Hydroclimatic relationships with planktonic time series from 1975 to 1992 in the north sea off Gravelines, France

Planktonic time series collected since 1975 off Gravelines, France, were analysed in the context of climatic changes. Principal component analysis and the cumulative sums method were applied to 30 data sets which included meteorological and hydrological parameters and planktonic descriptors. Eight groups of biological descriptors were linked to external parameters. The study of winds highlighled the importance of cyclonic and anticyclonic influences. Seven year cycles appeared clearly in air temperature and in species abundance with different trophic levels for species such as Temora longicornis, Oikopleura dioica and Sagitta setosa, whereas an 11 yr cycle appeared for Pseudo-calanus minutus. A 3 to 4 yr cycle was detected for atmospheric pressure, precipitation and some species. This cycle may or may not be superimposed on another (for example, on an 11 yr cycle).