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GEOPHYSICAL RESEARCH LETTERS, VOL. 34, L12608, doi:10.1029/2007GL029957, 2007

A twenty year reversal in water mass trends in the subtropical North Atlantic

S. J. Leadbetter

Department of Earth and Ocean Sciences, University of Liverpool, Liverpool, UK


R. G. Williams

Department of Earth and Ocean Sciences, University of Liverpool, Liverpool, UK


E. L. McDonagh

National Oceanography Centre, Southampton, UK


B. A. King

National Oceanography Centre, Southampton, UK


Abstract

Temperature and salinity changes have been compared along three repeat sections at 36°N in the North Atlantic. The principal changes, cooling of the upper waters and warming of the intermediate waters observed between 1959 and 1981, were reversed between 1981 and 2005. The controlling mechanisms for the changes over the two time periods differed through the water column. Neutral density surfaces over the upper 800 m were firstly uplifted and secondly depressed by typically 50 m, which is broadly consistent with the changes in thermocline thickness implied by the temporal changes in Ekman pumping. In contrast, the intermediate waters (800–2500 m) firstly became warmer and saltier and secondly became cooler and fresher. This change in the intermediate waters was controlled by water mass changes along neutral density surfaces suggesting a change in the source waters, principally Labrador Sea Water and Mediterranean Outflow Water.

Received 10 March 2007; accepted 23 May 2007; published 26 June 2007.

Keywords: decadal change; hydrographic data; North Atlantic.

Index Terms: 4271 Oceanography: General: Physical and chemical properties of seawater; 4279 Oceanography: General: Upwelling and convergences (4964); 4283 Oceanography: General: Water masses; 4513 Oceanography: Physical: Decadal ocean variability (1616, 1635, 3305, 4215); 4536 Oceanography: Physical: Hydrography and tracers.

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Citation: Leadbetter, S. J., R. G. Williams, E. L. McDonagh, and B. A. King (2007), A twenty year reversal in water mass trends in the subtropical North Atlantic, Geophys. Res. Lett., 34, L12608, doi:10.1029/2007GL029957.