The eastern Arabian Sea (EAS) experiences seasonal nutrient availability and productivity shifts driven by the Indian monsoon, influencing microbial contributions to biogeochemical cycles. This study explores carbon, nitrogen and sulfur cycling using metagenome-assembled genomes (MAGs) from water samples collected at chlorophyll maxima (C-Max) depths during non-monsoon and monsoon seasons. A total of 49 high-quality MAGs were reconstructed from 12 metagenomic samples, including four novel lineages from the phyla Pseudomonadota and Bacteroidota. These MAGs revealed distinct seasonal shifts in microbial composition and function. During the non-monsoon season, microbial communities dominated by Idiomarina and Marinobacter showed increased gene abundance for C1 compound metabolism, nitrogen cycling and sulfur oxidation, processes essential for managing climate-active gases such as carbon dioxide (CO) and nitrous oxide (NO), while also preventing toxic sulfide accumulation. In contrast, monsoon conditions enhanced organic matter influx, promoting nitrogen retention pathways driven by Sinimarinibacterium and Oleibacter, raising concerns about potential nutrient buildup and localized hypoxia. Despite seasonal variations, functional redundancy ensured the stability of nutrient cycling processes. PERMANOVA analysis (p < 0.001) confirmed that microbial functional gene distribution was primarily shaped by taxonomic structure, with genus-level composition playing a dominant role. The study highlights microbial adaptability and resilience, ensuring ecosystem stability in the dynamic EAS environment. Understanding microbial processes at C-Max depths has enhanced our understanding of biogeochemical cycling in the EAS. Although focused on oxygenated depths, these findings offer insights relevant to microbial functions in the OMZ, reflecting the distinct environmental conditions of EASs.