The response of phytoplankton chlorophyll to Typhoon Damrey in the South China Sea (SCS) in September 2005 was studied by remote sensing. Chl a concentration increased in 2 areas after the typhoon: (1) An offshore bloom along Damrey's track exhibited a chl a peak (4 mg m -3 ) 5 d after the typhoon's passage. It was preceded by sea-surface cooling (-5°C), mainly on the right side of the typhoon track, and sea-level decrease (-25 cm) along the typhoon track 1 d post-typhoon. The offshore bloom was due to nutrient increase from mixing and upwelling. (2) A nearshore chl a increase succeeded typhoon rain (> 300 mm on 26 September) on Hainan Island in the northwest SCS. In the bloom region, the water was rich in suspended sediments, phytoplankton, and colored dissolved organic matter, and was entrained by an eddy. This nearshore feature may have resulted from rainwater discharge and seaward advection by a typhoon-induced current. By these 2 mechanisms, both typhoon winds and rain can enhance production of marine phytoplankton.

Spectrophotometric measurement of particulate matter retained on filters is the most common and practical method for routine determination of the spectral light absorption coefficient of aquatic particles, a_p(λ), at high spectral resolution over a broad spectral range. The use of differing geometrical measurement configurations and large variations in the reported correction for pathlength amplification induced by the particle/filter matrix have hindered adoption of an established measurement protocol. We describe results of dedicated laboratory experiments with a diversity of particulate sample types to examine variation in the pathlength amplification factor for three filter measurement geometries; the filter in the transmittance configuration (T), the filter in the transmittance-reflectance configuration (T-R), and the filter placed inside an integrating sphere (IS). Relationships between optical density measured on suspensions (OD_s) and filters (OD_f) within the visible portion of the spectrum were evaluated for the formulation of pathlength amplification correction, with power functions providing the best functional representation of the relationship for all three geometries. Whereas the largest uncertainties occur in the T method, the IS method provided the least sample-to-sample variability and the smallest uncertainties in the relationship between OD_s and OD_f. For six different samples measured with 1 nm resolution within the light wavelength range from 400 to 700 nm, a median error of 7.1% is observed for predicted values of OD_s using the IS method. The relationships established for the three filter-pad methods are applicable to historical and ongoing measurements; for future work, the use of the IS method is recommended whenever feasible.

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