Is observed variability in the long-term results of the Continuous Plankton Recorder survey a response to climate change?

In the more than 50 years that the Continuous Plankton Recorder (CPR) surve y has operated on a regular monthly basis in the north-east Atlantic and No rth Sea, large changes have been witnessed in the planktonic ecosystem. The se changes have taken the form of long-term trends in abundance for certain species or stepwise changes for others, and in many cases are correlated w ith a mode of climatic variability in the North Atlantic, either: (1) the N orth Atlantic Oscillation (NAO), a basin-scale atmospheric alteration of th e pressure field between the Azores high pressure cell and the Icelandic Lo w; or (2) the Gulf Stream Index (GSI); which measures the latitudinal posit ion of the north wall of the Gulf Stream. Recent work has shown that the ch anges in the GSI are coupled with the NAO and Pacific Southern Oscillation with a 2 year lag. The plankton variability is also possibly linked to chan ges observed in the distribution and flux of water masses in the surface, i ntermediate and deep waters of the North Atlantic. For example, in the last two decades, the extent and location of the formation of North Atlantic De ep Water, Labrador Sea Intermediate Water and Norwegian Sea intermediate an d upper-layer water has altered considerably. This paper discusses the exte nt to which observed changes in plankton abundance and distribution may be linked to this basin-scale variability in hydrodynamics. The results are al so placed within the context of global climate warming and the possible eff ects of the observed melting of Arctic permafrost and sea ice on the subpol ar North Atlantic.