In an attempt to investigate the sources of variability in salinity and dissolved inorganic phosphate (DIP) in the English Channel, Irish Sea, and southern North Sea, time series (20–40 yr) of observations at four different stations were studied. Highest salinities and lowest DIP, both associated with the lowest residuals, were found at station E1 in the English Channel near Plymouth, which is assumed to be representative of the natural signal of Atlantic Water entering the shelf seas. The influence of freshwater run-off, reflected in lower salinities and, more recently, in increased DIP concentration, is clearly shown at the station near the Isle of Man in the Irish Sea and at two stations in the Dutch coastal zone. However, comparison of the time series at the four different stations revealed that, while the two stations in the Dutch coastal zone were correlated to some extent, there was no significant cross-correlation between the other stations. The conclusion is that physical, chemical, and biological processes in the different areas affect the natural variability of the Atlantic signal to such an extent that the different properties studied at the stations are not related.