, causing current global warming. Human influence is the principal driver of changes to the cryosphere, of which glaciers are a part. The glacier mass balance is the key determinant of the health of a glacier. If the amount of frozen precipitation in the accumulation zone exceeds the quantity of glacial ice the ablation zone lost due to melting, a glacier will advance. If the accumulation is less than the ablation, the glacier will retreat. Glaciers in retreat will have negative mass balances. They will eventually disappear if they do not reach an equilibrium between accumulation and ablation. Mid-latitude mountain ranges show some of the largest proportionate glacial losses. Examples of such mountain ranges are the Himalayas in Asia, the Rocky Mountains and the Cascade Range in North America, the Alps in Europe, the Southern Alps in New Zealand, the southern Andes in South America, as well as isolated tropical summits such as Mount Kilimanjaro in Africa. The continued demise of glacier ice will result in a short-term increase, followed by a long-term decrease in glacial melt water flowing into rivers and streams. === Northern hemisphere – North America === North American glaciers are primarily located along the spine of the Rocky Mountains in the United States and Canada, and the Pacific Coast Ranges extending from northern California to Alaska. While Greenland is geologically associated with North America, it is also a part of the Arctic region. Both are more than 2.5 km (1.6 mi) shorter than a century ago. These large, rapidly flowing glaciers situated on steep slopes have been very reactive to small mass-balance changes. A few years of conditions favorable to glacier advance, such as more westerly winds and a resulting increase in snowfall, are rapidly echoed in a corresponding advance, followed by equally rapid retreat when those favorable conditions end. == Polar regions == Despite their proximity and importance to human populations, the mountain and valley glaciers of tropical and mid-latitude glaciers amount to only a small fraction of glacial ice on the Earth. About 99 percent of all freshwater ice is in the great ice sheets of polar and subpolar Antarctica and Greenland. These continuous continental-scale ice sheets, 3 km (1.9 mi) or more in thickness, cap much of the polar and subpolar land masses. Like rivers flowing from an enormous lake, numerous outlet glaciers transport ice from the margins of the ice sheet to the ocean. === North America === ==== Greenland ==== In Greenland, glacier retreat has been observed in outlet glaciers, resulting in an increase of the ice flow rate and destabilization of the mass balance of the ice sheet that is their source. Mass-balance measurements of Iceland's glaciers show alternating positive and negative mass balance of glaciers during the period 1987–1995, but the mass balance has been predominantly negative since. On Hofsjökull ice cap, mass balance has been negative each year from 1995 to 2005. Most of the Icelandic glaciers retreated rapidly during the warm decades from 1930 to 1960, slowing down as the climate cooled during the following decade, and started to advance after 1970. The rate of advance peaked in the 1980s, after which it slowed down until about 1990. The continent-wide average surface temperature trend of Antarctica is positive and significant at >0.05 °C/decade since 1957. The Antarctic sheet is divided by the Transantarctic Mountains into two unequal sections known as the East Antarctic ice sheet (EAIS) and the smaller West Antarctic Ice Sheet (WAIS). The EAIS rests on a major land mass but the bed of the WAIS is, in places, more than 2,500 metres below sea level. It would be seabed if

A glacier's mass balance or surface mass balance (SMB)—the difference between accumulation and ablation (sublimation and melting)—is crucial to the survival A glacier's mass balance or surface mass balance (SMB)—the difference between accumulation and ablation (sublimation and melting)—is crucial to the survival of the glacier. Climate change may cause variations in both temperature and snowfall, causing changes in the surface mass balance. Changes in mass balance control a glacier's long-term behavior and are the most sensitive climate indicators on A glacier's mass balance or surface mass balance (SMB)—the difference between accumulation and ablation (sublimation and melting)—is crucial to the survival of the glacier. Climate change may cause variations in both temperature and snowfall, causing changes in the surface mass balance. Changes in mass balance control a glacier's long-term behavior and are the most sensitive climate indicators on a glacier. From 1980 to 2012, the mean cumulative mass loss of glaciers reporting mass balance to the World Glacier Monitoring Service is −16 m. This includes 23 consecutive years of negative mass balances. A glacier with… A glacier's mass balance or surface mass balance (SMB)—the difference between accumulation and ablation (sublimation and melting)—is crucial to the survival of the glacier. Climate change may cause variations in both temperature and snowfall, causing changes in the surface mass balance. Changes in mass balance control a glacier's long-term behavior and are the most sensitive climate indicators on a glacier. From 1980 to 2012, the mean cumulative mass loss of glaciers reporting mass balance to the World Glacier Monitoring Service is −16 m. This includes 23 consecutive years of negative mass balances. A glacier with a sustained negative balance is out of equilibrium and will retreat, while one with a sustained positive balance is out of equilibrium and will advance. Glacier retreat results in the loss of the low elevation region of the glacier. Since higher elevations are cooler than lower ones, the disappearance of the lowest portion of the glacier reduces overall ablation, thereby increasing mass balance and potentially reestablishing equilibrium. However, if the mass balance of a significant portion of the accumulation zone of the glacier is negative, it is in disequilibrium with the local climate. Such a glacier will melt away with a continuation of this local climate. The key symptom of a glacier in disequilibrium is thinning along the entire length of the glacier. For example, Easton Glacier (pictured below) will likely shrink to half its size, but at a slowing rate of reduction, and stabilize at that size, despite the warmer temperature, over a few decades. However, the Grinnell Glacier (pictured below) will shrink at an increasing rate until it disappears. The difference is that the upper section of Easton Glacier remains healthy and snow-covered, while even the upper section of the Grinnell Glacier is bare, melting and has thinned. Small glaciers with shallow slopes such as Grinnell Glacier are most likely to fall into disequilibrium if there is a change in the local climate. In the case of positive mass balance, the glacier will continue to advance expanding its low elevation area, resulting in more melting. If this still does not create an equilibrium balance the glacier will continue to advance. If a glacier is near a large body of water, especially an ocean, the glacier may advance until iceberg calving losses bring about equilibrium. a – ablation c – accumulation b – mass balance (c + a) ρ – density h – glacier thickness S – area V – volume AAR – accumulation-area ratio ELA – equilibrium-line altitude By default, a term in lower case refers to the value at a specific point on the glacier's surface; a term in upper case refers to the value across the entire glacier. Mass balance studies have been carried out in various countries worldwide, but have mostly conducted in the Northern Hemisphere due to there being more mid-latitude glaciers in that hemisphere. The World Glacier Monitoring Service annually compiles the mass balance measurements from around the world. From 2002 to 2006, continuous data is available for only 7 glaciers in the southern hemisphere and 76 glaciers in the Northern Hemisphere. The mean balance of these glaciers was its most negative in any year for 2005/06. The similarity of response of glaciers in western North America indicates the large scale nature of the driving climate change. The Tarfala research station in the Kebnekaise region of northern Sweden is operated by Stockholm University. It was here that the first mass balance program was initiated immediately after World War II, and continues to the present day. This survey was the initiation of the mass balance record of Storglaciären Glacier, and constitutes the longest continuous study of this type in the world. Storglaciären has had a cumulative negative mass balance from 1946 to 2006 of −17 m. The program began monitoring the Rabots Glaciär in 1982, Riukojietna in 1985, and Mårmaglaciären in 1988. All three of these glaciers have had a strong negative mass balance since initiation. World Glacier Monitoring Service How does mass balance vary over Antarctica? An introduction to Glacier Mass Balance

cover Mass balance 2.5.1. Definitions 2.5.2. Measurement of mass balance 2.5.3 Annual mass balance cycles … 1991) 1.1.1 MASS BALANCE The gain and loss of ice in glacier systems is known as the mass balance. Snow and … controlled by surface mass balance (section 5.2.1). Thus, ice temperatures and mass balance need to be considered