Boat-based measurements had shown a 30% slowing of the current that brings warm water to UK shores (ENDS Report 381, pp 34-36 ). But results from automatic sensors installed by the National Oceanography Centre in 2004 reveal a more complicated picture.1
The sensors recorded considerable daily variation with flows ranging from four million tonnes of water a second to 35Mt/second during the first year. The average figure – 19 Mt/second – is higher than the most recent boat-based readings.
The findings are supported by another recent study charting changes in salinity.2 The system is driven by cooler water sinking in the polar region, dragging warm surface water north from the equator. Fears for its stability are based on geological evidence that inputs of freshwater from melting ice sheets have stalled the current in the past.
The US National Oceanic and Atmospheric Administration has tracked salinity changes in the North Atlantic since the 1950s. Its results show a fall in salinity from the late 1960s to the early 1990s, followed by an increase.