The land bridge that once connected North America and Asia rose from the seas 80,000 years ago. And at the same time, North America's climate began experiencing violent climate swings, with average temperatures shifting as much as ten degrees every decade.
That pattern of massive temperature swings lasted a whopping 70,000 years, which just so happens to be pretty much the exact same time period the land bridge connected Alaska and Siberia. Known as Beringia, this bridge was really its own vast landmass, a thousand miles across in places and home to its own relatively comfortable ecological refuge. We know animals used Beringia to move between the two continents, and although there's now evidence to suggest humans actually used coastal boats to reach the Americas, it's likely Beringia played a role in human colonization of the Americas.
As such, the land bridge is hugely important to the Earth's recent biological and anthropological history. But according to a team led by Aixue Hu, a climate scientist at the National Center for Atmospheric Research, Beringia pretty much rewrote the climate patterns of North America for tens of thousands of years. ScienceNOW has the story:
Hu's team ran two sets of climate simulations: one in which the Bering Strait was open, as it is today, and one in which it was blocked, separating the North Pacific from the Arctic Ocean. In each set of simulations, the researchers gradually added large amounts of fresh water to the North Atlantic between the latitudes of 20° and 50°. At the time, the researchers propose, this swath, which spans the latitudes from southern Cuba to southern England, would have received large amounts of meltwater from Northern Hemisphere ice sheets during warm spells that occasionally punctuated the ice age. Today, the surface waters in this swath affect the temperature and salinity of water even farther north in the Atlantic, a region where surface waters cool, sink to the seafloor, and then flow southward-a critical link of the worldwide conveyor belt of ocean circulation. If waters of the far North Atlantic don't sink, says Hu, much of the large-scale ocean circulation worldwide temporarily collapses. One result: the Gulf Stream, which brings climate-warming waters from the equator to the North Atlantic, comes to a halt.
Cutting off the Pacific from the Arctic Ocean caused the standard ocean circulation patterns to fall apart. Without this reliable movement of ocean water, the surrounding climate couldn't stabilize, explaining these massive temperature swings, which could see changes of ten degrees Celsius in average temperatures over a single decade. You can check out the original paper here.
For more, check out ScienceNOW.