Department Seminar: Max Zhao

Title: Radiocarbon constraints on organic carbon sources, transport and burial from land to sea: A case study of the China marginal seas

Abstract: Constraining the sources, transport, and burial of organic carbon (OC) in marine sediments is of fundamental importance for understanding the carbon cycle on a range of spatial and temporal scales. In addition to marine primary production, marginal seas receive substantial amount of terrestrial inputs from rivers and comprise hotspots for both OC burial and remineralization. However, much remains unknown about factors that control the sources, transport processes and burial efficiencies of different OC pools in response to natural and anthropogenic processes in marginal seas. Here we employ novel approaches of dual carbon isotopic (Δ14C and δ13C) measurements of both bulk OC and especially source-specific biomarkers to gain deeper insights into the fates of terrestrial OC in China marginal sea systems. We systematically assess the characteristics, quantify the contributions of different-sourced and different aged OC and reveal their spatial distributions, and then constrain the burial efficiencies of terrestrial OC in China marginal seas. We also explore the role of transport processes (e.g., hydrodynamic sorting) in the alteration and evolution of OC along the river-estuary-coastal ocean continuum. Our results reveal that estuaries serve as critical zones for OC degradation and aging, which in turn affect OC burial in marginal seas. By applying the same approaches in down-core sediments, we examine the longer-term controls on OC composition, age and burial over centennial to millennial timescales, revealing the distinct variations and mechanisms for terrestrial OC fates in China marginal seas.