Chemical Oceanography and Marine Biogeochemical Cycles in the Anthropocene

Although critical regulators of Earth's climate and ecosystem stability, the marine biogeochemical cycles associated with coastal and open ocean environments are facing unprecedented disruption due to Anthropocene-era pressures. This paper therefore offers a comprehensive review and synthesis of the chemical oceanographic processes that govern the cycling of carbon, nitrogen, phosphorus, and trace elements in coastal and open ocean environments, with particular emphasis placed upon escalating human activities (e.g. combustion of fossil fuels, agricultural runoff, plastic pollution and ocean acidification) that are changing these fundamental biogeochemical cycles. Using spatial data collected from coastal zones of the southeastern Arabian Sea and Bay of Bengal (India), a multiparameter analytical framework was developed based on in situ water collection, stable isotopic analyses, satellite-derived biogeochemical tracers, and geochemical modelling to assess the extent of human caused perturbations. The key findings indicate that coastal primary productivity has declined by 12–18%, measurable changes in N:P Redfield ratios have occurred and dissolved inorganic carbon concentrations have increased due to anthropogenic CO2 forcing. Furthermore, mercury isotope signatures suggest nearshore food webs have experienced substantial trophic transfer anomalies. Finally, comparative analyses of mangrove-associated coastal zones highlight significantly greater potential for blue carbon sequestration (up to 4.2 Mg C ha⁻¹ yr⁻¹) in mangroves than in degraded coastal environments. Thus, there is an urgent need for integrated ocean monitoring frameworks and global coordinated biogeochemical observation networks to sustain marine ecosystem services through the 21st century.