Phytoplankton bloom in the Bay of Bengal during the northeast monsoon and its intensification by cyclones

Abstract

Satellite derived chlorophyll a imageries are used to present a phytoplankton bloom in the Bay of Bengal during the northeast monsoon (November–February) and the mechanisms that can upwell nutrients to sustain the bloom are investigated using sea level anomalies and winds. OCTS and SeaWiFS chlorophyll a images show that there is a phytoplankton bloom in the southwestern part of the bay during November–January. The chlorophyll a concentration of the bloom can be as high as 2 mg m−3 compared to near zero value before the bloom. Open ocean upwelling driven by Ekman pumping causes the bloom. The cyclones which are common during this period lead to localized intense blooms in the western Bay of Bengal. The offshore extent and the intensity of the bloom varies from year to year. The bloom was absent during 1997 due to weak Ekman pumping.

Mixed layer variability and chlorophyll <i>a</i> biomass in the Bay of Bengal

“…However, the winds, though strong in the northern Bay of Bengal, were unable to break the stratification and initiate deep wind mixing as inferred from the static stability parameter. A similar result was arrived at by Shenoi et al (2002) based on kinetic energy and by Vinayachandran et al (2002) in the context of barrier layer formation (see also Thadathil et al, 2007). Using modelling, Han et al (2001) also obtained a thin mixed layer in the region where precipitation exceeded evaporation.…”

“…While comparing the total kinetic energy available for mixing in the Arabian Sea and the Bay of Bengal, Shenoi et al (2002) stated that the shallow mixed layer depth in the Bay of Bengal during the summer monsoon is primarily driven by a combination of weaker winds and strong near-surface stratification. Subsequently, Vinayachandran et al (2002) argued that strong stratification associated with the barrier layer curtails the vertical mixing leading to the formation of a shallow mixed layer. In contrast, with help of a one-dimensional turbulent closure model Prasad (2004) studied the physical mechanism governing the seasonal evolution of mixed layer depth along two transects along the central Arabian Sea and Bay of Bengal and concluded that the surface forcing controls mixed layer depth in the Bay of Bengal rather than the vertical salinity stratification.…”

Amino sugars in suspended particulate matter from the Bay of Bengal during the summer monsoon of 2001

“…The fresh water inputs result in the stratification of the upper 50 m of the water column (Kumar et al 2002). Moreover, the frequently occurring cyclones are additional sources of phosphate and nitrates in the surface waters of the Bay (Vinayachandran and Mathew 2003). This nutrient supply results in the formation of intense localized blooms.…”

Microbial and viral metagenomes of a subtropical freshwater reservoir subject to climatic disturbances

“…Strong winds and torrential rain are typical components of typhoons that disrupt the natural environment. Strong wind-induced vertical mixing and upwelling pump nutrients (carbon, nitrogen, phosphorus and silicon) from deep water, and enhance chlorophyll a concentration (Vinayachandran and Mathew, 2003;Walker et al, 2005;Byju and Kumar, 2011;Hung and Gong, 2011). Abrupt torrential rain contributes to the concentrated influx of organic carbon and nutrients to the ocean (West et al, 2011), which is considered as the main cause of the post-storm increase in phytoplankton growth and primary production in coastal and estuary ecosystems (Chang et al, 1996;Shiah et al, 2000;Paerl et al, 2006).…”