This study comprehensively assesses the long-term variability of temperature, ocean acidity changes, and their implications on sound absorption and acoustic propagation in the Bay of Bengal. The analysis reveals a persistent warming trend in the Indian Ocean over the past 50 years, with a significant increase in temperature observed during the Sagar Maitri cruise in 2019. Thermal structure analysis using HadleySST EN4 data indicates warming in the upper 50m but a cooling trend in the 100-200m depth range. Oceanic Heat Content analysis highlights an increasing tendency of heat storage in the upper 50m, indicative of global warming.
In the context of surface ducted propagation, Sonic Layer Depth (SLD) and gradients in the Sound Speed Profile (SSP) were crucial factors influencing acoustic energy behavior. The study revealed a decreasing trend in in-layer gradient (Gr_SL) since 1990, intensifying after that period. The below-layer gradient (Gr_BL) also exhibited a decreasing trend, implying complex dynamics in the sonic layer with potential implications for sound propagation in the surface duct.
The investigation into pH changes spanning 65 years demonstrates a declining trend, particularly since the 1990s, attributed to increased atmospheric CO2 dissolution. The study linked this decrease to anthropogenic activities, aligning with global trends. The analysis of sound absorption illustrated a nonlinear relationship between absorption, frequency, and pH, emphasizing a significant impact of ocean acidification on sound absorption in the Bay of Bengal. The acoustic propagation modeling further highlighted a decrease in transmission loss with reducing pH, leading to increased sound travel and potentially noisier oceans. Salinity variations play a more significant role than temperature in influencing sound absorption.
Maheswaran P. A., Deepulal P. M., Harikishnan M., Satheeshkumar S. & Raghunadha Rao A., 2025. Long term variability of temperature and pH in the Bay of Bengal: an investigation on acoustic perspective. Research Square. Article.
