Carbon Processing in the Land-to-Ocean Aquatic Continuum (LOAC): Challenges in the 21st Century

Roughly 90% of the organic carbon (OC) buried in the global ocean is stored in muddy sediments along continental margins. Estuarine "hotspots" are especially important, with deltas accounting for about 40% of this burial and fjords for around 12%. To understand the sources and fate of OC in aquatic systems, researchers have widely applied molecular biomarkers and bulk geochemical proxies. In my work, I will explore the application of both bulk analytical techniques and molecular biomarkers to investigate how environmental changes across the land–to-ocean aquatic continuum (LOAC) are influencing OC burial and long-term carbon sequestration.  These muds produced by rock weathering play a critical role in the global carbon cycle by binding and shielding OC from degradation. The quantity and characteristics of OC stored in these muds influence the extent, duration, and mechanisms of carbon sequestration.

Human activities, including dam construction, levee building, and climate change, have profoundly reshaped patterns of mud accumulation and organic carbon (OC) storage across diverse environments. I demonstrate that climate warming has generally increased mud–OC fluxes through processes such as glacier melt, enhanced erosion, and dam-driven sediment burial, although these effects vary regionally. From 1950 to 2010, dams reduced global riverine sediment delivery to the oceans by approximately 49%, despite rising upstream sediment loads, trapping an estimated ~60 TgC yr⁻¹ of organic carbon. At the same time, global coastal wetlands experienced a net loss of about 4,000 km² between 1999 and 2019, yet they continue to sequester substantial amounts of carbon (up to ~60 TgC yr⁻¹). In the Arctic, warming has accelerated permafrost erosion, mobilizing roughly 14 TgC yr⁻¹. Together, these examples highlight the complex and often competing influences of human activity and climate change on river systems and the global carbon cycle, with coastal zones emerging as both highly vulnerable and critically important for carbon sequestration. However, whether these changes ultimately enhance or diminish long-term OC storage remains uncertain, given the complexity and variability of the processes and timescales involved.