"The Earth’s climate system and ecosystems often exhibit non-linear behavior and abrupt changes, the latter especially challenging societies ability to adapt. More specifically, abrupt changes in marine ecosystems are of great socioeconomic concern. Past regime shifts in marine ecosystems such as observed in 1977 and in 1998 in the North Pacific in several trophic levels challenged the marine resources managers because of the scale (throughout the North Pacific) and the abruptness (occurred within a year or so) of the change. For example, after the 1998 regime shift in the western North Pacific, herring, capelin and anchovy replaced the previously dominant Japanese sardine. In marine ecosystems, abrupt changes can be induced by climate variability or can also be generated randomly from within the system. Abrupt changes can also be triggered when the system responds in a gradual way to forcing until it crosses some threshold, after which it rapidly transitions to a new state. Since regime shifts may be detectable earlier in marine plankton than in upper trophic levels, this project aims to investigate the presence of abrupt changes in time series of marine phytoplankton and zooplankton abundance and to identify the physical mechanisms responsible for inducing abrupt changes. This project will further investigate the presence of threshold effects between marine plankton and their physical forcings, where a small increase in forcing leads to a larger change in phytoplankton and zooplankton abundance. The presence of early warning indicators before abrupt changes in marine plankton will be assessed to determine whether these changes could be anticipated in the future."