Radiocarbon age offsets in loess sediments from the southern Tibetan Plateau: modulated by vegetation productivity and aeolian dynamics

Bulk organic matter (OM) is commonly used as an alternative when reliable radiocarbon dating materials are unavailable. However, due to its heterogeneous carbon sources, bulk OM often yields significant age offsets (Δt). While such offsets have provided insights into carbon cycle dynamics in lacustrine and marine sediments, their variability patterns and underlying mechanisms in aeolian loess remain poorly understood. Here, we reconstruct centennial to millennial scale Δt variations from the GG loess-paleosol sequence on the southern Tibetan Plateau by comparing bulk OM ages with reliable charcoal controls. Δt values fluctuate markedly (700–4050 yrs) and exhibit strong covariation with environmental proxies, including loss-on-ignition, magnetic susceptibility, and grain size. Our results show that Δt variability is primarily shaped by (1) climate-controlled vegetation productivity, (2) aeolian-regulated sediment supply, and a limited influence of (3) post-depositional alteration. These findings refine our understanding of organic carbon dynamics in loess systems and help improve the reliability of bulk OM-based chronologies in arid and semi-arid environments.