The ICES Report on Ocean Climate presents the latest information on the status and trends of sea temperature and salinity in the North Atlantic and Nordic Seas. It is the main product of the ICES Working Group on Oceanic Hydrography, published annually. Bringing together multiple time-series from across the ICES and NAFO regions offers insight into the concurrent spatial and temporal trends in ocean temperature and salinity. This paper presents an overview of the physical variability in the North Atlantic Ocean at decadal and longer time-scales and reviews the current state of understanding of the causes and mechanisms of this variability. Between the 1960s and the 1990s, the North Atlantic Oscillation (NAO) index increased from a persistent negative phase in the 1960s to a strong positive phase during the 1980s and early 1990s. However, during the decade 20002009, because of shifts in atmospheric pressure patterns, the NAO was weak and the NAO index was not a good indicator of atmospheric forcing. Marked changes were also observed in oceanographic indices such as the Subpolar Gyre index during the mid-1990s and, as a consequence, conditions in the decade 20002009 have been very different from those of the previous four decades.
- multidecadal variability
- North Atlantic