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Variation of Water Column Density in the Bay of Bengal Aquatic Ecosystem

K M Azam Chowdhury
Department of Oceanography, University of Dhaka, Bangladesh

Abu Sharif Md. Mahbub-E-Kibria
Department of Oceanography, University of Dhaka, Bangladesh

Shaila Akhter
Department of Mathematics, University of Dhaka, Bangladesh

Nuruddin Md. Khaled Chowdhury
Graduate Research Assistant & Helen DeVitt Jones Fellow at Texas Tech University, USA

Md. Marufujjaman Mithu
Department of Fisheries, University of Dhaka, Bangladesh

Abstract/ Executive Summary:

Water column stratification is very important to investigate the ocean dynamics. For this study, the Bay of Bengal was divided into some sub-regions and division wise temperature and salinity data were taken to study the distribution of water column density comprehensively from Argo profiling floats for the period January 2009 to December 2013. To understand the processes affecting the sigma-t variability, we also examined static stability parameters for the same region. In winter, temperature profiles of regions 1, 2 and 3 were showed a distinct thermal inversion. It may occur due to maximum net heat loss. In spring, the basin averaged temperature profile were showed no thermal inversion. Salinity was increased sharply from 25m to 85m. During spring temperature remained same, but a decrease was observed in salinity (0.5 psu) and sigma-t (0.2 kg m-3). Considering all regions, salinity was increased sharply from 15m to 65m whereas salinity at 5m was 33.1 psu, during summer. During fall season, Along the southern bay from west (Region-7) to east (Region 9) a decrease in temperature (0.3 °C), salinity (0.3 psu) and sigma-t (0.1 kg m-3) occurred. In winter and spring, southern bay stability was stronger than northern. In summer and fall, northern bay stability was stronger than southern and also highest compared to other season. Ship cruise CTD data can be collected for further study.

Keywords: Bay of Bengal, Water column, Density, Sigma-t, Static stability

Location: Bay of Bengal

Start Date: 00-01-2009

End Date: 00-12-2013

Program Area: Animal Health and Management

Commodity: Water quality

Objectives:

The upper layer heat content known as cyclonic heat potential is the important energy required for intensification and movement of tropical cyclone for this basin. So, the study of water column becomes more important as the rate of intensification of cyclones is sensitive to water column structure. Therefore, the main objective of the study is to investigate spatial variability of the temperature, salinity and sigma-t and its seasonal cycle in the bay.

Methodology:

The data pertaining to temperature, salinity to understand the formation and variability of the water column density/sigma-t were obtained from Argo profiling floats in the Bay of Bengal for the period of January 2009 to December 2013. All Argo floats carry sensors to measure the temperature and salinity of the ocean as they vary with depth. The quality control procedures reduced the total number of profile and finally, 8058 numbers (nos) of profiles were used for this study. Each profile was interpolated by using Cubic Spline Method within the interval of 1meter starting from the depth of 5 meters.

Source of Information: International Journal of Fisheries and Aquatic Studies 2017; 5(6): 34-40

Article Link (Online Journal):

Funding Source:

Budget:

Total Budget (Tk.) :

Achievement/Findings:

Thermal inversion is a phenomenon that occurs most prominently in the northern Bay of Bengal during winter. High heat flux causes upper layer thermally stratified during spring and fall season that prohibits to exchange temperature towards deeper layer. During winter, there was a zonal decrease in temperature (0.8 °C), salinity (0.6 psu) and sigma-t (0.2 kg m-3) from west (Region-1) to east (Region-3) along the northern bay. During spring temperature remained same, but a decrease was observed in salinity (0.5 psu) and sigma-t (0.2 kg m-3). The Region-3 showed the lowest temperature, salinity and sigma-t from west (Region-1) to east (Region-3) along the northern Bay. In spring there was a meridional increase (Region-1 to Region-7) in temperature (1.1 °C), salinity (0.9 psu) and Thermal inversion is a phenomenon that occurs most prominently in the northern Bay of Bengal during winter. High heat flux causes upper layer thermally stratified during spring and fall season which prohibits to exchange temperature towards deeper layer. During winter, there was a zonal decrease in temperature (0.8 °C), salinity (0.6 psu) and sigma-t (0.2 kg m-3) from west (Region-1) to east (Region-3) along the northern bay. During spring temperature remained same, but a decrease was observed in salinity (0.5 psu) and sigma-t (0.2 kg m-3). Region-3 showed the lowest temperature, salinity and sigma-t from west (Region-1) to east (Region-3) along the northern Bay. In spring there was a meridional increase (Region-1 to Region-7) in temperature (1.1 °C), salinity (0.9 psu).

Knowledge Management: Journal