Wind-induced modulation of seasonal phytoplankton blooms in the North Atlantic derived from satellite observations

We examined the interannual variability in the timing and magnitude of seasonal phytoplankton blooms in the North Atlantic (70ЊN–10ЊN, 90ЊW–10ЊE) in relation to variability in wind forcing during the bloom period using satellite data from 1998 through 2004. When averaged over the period extending from 1998 to 2004, seasonal increases in phytoplankton in the subpolar North Atlantic were observed predominantly during the spring, while the increases occurred between autumn and winter in the subtropical region. The major modes of interannual variability in bloom timing and magnitude from empirical orthogonal function analysis exhibited large spatial coherency across the North Atlantic. These patterns of variability can be explained, in large part, by the pattern of interannual variability in bloom-period wind mixing. Although convection is important in the seasonal development of blooms, wind-induced mixing during the bloom period appeared to be the key forcing agent contributing to interannual variability in the intensity of blooms. Increased wind-induced mixing during the bloom period reduced bloom magnitude over the subpolar and northern subtropical regions while enhancing it over the southern subtropical region. Atmospheric variations associated with interannual variability in wind mixing during the bloom period also appeared to affect variability in the timing of bloom onset. The major mode of interannual variability in the timing of North Atlantic blooms indicates a possible link to the North Atlantic Oscillation.