In the North Atlantic both phytoplankton and zooplankton species plus communities have been associated with Northern Hemisphere Temperature (NHT) trends and variations in the North Atlantic Oscillation (NAO) index. These have included changes in species distribution and abundance, the occurrence of sub-tropical species in temperate waters, changes in overall phytoplankton biomass and season length, changes in the North Sea ecosystem, community shifts, phenological changes and changes in species interaction. Over the last decade numerous other investigations have established links between the NAO and the biology of the North Atlantic including the benthos, fish, seabirds and whales. While the NAO index integrates variability in many hydro-climatic parameters, it is assumed that the increase in temperature over the last decade has had a primary role in influencing the ecology of the North Atlantic. Indirectly the progressive freshening of the Labrador Sea region, attributed to climate warming and the increase in freshwater input to the ocean from melting ice, has resulted in increasing abundance, blooms and shifts in seasonal cycles of dinoflagellates due to the increased stability of the water-column.

Like the North Atlantic, many long-term biological investigations in the Pacific have established links between changes in the biology and regional climate oscillations such as the El Niño/Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO). In the case of the Pacific these biological changes are most strongly associated with El Niño events which can cause rapid and sometimes dramatic responses to the short-term Sea Surface Temperature (SST) changes accompanying El Niño events. Changes in mesozooplankton abundance have also been related to large-scale climate influences in the Californian upwelling system. In the Southern Ocean the long-term decline in krill stock has been linked to changes in the extent of winter ice, which has been related to warming temperatures.

Evidence of observed changes is biased towards areas that have had some form of biological monitoring in place over a consistently long period. For this reason some of the strongest evidence detected for observed changes in marine ecosystems comes from the North Atlantic where an extensive spatial and long-term biological survey exists in the form of the Continuous Plankton Recorder (CPR) survey. The CPR survey has been in operation in the North Sea and North Atlantic since 1931 and has systematically sampled up to 400 planktonic taxa from the major regions of the North Atlantic at a monthly resolution. Recent macroscale research has shown that the increase in regional sea temperatures has triggered a major re-organisation in calanoid copepod species composition and biodiversity over the whole North Atlantic basin. During the last 40 years there has been a northerly movement of warmer water plankton by 10° latitude in the north-east Atlantic and a similar retreat of colder water plankton to the north. This geographical movement is much more pronounced than any documented terrestrial study, presumably due to advective processes. Highly significant relationships have been found between plankton, salmon returns to home waters, cod recruitment and three indices of hydro-meteorological forcing Northern Hemisphere temperature (NHT), SST in the eastern Atlantic and the NAO. These relationships have been reinforced by a strong link with NHT from the 1980s onwards. In terms of marine phenological changes and climate, the plankton of the North Sea has been extensively studied using CPR data. Using 66 taxa it was found that the plankton community was responding to changes in SST by adjusting their seasonality (in some cases a shift in seasonal cycles of over six weeks was detected), but more importantly the response to climate warming varied between different functional groups and trophic levels, leading to a mismatch. It is thought that temperate marine environments are particularly vulnerable to phenological changes caused by climatic warming since the recruitment success of higher trophic levels is highly dependant on synchronisation with pulsed planktonic production. The rapid changes in plankton communities observed over the last few decades in the North Atlantic, related to regional climate changes, have enormous consequences for other trophic levels and biogeochemical processes.