Publications

Nayak, RK; Swapna, M; Manche, SS; Mohanty, PC; Sheshasai, MVR; Dadhwal, VK; Kumar, R (2023). Assessment of Chlorophyll-a Seasonal Cycle in the North Indian Ocean Using Observations from OCM2, MODIS, and SeaWiFS. JOURNAL OF THE INDIAN SOCIETY OF REMOTE SENSING.

Abstract
A study on the seasonal variability of Chlorophyll-a concentration (Chl-a) in the north Indian Ocean is carried out based on observations from the moderate-resolution imaging spectroradiometer (MODIS) during 2002-2017, Sea-Viewing Wide Field-of-View Sensor (SeaWiFS) during 1999-2009 and Ocean Color Monitor 2 during 2010-2020. The number of valid data points varied from 40-60% for OCM2 to > 60% for MODIS and SeaWiFS. Although OCM2 exhibits a similar probability distribution as that of the MODIS and SeaWiFS, it differs significantly in its mean and variance. The OCM2 has 80% pixels below 1 mg m(-3) Chl-a in the continental shelf domain (10-150 depth contours) with a mean of 3.5 +/- 5.5 mg m(-3) while MODIS and SeaWiFS are highly coherent with each other and exhibit 60% pixels in the same range with the smaller mean of 2.5 +/- 3.05 mg m(-3). In the continental slope and open ocean domain, 20% of OCM2 pixels vary in the lower range (< 0.25 mg m(-3)) and 60% pixels in the moderate range (0.25-0.75 mg m(-3)), while 60% of the MODIS and SeaWiFS pixels are in the lower range, and 20% in the moderate range. The spatial patterns of the annual and semiannual amplitudes are coherent among the datasets with a high Chl-a climatology (> 0.5 mg m(-3)), intense seasonality in the north Arabian Sea, and north Bay of Bengal and continental shelf around India and Sri Lanka. Moderate magnitudes of Chl-a climatology with reduced seasonality occur in the central Arabian Sea and Somalia offshore and southwestern Bay of Bengal adjacent to Sri Lanka. On the other hand, major parts of the open oceanic domain of the Bay, Equatorial Indian Ocean, and southeastern part of Arabian Sea show a very smaller climatological mean of Chl-a with reduced seasonality. The regions of high climatology and intense seasonality of Chl-a are co-occurring with upwelling and nutrient-rich zones. Chl-a also exhibits significant inter-annual variability in the areas of high climatological mean as a response to the background oceanic conditions and availability of nutrients which needs to be investigated.

DOI:
10.1007/s12524-022-01642-4

ISSN:
0974-3006