Cryosphere

From Wikipedia, the free encyclopedia

Overview of the Cryosphere and its larger components, from the UN Environment Programme Global Outlook for Ice and Snow.

 

The cryosphere (from the Greek κρύος kryos, "cold", "frost" or "ice" and σφαῖρα sphaira, "globe, ball") is those portions of Earth's surface where water is in solid form, including sea ice, lake ice, river ice, snow cover, glaciers, ice caps, ice sheets, and frozen ground (which includes permafrost). Thus, there is a wide overlap with the hydrosphere. The cryosphere is an integral part of the global climate system with important linkages and feedbacks generated through its influence on surface energy and moisture fluxes, clouds, precipitation, hydrology, atmospheric and oceanic circulation. Through these feedback processes, the cryosphere plays a significant role in the global climate and in climate model response to global changes. The term deglaciation describes the retreat of cryospheric features. Cryology is the study of cryospheres.

Structure

Extent of the regions affected by components of the cryosphere around the world from the IPCC Fifth Assessment Report

 

Frozen water is found on the Earth’s surface primarily as snow cover, freshwater ice in lakes and rivers, sea ice, glaciers, ice sheets, and frozen ground and permafrost (permanently frozen ground). The residence time of water in each of these cryospheric sub-systems varies widely. Snow cover and freshwater ice are essentially seasonal, and most sea ice, except for ice in the central Arctic, lasts only a few years if it is not seasonal. A given water particle in glaciers, ice sheets, or ground ice, however, may remain frozen for 10-100,000 years or longer, and deep ice in parts of East Antarctica may have an age approaching 1 million years.

Most of the world’s ice volume is in Antarctica, principally in the East Antarctic Ice Sheet. In terms of areal extent, however, Northern Hemisphere winter snow and ice extent comprise the largest area, amounting to an average 23% of hemispheric surface area in January. The large areal extent and the important climatic roles of snow and ice, related to their unique physical properties, indicate that the ability to observe and model snow and ice-cover extent, thickness, and physical properties (radiative and thermal properties) is of particular significance for climate research.

There are several fundamental physical properties of snow and ice that modulate energy exchanges between the surface and the atmosphere. The most important properties are the surface reflectance (albedo), the ability to transfer heat (thermal diffusivity), and the ability to change state (latent heat). These physical properties, together with surface roughness, emissivity, and dielectric characteristics, have important implications for observing snow and ice from space. For example, surface roughness is often the dominant factor determining the strength of radar backscatter . Physical properties such as crystal structure, density, length, and liquid water content are important factors affecting the transfers of heat and water and the scattering of microwave energy.

The surface reflectance of incoming solar radiation is important for the surface energy balance (SEB). It is the ratio of reflected to incident solar radiation, commonly referred to as albedo. Climatologists are primarily interested in albedo integrated over the shortwave portion of the electromagnetic spectrum (~300 to 3500 nm), which coincides with the main solar energy input. Typically, albedo values for non-melting snow-covered surfaces are high (~80-90%) except in the case of forests. The higher albedos for snow and ice cause rapid shifts in surface reflectivity in autumn and spring in high latitudes, but the overall climatic significance of this increase is spatially and temporally modulated by cloud cover. (Planetary albedo is determined principally by cloud cover, and by the small amount of total solar radiation received in high latitudes during winter months.) Summer and autumn are times of high-average cloudiness over the Arctic Ocean so the albedo feedback associated with the large seasonal changes in sea-ice extent is greatly reduced. Groisman et al. observed that snow cover exhibited the greatest influence on the Earth radiative balance in the spring (April to May) period when incoming solar radiation was greatest over snow-covered areas.

The thermal properties of cryospheric elements also have important climatic consequences. Snow and ice have much lower thermal diffusivities than air. Thermal diffusivity is a measure of the speed at which temperature waves can penetrate a substance. Snow and ice are many orders of magnitude less efficient at diffusing heat than air. Snow cover insulates the ground surface, and sea ice insulates the underlying ocean, decoupling the surface-atmosphere interface with respect to both heat and moisture fluxes. The flux of moisture from a water surface is eliminated by even a thin skin of ice, whereas the flux of heat through thin ice continues to be substantial until it attains a thickness in excess of 30 to 40 cm. However, even a small amount of snow on top of the ice will dramatically reduce the heat flux and slow down the rate of ice growth. The insulating effect of snow also has major implications for the hydrological cycle. In non-permafrost regions, the insulating effect of snow is such that only near-surface ground freezes and deep-water drainage is uninterrupted.

While snow and ice act to insulate the surface from large energy losses in winter, they also act to retard warming in the spring and summer because of the large amount of energy required to melt ice (the latent heat of fusion, 3.34 x 10⁵ J/kg at 0 °C). However, the strong static stability of the atmosphere over areas of extensive snow or ice tends to confine the immediate cooling effect to a relatively shallow layer, so that associated atmospheric anomalies are usually short-lived and local to regional in scale. In some areas of the world such as Eurasia, however, the cooling associated with a heavy snowpack and moist spring soils is known to play a role in modulating the summer monsoon circulation. Gutzler and Preston (1997) recently presented evidence for a similar snow-summer circulation feedback over the southwestern United States.

The role of snow cover in modulating the monsoon is just one example of a short-term cryosphere-climate feedback involving the land surface and the atmosphere. From Figure 1 it can be seen that there are numerous cryosphere-climate feedbacks in the global climate system. These operate over a wide range of spatial and temporal scales from local seasonal cooling of air temperatures to hemispheric-scale variations in ice sheets over time-scales of thousands of years. The feedback mechanisms involved are often complex and incompletely understood. For example, Curry et al. (1995) showed that the so-called “simple” sea ice-albedo feedback involved complex interactions with lead fraction, melt ponds, ice thickness, snow cover, and sea-ice extent.

Snow

Snow cover has the second-largest areal extent of any component of the cryosphere, with a mean maximum areal extent of approximately 47 million km². Most of the Earth’s snow-covered area (SCA) is located in the Northern Hemisphere, and temporal variability is dominated by the seasonal cycle; Northern Hemisphere snow-cover extent ranges from 46.5 million km² in January to 3.8 million km² in August. North American winter SCA has exhibited an increasing trend over much of this century largely in response to an increase in precipitation. However, the available satellite data show that the hemispheric winter snow cover has exhibited little interannual variability over the 1972-1996 period, with a coefficient of variation (COV=s.d./mean) for January Northern Hemisphere snow cover of < 0.04. According to Groisman et al. Northern Hemisphere spring snow cover should exhibit a decreasing trend to explain an observed increase in Northern Hemisphere spring air temperatures this century. Preliminary estimates of SCA from historical and reconstructed in situ snow-cover data suggest this is the case for Eurasia, but not for North America, where spring snow cover has remained close to current levels over most of this century. Because of the close relationship observed between hemispheric air temperature and snow-cover extent over the period of satellite data (IPCC 1996), there is considerable interest in monitoring Northern Hemisphere snow-cover extent for detecting and monitoring climate change. 

Snow cover is an extremely important storage component in the water balance, especially seasonal snowpacks in mountainous areas of the world. Though limited in extent, seasonal snowpacks in the Earth’s mountain ranges account for the major source of the runoff for stream flow and groundwater recharge over wide areas of the midlatitudes. For example, over 85% of the annual runoff from the Colorado River basin originates as snowmelt. Snowmelt runoff from the Earth’s mountains fills the rivers and recharges the aquifers that over a billion people depend on for their water resources. Further, over 40% of the world’s protected areas are in mountains, attesting to their value both as unique ecosystems needing protection and as recreation areas for humans. Climate warming is expected to result in major changes to the partitioning of snow and rainfall, and to the timing of snowmelt, which will have important implications for water use and management. These changes also involve potentially important decadal and longer time-scale feedbacks to the climate system through temporal and spatial changes in soil moisture and runoff to the oceans.(Walsh 1995). Freshwater fluxes from the snow cover into the marine environment may be important, as the total flux is probably of the same magnitude as desalinated ridging and rubble areas of sea ice. In addition, there is an associated pulse of precipitated pollutants which accumulate over the Arctic winter in snowfall and are released into the ocean upon ablation of the sea-ice .

Sea ice

Sea ice covers much of the polar oceans and forms by freezing of sea water. Satellite data since the early 1970s reveal considerable seasonal, regional, and interannual variability in the sea-ice covers of both hemispheres. Seasonally, sea-ice extent in the Southern Hemisphere varies by a factor of 5, from a minimum of 3-4 million km² in February to a maximum of 17-20 million km² in September. The seasonal variation is much less in the Northern Hemisphere where the confined nature and high latitudes of the Arctic Ocean result in a much larger perennial ice cover, and the surrounding land limits the equatorward extent of wintertime ice. Thus, the seasonal variability in Northern Hemisphere ice extent varies by only a factor of 2, from a minimum of 7-9 million km² in September to a maximum of 14-16 million km² in March.

The ice cover exhibits much greater regional-scale interannual variability than it does hemispherical. For instance, in the region of the Sea of Okhotsk and Japan, maximum ice extent decreased from 1.3 million km² in 1983 to 0.85 million km² in 1984, a decrease of 35%, before rebounding the following year to 1.2 million km². The regional fluctuations in both hemispheres are such that for any several-year period of the satellite record some regions exhibit decreasing ice coverage while others exhibit increasing ice cover. The overall trend indicated in the passive microwave record from 1978 through mid-1995 shows that the extent of Arctic sea ice is decreasing 2.7% per decade. Subsequent work with the satellite passive-microwave data indicates that from late October 1978 through the end of 1996 the extent of Arctic sea ice decreased by 2.9% per decade while the extent of Antarctic sea ice increased by 1.3% per decade. The Intergovernmental Panel on Climate Change publication Climate change 2013: The Physical Science Basis stated that sea ice extent for the Northern Hemisphere showed a decrease of 3.8% ± 0.3% per decade from November 1978 to December 2012.

Lake ice and river ice

Ice forms on rivers and lakes in response to seasonal cooling. The sizes of the ice bodies involved are too small to exert other than localized climatic effects. However, the freeze-up/break-up processes respond to large-scale and local weather factors, such that considerable interannual variability exists in the dates of appearance and disappearance of the ice. Long series of lake-ice observations can serve as a proxy climate record, and the monitoring of freeze-up and break-up trends may provide a convenient integrated and seasonally specific index of climatic perturbations. Information on river-ice conditions is less useful as a climatic proxy because ice formation is strongly dependent on river-flow regime, which is affected by precipitation, snow melt, and watershed runoff as well as being subject to human interference that directly modifies channel flow, or that indirectly affects the runoff via land-use practices.

Lake freeze-up depends on the heat storage in the lake and therefore on its depth, the rate and temperature of any inflow, and water-air energy fluxes. Information on lake depth is often unavailable, although some indication of the depth of shallow lakes in the Arctic can be obtained from airborne radar imagery during late winter (Sellman et al. 1975) and spaceborne optical imagery during summer (Duguay and Lafleur 1997). The timing of breakup is modified by snow depth on the ice as well as by ice thickness and freshwater inflow.

Frozen ground and permafrost

Frozen ground (permafrost and seasonally frozen ground) occupies approximately 54 million km² of the exposed land areas of the Northern Hemisphere (Zhang et al., 2003) and therefore has the largest areal extent of any component of the cryosphere. Permafrost (perennially frozen ground) may occur where mean annual air temperatures (MAAT) are less than -1 or -2 °C and is generally continuous where MAAT are less than -7 °C. In addition, its extent and thickness are affected by ground moisture content, vegetation cover, winter snow depth, and aspect. The global extent of permafrost is still not completely known, but it underlies approximately 20% of Northern Hemisphere land areas. Thicknesses exceed 600 m along the Arctic coast of northeastern Siberia and Alaska, but, toward the margins, permafrost becomes thinner and horizontally discontinuous. The marginal zones will be more immediately subject to any melting caused by a warming trend. Most of the presently existing permafrost formed during previous colder conditions and is therefore relic. However, permafrost may form under present-day polar climates where glaciers retreat or land emergence exposes unfrozen ground. Washburn (1973) concluded that most continuous permafrost is in balance with the present climate at its upper surface, but changes at the base depend on the present climate and geothermal heat flow; in contrast, most discontinuous permafrost is probably unstable or "in such delicate equilibrium that the slightest climatic or surface change will have drastic disequilibrium effects".

Under warming conditions, the increasing depth of the summer active layer has significant impacts on the hydrologic and geomorphic regimes. Thawing and retreat of permafrost have been reported in the upper Mackenzie Valley and along the southern margin of its occurrence in Manitoba, but such observations are not readily quantified and generalized. Based on average latitudinal gradients of air temperature, an average northward displacement of the southern permafrost boundary by 50-to-150 km could be expected, under equilibrium conditions, for a 1 °C warming.

Only a fraction of the permafrost zone consists of actual ground ice. The remainder (dry permafrost) is simply soil or rock at subfreezing temperatures. The ice volume is generally greatest in the uppermost permafrost layers and mainly comprises pore and segregated ice in Earth material. Measurements of bore-hole temperatures in permafrost can be used as indicators of net changes in temperature regime. Gold and Lachenbruch (1973) infer a 2-4 °C warming over 75 to 100 years at Cape Thompson, Alaska, where the upper 25% of the 400-m thick permafrost is unstable with respect to an equilibrium profile of temperature with depth (for the present mean annual surface temperature of -5 °C). Maritime influences may have biased this estimate, however. At Prudhoe Bay similar data imply a 1.8 °C warming over the last 100 years (Lachenbruch et al. 1982). Further complications may be introduced by changes in snow-cover depths and the natural or artificial disturbance of the surface vegetation. 

The potential rates of permafrost thawing have been established by Osterkamp (1984) to be two centuries or less for 25-meter-thick permafrost in the discontinuous zone of interior Alaska, assuming warming from -0.4 to 0 °C in 3–4 years, followed by a further 2.6 °C rise. Although the response of permafrost (depth) to temperature change is typically a very slow process (Osterkamp 1984; Koster 1993), there is ample evidence for the fact that the active layer thickness quickly responds to a temperature change (Kane et al. 1991). Whether, under a warming or cooling scenario, global climate change will have a significant effect on the duration of frost-free periods in both regions with seasonally and perennially frozen ground.

Glaciers and ice sheets

Ice sheets and glaciers are flowing ice masses that rest on solid land. They are controlled by snow accumulation, surface and basal melt, calving into surrounding oceans or lakes and internal dynamics. The latter results from gravity-driven creep flow ("glacial flow") within the ice body and sliding on the underlying land, which leads to thinning and horizontal spreading. Any imbalance of this dynamic equilibrium between mass gain, loss and transport due to flow results in either growing or shrinking ice bodies.

Ice sheets are the greatest potential source of global freshwater, holding approximately 77% of the global total. This corresponds to 80 m of world sea-level equivalent, with Antarctica accounting for 90% of this. Greenland accounts for most of the remaining 10%, with other ice bodies and glaciers accounting for less than 0.5%. Because of their size in relation to annual rates of snow accumulation and melt, the residence time of water in ice sheets can extend to 100,000 or 1 million years. Consequently, any climatic perturbations produce slow responses, occurring over glacial and interglacial periods. Valley glaciers respond rapidly to climatic fluctuations with typical response times of 10–50 years. However, the response of individual glaciers may be asynchronous to the same climatic forcing because of differences in glacier length, elevation, slope, and speed of motion. Oerlemans (1994) provided evidence of coherent global glacier retreat which could be explained by a linear warming trend of 0.66 °C per 100 years.

While glacier variations are likely to have minimal effects upon global climate, their recession may have contributed one third to one half of the observed 20th Century rise in sea level (Meier 1984; IPCC 1996). Furthermore, it is extremely likely that such extensive glacier recession as is currently observed in the Western Cordillera of North America, where runoff from glacierized basins is used for irrigation and hydropower, involves significant hydrological and ecosystem impacts. Effective water-resource planning and impact mitigation in such areas depends upon developing a sophisticated knowledge of the status of glacier ice and the mechanisms that cause it to change. Furthermore, a clear understanding of the mechanisms at work is crucial to interpreting the global-change signals that are contained in the time series of glacier mass balance records.

Combined glacier mass balance estimates of the large ice sheets carry an uncertainty of about 20%. Studies based on estimated snowfall and mass output tend to indicate that the ice sheets are near balance or taking some water out of the oceans. Marine based studies suggest sea-level rise from the Antarctic or rapid ice-shelf basal melting. Some authors (Paterson 1993; Alley 1997) have suggested that the difference between the observed rate of sea-level rise (roughly 2 mm/y) and the explained rate of sea-level rise from melting of mountain glaciers, thermal expansion of the ocean, etc. (roughly 1 mm/y or less) is similar to the modeled imbalance in the Antarctic (roughly 1 mm/y of sea-level rise; Huybrechts 1990), suggesting a contribution of sea-level rise from the Antarctic. 

Relationships between global climate and changes in ice extent are complex. The mass balance of land-based glaciers and ice sheets is determined by the accumulation of snow, mostly in winter, and warm-season ablation due primarily to net radiation and turbulent heat fluxes to melting ice and snow from warm-air advection,(Munro 1990). However, most of Antarctica never experiences surface melting. Where ice masses terminate in the ocean, iceberg calving is the major contributor to mass loss. In this situation, the ice margin may extend out into deep water as a floating ice shelf, such as that in the Ross Sea. Despite the possibility that global warming could result in losses to the Greenland ice sheet being offset by gains to the Antarctic ice sheet, there is major concern about the possibility of a West Antarctic Ice Sheet collapse. The West Antarctic Ice Sheet is grounded on bedrock below sea level, and its collapse has the potential of raising the world sea level 6–7 m over a few hundred years.

Most of the discharge of the West Antarctic Ice Sheet is via the five major ice streams (faster flowing ice) entering the Ross Ice Shelf, the Rutford Ice Stream entering Ronne-Filchner shelf of the Weddell Sea, and the Thwaites Glacier and Pine Island Glacier entering the Amundsen Ice Shelf. Opinions differ as to the present mass balance of these systems (Bentley 1983, 1985), principally because of the limited data. The West Antarctic Ice Sheet is stable so long as the Ross Ice Shelf is constrained by drag along its lateral boundaries and pinned by local grounding.

Louis Agassiz (updated)

From Wikipedia, the free encyclopedia

Louis Agassiz ForMemRS
Born	May 28, 1807 Haut-Vully, Switzerland
Died	December 14, 1873 (aged 66) Cambridge, Massachusetts
Citizenship	United States
Alma mater	University of Erlangen-Nuremberg
Known for	Polygenism
Spouse(s)	Cecilie Braun Elizabeth Cabot Cary
Children	Alexander, Ida, and Pauline
Awards	Wollaston Medal (1836)
Scientific career
Fields	Paleontology Glaciology Geology Natural history
Institutions	University of Neuchâtel Harvard University Cornell University
Doctoral advisor	Carl Friedrich Philipp von Martius
Other academic advisors	Ignaz Döllinger, Georges Cuvier, Alexander von Humboldt
Notable students	William Stimpson, William Healey Dall, Karl Vogt
Signature

Jean Louis Rodolphe Agassiz was a Swiss-American biologist and geologist recognized as an innovative and prodigious scholar of Earth's natural history. Agassiz grew up in Switzerland. He received Doctor of Philosophy and medical degrees at Erlangen and Munich, respectively. After studying with Cuvier and Humboldt in Paris, Agassiz was appointed professor of natural history at the University of Neuchâtel. He emigrated to the United States in 1847 after visiting Harvard University. He went on to become professor of zoology and geology at Harvard, to head its Lawrence Scientific School, and to found its Museum of Comparative Zoology.

Agassiz is known for his regimen of observational data gathering and analysis. He made vast institutional and scientific contributions to zoology, geology, and related areas, including writing multi-volume research books running to thousands of pages. He is particularly known for his contributions to ichthyological classification, including of extinct species, and to the study of geological history, including to the founding of glaciology. In the 20th and 21st centuries, Agassiz's resistance to Darwinian evolution, belief in creationism, and the scientific racism implicit in his writings on human polygenism, have tarnished his reputation and led to controversies over his legacy.

Early life

Louis Agassiz was born in Môtier (now part of Haut-Vully) in the Swiss canton of Fribourg. The son of a pastor, Agassiz was educated first at home, he then spent four years of secondary school in Bienne, entering in 1818 and completing his elementary studies in Lausanne. Agassiz studied successively at the universities of Zürich, Heidelberg, and Munich; while there, he extended his knowledge of natural history, especially of botany. In 1829 he received the degree of doctor of philosophy at Erlangen, and in 1830 that of doctor of medicine at Munich. Moving to Paris, he came under the tutelage of Alexander von Humboldt (and later his financial benevolence). Humboldt and Georges Cuvier launched him on his careers of geology and zoology respectively. Ichthyology soon became a focus of his life's work.

Work

Agassiz in 1870

 

In 1819–1820, the German biologists Johann Baptist von Spix and Carl Friedrich Philipp von Martius undertook an expedition to Brazil. They returned home to Europe with many natural objects, including an important collection of the freshwater fish of Brazil, especially of the Amazon River. Spix, who died in 1826, did not live long enough to work out the history of these fish, and Martius selected Agassiz for this project. Agassiz threw himself into the work with an enthusiasm that would go on to characterize the rest of life's work. The task of describing the Brazilian fish was completed and published in 1829. This was followed by research into the history of fish found in Lake Neuchâtel. Enlarging his plans, in 1830 he issued a prospectus of a History of the Freshwater Fish of Central Europe. It was only in 1839, however, that the first part of this publication appeared, and it was completed in 1842.

In 1832, Agassiz was appointed professor of natural history at the University of Neuchâtel. The fossil fish in the rock of the surrounding region, the slates of Glarus and the limestones of Monte Bolca, soon attracted his attention. At the time, very little had been accomplished in their scientific study. Agassiz, as early as 1829, planned the publication of a work which, more than any other, laid the foundation of his worldwide fame. Five volumes of his Recherches sur les poissons fossiles ("Research on Fossil Fish") were published from 1833 to 1843. They were magnificently illustrated, chiefly by Joseph Dinkel. In gathering materials for this work Agassiz visited the principal museums in Europe, and, meeting Cuvier in Paris, he received much encouragement and assistance from him. They had known him for seven years at the time. 

With Benjamin Peirce

 

Agassiz found that his palaeontological analyses required a new ichthyological classification. The fossils he examined rarely showed any traces of the soft tissues of fish, but, instead, consisted chiefly of the teeth, scales, and fins, with the bones being perfectly preserved in comparatively few instances. He, therefore, adopted a classification that divided fish into four groups: Ganoids, Placoids, Cycloids and Ctenoids, based on the nature of the scales and other dermal appendages. This did much to improve fish taxonomy, but Aggasiz's classification has since been superseded.

Agassiz needed financial support to continue his work. The British Association and the Earl of Ellesmere—then Lord Francis Egerton—stepped in to help. The 1,290 original drawings made for the work were purchased by the Earl, and presented by him to the Geological Society of London. In 1836, the Wollaston Medal was awarded to Agassiz by the council of that society for his work on fossil ichthyology; and, in 1838, he was elected a foreign member of the Royal Society. Meanwhile, invertebrate animals engaged his attention. In 1837, he issued the "Prodrome" of a monograph on the recent and fossil Echinodermata, the first part of which appeared in 1838; in 1839–40, he published two quarto volumes on the fossil Echinoderms of Switzerland; and in 1840–45 he issued his Études critiques sur les mollusques fossiles ("Critical Studies on Fossil Mollusks").

Before Agassiz's first visit to England in 1834, Hugh Miller and other geologists had brought to light the remarkable fossil fish of the Old Red Sandstone of the northeast of Scotland. The strange forms of the Pterichthys, the Coccosteus and other genera were then made known to geologists for the first time. They were of intense interest to Agassiz, and formed the subject of a monograph by him published in 1844–45: Monographie des poissons fossiles du Vieux Grès Rouge, ou Système Dévonien (Old Red Sandstone) des Îles Britanniques et de Russie ("Monograph on Fossil Fish of the Old Red Sandstone, or Devonian System of the British Isles and of Russia"). In the early stages of his career in Neuchatel, Agassiz also made a name for himself as a man who could run a scientific department well. Under his care, the University of Neuchâtel soon became a leading institution for scientific inquiry.

Portrait photograph by John Adams Whipple, c. 1865

 

In 1842–1846, Agassiz issued his Nomenclator Zoologicus, a classification list, with references, of all names used in zoological genera and groups.

Ice age

In 1837, Agassiz proposed that the Earth had been subjected to a past ice age. He presented the theory to the Helvetic Society that ancient glaciers had not only flowed outward from the Alps, but that even larger glaciers had covered the plains and mountains of Europe, Asia, and North America, smothering the entire northern hemisphere in a prolonged ice age. In the same year, he was elected a foreign member of the Royal Swedish Academy of Sciences. Prior to this proposal, Goethe, de Saussure, Venetz, Jean de Charpentier, Karl Friedrich Schimper and others had studied the glaciers of the Alps, and Goethe, Charpentier and Schimper had even concluded that the erratic blocks of alpine rocks scattered over the slopes and summits of the Jura Mountains had been moved there by glaciers. These ideas attracted the attention of Agassiz, and he discussed them with Charpentier and Schimper, whom he accompanied on successive trips to the Alps. Agassiz even had a hut constructed upon one of the Aar Glaciers, which for a time he made his home, to investigate the structure and movements of the ice.

In 1840, Agassiz published a two-volume work entitled Études sur les glaciers ("Studies on Glaciers"). In this, he discussed the movements of the glaciers, their moraines, their influence in grooving and rounding the rocks, and in producing the striations and roches moutonnees seen in Alpine-style landscapes. He accepted Charpentier's and Schimper's idea that some of the alpine glaciers had extended across the wide plains and valleys of the Aar and Rhône. But he went further, concluding that, in the recent past, Switzerland had been covered with one vast sheet of ice, originating in the higher Alps and extending over the valley of northwestern Switzerland to southern slopes of the Jura. The publication of this work gave fresh impetus to the study of glacial phenomena in all parts of the world.

Familiar, then, with recent glaciation, Agassiz and the English geologist William Buckland visited the mountains of Scotland in 1840. There they found clear evidence in different locations of glacial action. The discovery was announced to the Geological Society of London in successive communications. The mountainous districts of England, Wales, and Ireland were understood to have been centres for the dispersion of glacial debris. Agassiz remarked "that great sheets of ice, resembling those now existing in Greenland, once covered all the countries in which unstratified gravel (boulder drift) is found; that this gravel was in general produced by the trituration of the sheets of ice upon the subjacent surface, etc."

The man-sized iron auger used by Agassiz to drill up to 7.5 metres deep into the Unteraar Glacier to take its temperature.

United States

With the aid of a grant of money from the King of Prussia, Agassiz crossed the Atlantic in the autumn of 1846 to investigate the natural history and geology of North America and to deliver a course of lectures on "The Plan of Creation as shown in the Animal Kingdom," by invitation from J. A. Lowell, at the Lowell Institute in Boston, Massachusetts. The financial offers presented to him in the United States induced him to settle there, where he remained to the end of his life. He was elected a Foreign Honorary Member of the American Academy of Arts and Sciences in 1846. Agassiz had a cordial relationship with Harvard botanist Asa Gray, but they disagreed on some scientific issues. For example, Agassiz was a member of the Scientific Lazzaroni, a group of mostly physical scientists who wanted American academia to mimic the autocratic academic structures of European universities, whereas Gray was a staunch opponent of that group. Agassiz also felt each human race had different origins, but Gray believed in the unity of all humans.

Agassiz's engagement for the Lowell Institute lectures precipitated the establishment, in 1847, of the Lawrence Scientific School at Harvard University, with Agassiz as its head. Harvard appointed him professor of zoology and geology, and he founded the Museum of Comparative Zoology there in 1859, serving as the museum's first director until his death in 1873. During his tenure at Harvard, Agassiz studied the effect of the last ice age on North America.

Agassiz continued his lectures for the Lowell Institute. In succeeding years, he gave lectures on "Ichthyology" (1847–48 season), "Comparative Embryology" (1848–49), "Functions of Life in Lower Animals" (1850–51), "Natural History" (1853–54), "Methods of Study in Natural History" (1861–62), "Glaciers and the Ice Period" (1864–65), "Brazil" (1866–67) and "Deep Sea Dredging" (1869–70). In 1850, he married an American college teacher, Elizabeth Cabot Cary, who later wrote introductory books about natural history and a lengthy biography of her husband after he died.

Agassiz served as a non-resident lecturer at Cornell University while also being on faculty at Harvard. In 1852, he accepted a medical professorship of comparative anatomy at Charlestown, Massachusetts, but he resigned in two years. From this time, Agassiz's, scientific studies dropped off, but he became one of the best-known scientists in the world. By 1857, Agassiz was so well-loved that his friend Henry Wadsworth Longfellow wrote "The fiftieth birthday of Agassiz" in his honor, and read it at a dinner given for Agassiz by the Saturday Club in Cambridge. His own writing continued with four (of a planned ten) volumes of Natural History of the United States, published from 1857 to 1862. He also published a catalog of papers in his field, Bibliographia Zoologiae et Geologiae, in four volumes between 1848 and 1854.

Stricken by ill health in the 1860s, Agassiz resolved to return to the field for relaxation and to resume his studies of Brazilian fish. In April 1865, he led a party to Brazil. Returning home in August 1866, an account of this expedition, entitled A Journey in Brazil, was published in 1868. In December 1871 he made a second eight-month excursion, known as the Hassler expedition under the command of Commander Philip Carrigan Johnson (brother of Eastman Johnson), visiting South America on its southern Atlantic and Pacific seaboards. The ship explored the Magellan Strait, which drew the praise of Charles Darwin.

Elizabeth Agassiz wrote, at the Strait: '. ... .the Hassler pursued her course, past a seemingly endless panorama of mountains and forests rising into the pale regions of snow and ice, where lay glaciers in which every rift and crevasse, as well as the many cascades flowing down to join the waters beneath, could be counted as she steamed by them. ... These were weeks of exquisite delight to Agassiz. The vessel often skirted the shore so closely that its geology could be studied from the deck.'

Legacy

Agassiz in middle age

 

From his first marriage to Cecilie Bruan, Agassiz had two daughters in addition to son Alexander. In 1863, Agassiz's daughter Ida married Henry Lee Higginson, who later founded the Boston Symphony Orchestra and was a benefactor to Harvard University and other schools. On November 30, 1860, Agassiz's daughter Pauline was married to Quincy Adams Shaw (1825–1908), a wealthy Boston merchant and later benefactor to the Boston Museum of Fine Arts.

In the last years of his life, Agassiz worked to establish a permanent school where zoological science could be pursued amid the living subjects of its study. In 1873, a private philanthropist (John Anderson) gave Agassiz the island of Penikese, in Buzzards Bay, Massachusetts (south of New Bedford), and presented him with $50,000 to permanently endow it as a practical school of natural science, especially devoted to the study of marine zoology. The John Anderson school collapsed soon after Agassiz's death; it is considered a precursor of the Woods Hole Marine Biological Laboratory, which is nearby.

Agassiz had a profound influence on the American branches of his two fields, teaching many future scientists that would go on to prominence, including Alpheus Hyatt, David Starr Jordan, Joel Asaph Allen, Joseph Le Conte, Ernest Ingersoll, William James, Nathaniel Shaler, Samuel Hubbard Scudder, Alpheus Packard, and his son Alexander Emanuel Agassiz, among others. He had a profound impact on paleontologist Charles Doolittle Walcott and natural scientist Edward S. Morse. Agassiz had a reputation for being a demanding teacher. He would allegedly "lock a student up in a room full of turtle-shells, or lobster-shells, or oyster-shells, without a book or a word to help him, and not let him out till he had discovered all the truths which the objects contained." Two of Agassiz's most prominent students detailed their personal experiences under his tutelage: Scudder, in a short magazine article for Every Saturday, and Shaler, in his Autobiography. These and other recollections were collected and published by Lane Cooper in 1917, which Ezra Pound was to draw on for his anecdote of Agassiz and the sunfish.

In the early 1840s, Agassiz named two fossil fish species after Mary Anning —Acrodus anningiae, and Belenostomus anningiae— and another after her friend, Elizabeth Philpot. Anning was a paleontologist known around the world for important finds, but, because of her gender, she was often not formally recognized for her work. Agassiz was grateful for the help the women gave him in examining fossil fish specimens during his visit to Lyme Regis in 1834.

Agassiz died in Cambridge, Massachusetts in 1873 and was buried at Mount Auburn Cemetery, joined later by his wife. His monument is a boulder from a glacial moraine of the Aar near the site of the old Hôtel des Neuchâtelois, not far from the spot where his hut once stood; his grave is sheltered by pine trees from his old home in Switzerland.

The Cambridge elementary school north of Harvard University was named in his honor and the surrounding neighborhood became known as "Agassiz" as a result. The school's name was changed to the Maria L. Baldwin School on May 21, 2002, due to concerns about Agassiz's alleged racism, and to honor Maria Louise Baldwin the African-American principal of the school who served from 1889 until 1922. The neighborhood, however, continues to be known as Agassiz. An elementary school called the Agassiz Elementary School in Minneapolis, Minnesota existed from 1922–1981.

Agassiz's grave, Mt Auburn Cemetery, Cambridge, Massachusetts, is a boulder from the moraine of the Aar Glaciers, near where he once lived.

 

An ancient glacial lake that formed in the Great Lakes region of North America, Lake Agassiz, is named after him, as are Mount Agassiz in California's Palisades, Mount Agassiz, in the Uinta Mountains, Agassiz Peak in Arizona and in his native Switzerland, the Agassizhorn in the Bernese Alps. Agassiz Glacier (Montana) and Agassiz Creek in Glacier National Park and Agassiz Glacier (Alaska) in Saint Elias Mountains, Mount Agassiz in Bethlehem, New Hampshire in the White Mountains also bear his name. A crater on Mars Crater Agassiz and a promontorium on the Moon are also named in his honour. A headland situated in Palmer Land, Antarctica is named in his honor, Cape Agassiz. A main-belt asteroid named 2267 Agassiz is also named in association with Louis Agassiz. 

Several animal species are named in honor of Louis Agassiz, including Apistogramma agassizii Steindachner, 1875 (Agassiz's dwarf cichlid); Isocapnia agassizi Ricker, 1943 (a stonefly); Publius agassizi (Kaup, 1871) (a passalid beetle); Xylocrius agassizi (LeConte, 1861) (a longhorn beetle); Exoprosopa agassizi Loew, 1869 (a bee fly); Chelonia agassizii Bocourt, 1868 (Galápagos green turtle); Philodryas agassizii (Jan, 1863) (a South American snake); and the most well-known, Gopherus agassizii (Cooper, 1863) (the desert tortoise).

In 2005 the EGU Division on Cryospheric Sciences established the Louis Agassiz Medal, awarded to individuals in recognition of their outstanding scientific contribution to the study of the cryosphere on Earth or elsewhere in the solar system.

Agassiz took part in a monthly gathering called the Saturday Club at the Parker House, a meeting of Boston writers and intellectuals. He was therefore mentioned in a stanza of the Oliver Wendell Holmes Sr. poem "At the Saturday Club":

There, at the table's further end I see
In his old place our Poet's vis-à-vis,
The great PROFESSOR, strong, broad-shouldered, square,
In life's rich noontide, joyous, debonair
...
How will her realm be darkened, losing thee,
Her darling, whom we call our AGASSIZ!

Polygenism

After Agassiz came to the United States, he wrote prolifically on polygenism, which holds that animals, plants and humans were all created in "special provinces" with distinct populations of species created in and for each province, and that these populations were endowed with unequal attributes. Agassiz denied that migration and adaptation could account for the geographical age or any of the past. Adaptation takes time; in an example, Agassiz questioned how plants or animals could migrate through regions they were not equipped to handle. According to Agassiz the conditions in which particular creatures live "are the conditions necessary to their maintenance, and what among organized beings is essential to their temporal existence must be at least one of the conditions under which they were created". Agassiz was opposed to monogenism and evolution, believing that the theory of evolution reduced the wisdom of God to an impersonal materialism.

Agassiz was influenced by philosophical idealism and the scientific work of Georges Cuvier. Agassiz believed there is one species of humans but many different creations of races. These ideas are now included under the rubric of scientific racism. According to Agassiz, genera and species were ideas in the mind of God; their existence in God's mind prior to their physical creation meant that God could create humans as one species yet in several distinct and geographically separate acts of creation. Agassiz was in modern terms a creationist who believed nature had order because God created it directly. Agassiz viewed his career in science as a search for ideas in the mind of the creator expressed in creation.

After the 1906 San Francisco earth­quake, toppled Agassiz's statue from the façade of Stanford's zoology building, Stanford President David Starr Jordan wrote that "Somebody‍—‌Dr. Angell, perhaps‍—‌remarked that 'Agassiz was great in the abstract but not in the concrete.'"

 

Agassiz, like other polygenists, believed the Book of Genesis recounted the origin of the white race only and that the animals and plants in the Bible refer only to those species proximate and familiar to Adam and Eve. Agassiz believed that the writers of the Bible only knew of regional events, for example Noah's flood was a local event only known to the regions near those that were populated by ancient Hebrews.

Stephen Jay Gould asserted that Agassiz's observations sprang from racist bias, in particular from his revulsion on first encountering African-Americans in the United States. However, others have asserted that, despite favoring polygenism, Agassiz rejected racism and believed in a spiritualized human unity. Agassiz believed God made all men equal, and that intellectualism and morality, as developed in civilization, make men equal before God. Agassiz never supported slavery, and claimed his views on polygenism had nothing to do with politics.

Accusations of racism against Agassiz have prompted the renaming of landmarks, schoolhouses, and other institutions (which abound in Massachusetts) that bear his name. Opinions on these events are often mixed, given his extensive scientific legacy in other areas. In 2007, the Swiss government acknowledged the "racist thinking" of Agassiz but declined to rename the Agassizhorn summit. In 2017, the Swiss Alpine Club declined to revoke Agassiz's status as a member of honor, which he received in 1865 for his scientific work, because the club considered this status to have lapsed on Agassiz's death. Civil rights attorney Benjamin Crump representing descendant Tamara Lanier filed a lawsuit against Harvard University over ownership of images of Renty and his daughter Delia collected by Agassiz in support of his theories.

Works

• Recherches sur les poissons fossiles (1833–1843)
• History of the Freshwater Fishes of Central Europe (1839–1842)
• Études sur les glaciers (1840)
• Études critiques sur les mollusques fossiles (1840–1845)
• Nomenclator Zoologicus (1842–1846)
• Monographie des poissons fossiles du Vieux Gres Rouge, ou Systeme Devonien (Old Red Sandstone) des Iles Britanniques et de Russie (1844–1845)
• Bibliographia Zoologiae et Geologiae (1848)
• (with A. A. Gould) Principles of Zoology for the use of Schools and Colleges (Boston, 1848)
• Lake Superior: Its Physical Character, Vegetation and Animals, compared with those of other and similar regions (Boston: Gould, Kendall and Lincoln, 1850)
• Contributions to the Natural History of the United States of America (Boston: Little, Brown, and Co., 1857–1862)
• Geological Sketches (Boston: Ticknor & Fields, 1866)
• A Journey in Brazil (1868)
• De l'espèce et de la classification en zoologie [Essay on classification] (Trans. Felix Vogeli. Paris: Bailière, 1869)
• Geological Sketches (Second Series) (Boston: J.R. Osgood, 1876)
• Essay on Classification, by Louis Agassiz (1962, Cambridge)