Raw data for water-extractable organic matter (WEOM) and base-extractable organic matter (BEOM) in eight sediment cores collected from four trenches

Hadal trenches represent significant long-term repositories for organic carbon (OC) and dynamic hotspots for early diagenesis in the deep sea; however, there is considerable regional variability in the composition, reactivity, and burial flux of OC. In this study, we investigated water-extractable organic matter (WEOM) and base-extractable organic matter (BEOM) in eight sediment cores collected from four trenches: the Mariana, New Britain, Kermadec, and Atacama trenches. Although the concentration of dissolved organic carbon (DOC) in WEOM is consistently lower than that in BEOM, the WEOM/BEOM ratio increases with depth in the sediments. Significant correlations between δ¹³COC and optical indices (e.g., SUVA₂₅₄, FI, and HIX) indicate that trench-specific environmental factors, such as terrestrial inputs and microbial activity, influence OC composition. Using ultrahigh-resolution mass spectrometry, we identified distinct molecular differences between WEOM and BEOM from the trench axis and adjacent non-hadal sites. BEOM exhibited a corresponding enrichment of aromatic and humic molecules, while WEOM was characterized by higher abundance of protein-rich molecules and higher biolability. Comparative analysis of hadal and non-hadal cores within the Atacama Trench region revealed distinct depth profiles of radiocarbon (¹⁴C) activity, oxygen penetration depth, Fe2+ concentration, and WEOM/BEOM ratios. These findings suggest that unstable depositional conditions induced by seismic activity contribute to the unique carbon cycling dynamics in hadal trenches. As burial depth increases and iron minerals undergo gradual reduction, OM transitions from a mineral-bound state to a free state, subsequently migrating upward into surface sediments and overlying waters due to sediment resuspension, thereby supplying nutrients and energy to benthic microorganisms in the deepest parts of the ocean.