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TOPIC: Ancient climate


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Lake Van
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Turkey's Lake Van provides a uniquely precise insight into Eurasia's climate history The bottom of Turkey's Lake Van is covered by a layer of mud several hundreds of metres deep. For climatologists this unprepossessing slime is worth its weight in gold: summer by summer pollen has been deposited from times long past. From it they can detect right down to a specific year what climatic conditions prevailed at the time of the Neanderthals, for example. These archives may go back as much as half a million years. An international team of researchers headed by the University of Bonn now wants to tap this treasure. Preliminary investigations have been a complete success: the researchers were able to prove that the climate has occasionally changed quite suddenly – sometimes within ten or twenty years.

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RE: Ancient climate
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Long-term climate records are a key to understanding how Earth's climate changed in the past and how it may change in the future. Direct measurements of light energy emitted by the sun, taken by satellites and other modern scientific techniques, suggest variations in the sun's activity influence Earth's long-term climate. However, there were no measured climate records of this type until the relatively recent scientific past.
Scientists have traditionally relied upon indirect data gathering methods to study climate in the Earth's past, such as drilling ice cores in Greenland and Antarctica. Such samples of accumulated snow and ice drilled from deep within ice sheets or glaciers contain trapped air bubbles whose composition can provide a picture of past climate conditions. Now, however, a group of NASA and university scientists has found a convincing link between long-term solar and climate variability in a unique and unexpected source: directly measured ancient water level records of the Nile, Earth's longest river.
Alexander Ruzmaikin and Joan Feynman of NASA's Jet Propulsion Laboratory, Pasadena, Calif., together with Dr. Yuk Yung of the California Institute of Technology, Pasadena, Calif., have analysed Egyptian records of annual Nile water levels collected between 622 and 1470 A.D. at Rawdah Island in Cairo. These records were then compared to another well-documented human record from the same time period: observations of the number of auroras reported per decade in the Northern Hemisphere. Auroras are bright glows in the night sky that happen when mass is rapidly ejected from the sun's corona, or following solar flares. They are an excellent means of tracking variations in the sun's activity.
Feynman said that while ancient Nile and auroral records are generally "spotty," that was not the case for the particular 850-year period they studied.

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River Thames frost fairs
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In periods when the British climate was more severe than it is now the River Thames sometimes froze over in the winter. A number of fairs, known as the River Thames frost fairs were held on the river.
One of the earliest accounts of the Thames freezing over comes from A.D. 250 when it was frozen hard for nine weeks. In A.D. 923 the river was open to wheeled traffic for trade and the transport of goods for thirteen weeks; again in 1410, for fourteen. The period from the mid-14th century to the 19th century in Europe has been called the "Little Ice Age" on account of the severity of the climate at the time, especially the severe winters. When the ice was thick enough and lasted long enough, Londoners held a festival on the river.

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Maunder Minimum
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The Late Maunder Minimum (1675-1704 AD) is a multi-decadal period during which sunspots almost entirely disappeared. This lack of solar activity on its surface is generally associated with reduced irradiance. Because of unusually cold conditions, particularly in Western Europe during winter, the Maunder Minimum has often been used as synonymous for the Little Ice Age with the sun being the primary driver of overall conditions. Interestingly, the climate conditions during the Maunder Minimum did not remain cold over the entire period but exhibited a number of very cold, pulse-like episodes of a few years length. While these pulses could be expressions of internal climate variability superposed on a cold baseline, other forcing factors should be considered as well.

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Title: Largest explosive eruption in historical times in the Andes at Huaynaputina Volcano, A.D. 1600, southern Peru
Authors: Jean-Claude Thouret, Jasmine Davila, and Jean-Philippe Eissen

The largest explosive eruption (volcanic explosivity index of 6) in historical times in the Andes took place in A.D. 1600 at Huaynaputina volcano in southern Peru. According to chronicles, the eruption began on February 19 with a Plinian phase and lasted until March 6. Repeated tephra falls, pyroclastic flows, and surges devastated an area 70X40 km² west of the vent and affected all of southern Peru, and earthquakes shook the city of Arequipa 75 km away. Eight deposits, totalling 10.2-13.1 km³ in bulk volume, are attributed to this eruption: (1) a widespread, approximately 8.1 km³ pumice-fall deposit; (2) channelled ignimbrites (1.6-2 km³ ) with (3) ground-surge and ash-cloud-surge deposits; (4) widespread co-ignimbrite ash layers; (5) base-surge deposits; (6) unconfined ash-flow deposits; (7) crystal-rich deposits; and (8) late ash-fall and surge deposits. Disruption of a hydrothermal system and hydromagmatic interactions are thought to have fuelled the large-volume explosive eruption. Although the event triggered no caldera collapse, ring fractures that cut the vent area point to the onset of a funnel-type caldera collapse.

Latitude:, 16.608°S, . Longitude:, 70.85°W

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1600 eruption of Huaynaputina volcano
1783 eruption of Laki volcano
1815 eruption of Tambora volcano

There is no agreed beginning year to the Little Ice Age, although there are a frequently referenced series of events preceding the known climatic minima. Starting in the 13th century, pack ice began advancing southwards in the North Atlantic, as did glaciers in Greenland. The three years of torrential rains beginning in 1315 ushered in an era of unpredictable weather in Northern Europe which did not lift until the 19th century. There is anecdotal evidence of expanding glaciers almost worldwide. In contrast a climate reconstruction based on glacial length shows no great variation from 1600 to 1850, though it shows strong retreat thereafter.

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RE: Ancient climate
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The bottom of Turkey’s Lake Van is covered by a layer of mud several hundreds of metres deep. For climatologists this unprepossessing slime is worth its weight in gold: summer by summer pollen has been deposited from times long past. From it they can detect right down to a specific year what climatic conditions prevailed at the time of the Neanderthals, for example. These archives may go back as much as half a million years. An international team of researchers headed by the University of Bonn now wants to tap this treasure. Preliminary investigations have been a complete success: the researchers were able to prove that the climate has occasionally changed quite suddenly – sometimes within ten or twenty years.
Every summer an inch-thick layer of lime – calcium carbonate – trickles down to find its final resting place at the bottom of Lake Van. Day by day during this period millions and millions of pollen grains float down to the depths. Together with lime they form a light-coloured layer of sediment, what is known as the summer sediment.
In winter the continual ‘snowdrift’ beneath the surface changes its colour: now clay is the main ingredient in the sediment, which is deposited as a dark brown winter sediment on top of the pollen-lime mix. At a depth of 400 metres no storm or waves disturb this process. These ‘annual rings’ in the sediment can be traced back for hundreds of thousands of years.

"In some places the layer of sediment is up to 400 metres thick. There are about 20,000 annual strata to every 10 metres. We presume that the bottom of Lake Van stores the climate history of the last 800,000 years – an incomparable treasure house of data which we want to tap for at least the last 500,000 years" - Professor Thomas Litt, Bonn palaeontologist.

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 Carbon dioxide, a greenhouse gas that has become a bane of modern society, may have saved Earth from freezing over early in the planet's history, according to the first detailed laboratory analysis of the world's oldest sedimentary rocks.
Scientists have theorized for years that high concentrations of greenhouse gases could have helped Earth avoid global freezing in its youth by allowing the atmosphere to retain more heat than it lost. Now a team from the University of Chicago and the University of Colorado at Boulder that analysed ancient rocks from the eastern shore of Hudson Bay in northern Quebec, Canada, have discovered the first direct field evidence supporting this theory.
The study shows carbon dioxide in Earth's atmosphere could have sustained surface temperatures above freezing before 3.75 billion years ago according to the researchers, led by University of Chicago Assistant Professor Nicolas Dauphas. Co-authors on the study, which appeared online Jan. 16 in the journal Earth and Planetary Science Letters, included Assistant Professor Stephen Mojzsis and doctoral student Nicole Cates of CU-Boulder's geological sciences department and Vincent Busigny, now of the Institut de Physique du Globe in Paris.

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Canary Islands forests
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A team comprised of two La Laguna University researchers and a professor from Oxford University have discovered indisputable proof that the islands were once populated by now-vanished forests of tree species experts had never even suspected grew in the archipelago.
The discovery looks set to change the accepted views on Canary Islands natural history.
From the evidence they have uncovered the scientists engaged on the research conclude that once upon a time large tracts of forests of trees related to oaks and hornbeams covered the islands.
The project set out to determine the impact of past climates and human activities on the development of the existing diverse forest types on the islands which include vestiges of laurel forests from the Tertiary age. The work has now taken a new twist.
According to the team’s findings the landscape of the Tenerife of 5,000 to 2,000 years ago was very different to what we see today where neither Quercus, commonly found these days in Mediterranean regions, and Carpinus betulus, which in Spain is now confined to the Pyrenees, have survived.

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RE: Ancient climate
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A glassy stick made by lightning striking Libyan sands has now been used to date the lightning and detect the ancient climate.
It turns out that the root-like glass "fulgurite" structure made of melted and welded sand from the Libyan Desert contains miniscule bubbles of trapped gases from the time it was made. These gases, carbon dioxide (CO2), carbon monoxide (CO) and nitric oxide (NO) harbour hints of the type of plants that were zapped along with the sandy ground some 15,000 years ago.
Careful analysis of those gases and the weights of the carbon atoms in them reveal the plants were probably the sort which used what’s called C4 photosynthesis — best for plants living in hot, arid climates. This, in turn, implies that the semi-arid Sahel region of today reached much further north during the Pleistocene (1.8 million to 10,000 years ago).
In other words, the Libyan Desert was once a lot less arid than it is today.

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U.S. scientists have created the first historic temperature record of the North American Great Plains -- an area stretching from Canada to north Texas.
Baylor University geology Professor Lee Nordt, along with Professor Joseph von Fisher of Colorado State University and Larry Tieszen of the U.S. Geological Survey, produced the 12,000-year temperature record by studying the stable isotopic composition of buried soils.

"The results really surprised us, especially between 12,000 and 7,000 years ago. Earth temperatures should have been getting warmer during that time, but they weren't. We concluded it was caused by negative feedback from the melting glaciers. The ocean water temperature was colder because the glaciers were melting. That, in turn, caused temperatures to drop" - Professor Lee Nordt

Nordt said the sun's intensity on the Earth is the main reason why temperatures generally increased during the last 12,000 years. That intensity is decreasing but temperatures are not.

"Is this caused by global warming or are temperatures just lagging behind? We don't know."

The research is detailed in the February issue of the journal Geology.

Source UPI

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Drumlin Formation
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For the first time, a drumlin - a mound of sediment and rock - has been observed mid-formation.
The streamlined, elongated hills form underneath ice-sheets as they scrape up material as they move.
While many relic drumlins are well known features in once ice-covered areas, this is the first time an active one has been observed.

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