Climate research in the geologic past

Fig.1. Global map as published by Lyell in his "Principles of Geology" (8th edition 1850) to illustrate the past climatic changes.

The climate of a region, as experienced by daily observations of a cool morning and hot midday, was for very long time considered simply the result of the height of the sun above the horizon. This idea forced a very simple view of the distribution of climates on Earth, to the poles temperature dropped, to the equator it raised, forming so large parallel climatic belts. Such a static view of the Earth also didn’t need or even allow climate changes in the past or in the future time.
With the establishment of the deep geological time by the first geologists and naturalists it became clear that not only the distribution of sea and land changed over time, but so did climate.

Read on how Lyell explained climate change by shifting "pseudo"-continents over the globe in the post at the American Scientific Guest Blog.

The discovery of the ruins of ice

"It has already been said, that no small part of the present work refers to the nature and phenomena of glaciers. It may be well, therefore, before proceeding to details, to explain a little the state of our present knowledge respecting these great ice-masses, which are objects of a kind to interest even those who know them only from description, whilst those who have actually witnessed their wonderfully striking and grand characteristics can hardly need an inducement to enter into some inquiry respecting their nature and origin."

James, D. Forbes (1900): "Travels Trough the Alps." [page 17]

Fig.1. C. Wolf and M. Descourtis "La Grosse Pierre Sur Le Glacier de Vorderaar Canton de Berne Province d'Oberhasli", Amsterdam 1785.

Today worldwide glaciers were studied and monitored as climate proxies, and the recent measurements show that almost all of them are retreating fast. The story about glaciers, their influence on the landscape and their possible use to reconstruct and monitor climate is an intriguing one, with many triumphs, setbacks and changes of mind.

For centuries, if not even millennia, the high altitude belt of mountain ranges were a region visited and travelled by man, however also haunted and forbidding places. The glaciers, masses of ice enclosing peaks and extending their tongues into valleys, were considered the residence of mountain spirits, then during the medieval times the prison of damned souls (the Italian poet Dante Alighieri 1265-1321 imagined the centre of hell as a frozen wasteland) and the playground of demons, who from time to time send avalanches and debris flows into the valley.
Despite these myths there was some early insights of what glaciers actually really are made, the Greek historian and geographer Strabo (63 - 23) describes a voyages trough the Alps during the reign of Augustus and mentions

"…there is no protection against the large quantities of snow falling, and that form the most superficial layers of a glacier…[]. It's a common knowledge that a glacier is composed by many different layers lying horizontally, as the snow when falling and accumulating becomes hard and crystallises...[]."

However the knowledge got lost, and was only rediscovered during the Renaissance. Leonardo da Vinci´s (1452-1519) is considered one of the greatest Renaissance-geniuses, he studied anatomy, biology and geology, however regarding the glaciers of the Alps his ideas were somehow confused, the thought glaciers were formed by not melted hail accumulating through the summer. But soon the study of nature experiences an incredible raise, and glaciers find place in various descriptions of travelling scholars.

Between 1538 and 1548 glaciers were labelled (even if not depicted) with the term "Gletscher" on topographic maps of Switzerland. In his account on the Swiss land the Theologian Josias Simler in 1574 describes the Rhone-glacier.
The first historic depiction of a glacier is considered the watercolour-paint of the Vernagtferner in the Ötztaler Alps from 1601. The Vernagtferner was a glacier that repeatedly dammed up the Rofen-lake (named after the Rofen-valley), which outbursts caused heavy damage and loss of property, particularly in the years 1600, 1678, 1680, 1773, 1845, 1847 and 1848.
In 1642 the Swiss editor Matthaeus Merian the Older in his "Topographie Helvetiae, Rhaetiae et Valesiae" published various copper engravings of glaciers, and in 1706 Johann Heinrich Hottinger is interested to explain the motion of "the mountains of ice" in his "Descriptio Montium Glacialium Helveticorum."
Johann Jakob Scheuchzer, visiting in the year 1705 the Rhône Glacier, published his observations of the "true nature of the springs of the river Rhône" in the opus "Itinera per Helvetiae alpinas regiones facta annis 1702-1711", and confirms the idea that glaciers are formed by the accumulation of snow and they move and flow.

Fig.2. The description of the Rhone glacier according to Scheuchzer´s "Itinera per Helvetiae alpinas regiones facta annis 1702-1711", the engraving shows the "false springs at the mountain Furca" (M, N, O - left and right of the picture) and the "true springs" (J, K, L) coming from the snout of the "great glacier" (A-F), surrounded by the "small glacier" (G, H).

The increasing interest to study glaciers in the Alps is also encouraged by enthusiastic travel reports; in his "Voyage pittoresque aux glaciers" the A.C. Bordier of 1773 describes the Bosson glacier as a "huge marble ruins of a devastated city".
The naturalist Horace Benedict de Saussure (1740-1799) is fascinated by the mountains of his homeland, he climbed mountains around Geneva since 1758, and after 1760 he travelled more than 14 times trough the Alps (considering the possibilities in this time an extraordinary achievement). Between 1767 to 1779 the first volume of his "Voyages dans les Alpes" is published, were he reassumes his observations and theories about the visited glaciers, he recognized moraines and large boulders as the debris accumulated by the glacier tongue and proposes to map them to interfere the former extent of glaciers. Despite this exact statement, de Saussure failed to connect large boulders found in the foreland of the mountains to the glaciers of the Alps. He assumed that these rocks were transported on their recent locations by an immense flood. That seemed to explain why most of the boulders found scattered around the plains of Germany came in first place from the regions of Scandinavia, where the same lithology where found in the crystalline continental basement, like Precambrian metamorphic rocks and paleozoic sediments. The theory worked lesser to explain the foreland Alpine rocks - to transport boulders from the Alps the flood at least had to reach 1000 of meters.
The idea of a flood as the explanation for "glacial" deposits became largely accepted, it seemed to fit the description of the biblical flood; even Lyell and Darwin assumed that huge erratic boulders were transported by swimming ice drafts on top of a flood wave.
That glaciers could propagate far out of their valleys was however not an unusual idea for local inhabitants, who observed and experienced the growth and recess of glaciers. In academic circle this approach was a little more difficult.
A contest thought to demonstrate the former extension of Swiss glaciers initiated by the Swiss pastor Jakob Samuel Wyttenbach in 1781 (maybe inspired be the advance of the Alpine glacier in 1770) didn't arise any interest.

"Could it be proven to ourselves on the available documentation that both by the progress of our ice mountains as by our misbehaviour once for pasture most suitable land is currently covered by ice…[]"

There were only careful speculations considering a former expansion of glacier: the geologists James Hutton (1726-1797) and his friend John Playfair (1748-1819) speculated about glaciations of the northern hemisphere. In 1826 a publication by the Danish mineralogist and mountain climber Jens Esmark (1763-1839) was translated into English, in this paper Jesmark discussed the possibilities that glaciers where much greater in the past then today. J.D. Forbes and Robert Jameson (who were the geology professors of Charles Darwin at Edinburgh University, Darwin in his autobiography of 1876 remembers "The sole effect they produced on me was the determination never as long as I lived to read a book on Geology or in any way to study the science.") discussed glacial theories during their lectures. And even Buckland, who still in 1831 argued "northern region of the earth seems to have undergone successive changes from heat to cold", in 1837 was converted to Lyell's uniformatism and considered that sudden changes, like an ice age and glacier expansion, simply don't happen in geology.

In 1815 Jean Pierre Perraudin, a chamois hunter in the Val de Bagnes, told to the engineer Ignatz Venetz his theory that the glaciers once covered the entire valley, and Venetz mapped features that made him even recognize that once the entire Swiss was covered by ice. Vernetz´s lecture on the assembly of the Swiss association for natural history in 1829 found little interest, only Jean de Charpentier, director of the salt mine in the city of Bex (Western Swiss), who 14 years earlier had meet and discussed with Perraudin, this time accepted and got interested in this theory.
He begun a detailed mapping project, and in 1834 Charpentier presented again before the Swiss association the results of his investigations, but the flood theory had still much supporter. One of the critics in the public was a former student of Charpentier, named Jean Louis Rodolphe Agassiz, respected palaeontologist by the establishment. Charpentier invited Agassiz to visit the city of Bex and surrounding mountains, and to observe glaciers.
In the following year (1837) Agassiz held an enthusiastic lecture about glaciers, ice ages and ice shields, and in 1840 published a detailed study of modern glaciers, their deposits and their spurs in his "Etudes sur les glaciers."
Agassiz experienced the same scepticism as many other ice-age proponents before.

"I think that you should concentrate your moral and also your pecuniary strength upon this beautiful work on fossil fishes .... In accepting considerable sums from England, you have, so to speak, contracted obligations to be met only by completing a work which will be at once a monument to your own glory and a landmark in the history of science ...[ ]...No more ice, not much of echinoderms, plenty of fish..."
Alexander von Humboldt in a letter to Agassiz on 2. December 1837

However Agassiz had good connections to the most important geologist of his time. Soon he could persuade William Buckland and later Charles Lyell. After that the most respected geologist gets convinced, the rest, as always, is history:

"advice - never try & persuade ye world of a new theory - persuade 2 or 3 of ye tip top men - & ye rest will go with ye stream, as Dr B. did with Sir H. Davy and Dr. Wollaston in case of Kirkdale Cave"
Edward Jackson, about an advice given by his professor Buckland in 1832

Fig.3. Reconstruction of the glacier that filled the valley of St. Amarin (southern Vosges, France), probably the first tentative reconstruction of an ice age glacier - from COLLOMB (1847): "Preuves de l´existence d´anciens glaciers dans les vallées des Vosges."

Agassiz research on the Unteraar-glacier established the foundations of glaciology; he recorded the dimension of the glacier, his velocity and even ventured inside the glacier by passing trough a glacial mill. Soon after 1850 the measurements methods introduced by Agassiz were carried out on various glaciers of the Alps and repeated nearly every year.

Fig.4. The Hintereis-glacier (in the centre of the picture), Hochjoch-glacier (left) and the Kesselwand- glacier, drawing by Schmetzer 1891, the Hintereis-glacier is one of the glacier with the longest active monitoring program, values about his length change reach back to 1848, since then the glacier lost 3km of his tongue.
"Aus den tiroler Alpen: Der Abschluß des Oetzthales mit dem Hochjochgletscher (links), dem Hintereisferner (in der Mitte) und dem Kesselwandferner (rechts oben). Nach der Natur gezeichnet von K. Schmetzer (1891)."

These records showed various fluctuations, but from 1850 onward a general trend of recession of glaciers in the Alps is observable. This trend has experienced a strong increase in the last 50 years, causing concern for the fast change in the landscape, the destabilisation of the rock walls once supported by the melting glaciers and the alteration of the discharge and hydrology of mountain ranges.

Fig.5. Temperature rise in the Alps and length loss of the glaciers of the Ötztaler Alps (western Austria) in the period 1900-2010. The valley glaciers with their tongues extending in the valleys showed the strongest retreat and degradation of the studied Austrian glaciers.

Geology and Cyclicity: Milankovitch´s idea

"I do not think that's my duty to teach to the ignorant the most basic things, and I have never forced anyone to accept my theory, on so far nobody could expose something."

Milutin Milankovitch in 1950

Milutin Milankovitch (1879 - 1958) was born in a relatively wealthy Serbian family, so it was almost a kind of obligation for him to archive a higher education degree and later take over the family business. So he studied agriculture, but following a passion for natural sciences he went to Vienna, where he in 1904 concluded his studies as an engineer.
Five years later he returned to Belgrad where he found employment as professor for mathematical studies at the University. Like Croll he was in search of a scientific problem worth his efforts, and in 1911, sharing some presumably good wine with a friend, he decided to develop a mathematical theory to explain climate changes on the planets of the solar system.

He studied the work of Croll, recognized his previous achievements but also noted his insufficient data. Milankovitch also consulted the work of the German mathematician Ludwig Pilgrim, who in 1904 published exact calculations of the orbital eccentricity, earth's obliquity and the rotation of the axis of earth (change of the perihelion). Pilgrim also tried to correlate the eccentricity with the occurrence of ice ages.
Between 1912 and the beginning of World War I Milankovitch published some preliminary abstracts of his developing theory, concluding that all three factors, in contrast to previous authors, are important to explain earth's climate. At the beginning of the War, Milankovitch was arrested as Serbian officer and imprisoned in his hometown Daly, but fortunately he was carrying with him his work, and so even in the first night as prisoner he continued to work. "When after midnight I looked around in the room, I needed some time to realize where I was. The small room seemed to me like an accommodation for one night during my voyage in the Universe."
Soon after he was released and travelled back to Belgrad, where he continued his work during the entire War and published some ideas about the climate of Mars and Venus.

Finally he published his theory in 1920 "Mathematische Theorie der durch Sonneneinstrahlung ausgelösten Wärmephänomene" (Mathematical theory of thermal phenomena caused by solar radiation).

Fig.1. Variations in the Earth's orbital parameters:
1. Eccentricity: the shape of the orbit around the sun.
2. Changes in obliquity: changes in the angle that Earth's axis makes with the plane of Earth's orbit.
3. Precession: the change in the direction of the Earth's axis of rotation, i.e., the axis of rotation behaves like the spin axis of a top that is winding down; hence it traces a circle on the celestial sphere over a period of time.
Together, the periods of these orbital motions have become known as Milankovitch cycles. These parameters influence the amount of solar energy on earth´s surface, especially during summer of the northern hemisphere (55°-65°N).

In his theory he postulated:
- Glaciations are caused by variations of astronomical parameters
- The parameters influence the amount of solar energy on earth´s surface, especially during summer of the northern hemisphere (55°-65°N)
- It is possible to calculate these changes, and so calculate the climate in the past.

The German meteorologists Wladimir Köppen and Alfred Wegener supported the new theory, and noted the apparent coincidence of the calculated curve with the by Penck and Brückner postulated four European glaciations.

Fig. 2. Figure from KÖPPEN & WEGENER 1924, where they correlated the calculated cycles to the know ice ages at that time.

Fig.3. Outcrop of the Trubi-Formation at Capo Spartivento (South-Italy), a succession of Globigerina-marls from the Pliocene-Pleistocene transition. The regular stripes are caused by organic rich layers, thought to be caused by changes in the biological productivity in response of changes of the astronomical parameters - the Milankovitch cycles.

References:

CHORLTON, W. (ed) (1985): Ice Ages (Planet Earth). Time-Life Books: 176
KÖPPEN, W. & WEGENER, A. (1924): Die Klimate der geologischen Vorzeit. Borntraeger, Berlin: 256

Resources:

NASA Earth Observatory: Milutin Milankovitch (1879 - 1958). Accessed 26.06.2010

Geology and Cyclicity

1842, 5 years after Agassiz's "Discourse of Neuchatel", the French mathematician Joseph Alphonse Adhémar elaborated a hypothesis to explain a cyclic occurring of ice ages. He calculated the variations of the "direction" and declination of earth axis and the "movements" of earth around the sun during the geological past.
These cyclic factors influence the time and the energy density of solar radiation that reach earth from sun, causing cyclic climatic change. Adhémar proposed that in a period of 11.000 years the hemisphere that experiences a longer winter, resulting from these three astronomical factors, would develop in an ice age.
But in 1852 Alexander von Humboldt noted that Adhémar didn't consider an important factor in his calculations, even if one hemisphere experience lower radiation, the opposite hemisphere experience an increase, so in the end the total sum remains more or less identical.

Nevertheless the idea of the French mathematician was intriguing, and would influence later researchers.

In 1833, James Croll (1821-1890), son of a poor stonecutter of Perthshire, purchased a copy of the "Penny Magazine", a magazine for children education. He was fascinated and began extensively to read, and some time later acquired he's first books dealing with natural science; "At first I was totally confused, but then the beauty and simplicity of the ideas provided me with delight and surprise, and I began seriously to study the matter."

Croll had no easy living in the next 20 years; he travelled the country, most time working as casual labourer, and in 1850 managed (for a brief time) the only Scottish pub were no alcohol was allowed.
He then found work as a maintenance supervisor of the Andersonian College in Glasgow, where he had access to the library and the hosted scientific works, a knowledge resource that he grateful exploited.
"At that time, the question of what could have triggered the ice age was much discussed among geologists. So in the spring of 1864, I directed my attention to this topic."
From 1864, Croll corresponded with Sir Charles Lyell, on links between ice ages and variations in the Earth's orbit. This led to a position in the Edinburgh office of the Geological Survey of Scotland, as keeper of maps and correspondence, where the director, Sir Archibald Geikie, encouraged his research. He also corresponded with Charles Darwin on erosion by rivers.

Croll, based on observations of the astronom Urbain Jean Josef Leverrier, used in his calculations an important factor that Adhémar did not know, the "movements" of the perihelion and aphelion on earth's ecliptic (precession of the equinoxes). He published his research in the book "Climate and Time, in Their Geological Relations" in 1875.

Fig.1. Glacial and interglacial conditions when eccentricity is at its superior limit, from CROLL1875, frontispiece (from FLEMING 2006).

Fig.2. Variations in the earth's orbit for three million years before 1800 A.D. and one million years after it, from CROLL 1875, following p. 312 (from FLEMING 2006).

Geikie wrote about the work of Croll: "The astronomical theory seems to me the best solution to the present ice age riddle. It bears in it all the decisive factors for the occurrence of alternating cold and warm periods, and accounts for the peculiar character of glacial and interglacial climates."

But there was a problem, even if dating methods at these times were only approximate, geological evidences supported a very young age of glacial deposits, but after Croll´s theory the last glacial period had ended 80.000 years ago. When Croll died, highly respected, geologists considered his theory wrong.
Geikie resumed: "It may well be, that with certain modifications of his views; one day we will solve the secret. But for now we must be continue to work and wait."

The modifications as hoped by Geikie will come only years later, and a glass wine will be the first step to solve the problem of the cyclicity of glacial periods: Geology and Cyclicity: Milankovitch´s idea.

Fig.3. Orbitally forced cyclic sedimentation in the Trubi Formation of Zanclean age at Scala dei Turchi, in the Rossello composite section (Sicily), that represents the template for the Pliocene Series.

Fig.4. Orbitally forced cyclic sedimentation as expressed in the uppermost part of the Trubi Formation and in the overlying Monte Narbone Formation at Punta Piccola (Sicily), where the Piacenzian GSSP has been defined.

References:

CHORLTON, W. (ed) (1985): Ice Ages (Planet Earth). Time-Life Books: 176
CROLL, J. (1875): Climate and Time, in their Geological Relations. A theory of secular changes of the Earth's Climate. D. Appleton and Company, New York: 630
FLEMING, J.R. (2006): James Croll in Context: The Encounter between Climate Dynamics and Geology in the Second Half of the Nineteenth Century. History of Meterology 3: 43 - 54

The first geological map depicting loess (1865)

Loess is silt dominated sediment with minor amounts of sand and clay. This homogenous particle distribution is a result of the formation of the up to hundred of meters thick massive deposit; it's a terrestrial, windblown sediment, most time with homogenous bright, yellowish colour. Primary sedimentary structures in loess are subtle, so the true origin of this sediment was for a very long time unclear. Lyell in his first editions of Geology books interpreted loess as fluviatile loam.*

Loess covers a significant amount of the Earth's land surface, perhaps as much as 10%. Because of its widespread distribution, texture and mineralogy, it forms some of the world's most important agricultural soils.
There exist two main models to explain the formation and distribution of loess. The classical hypothesis interpret it as primarily glacial eroded and reworked material, from where the finer fractions become subsequently selective transported and accumulated by wind. The second model explain the main source of the windblown material to coming from deserts or arid areas, not necessarily related to glaciers, as a result of dry climate conditions during glacial periods.

Fig.1. Carl Maria PAUL, Guido STACHE and in the middle Franz Ritter VON HAUER, the author of the first loess map of Central Europe.

The geologist Franz Ritter von Hauer was the second Director of the Geological Survey in Vienna (1866-1885). One of his main contributions to Quaternary science was the geology textbook of the former Austro-Hungarian Monarchy, which provided a resource to access recent developments in geology and notably loess research to many scientists. In the middle of the 19th century he also coordinated the geological mapping of the monarchy, initiated mainly for economical reasons to record the mining activities and map future potential mineralogical resources.
Even if quaternary sediments were not the primary interest of the project, Hauer tried to establish a first approach to mapping and classification of these deposits.

Fig.2. The second edition of the General Geological General Map of the Austro-Hungarian Monarchy compiled by von Hauer (Archive of the Austrian Federal Geological Survey) compare to Fig.4. for the loess formation (mainly yellow and ligth green coloured area), from GAUDENYI & JOVANOVIC 2010.

Fig.3. Enlargement of the map in Fig.2.

The General Geological Map of the Austro-Hungarian Monarchy presented in 1865, and produced between 1850 and 1856, was one of the most comprehensive and complete geological map of Central Europe during that period of time.

The Quaternary formations were subdivided in two groups: Pleistocene and Holocene formations. The Pleistocene formations identified as "Dilluvial" included predominantly fluvial gravels and sand, but also loess. The Holocene formations were denominated "Alluvial" and included peat, lime tuff, quicksand and other formations summarized only as "Alluvial formations".
Loess was mentioned exclusively as a Pleistocene ("Dilluvial") formation and the distribution clearly outlined, even if, for lack of detailed knowledge, the definition differs from the modern understanding of loess . In the Austrian geological map for example, the loess formation in some areas also included "loess-like" sediments, as for example colluvial deposits.

Nevertheless it was one of the first maps which documented the extent of loess deposits in Europe and West Asia.

Fig.4. Modern map of loess distribution, from HAASE et al. 2007.

*The Student's Elements of Geology (1870): "In some parts of the valley of the Rhine the accumulation of similar loam, called in Germany "loess," has taken place on an enormous scale [several hundred feet thick]. Its colour is yellowish-grey, and very homogeneous; and Professor Bischoff has ascertained, by analysis, that it agrees in composition with the mud of the Nile. Although for the most part unstratified, it betrays in some places marks of stratification, especially where it contains calcareous concretions, or in its lower part where it rests on subjacent gravel and sand which alternate with each other near the junction. Although this loam of the Rhine is unsolidified, it usually terminates where it has been undermined by running water in a vertical cliff, from the face of which shells of terrestrial, freshwater and amphibious mollusks project in relief. These shells do not imply the permanent sojourn of a body of freshwater on the spot, for the most aquatic of them, the Succinea, inhabits marshes and wet grassy meadows."

REFERENCES:

GAUDENYI, T. & JOVANOVIC, M. (2010): Franz Ritter von Hauer's work and one of the first loess map of Central Europe. Quaternary International. 10.1016/j.quaint.2010.04.008
HAASE, D., FINK, J., HAASE, G., RUSKE, R., PECSI, M., RICHTER, H., ALTERMANN, M., JÄGER, K. D. (2007): Loess in Europe - its spatial distribution based on a European Loess Map, scale 1:2,500,000. Quaternary Science Reviews 26 (9-10), 1301-1312