Spatiotemporal Variability and Long-Term Warming Trends of Sea Surface Temperature in Palk Bay (2000-2024)

Sea surface temperature is a key indicator of regional climate variability and ocean–atmosphere interactions, directly influencing marine productivity, fishery habitat suitability, and coastal ecosystem dynamics in tropical semi-enclosed basins. Palk Bay, a shallow coastal sea between Sri Lanka and southeastern India, is a climate-sensitive marine region that supports small-scale fisheries dependent on seasonal ocean conditions. Despite its regional significance, a long-term satellite-based thermal characterization of this basin remains limited.

This study examines SST variability and climate-driven warming trends in Palk Bay using the Copernicus Marine OSTIA satellite product spanning 2000–2024 at approximately 0.05° spatial resolution. Daily SST fields were extracted for the basin domain (9°00′–10°00′N, 79°18′–80°18′E), spatially averaged to derive basin-wide time series, and analyzed through seasonal climatology and linear regression.

Basin-wide daily SST ranged from 25.8°C to 32.3°C over the 25-year record, with an overall mean of 28.82°C. The seasonal climatology reveals a well-defined annual cycle, with minimum temperatures of ~26.8°C in January rising to a pre-monsoon peak of ~30.8°C in April—a seasonal amplitude of 4.02°C—followed by gradual cooling through the southwest and northeast monsoon periods, consistent with monsoon-driven atmospheric forcing and wind-induced coastal mixing. Long-term regression analysis reveals a weak but statistically significant warming trend of +0.27°C per decade (p = 0.007), indicating a measurable climate signal embedded within strong seasonal variability. Spatial analysis for 2015–2024 reveals a north-to-south thermal gradient, with warmer conditions in the northern bay and comparatively cooler waters in the south, reflecting differences in basin depth and local circulation.

These results provide a quantitative baseline for long-term thermal change in Palk Bay and highlight how monsoon-driven SST variability and gradual regional warming may affect fish spawning phenology, seasonal habitat suitability, and the productivity of coastal fisheries in this significant region.