Atlantic Multidecadal Oscillation
The Atlantic Multidecadal Oscillation (AMO) is a climate mode in the North Atlantic, occurring on multidecadal time scales. The AMO index is a measure of basinwide sea surface temperature variation in the North Atlantic, adjusted to remove trends in anthropogenically forced warming (Enfield et al., 2001; McCabe et al., 2004). Like other modes of variability (e.g., El Niño Southern Oscillation), the AMO has impacts on a large geographic scale via atmospheric teleconnections, and has been hypothesized to have an influence on a range of North Atlantic fisheries and ecosystems
(Edwards et al., 2013; Shackell et al., 2012). In the Gulf of Mexico, the AMO has been associated with changes in the strength of the Yucatan Current and Loop Current (Liu et al. 2012), precipitation in the Mississippi River watershed (Enfield et al., 2001), and depth of the mixed layer (Zhang et al., 2012). Through these relationships, the AMO may affect Gulf of Mexico ocean temperatures, stratification, surface plankton productivity, and the development of hypoxia at the outflow of the Mississippi River – processes that can in turn influence the dynamics of biological and human communities.
The AMO was in a warm phase from the 1920s to the 1960s, a cold phase from 1970s to the early 1990s, and then changed back to a warm phase in the mid-1990s. Although the index remains in the warm phase at present, it shows a slight decrease in the past 5 years, with the index dropping below average more frequently than in the decade 2000 - 2010.