Two phytoplankton blooms near Luzon Strait generated by lingering Typhoon Parma

Abstract

Two phytoplankton blooms near Luzon Strait triggered by Typhoon Parma in 2009 were investigated using remote sensing data and in situ observations. Parma was slow moving (a translation speed of ~2 m s −1 ) and relatively weak (a maximum sustained wind of ~30 m s −1 ) during its lingering path northwest of Luzon Island. After it reached a point (120.5°E, 20.3°N) west of Luzon Strait, Parma turned sharply back toward the northern Philippines along approximately the same course. Such long (~7 days) lingering typhoons are rather rare in the South China Sea (SCS). Before Parma, low Chl‐ a concentrations (<0.2 mg m −3 ) were observed in the northeastern SCS. After its passage, a strong offshore phytoplankton increase (Chl‐ a > 0.6 mg m −3 ) appeared west of the central Luzon Strait; a nearshore phytoplankton increase was also observed north of Luzon Island, together with high CDOM (color dissolved organic matter). During and after the typhoon, sea‐surface cooling (~3°C), stronger wind (>20 m s −1 ), and heavy rainfall (>100 mm day −1 ) were seen in the above regions. The offshore bloom occurred where Parma's translation speed was the slowest (~1 m s −1 ). It may be caused primarily by the Ekman pumping which brought nutrients upward to the euphotic zone and also by the entrainment mixing. The nearshore bloom may be triggered by the heavy typhoon‐induced rainfall, which supplied nutrients for the coast region north of Luzon Island. The rapid increase of CDOM in the nearshore region implied that terrestrial input may be the source of nutrients.