Oceans play a significant role in the global carbon cycle and climate change, and the most importantly it is a reservoir for
plenty of protein supply, and at the center of many economic activities. Ocean health is important and can be monitored
by observing different parameters, but the main element is the phytoplankton concentration (chlorophyll–a
concentration) because it is the indicator of ocean productivity. Many methods can be used to estimate chlorophyll–a
(Chl-a) concentration, among them, remote sensing technique is one of the most suitable methods for monitoring the
ocean health locally, regionally and globally with very high temporal resolution.
In this research, long term ocean health monitoring was carried out at the Bay of Bengal considering three facts i.e. i)
very dynamic local weather (monsoon), ii) large number of population in the vicinity of the Bay of Bengal, and iii) the
frequent natural calamities (cyclone and flooding) in and around the Bay of Bengal. Data (ten years: from 2001 to 2010)
from SeaWiFS and MODIS were used. Monthly Chl–a concentration was estimated from the SeaWiFS data using OC4
algorithm, and the monthly sea surface temperature was obtained from the MODIS sea surface temperature (SST) data.
Information about cyclones and floods were obtained from the necessary sources and in-situ Chl–a data was collected
from the published research papers for the validation of Chl-a from the OC4 algorithm. Systematic random sampling was
used to select 70 locations all over the Bay of Bengal for extracting data from the monthly Chl-a and SST maps. Finally
the relationships between different aspects i.e. i) Chl-a and SST, ii) Chl-a and monsoon, iii) Chl-a and cyclones, and iv)
Chl-a and floods were investigated monthly, yearly and for long term (i.e 10 years). Results indicate that SST, monsoon,
cyclone, and flooding can affect Chl-a concentration but the effect of monsoon, cyclone, and flooding is temporal, and
normally reduces over time. However, the effect of SST on Chl-a concentration can't be minimized very quickly
although the change of temperature over this period is not very large.
The Sea-Viewing Wide Field-of-view Sensor (SeaWiFS)-derived chlorophyll-a (Chl-a) data within 13-year full
SeaWiFS mission were analysed to understand the spatial and temporal variations of phytoplankton biomass in the
Malacca Straits. Other data from multi-sensors were also exploited to understand probable factors governing SeaWiFS
Chl-a variation. SeaWiFS Chl-a showed remarkable seasonal variation which was high and low during northeast
monsoon and southwest monsoon, respectively, especially in the north and middle regions of the Malacca Straits.
Analysis results on the long-term trend showed that SeaWiFS Chl-a has experienced long-term increase especially in the
south region of the Malacca Straits. In the north region on the other hand, SeaWiFS Chl-a was relatively stable within the
SeaWiFS full mission period. The observed seasonal variation and long-term increasing trend of SeaWiFS Chl-a in the
south region of the Malacca Straits however might not be associated with real phytoplankton biomass. High suspended
sediment due to both bottom sediment re-suspension and sediment loaded from the land by river discharge might lead to
incorrect Chl-a retrieval by SeaWiFS ocean color sensor. SeaWiFS Chl-a spatial and temporal variations in the north
region of the Malacca Straits seemed to be more determined by wind-driven physical forcing such as water column
mixing and/or upwelling.