A new study, led by the universities of Exeter and Oxford, and published in Nature Geoscience (paywall), pinpoints the causes of monthly and annual Atlantic meridional overturning circulation (AMOC) variation and finds a differing picture at two key locations.

The AMOC, which carries warm water from the tropics northward and makes areas including north-west Europe warmer than they would otherwise be, is expected to weaken over the coming decades, with widespread implications for regional and global climate.  While AMOC variability off the southern USA is dominated by the impact of winds, the combined effects of winds, heat and freshwater anomalies generate variability in the North Atlantic.

“Our reconstruction suggests that, compared to the subtropics, the overturning circulation in the subpolar North Atlantic is more sensitive to changes in the background ocean state such as shifts in the sites of deep convection … This implies that future climate change may alter annual AMOC variability in this region. It emphasises the need for continued observations of the subpolar North Atlantic ocean.”  Click here.

Scientists at Scripps Institution of Oceanography, San Diego, and colleagues have created an estimate of the journey water makes around the world ocean basins using information from more than 1 billion data points collected over 25 years.

Whilst the oceanographers found that random parcels of water will take hundreds or sometimes thousands of years to complete an epic journey back to their points of origin, they too found that the AMOC could be more vulnerable to disruption than previously understood.  Read more here and here (open access).

At a more local scale, a research collaboration led by the Technical University of Munich have conducted the first precise and comprehensive measurements of sea level rises in the Baltic Sea and the North Sea. A new method now makes it possible to determine sea level changes with millimetre accuracy even in coastal areas and in case of sea ice coverage. This is of vital importance for planning protective measures.  Click here and here.