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

MADRID, 14 (EUROPA PRESS)

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

The research, published in Nature Communications, shows that observations made over four years beginning in 2014 in the subpolar North Atlantic reveal no signs of strong winter ocean surface cooling at the density of the deepest boundary currents encountered. in the western regions of the ocean basins. Surprisingly, the authors also did not find a visible relationship between changes in those deep western boundary currents and variations in the strength of the MOC, the southern roll-over circulation, which is the zonally integrated component of shallow and deep currents in the Atlantic Ocean.

Knowledge of the physical processes that govern changes in the MOC is essential for accurate climate projections. The MOC brings large amounts of heat and salt to the North Atlantic 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 damaging impact on coastal communities and the land.

Previous analysis of the models has led scientists to think that changes in the strength of the MOC are associated with 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 wintry process called deep convection or deep water formation, where cold winds cool surface water, causing it to become very dense and sink to great depths (more of 2 km). The modeling relationship between convection, changes in deep western border currents, and MOC strength also supports the evidence for paleoclimate indicators for periods of reduced MOC and low European temperatures.

In 2014 scientific teams were placed in the subpolar North Atlantic (OSNAP) to observe these processes in real life. The surprising new results will stimulate a reconsideration of the view that profound changes in the western limits represent changing characteristics, with implications for future climate projections, as well as the interpretation of past climate change.