Chemical, biochemical and environmental DNA analysis of sediments from two seamounts of the deep Arabian Sea

This study examines the chemical and biochemical properties, as well as the benthic diversity, of seamounts in the Arabian Sea, with a focus on SMS2 and SMS3, located along the Laccadive Ridge in the deep Arabian Sea. The summits of these seamounts interact with oxygen minimum zones (OMZs) at 340 – 440 m, potentially shaping their unique biochemical properties and biodiversity. Sediment collected from the summit of these seamounts revealed significant concentrations of iron (SMS2: 6889 ppm, SMS3: 4888 ppm), manganese (SMS2: 48 ppm, SMS3: 39 ppm), nickel (SMS2: 42 ppm, SMS3: 36 ppm), vanadium (SMS2: 40 ppm, SMS3: 31 ppm), chromium (SMS2: 40 ppm, SMS3: 26 ppm) and zinc (SMS2: 32 ppm, SMS3: 20 ppm). The organic matter present in the sediments is predominantly refractory, characterized by a high carbon-to-nitrogen ratio (SMS2: 30.4, SMS3: 51.2) and low protein content (SMS2: 1131.5 µg g⁻¹, SMS3: 701.0 µg g⁻¹). The study employs environmental DNA (eDNA) techniques to reveal the benthic diversity of these seamounts, which is largely comprised of eDNA signatures from Annelids, Arthropods, and Cnidarians that thrive in low-oxygen, iron-rich environments. This research emphasizes the role of OMZs and geochemical factors in shaping biodiversity and ecological processes on seamounts. Furthermore, the regional variability in heavy metal composition and organic matter dynamics reflects distinct oceanographic conditions across these seamounts. Overall, the findings offer valuable insights into the biochemical composition, benthic biodiversity, and ecological significance of seamounts in the southeastern Arabian Sea, underscoring the necessity for broader investigations to enhance our understanding of deep-sea ecosystems.