Ecosystem effects of the Atlantic Multidecadal Oscillation Janet A. Nye a, ⁎, Matthew R. Baker b , Richard Bell c , Andrew Kenny d , K. Halimeda Kilbourne e , Kevin D. Friedland c , Edward Martino f , Megan M. Stachura g , Kyle S. Van Houtan h, i , Robert Wood f a United States Environmental Protection Agency, Office of Research and Development, National Health and Environmental Effects Research Laboratory, Atlantic Ecology Division, 27 Tarzwell Dr, Narragansett, RI 02882, USA b NOAA National Marine Fisheries Service, Alaska Fisheries Science Center, 7600 Sand Point Way N.E., Seattle, WA 98115, USA c NOAA National Marine Fisheries Service, Northeast Fisheries Science Center, 28 Tarzwell Dr., Narragansett, RI 02882, USA d Centre for Environment, Fisheries & Aquaculture Science, Lowestoft, UK e Chesapeake Biological Laboratory, Center for Environmental Science, University of Maryland, Box 38, Solomons, MD 20688, USA f National Oceanic and Atmospheric Administration, Cooperative Oxford Laboratory, Oxford, MD 21654, USA g School of Aquatic and Fishery Sciences, University of Washington, Box 355020, Seattle, WA 98195–5020, USA h NOAA Fisheries Service, Pacific Islands Fisheries Science Center, Honolulu, HI 96822, USA i Nicholas School of the Environment and Earth Sciences, Duke University, Durham, NC 27708, USA abstract article info Article history: Received 26 April 2012 Received in revised form 21 November 2012 Accepted 15 February 2013 Available online 21 February 2013 Keywords: Climate variability Climate change Ecosystem based management Multidecadal variability in the Atlantic Ocean and its importance to the Earth's climate system has been the sub- ject of study in the physical oceanography field for decades. Only recently, however, has the importance of this variability, termed the Atlantic Multidecadal Oscillation or AMO, been recognized by ecologists as an important factor influencing ecosystem state. A growing body of literature suggests that AMO-related fluctuations are asso- ciated with shifts in ecological boundaries, primary productivity, and a number of ecologically and economically important coastal and marine populations across the Atlantic basin. Although the AMO is a basin-wide index of SST, the drivers of ecosystem change encompass more than temperature anomalies and the mode of action dif- fers within each ecosystem. A common theme in assessing ecosystem change indicates that fluctuations in water masses and circulation patterns drive shifts in ecosystem states, but the magnitude and rate of change is depen- dent on the physical characteristics of the region. Because of the wide ranging geographic effects of the AMO, and considering its multidecadal nature, a more complete understanding of its causes and effects would allow scien- tists and managers to more effectively inform ecosystem-based management across the Atlantic Basin. © 2013 Elsevier B.V. All rights reserved. 1. Introduction There are several modes of climatic variability in the North Atlantic that affect ecosystem processes, but one mode of variability that has re- ceived relatively little attention until recently is the Atlantic Multidecadal Oscillation (AMO sensu Kerr, 2005) also known as Atlantic Multidecadal Variability (AMV sensu Delworth et al., 2007; Knight et al., 2005). It is hypothesized that fluctuations in the strength of Atlantic Meridional Overturning Circulation (AMOC) cause internal variability in sea surface temperature (SST), sea level pressure, and ocean circulation all of which are represented by the AMO index (Knight et al., 2005; Ting et al., 2011). Many biological oceanographers are familiar with the AMO index and refer to this large-scale phenomenon as the AMO. For consistency we will use this terminology throughout this review of its effect on ecosys- tems. However, the AMO index represents a wide variety of processes such that AMV is perhaps the more appropriate terminology for this phenomenon. In particular, records of past climate variability indicate that the AMO is not an oscillatory cycle with regular periods of fixed length (Gray et al., 2004; Knudsen et al., 2011). Instead it appears to be a climate system feature with variance concentrated at multidecadal scales. The AMO index (Fig. 1) is typically defined as the SST anomaly from 0-60 o N linearly detrended to account for the increase in temper- ature associated with anthropogenic climate change (Enfield et al., 2001; Sutton and Hodson, 2005). Modern observations of SST indicate that the AMO switches between positive and negative phases on the order of 65–70 years (Schlesinger and Ramankutty, 1994), but the length and consistency of the oscillatory cycle is the subject of considerable de- bate. The 65–70 year cycle is based on only ~130 years of observed and reconstructed SST data for which there are only 1.5-2 complete cycles of the AMO. Smoothing or detrending of SST to calculate the AMO index results in oscillations of different frequencies (Vincze and Janosi, 2011). Although the exact timing of the switch from the positive to neg- ative phase depends on how the index is calculated, it is generally agreed that negative/cold phases occurred from approximately 1900–1925 and 1971–1994 while positive/warm phases occurred from 1875–1899, 1926–1970 and 1990–present (Goldenberg et al., 2001). Journal of Marine Systems 133 (2014) 103–116 ⁎ Corresponding author at: School of Marine and Atmospheric Sciences, Stony Brook University, Stony Brook, NY 11794-5000, USA. Tel.: +1 401 782 3165. E-mail address: janet.nye@stonybrook.edu (J.A. Nye). 0924-7963/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jmarsys.2013.02.006 Contents lists available at ScienceDirect Journal of Marine Systems journal homepage: www.elsevier.com/locate/jmarsys