Coastal oceans are highly dynamic regions of ecological and economic importance that are vulnerable to different stressors. We investigated the spatio-temporal variations in the biogeochemistry of the coastal waters surrounding an archipelago in the Eastern Arabian Sea. Seawater was collected from six stations (S1-S6) around the Grande Island archipelago, located off the Goa coast, during the late Summer monsoon (SM, September 2022), Post-monsoon (PoM, November 2022), Winter monsoon (WM, January 2023), and Pre-monsoon (PrM, April 2023). We also sampled station G3, off Goa, during similar time points, as a station away from the island. Seasonal changes in the biogeochemistry were evident in the region. The bottom waters around the island showed larger variations compared to the surface seasonally. The bottom water was cold, highly saline, low pH, and had hypoxic to anoxic conditions during SM. By PrM, the water column was well-mixed with high-temperature, oxic, and highly saline seawater with a pH of roughly 8.0. A comparison of the chlorophyll-a concentration around the island to the G3 station indicated that the waters surrounding the island were more productive, possibly due to the micronutrient input (dissolved iron) from the landmass and active physical forcing around the island. There was a significant difference in biogeochemistry between the island's southern and northern sides. Therefore, we conclude that the island mass effect alters the biogeochemical conditions around the island and in the coastal seas, which in turn can impact the highly sensitive organisms such as coral reefs and other benthic organisms.
Keywords: Arabian Sea; Biogeochemistry; Chlorophyll; Island mass; Nutrients.
© 2025. The Author(s), under exclusive licence to Springer Nature Switzerland AG.
