strait serves as a gate for cooler, less salinized water from the
Pacific to flow to the warmer and saltier Atlantic. Their simulations
found that without this flow, the climate of North America fluctuates
much more rapidly – in the span of a few thousand years rather than
some tens of thousands – and helps explain constant temperature and
ice sheet modulation between 116,000 and 34,000 years ago, a time of
constant ice sheet advance and retreat.
In the past, this
pattern was often attributed to the Earth’s position along its
95,000 year orbital pattern, but the NCAR researchers found that when
correlated with the temperature and ice data, the orbit could not
explain the rapid fluctuations. Instead, it occurred to them that
changes to the Bering Strait itself could have a large impact on the
entire region due to the changes it would bring to the Pacific and
Atlantic ocean currents. Their models indicate that a slight change
in the strait would adversely affect the meridional overturning
circulation, an ocean current which helps drive the Atlantic
tropics-to-polar heat pump.
the simulation, they show that around 110 to 115 thousand years
ago, the northern climate cooled sufficiently to create giant ice
sheets over the northern regions of North America and all of
Greenland. As these ice sheets sucked up water from the global
oceans, sea levels dropped by as much as 100 feet. Eventually a vast
amount of the strait was no longer able to pass water – the average
depth of the strait is 100 - 190 feet. The new land bridge cut off a
vast portion of the ocean flow between the Pacific and Atlantic.
This, in turn, caused the Pacific ocean to become even cooler and
cleaner, but allowed the now saltier waters of the Atlantic to push
the meridional overturning circulation into overdrive, warming the
regional ocean, North America and Greenland by as much as 1.5C over a
few thousand years.
Next, the regional warming caused the iced
sheets to melt over another few thousand years, returning the oceans
to their previous depth and reopening the Bering Strait. With the
Atlantic’s access to cooler and cleaner water from the Pacific
restored, the cycle started all over again.
oscillations went on like a driver overcompensating for an icy road
fishtail until finally, around 34,000 years ago, the Earth’s
distance from the sun was so great that it literally froze the
fluctuation in place. About 10,000 years ago, the Earth had finally
gotten close enough to the sun again to warm up the northern
hemisphere to the point where the strait reopened slowly and the
temperature variations settled into a much more docile animal.
study helps to provide convincing data for two things: that a
significant change in something even so geographically small can
adversely affect the climate of an entire quadrant of hemisphere, if
not an even greater area, and that the planet has its own regulatory
devices to deal with such things. However, it remains to be seen how
long the cycle would have gone on if not for the fortuitous position
in the orbital cycle. Too, this study reflects nothing at all of
man’s influence on these climate systems in current times. The key
to understanding these things lies in first understanding the basic
driving forces behind climate systems and the NCAR study has shown us
how one such small system may operate.
quote: But it used to be more than ten times that...and we never had runaway global warming.