Antarctica has presented yet another mystery. Studying oceanographic data, collected
between 1980 and 2011, Purkey and Johnson have found the coldest water on
earth, Antarctic Bottom Water (ABW), has been disappearing. In fact ABW has been disappearing at a rate
of about eight million metric tons per second over the last few decades. This is fifty times the average flow of the
Mississippi river. Nobody knows why!
Previous studies have found that ABW has been warming and
freshening over the past few decades. This
most recent study, however, is the first that demonstrates an overall decrease
in ABW formed now, compared to the past.
ABW forms in different spots around Antarctica. Seawater is cooled by the cold air above and
made denser by ice formation. Normally
this denser saltier water sinks to the sea floor and eventually flows
northward. As it moves to higher latitudes,
it slowly mixes with the warmer water above.
ABW and the currents that circulate it around the globe are critical in
regulating where and how heat and carbon are transported around the
planet. Thus ABW is critical in shaping
global climate patterns.
With further study it will be interesting to see why ABW has
been showing such a dramatic decrease, and what affect this phenomenon may have
on the global climate.
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