Increased Terrestrial Organic Carbon Input and Mineralization by Turbidites Deposition in the Kermadec Trench

Hadal trenches are hotspots for organic carbon (OC) turnover, yet controls on benthic mineralization in pelagic trenches remain poorly constrained. Here we investigate how episodic sediment transport links tectonics to carbon cycling in the oligotrophic Kermadec Trench. Using sedimentological and molecular proxies (δ13C, lipid biomarkers, radiocarbon) from two gravity cores, we identify frequent earthquake-triggered turbidity-current deposits. Despite the trench's pelagic setting, molecular evidence (e.g., β-amyrin, C32 1,15-diol) confirms the delivery of terrestrial debris via mass wasting event deposition. Crucially, this allochthonous input is strongly coupled with enhanced benthic diffusive oxygen uptake (DOU; a proxy for benthic respiration) and higher relative abundance of refractory-carbon-degrading archaea (Bathyarchaeia). Our results demonstrate that the tectonically driven supply of terrestrial OC, rather than local surface-ocean primary productivity, regulates spatial heterogeneity benthic mineralization in this hadal system. This study highlights a fundamental geological control on biological carbon cycling in the deep ocean.