Dryas

Ice sheets, records of the past

The polar ice caps of Greenland and Antarctica are the bulk of the cryosphereLa cryosphere includes sea ice, frozen lakes and rivers, regions covered with snow, glaciers, ice sheets and frozen ground, permafrost. and represent more 90% of the volume of freshwater on the planet.
The caps are cool areas of the Earth and interact with the global climate.
They disappear in less than 10 000 years as was the case for caps in North America and Eurasia at the end of the last glacial period. Ice caps trace the history of the Earth, they are the records of the past because the study of mineral dust trapped, we can analyze the content and reasons for their issuance. The ice cores drilled in these continuous records traced the environment of the past, during the last climatic cycles. In the early 1970s, Americans realized drilling Byrd reached 2138 meters deep. The Russians at the same time realize a borehole 500 meters, then in 1975, a borehole 900 meters. After years of effort, refined techniques and drilling reached a depth of 2000 meters in 1982. We discover in the cores from Vostok, the end of the last glaciation that occurred about 15,000 years with a maximum around 25,000 years, but a previous age to interglacial 120,000 years of glaciation prior to -140 000 years. Much information is then collected by scientists, they have under their eyes, thanks to dust, the history of the composition of the atmosphere with carbon dioxide and methane, the changing chemistry of the atmosphere as well as atmospheric circulation.

In 1994 we reached 3,350 meters, and in January 1998, 3623 meters. Corers modern tubular assemblies are a dozen meters long, including a drilling head, a core barrel with its engine and control instruments. The assembly is attached to the end of an electro-carrying 3 or 4 km wound on a powerful winch.
Ice cores are studied on the spot for their physical properties and sampled for various laboratory measurements. Then, following a string of cold cores are sent to laboratories where they will be kept in cold room at -23 ° C.
The layers of volcanic dust can be traced back to different volcanoes eruptions have issued. Chemical compounds from the atmosphere can indicate changes in biogeochemical cycles between ice ages and interglacial, particularly sulfur and that of marine aerosols.
Gaseous compounds extracted from the atmosphere of air bubbles trapped in ice can trace the evolution of the atmosphere. The atmospheric concentration of CO2, the main greenhouse gases after water vapor, is now restored to 400,000 years plus or minus 10%. These holes, extremely informative, push scientists to pursue new drilling. Europeans are at Dome C in Antarctica, the Japanese bore the Dome Fuji, the Americans Siple Dome, the Danes in Greenland drill.

Image: These are the ice sheets that inform us of changes in climate and rainfall of the past. The study of gas bubbles trapped in the ice tells us about the composition of the atmosphere over time. The first set of samples, arrived in France in 1983, reveals a continuous history of climate on more than 140 000 years.

Dryas « - 14 000 à - 9 000 years »

After the end of the Würm glaciation, global warming has led to the climate we know today was interrupted by a new cold period, the Dryas.
Dryas, paleoclimatology name given to the Quaternary period, which corresponds to the last cooling.
From -14 000 to -9 000 years, temperatures dropped further.
A brief cooling and warming extremely fast, concluded this period. Before the rapid rise in temperature, the Younger Dryas saw him, a brief cooling about 1300 years, marked by a significant drop in mean temperature (10 degrees) in the northern hemisphere especially in Greenland.
The scenario suggested by paleo climatologists is that at the end of the Würm glaciers of the ice sheet in North America have melted, revealing, between Canada and the United States, a large lake, Lake Agassiz, a surface approximately 350 000 km² equivalent to half the size of France (675 417 km²).
The cold waters of the lake are then rushed to the St Lawrence.
It seems that this massive spill has disrupted the current scale of the oceans of the world that this place is the Gulf Stream.

The beginning of the Younger Dryas (Dryas III) is according to sources, between 12 700 and 11 500. In duration, it varies from 600 to 2500 years.

NB: The Wurm, or Würm glaciation, is the name given to the last global glaciation of the Pleistocene in the Alps, where the comments (ply fluvio-glacial moraines) showed a significant drop in mean temperatures over a long period in the Alps.

Image: Thermohaline circulation of ocean waters.

Image: Dryas was named after a flower called Dryas octopetala, but also Argentina and Tea in the Alps. This flower was one of the first to colonize the peatlands released by the glaciers of this period when its pollen was found in abundance.