Why do satellite imageries show exceptionally high chlorophyll in the Gulf of Mannar and the Palk Bay during the Norteast Monsoon?

Abstract

The Gulf of Mannar (GoM) and the Palk Bay (PB) are two least studied marine environments located between India and Sri Lanka. Exceptionally high chlorophyll a concentration in the GoM and the PB during the Northeast Monsoon (November-February) is a consistent feature in satellite imageries, which has been attributed to the intrusion of the Bay of Bengal (BoB) waters. The analyses of the Moderate Resolution Imaging Spectroradiometer (MODIS) and field chlorophyll data collected from 30 locations in the Indian sector of the GoM and the PB in January 2011 showed significant overestimations in the satellite data. This error was much higher in the PB (60-80 %) as compared to the GoM (18-28 %). The multivariate analyses evidenced that the exceptionally high satellite chlorophyll in the PB is contributed largely by turbidity, colored dissolved organic matter (CDOM), and bottom reflectance. The paper cautions that though MODIS is superior in estimating chlorophyll a in optically complex waters, there are still chances of overestimations in regions like the PB.

Why Gulf of Mannar is a Marine Biological Paradise?

“…The environmental variables collected during the first in-situ sampling during 2010-2011 (Table 1) shows that the hydrography of the GoM was very similar to the waters in the SEAS along the southwest coast of India [8][9][10][11][12] . At the same time, the vertical distribution of temperature and dissolved oxygen in the GoM during the Southwest Monsoon displayed two significant features, which were strikingly different from the southwest coast of India during the same period.…”

“…The surface currents reverse during the Northeast Monsoon (November -February) and bring the coastal low saline Bay of Bengal waters into the GoM (Table 1). This circulation pattern enables (a) GoM to receive a high amount of plankton stock from the Arabian Sea during the Southwest Monsoon and from the Bay of Bengal during the Northeast Monsoon 8,10,11 and, (b) Palk Bay to efficiently trap the suspended sediments coming from the Bay of Bengal during the Northeast Monsoon 10,11 . As a result, the bottom sediment in the GoM is mostly sandy and well-aerated conducive for the life of diverse corals and sensitive fauna 1,4 .…”

“…of India. As an outcome of this, a series of peer-reviewed publications have come out dealing with their general environmental setting [8][9][10][11][12] . Even though a large number of studies are available on the faunal diversity in the GoM, convincing explanation on its oceanographic causes is completely absent 1 .…”

“…The main objective of this paper is to establish the oceanographic and ecological reasons that facilitate an unusually rich and diverse fauna in the GoM. For which we examined here, the general characteristics of the GoM [8][9][10][11][12] besides elaborating upon a crucial environmental signal found in our 2010-11 in-situ studies in the GoM. Also verified these results using a recent oceanographic survey in 2018 covering the southwest coast of India up to the western boundary of the GoM (Tuticorin) augmented with satellite remote sensing data sets and Regional Ocean Model System (ROMS) projections.…”

In situ Photosynthetic Activities and Associated Biogeochemical Changes in Three Tropical Seagrass Species

“…Seagrass along the Tamil Nadu coast, India, is represented by 14 seagrass species (Purvaja et al, 2018) and contribute more than 77% of the total seagrass cover in the country (Geevarghese et al, 2018). Palk Bay, located in Tamil Nadu, adjacent to the Gulf of Mannar and surrounded by Vaigai basin in the north west (Figure 1), is a shallow flat basin (mean depth 9 m) along the South East coast of India covering an area of ∼13500 km 2 (Jyothibabu et al, 2014). The bay experiences stable climatic conditions with marginal spatiotemporal variability in terms of water quality and extremes in air/water temperature during dry season (February-September; Sridhar et al, 2008).…”