Mangrove ecosystems are highly vulnerable to environmental and natural changes. They are being swiftly destroyed and degraded by anthropogenic activities, resulting in the loss of their self-regulating ability and resilience to ongoing climate change. Such shifts in ecosystem function cause cascading effects on related human populations and regional biodiversity, with consequences at local scales to influence global climate cycles over extended periods. Therefore, high-resolution spatio-temporal studies are crucial to identify responses in nature to past environmental crises and to reconstruct paleoenvironmental conditions for future mitigation efforts. To address this, a sediment profile was collected from the coastal wetland ecosystem of the Karankadu mangrove along the Tamil Nadu coast, India. This site provides an ideal setting to examine the interplay of the southwest (SW) and northeast (NE) monsoon systems during the Holocene, and is also largely populated and economically significant.  Multiproxy analyses, including Total Organic Carbon (TOC %), Total Nitrogen (TN %), Total Sulfur (TS %), elemental ratios, stable isotopes (δ¹³C_TOC, δ¹⁵N_TN, δ³⁴S_TS), and microscopic examination of biotic remains, were employed. The ~1 m Karankadu core spans ~7800 cal yr BP and records major climatic events. δ¹³C_TOC values (−26.5‰ to −23.2‰) indicate the dominance of C₃ vegetation during the Holocene Climate Optimum (HCO), while enriched values (−23‰ to −17‰), coupled with increased grass remains, reflect arid conditions during the 4.2 ka event. Subsequent shifts suggest continued expansion of C₃ vegetation, possibly linked to the Roman Warm Period (RWP). Biotic assemblages further reveal mangrove diversity and redox fluctuations (oxic–anoxic conditions), which are also supported by sulfur isotopic records and environmental magnetism. Changes in the availability of salt-tolerant and true/core mangrove pollen further support regional sea level and land/marine dynamics over the eastern coast of India during 5.0 to 6.0 ka.  The preservation of authigenic magnetic minerals (pyrite and greigite) appears to have been influenced by salinity changes, organic productivity, and land-Sea interactions during different phases of the Holocene, which we have further linked with the sedimentary methane leaks. Overall, our data underscore ecosystem processes, climate change, and monsoon dynamics with associated biogeochemical alterations during the last 7800 cal yr BP over the east coast of India.
 

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