Long-term changes in the thermocline of the subtropical Northeast Atlantic (33°N, 22°W)

Data from almost thirty years of time series observations from a deep-sea mooring Kiel276 (33°N, 22°W), which was operated in the northeast Atlantic Ocean between 1980 and 2009, are studied to reveal information on the long term changes in the upper thermocline. This includes daily records of temperature and currents at two depths (240 m and 500 m). Until 1988, our analysis shows decreasing temperature in the entire thermocline followed by a slight increase at both depths; from 2000 on, extensive warming began at the shallower depth (240 m) and eight years later at the deeper (500 m) level. A northward displacement of the North Atlantic Subtropical Gyre is indicated by both current measurements and calculated kinetic energy between 1991 and 1998 resulting in an altered current regime in terms of absolute velocity and current directions in the last ten years compared to the first twenty years. Coherences of the currents with large scale climatic patterns such as North Atlantic Oscillation and El Niٌo/ Southern Oscillation evidence the atmospheric impact even at 500 m water depth.