Basin scale distribution of Trichodesmium spp. in the Arabian Sea using Oceansat I/ OCM

摘要

Trichodesmium spp. is widely spread in the Arabian Sea. It form dense patches. During 2000-2005 (5 years period) extensive sampling was done in the Arabian Sea covering large area and different months starting from November to May. Three prominent sites are identified as Trichodesmium bloom sites in the Arabian Sea: 1) Lakshadweep waters 2) Off Goa and 3) Off Gujarat area. Bloom of around 100 km~2 area with 4 to 400737 filamentsL~(-1) concentrations are recorded. Two species of Trichodesmium are encountered based upon seasonality and environmental conditions. OCM derived chlorophyll a during bloom was as high as 0.5 to 1 mgm~(-3), at time increased upto 5 mgm~(-3) and depends upon number of filaments in water. The Trichodesmium features were identified at 869, 670, 555nm in OCM data. Trichodesmium was detected as stripes and eddies in OCM images. The bloom patches appear darker which is taken as measurement of spread of the bloom in water. Total 133 stations are covered during 5 years period out of which 63 stations showed presence of Trichodesmium with discolouration of water. In offshore water Trichodesmium was detected as early as November and continued upto April month whereas in the coastal water Trichodesmium prevailed from February to May. The seasonality of these blooms was observed with respect to inshore/offshore and two species of Trichodesmium is discussed with the help of OCM data processed for chlorophyll a during Trichodesmium growth period, at 3 identified sites in the Arabian Sea.