Identification of Algal Blooms in the north Indian Ocean
Phytoplanktons are possibly the most important group of organisms on the planet as they generate most of the oxygen on earth. Phytoplankton converts the inorganic nutrients into vegetative matter in the presence of sunlight through the process of photosynthesis. This forms the primary source in the marine food web. Most individual phytoplanktons are too small to be seen with the naked eye. It also plays significant role in atmospheric CO2 concentration by altering the rate of carbon sequestration. When present in high numbers however, their presence may appear as dramatic discolouration of the water. This population growth can be rapid, and typically occur when temperature and nutrient levels rise, usually in late summer and winter. This phenomenon is named as "algal bloom" or "Eutrophication". The colour of a bloom can vary from a green to a dark red colour depending on the phytoplankton present. While blooms can provide more food to organisms in higher trophic level, too much phytoplankton can also do harm. Death and decay of these planktons along with organisms resulted in oxygen depletion. This can result in the death of other organisms including shellfish, crabs and fish. The main groups of Phytoplankton include Diatoms, Dinoflagelates, Coccolithophorids and Micro-Flagellates. Each of these groups has distinguishing features that allow specialists to identify them to species level. Phytoplankton blooms normally occur in response to either an increased supply of nutrients, or increased exposure to sunlight. Most of the phytoplankton blooms occurring in the oceans are induced by natural causes and seasonal cycles. Many such blooms are observed over the globe, such as the North Atlantic Bloom is the largest seasonal bloom observed every year. Such larger blooms are observed in the north Indian Ocean also every year on seasonal basis. However, there are differences between the blooms that occur in the Arabian Sea and Bay of Bengal every year in terms of their initiation and termination. We attempt here to study the possible factor responsible for bloom genesis in Arabian Sea and Bay of Bengal using in-situ and satellite derived information. In this regard, we made an attempt to study the bloom dynamics and occurrence in the Arabian Sea and Bay of Bengal separately. For this purpose we have used the data from the Indian global ocean colour sensor namely the 'Ocean Colour Monitor (OCM-2)' onboard Oceandat-2 satellite. This sensor provides both local area coverage (LAC) and global area coverage (GAC) data with 360m and 1km resolutions respectively. For this present study 360m LAC Level-1B radiance product from January 2009 to January 2012 was used for estimating the chlorophyll-a concentration to study the occurrence and dynamics of the blooms in the north Indian Ocean. The global ocean colour processing software called 'SeaDAS' was used for processing the OCM-2 data.