Science. Doubts about the origin of changes in the North Atlantic currents

Madrid, 14 (Europe Press)

A new study casts doubt that differences in density in the deep currents of the North Atlantic during winter represent changes in the strength of ocean circulation.

The research, published in Nature Communications, shows that observations made over four years starting in 2014 in the sub-North Atlantic Ocean do not reveal any signs of strong cooling of the winter ocean surface at the density of the deepest boundary currents encountered in the western regions. from ocean basins. . Surprisingly, the authors also did not find a clear relationship between changes in those deep western boundary currents and differences in the strength of the MOC, the southern rolling circulation, which is the region’s integral component of shallow and deep currents in the Atlantic.

Knowledge of the physical processes that govern changes in the MOC is essential for accurate climate projections. MOC brings large amounts of heat and salt to the North Atlantic Ocean through the Gulf Stream and the North Atlantic Stream. Changes in the strength of the MOC directly affect sea level, climate, and weather in Europe, North America, and parts of the African continent. All climate projections predict a slowdown in MOC as a result of greenhouse gas emissions, with potentially adverse effects on coastal communities and land.

Previous analysis of the models led scientists to believe that changes in the strength of the MOC are related to changes in the density of the deep western boundary currents that make up most of the return flow south of the MOC loop. In models, density can be strongly affected by a winter process called deep convection or deep water formation, in which cold winds cool surface waters, making them very dense and sinking to great depths (more than 2 km). The modeling relationship between convection and changes in deep western boundary currents and MOC strength also supports evidence for paleoclimate indices for periods of low MOC and European low temperatures.

In 2014, scientific teams were stationed in the North Atlantic Subregion (OSNAP) to monitor these processes in real life. The surprising new findings will prompt a reconsideration of the view that deep changes in the western boundary represent shifting properties, with implications for future climate projections, as well as an explanation of past climate change.