Dam construction has altered riverine organic carbon (OC) composition, but its impact on deltaic OC burial remains unclear. Analysis of a four-decadal dataset of suspended and surface sediments in the Changjiang subaqueous delta reveals a temporal increase in freshwater algal OC and a decrease in petrogenic OC input to the East China Sea. This shift toward more labile OC reduced OC preservation efficiency from 15.1% to 10.7%, resulting in an approximately 50% loss of net OC preservation.

We present a novel analytical system that simultaneously measures mass loss, heat flow, gas emissions, and oxygen consumption during controlled heating. The method reveals how carbon, oxygen, and sulfur are stored, transformed, and recycled in geological materials. By providing high-resolution insights into thermal reactivity and redox processes, it helps identify hidden environmental changes and offers a powerful new tool for studying biogeochemical cycles and Earth’s environmental evolution.