| Summary: | International audience Recent studies using models have reported opposite trends in the past decadal evolution of phytoplankton in the subpolar North Atlantic. In another hand, while long time series of phytoplankton observations are available in this region, they never have been investigated in parallel to physical forcing to understand their variability. Here, we investigated the multi decadal variability of phytoplankton and its underlying mechanisms since the 1960s, thanks to fifty years of in situ observations combined with satellite missions, reanalysed and model products. We show that a phytoplankton increase paralleled a deepening of the mixed layer depth (MLD) since the 1960s. This MLD deepening was related to a strengthening of the winds and net heat loss of the ocean after the mid-1980s following the low frequency signal of the North Atlantic Oscillation. Moreover, the decadal increase of sea surface temperature reported in this region was not associated with the expected scenario of shallower MLD. Our results run counter to the paradigm about how global warming could impact on MLD and phytoplankton abundance.
|
|---|