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TOPIC: Ancient climate


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New research challenges the generally accepted belief that substantial ice sheets could not have existed on Earth during past super-warm climate events.
The study by researchers at Scripps Institution of Oceanography at UC San Diego provides strong evidence that a glacial ice cap, about half the size of the modern day glacial ice sheet, existed 91 million years ago during a period of intense global warming.
Posted in Science, Isotopic Evidence for Glaciation During the Cretaceous Supergreenhouse examines geochemical and sea level data retrieved from marine microfossils deposited on the ocean floor 91 million years ago during the Cretaceous Thermal Maximum. This extreme warming event in Earths history raised tropical ocean temperatures to 35-37C (95-98.6F), about 10C (50F) warmer than today, thus creating an intense greenhouse climate.
Using two independent isotopic techniques, researchers at Scripps Oceanography studied the microfossils to gather geochemical data on the growth and eventual melting of large Cretaceous ice sheets. The researchers compared stable isotopes of oxygen molecules (d18O) in bottom-dwelling and near-surface marine microfossils, known as foraminifera, to show that changes in ocean chemistry were consistent with the growth of an ice sheet. The second method in which an ocean surface temperature record was subtracted from the stable isotope record of surface ocean microfossils yielded the same conclusion.
These independent methods provided Andre Bornemann, lead author of the study, with strong evidence to conclude that an ice sheet about 50-60 percent the size of the modern Antarctic ice cap existed for about 200,000 years. Bornemann conducted this study as a postdoctoral researcher at Scripps Oceanography and continues this research at Universitat Leipzig in Germany.

Until now it was generally accepted that there were no large glaciers on the poles prior to the development of the Antarctic ice sheet about 33 million years ago. This study demonstrates that even the super-warm climates of the Cretaceous Thermal Maximum were not warm enough to prevent ice growth - Richard Norris, professor of paleobiology at Scripps Oceanography and co-author of the study.

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A new study has indicated that global warming 55 million years ago triggered a massive release of greenhouse gases into the atmosphere which led to a huge spike in temperatures.
Appy Sluijs, a paleoecologist at Utrecht University in the Netherlands, and his colleagues, carried out the study.
Evidence in support of this theory comes from the abundance and distribution of marine algae, which indicate that the environment started to change and the ocean surface began to warm several thousand years before the large temperature spike.
Scientists have long studied this ancient temperature spike, called the Palaeocene-Eocene thermal maximum (PETM), for clues to what could happen as a result of todays global warming.

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New Ice Age Map Reveals Geologic Wonders of Downeast Region

My first inkling that coastal Maine was not always terra firma came with finding tiny mollusc shells in a gravel pit where I used to play, growing up near Portland.
Indeed, some 15,000 years ago the Maine coast, weighted down under the 1.5-mile-deep Laurentide Ice Sheet, was inundated by ocean waters

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Researchers have long speculated that ancient climate changes have had a powerful influence on human evolution, spurring our ancestors to walk upright, to migrate out of Africa, and to adapt to varied habitats. Now, scientists have found a concrete example: evidence of intense droughts in tropical Africa right when many anatomically modern humans were probably dying. The new findings provide an ecological explanation for the Out-of-Africa hypothesis that all modern humans are descended from a small number of ancestors who survived a population bottleneck in Africa between 150,000 and 70,000 years ago and gave rise to offspring who migrated to Asia and Europe.

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Scientists have discovered that some deep sea sponges have growth bands that, like tree rings, can reveal past environmental conditions. The bands show that, far from being a constant environment, the deep ocean experiences changes akin to seasons.
Scientists from New Zealands National Institute of Water & Atmospheric Research (NIWA) and New Caledonias Institut de Recherche pour le Developement (IRD) found seasonal fluctuations in levels of carbon and trace metals in a lithistid (rock) sponge aged over 135 years. The research was published in the September issue of the journal Limnology & Oceanography.

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When Georgia Tech Assistant Professor Kim Cobb and graduate student Jud Partin wanted to understand the mechanisms that drove the abrupt climate change events that occurred thousands of years ago, they didnt drill for ice cores from the glaciers of Greenland or the icy plains of Antarctica, as is customary for paleoclimatolgists. Instead, they went underground.
Growing inside the caves of the tropical Pacific island of Borneo are some of the keys to understanding how the Earths climate suddenly changed - several times - over the last 25,000 years. By analysing stalagmites, the pillar-like rock formations that stem from the ground in caves, they were able to produce a high-resolution and continuous record of the climate over this equatorial rainforest.

"These stalagmites are, in essence, tropical ice cores forming over thousands of years. Each layer of the rock contains important chemical traces that help us determine what was going on in the climate thousands of years ago, much like the ice cores drilled from Greenland or Antarctica - Jud Partin.

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A 55 million-year-old British bog uncovered by the Channel Tunnel rail link is giving scientists insights into a ancient period of global warming.
The researchers found methane released from the bogs played a major role in the Palaeocene-Eocene thermal maximum, when temperatures suddenly rose.
They suggest in the journal Nature that this is likely to clarify the role of bogs in present-day global warming.
Methane released by warmer conditions could make temperatures rise faster.

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The Eocene epoch
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Dispelling the myth of bipolar glaciation 41 million years ago

Large continental ice sheets did not exist in both hemispheres around 41 million years ago during the warmer-than modern conditions of the time.
This is the finding of scientists from the University of Southampton's School of Ocean and Earth Science at the National Oceanography Centre, Southampton (NOCS), reported in Nature.
The Eocene epoch (55 to 34 million years ago) was the last interval of sustained global warmth in Earth's history, a likely consequence of atmospheric carbon dioxide levels much higher than today. It has been known for some time that, at the end of the Eocene, ice sheets on Antarctica first expanded to close their modern size. However, in a recent controversial move, it was proposed that, despite the high global temperatures of the time, very large ice sheets existed 8 million years earlier, not just on Antarctica but also in the Northern Hemisphere.
New findings from NOCS researchers show that, if ice sheets did exist during the controversial interval they must have been small and would have been easily accommodated on Antarctica with no need to invoke Northern Hemisphere glaciation. This result is more in keeping with other geological records and climate model results suggesting that the threshold for ice sheet inception would have been crossed earlier in the Southern Hemisphere than in the Northern Hemisphere because the South Pole has a continent sitting over it (Antarctica) while the North Pole has an ocean (the Arctic).
The NOCS group also identifies a short-lived event immediately preceding the controversial interval during which ocean temperatures briefly increased, the deep ocean became more acidic and the carbon cycle was perturbed by the contribution of isotopically light carbon to the ocean/atmosphere system. This finding hints at the operation of carbon cycle processes common to those thought responsible for the famous transient extreme warming events that occurred between 50 and 55 million years ago, providing a focus for future work aimed at better understanding climate-carbon cycle feedbacks.

Kirsty Edgar, Dr Paul Wilson and Philip Sexton of the University of Southampton's School of Ocean and Earth Science, based at NOCS, used stable isotope analysis of fossil shells of foraminifera (microscopic marine organisms) and bulk sediment from deep-sea sediments to generate a record of climate change and estimate potential global ice volumes in the Eocene. Sediment cores were taken in the tropical Atlantic Ocean by the Ocean Drilling Program (ODP).
The Natural Environment Research Council funded this research via a UK ODP grant. Collaborator Yusuke Suganuma is based at the University of Tokyo, Japan.

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Cool periods in China, and the resulting scarcity of resources, are closely linked with a higher frequency of wars over the past 1000 years, according to Chinese researchers.
The research, which compared variations in climate with data from 899 wars in eastern China between 1000 and 1911, was published earlier this month (9 July) in the journal Human Ecology.

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Fossilised midges have helped scientists at the University of Liverpool identify two episodes of abrupt climate change that suggest the UK climate is not as stable as previously thought.
The episodes were discovered at a study in Hawes Water in Northern Lancashire, where the team used a unique combination of isotope studies and analysis of fossilised midge heads. Together they indicated where the climate shifts occurred and the temperature of the atmosphere at the time.
The first shift detected occurred around 9,000 years ago and the second around 8,000 years ago. Evidence suggests that these shifts were due to changes in the Gulf Stream, which normally keeps the UK climate warm and wet.
During each shift the North West climate cooled with an average summer temperature fall of 1.6 degrees approximately three times the amount of temperature change currently attributed to global warming.
Scientists found that the atmosphere cooled rapidly and cold periods lasted up to 50 years for one event and 150 years for the other. The detection of these events will allow experts to understand more clearly what can happen when the climate system is disturbed.

At Hawes Water mud has been deposited continuously without any gaps, which allows us to measure an accurate timeline of events. We have monitored the modern environment of the lake for the past eight years and this has shown us how to read the past climate record from the ancient mud in the lake. Isotope analysis helped us identify the episodes of climate change. We then used fossilised heads of non-biting midges, which are preserved in every spoonful of mud. They tell us the temperature at the time the mud was deposited. We compare the population of midge heads in each sediment sample with the population of midges in Scandinavian lakes, which span a wide range of modern day temperatures - Professor Jim Marshall, from the Universitys Department of Earth and Ocean Sciences.

The team found the two abrupt climate changes correlated directly with two episodes of sharp climate deterioration in areas such as Greenland, suggesting that a change in the Gulf Stream had occurred.

People are worried that the melting of the polar ice caps could result in a slow-down of what we call the Atlantic Conveyer. This is where cold water that sinks in the far north is replaced by warmer water from the tropics in its circulation of the North Atlantic Ocean. A number of studies suggest that the conveyer may be unstable and may be able to slow down or switch off completely, making our climate suddenly colder. Our study provides evidence that the two climate shifts we detected were directly linked to a slow-down in the conveyer - Professor Jim Marshall.

Scientists believe that this new data will provided a unique test for the global climate computer models that are being used to simulate future climate change.
The research - in collaboration with University of Swansea; the Open University; University of Exeter; Edge Hill University and University College London - is published in Geology.

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