Global Warming Could Reverse Ocean Circulation

A recent article in Nature details how data from isotopes of uranium in seawater are showing that Atlantic Ocean circulation was very different in the past, at times the reverse of current circulation. Ocean currents are driven by both temperature and salinity gradients; they transport warm water (and energy) from the tropics to the poles, and move carbon from the surface to the deep ocean. In the Atlantic Ocean, this pole-to-pole and surface-to-depths circulation is called the meridional overturning circulation (MOC); it has a major influence on climate. The new isotope data indicates that during the Last Glacial Maximum 20,000 years ago, basin-scale deep-ocean circulation was probably reversed, dominantly northward rather than southward as it is now.  

According to ScienceDaily, these findings highlight the sensitivity of the MOC to changes in salinity; this finding has implications for the future, as global warming over the next 100 years is expected to cause similar changes in ocean salinity, which could in turn cause the circulation patterns to change.  Since the world’s oceans are interconnected, changes in circulation in one ocean will affect circulation—and thus climate—around the world. This new data is expected to be particular useful for calibrating climate models and predicting future conditions.