Arctic Changes Influenced Ice Age Global Climate Patterns
13.01.2010 - Atmosphere & Space, Water & Oceans, Land & Geology, Ice & Snow, Arctic
An international study led by scientists at the National Center for Atmospheric Research (NCAR) is being published this week in Nature Geoscience. The study shows that water levels in the Bering Strait helped drive global climate patterns during ice ages dating back more than 100,000 years.
Whereas in previous studies scientists have associated major changes in climate with fluctuations in Earth's orbit around the sun, the orbital pattern of the period that the research team looked at did not correspond with the geologic movement of the ice sheets and associated sea level changes.
Using new supercomputers at NCAR, the researchers ran the NCAR-based Community Climate System Model (CCSM), which enabled them to focus on smaller geographic features that could not be captured in long-term simulations of global climate before. The model showed that:
- Northern ice sheets expanded as a result of climate cooling, causing a global sea level drop and created a land bridge from Asia to North America.
- The flow of relatively fresh water from the Pacific to the Atlantic disappeared, causing the Atlantic to grow more saline, leading to an intensification of the Atlantic's meridional overturning circulation, a current of rising and sinking water that, like a conveyor belt, pumps warmer water northward from the tropics.
- This circulation warmed Greenland and parts of North America by about 1.5 degrees Celsius, reversing the advance of ice sheets in those regions and reducing their height by almost 112 meters every thousand years.
- Over thousands of years, the Greenland and North American ice sheets melted enough to raise sea levels and reopen the Bering Strait.
- The new inflow of fresher water from the Pacific weakened the meridional overturning circulation, allowing North America and Greenland to cool over time and repeat the entire cycle.
The pattern was finally broken about 34,000 years ago - the point in Earth's 95,000-year orbital cycle at which the planet was so far from the sun at certain times of year that the ice sheets continued to grow even when the Bering Strait closed. When the orbital cycle brought Earth closer to the sun during the boreal (northern) winter, the ice sheets retreated sufficiently about 10,000 years ago to reopen the strait. This helped lead to a relatively stable climate, nurturing the rise of civilization.
"The global climate is sensitive to impacts that may seem minor," says NCAR scientist Aixue Hu, the lead author. "Even small processes, if they are in the right location, can amplify changes in climate around the world."
