Possible biogeochemical response to the passage of Hurricane Fabian observed by satellites

Physical and biogeochemical changes induced by the HurricaneFabian in the Northwest Atlantic in early September 2003 wereobserved using composite satellite images. After the passageof the hurricane, the mean sea surface temperature (SST) alongthe track decreased on average by about 1.3°C with maximumdecrease of 10°C. At the same time, the mean Chl a concentrationincreased by about 42%. Entrainment of cold, nutrient-rich watersby vertical mixing induced by the hurricane seems to have enhancedthe phytoplankton production. Asymmetric distribution of changesin SST and Chl a (strong intensity on the right side of thestorm track) was observed from the satellite data. The storm-inducednitrate increase estimated from the satellite SST, using a localrelationship between nitrate and temperature measurements wasabout 40% on average along the track of the storm. A numericalmodel study and climatological nutrient profile showed an increasein mixed-layer depth of 26 m and nitrate increase of about 0.2µmol L^–1 after the storm passage. In addition toaltering the physicochemical conditions of the water column,physical forcing by the hurricane also changed the taxonomiccomposition of phytoplankton. It is inferred that the dominanceof diatoms after the storm is a result of the increase in nutrientconcentration within the mixed layer due to the wind forcingof the storm.