Gerard De Geer

Gerard De Geer
Born 20 November 1858 (1858-11-20)
Stockholm, Sweden
Died 24 July 1943(1943-07-24) (aged 84)
Stockholm, Sweden
Residence Sweden
Citizenship Sweden
Nationality Swede
Fields Quaternary geology
Institutions Stockholm University
Alma mater Uppsala University
Doctoral students Ernst Antevs
Known for Varve geochronology
Notable awards Vega Medal (1915)
Wollaston Medal (1920)
Children Sten De Geer

Baron Gerard Jacob De Geer ForMemRS[1] (20 November 1858 – 24 July 1943) was a Swedish geologist who made significant contributions to Quaternary geology, particularly geomorphology and geochronology. De Geer is best known for his discovery of varves.[2]

Early life and family

De Geer was born in Stockholm, Sweden, on October 2, 1858. His family, originally Dutch nobility who had emigrated to Sweden in the early seventeenth century, included prominent industrialists and politicians. Both De Geer's father (Louis De Geer) and older brother were Prime Minister of Sweden, and De Geer himself was a member of the Swedish Parliament from 1900 to 1905.

De Geer's discovery of varves

De Geer graduated from Uppsala University in 1879, after joining the Swedish Geological Survey the previous year, and began what was to be his life's work studying the late Quaternary deposits and landforms of southern Sweden. De Geer's early studies of raised beaches, used to reconstruct glacio-isostatic sea level changes, and his mapping of glacial moraines to reconstruct the extent of the last Scandinavian ice sheet and its pattern of deglaciation (the particular type of moraine he studied is now referred to as De Geer moraine), were well received. However, De Geer is most famous for discovering varves and pioneering their use in geochronology.

During fieldwork in 1878, De Geer noticed that the appearance of laminated sediments deposited in glacial lakes at the margin of the retreating Scandinavian ice sheet at the end of the last ice age, closely resembled tree-rings. In his best known work Geochronologia Sueccia, published in 1940, De Geer wrote "From the obvious similarity with the regular, annual rings of the trees I got at once the impression that both ought to be annual deposits" (1940, p. 13).

While this observation was not new, De Geer was the first geologist to exploit its potential application. De Geer called these annual sedimentary layers varves and throughout the 1880s further developed his theory, publishing a brief outline of his discovery in 1882, which he followed with a presentation to the Swedish Geological Society in 1884. It was not until 1910, at the International Geological Congress, that De Geer's pioneering work reached the wider international scientific community.

The 1910 International Geological Congress

In 1910, the eleventh International Geological Congress was held in Stockholm. In addition to presenting his research on varves, De Geer presided over the congress. De Geer began his paper "A geochronology of the last 12000 years" by writing "Geology is the history of the earth, but hitherto it has been a history without years." At the congress De Geer formally introduced the term varve defining it as any annual sedimentary layer, and also proposed that the term geochronology be restricted to varve dating, other existing techniques being less accurate and precise.

By then, observations of the stratigraphic relationship between varved sediment and recessional moraines, and the correlation of varve sequences between geographically distant sites, added more compelling evidence to De Geer's essentially circumstantial speculation. The geological community accepted that it was unlikely that the couplets were unlikely to represent any period other than the year.

The Swedish Time Scale

In 1897 De Geer was appointed professor of geology at Stockholm University, and went on to become the university's president from 1902-1910. With the help of numerous students from both Stockholm and Uppsala, De Geer began to piece together short, but overlapping, varve sequences in south east Sweden to create a longer year-by-year chronology of glacial retreat for the Lateglacial period. The urban expansion of Stockholm provided perfect conditions for De Geer and his colleagues, who made good use of numerous exposures of laminated sediment in the many pits and cuttings that exposed the glacial lake sediments of the Baltic basin. Estuarine sediments exposed along the valley of the Angermanalven River, allowed De Geer to further extend the chronology into the early Holocene.The resulting varve chronology was called the Swedish Time Scale, and geologists outside Sweden soon followed suit using varved sediments to build high-resolution chronologies of glacial retreat, most notably Matti Sauramo in Finland.

Global expeditions, teleconections, and controversy

De Geer firmly believed the main control on varve sedimentation was solar radiation acting on glacier meltwater production, and that consequently, varved sediments represented a "..gigantic, natural self-registering thermograph" (De Geer 1926) and varve curves (varve thickness plotted against varve number or year), which he often referred to as 'solar curves', a reliable proxy for past changes in solar radiation. Ultimately, De Geer hoped his studies of varves would explain the fundamental cause of Ice Ages - "If the last glaciation everywhere should show to be synchronous and the origin of the last Ice Age thus to be of a general nature, the assumption of a cosmic cause would scarcely be avoidable."

In 1915 De Geer matched, or 'teleconnected', varve curves from Sweden to varve curves from Finland and Norway. This first attempt at long distance correlation marked the start of two decades travelling around the world by De Geer and his colleagues, searching out varve sequences for potential teleconnections. In 1920, De Geer travelled to North America with his wife and two assistants, Ernst Antevs, and Ragnar Liden. Antevs remained in North America at the end of the trip, where he worked on the North American varve chronology. Further trips included Erik Norin's visit to the Himalayas (1924–1925), Erik Nilsson's visit to East Africa (1927–28), and Carl Caldenius' visit to South America (1925–1929), and later New Zealand (1932–34).

However, by the mid-1930s De Geer's teleconnections had become the subject of increasing criticism from his former student Ernst Antevs. Antevs correctly argued that the teleconnections were bad science, and that De Geer's Trans-Atlantic correlations were inaccurate. De Geer felt his position was being caricatured and intentionally misunderstood by Antevs, but did little scientifically to rebuff the criticisms levelled at him.

In 1924 De Geer retired from teaching and became the founder-director of the Geochronological Institute at Stockholm University.

Geochronologia Suecica Principles

In 1940, De Geer published his longest and best-known work Geochronologia Suecica Principles, in which he presented part of the Swedish Time Scale in detail, and expounded upon his theories and work regarding varves.

Almost immediately after the publication of Geochronologia Suecica Principles De Geer's Swedish Time Scale underwent the first of many revisions, as other geologists became involved in the study of varves and more sites were examined.

However, international interest in varves diminished. The bitter dispute between De Geer and Antevs, coupled with the advent of new dating techniques, most importantly radiocarbon dating, showed varves in a bad light.

De Geer died in Stockholm on July 24, 1943. His wife, Ebba Hult De Geer, continued to publish his work, and add to it, into the 1950s.

Awards and recognition

De Geer's contributions to geology were recognised in the UK, where the Geological Society awarded De Geer the Wollaston Medal in 1920, and the Royal Society elected De Geer a foreign member in 1930.[1] The ancient DeGeer Sea in modern-day Maritime Canada was named in his honour.[3] The Swedish Antarctic Expedition (1901–1904) named a glacier on South Georgia Island in the southern Atlantic Ocean after De Geer. The British would later rename the glacier Harker Glacier after a contemporary English geologist, Alfred Harker.

The valley of De Geerdalen at Spitsbergen, Svalbard is named after him.[4]

De Geer from a modern perspective

De Geer's most significant contribution to Quaternary science was unquestionably the identification of varves, and his recognition of their potential in establishing annual chronologies of past climatic and environmental change. The Swedish Time Scale was the most precise and accurate geological timescale of its day, and it is still being improved and added to today. His insistence that varves represented quantifiable proxies for past climate has since been borne out to a degree, but the relationship between varve thickness and hydrometeorological conditions is not as simple as he presumed. Varves have recently experienced a renaissance as methods and techniques of study have improved, and varves are now regularly used to calibrate radiocarbon timescales.

In many ways, De Geer's concerns mirror that of modern Quaternary geologists and palaeoclimatologists, particularly his recognition of the need for high-resolution natural archives of past change, and the importance of testing whether global change is synchronous. De Geer's principle failing was his faith in teleconnections, where his findings were clearly influenced by his preconceptions. His belief that variations in solar radiation were the principal agent of all climate change has also since been shown to be incorrect. Nevertheless, De Geer asked all the right questions, and his errors can be attributed as much to over-enthusiasm and a single-minded passion, as they can to bad science.

Selected English language works

Biography

References

  1. 1 2 Bailey, E. B. (1943). "Gerard Jacob De Geer. 1858-1943". Obituary Notices of Fellows of the Royal Society. 4 (12): 475–426. doi:10.1098/rsbm.1943.0017.
  2. ↑ Bailey, E. B. (1943). "Baron Gerard de Geer, For. Mem.R.S". Nature. 152 (3851): 209. doi:10.1038/152209a0.
  3. ↑ http://www.bofep.org/Publications/Fundy%20issues/ecochang.htm
  4. ↑ "De Geerdalen (Svalbard)". Norwegian Polar Institute. Retrieved 27 July 2015.

External links

This article is issued from Wikipedia - version of the 11/1/2016. The text is available under the Creative Commons Attribution/Share Alike but additional terms may apply for the media files.