Page - October 19, 2006
The water in our world's oceans is always moving – pulled by tides, blown by waves, and slowly circulating around the globe by the force of the Great Ocean Conveyor Belt (aka thermohaline circulation). The Conveyor is powered by differences is water temperature and salinity, and one of its most well know parts, the Gulf Stream, is what gives Europe it's relatively mild climate.
How it works
Warmsalty water from the Gulf Stream is cooled when it reaches
the NorthAtlantic. It becomes denser and sinks to deeper layers of
the ocean,'pumping' cold water south in the deep ocean, past Africa
into theSouth Atlantic. Salt rejected as sea ice forms also
increases thedensity of these waters and contributes to the
process.
Thedense, cooled water becomes part of what is called the Ocean
Conveyor,and the water eventually returns to the surface in the
Indian andPacific Oceans. As warm water returns to the Atlantic,
the currentmoves pole-wards as the Atlantic Gulf Stream and North
Atlantic Drift,warming northwestern Europe substantially.
Aside from keepingEurope warm, and playing an important role in
the global climate, theConveyor provides an up welling of bottom
ocean nutrients, andincreases the oceanic absorption of carbon
dioxide. The GulfStream is what moderates European climate, the
whole system is calledThe Great Conveyor Belt, the Great Ocean
Conveyor, or whatever otherpopular name you want to give to the
thermohaline circulation system.
What could go badly wrong
Worryingly,recent studies warn that we may already have evidence
of a slowerConveyor circulation over the Scotland-Greenland deep
ocean ridge. Andwhile the Conveyor appears to have operated fairly
reliably over thepast several thousand years, an examination of ice
cores from bothGreenland and Antarctica shows that this has not
always been the case.In the more distant past, changes to the
Conveyor circulation areassociated with abrupt climate change.
In short, dilution of theocean's salinity - from meting Arctic
ice (such as the Greenland icesheet) and/or increased precipitation
- could switch off, slow down ordivert the Conveyor. This dramatic
cooling would mean a massivedisruption to European agriculture and
climate, and impact other seacurrents and temperatures around the
globe.
More information:
Abrupt climate change - Woods Hole Oceanographic
Institution