* Astronomy

Global Ice Age Climate Patterns Influenced by Bering Strait

In a vivid example of how a small geographic feature may have far-reaching impacts on climate, new research shows that water levels in the Bering Strait helped drive global climate patterns during ice age episodes dating back more than 100,000 years.
The international study, led by scientists at the National Centre for Atmospheric Research (NCAR) in Boulder, Colorado, found that the repeated opening and closing of the narrow strait due to fluctuating sea levels affected currents that transported heat and salinity in the Atlantic and Pacific Oceans.
As a result, summer temperatures in parts of North America and Greenland oscillated between comparatively warm and cold phases, causing ice sheets to alternate between expansion and retreat and affecting sea levels worldwide.
While the findings do not directly bear on current global warming, according to Steve Nelson, NSF program director for NCAR, they highlight the complexity of Earth's climate system and the fact that seemingly insignificant changes can lead to dramatic tipping points for climate patterns, especially in and around the Arctic.
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Ice Ages Linked To Slight Shifts In Solar Radiation
Sometime around now, scientists say, the Earth should be changing from a long interglacial period that has lasted the past 10,000 years and shifting back towards conditions that will ultimately lead to another ice age unless some other forces stop or slow it. But these are processes that literally move with glacial slowness, and due to greenhouse gas emissions the Earth has already warmed as much in about the past 200 years as it ordinarily might in several thousand years, Clark said.
A team of researchers says it has largely put to rest a long debate on the underlying mechanism that has caused periodic ice ages on Earth for the past 2.5 million years - they are ultimately linked to slight shifts in solar radiation caused by predictable changes in Earth's rotation and axis.
In a publication to be released Friday in the journal Science, researchers from Oregon State University and other institutions conclude that the known wobbles in Earth's rotation caused global ice levels to reach their peak about 26,000 years ago, stabilises for 7,000 years and then begin melting 19,000 years ago, eventually bringing to an end the last ice age.

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Crews excavating the World Trade Centre site this summer for the foundations of a new skyscraper have uncovered features carved into the bedrock by glaciers about 20,000 years ago, including a 40-foot-deep pothole.
Exposing the solid rock beneath at the ground zero site in lower Manhattan is critical for supporting what will be Tower 4 of the new World Trade Centre, being built by Silverstein Properties.
The reminders of the power of glaciers won't be around for long. The pothole and other features are being covered, filled in or blasted away.

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The geologists are digging in the bed on the western bank of what was once a 700-800 kilometre-long lake along the 62nd parallel in Russia. Large lakes, dammed up by a huge ice sheet one or more times during the last Ice Age, used to dominate this enormous plain.
The location is just beyond the ice margin from the maximum of the last Ice Age, where it has been mapped 100 kilometres north of the town of Kotlas in north-western Russia.
At Tolokonka, in a four kilometre-long cutting beside the River Dvina, an international team of scientists is busy studying the past changes in climate.

Lakes have probably been situated here in two periods during the last Ice Age. Weve found river delta deposits which suggest that the oldest lake formed some 65 000 years ago - Eiliv Larsen, a geologist at the Geological Survey of Norway (NGU).

He is in charge of fieldwork being done in Russia as part of the SciencePub project during the International Polar Year. Along with colleagues from NGU, the University Centre in Svalbard (UNIS) and Hertzen University in St. Petersburg, he is continually finding new pieces to fit into the last Ice Age jig-saw puzzle.
The enormous lake stretched from Kotlas in the west to the village of UstNem in the east, just a few tens of kilometres from the Ural Mountains. Last year, the scientists found remnants of a lake near UstNem. Now, the same lake has been found 700-800 kilometres further west, in the long cutting at Tolokonka. The mighty River Dvina, meandering north-westwards through the flat landscape to Archangel, dominates this region today.

Were trying to find out just what these lakes have looked like. Where did the sediments come from and how did the lakes influence the environment and the climate in the region? Even though were just beyond the ice margin, were finding traces of the snout of a glacier that calved into the lake from the north. This probably took place around 20 000 years ago and this was the youngest lake in the region - Eiliv Larsen.

The scientists also tell me that it is very interesting to find out what took place when the ice finally melted, the dams burst and the enormous volumes of dammed up fresh water poured into the Arctic Ocean. This must have had consequences for the climate system and the oceanic circulation, for example.

We ourselves are urged on by curiosity. When we started working in these parts of Russia 12 or 13 years ago, very little research had been done on the Ice Age. The results of our work now form part of the framework which climate researchers are using to calculate the future climate. From a distance, you see hardly anything of the inside of the room, but the closer you manage to put your eye to the keyhole, the more of the room becomes apparent. Its the same with the research here in north-western Russia, were uncovering more and more of the Ice Age history and hence the past climate changes - Eiliv Larsen.

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