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.