Tectonically-triggered sediment and carbon export to the Hadal zone

Abstract

Sediments in deep ocean trenches may contain crucial information on past earthquake history and constitute important sites of carbon burial. Here we present ¹⁴C data on bulk organic carbon (OC) and its thermal decomposition fractions produced by ramped pyrolysis/oxidation for a core retrieved from the >7.5 km-deep Japan Trench. High-resolution ¹⁴C measurements, coupled with distinctive thermogram characteristics of OC, reveal hemipelagic sedimentation interrupted by episodic deposition of pre-aged OC in the trench. Low δ¹³C values and diverse ¹⁴C ages of thermal fractions imply that the latter material originates from the adjacent margin, and the co-occurrence of pre-aged OC with intervals corresponding to known earthquake events implies tectonically triggered, gravity-flow-driven supply. We show that ¹⁴C ages of thermal fractions can yield valuable chronological constraints on sedimentary sequences. Our findings shed new light on links between tectonically driven sedimentological processes and marine carbon cycling, with implications for carbon dynamics in hadal environments.

Fig. 1

Location and lithology of core GeoB 16431-1 in the Japan Trench, and thermograms of RPO of five sub-samples. a Map with location of core GeoB 16431-1 (7542 m water depth) in the Japan Trench, where the sediment sequence records historical earthquakes and volcanic eruptions. b Lithology of core GeoB 16431-1 and depths of samples (A–E) selected for in-depth study are presented; samples A, B, and D are from inferred earthquake deposits, characterized by graded fine-sand layers fining-upward into homogenous mud, that are sedimentologically distinct from the bioturbated muds that reflect background sedimentation (samples C and E). The colored boxes show tectonic events. These event deposits correlate with prior earthquakes (ad 2011, ad 1454, and ad 869) and volcanic eruptions (ad 915) documented in Japanese historical records. c, d, e, f, g Thermograms from RPO analysis of samples A–E are shown; Y-axis is mass-normalized CO₂ concentration, X-axis indicates temperature gradient

Fig. 2

Lithology of core GeoB 16431-1. A high-resolution bulk OC ¹⁴C age profile and corresponding OC fluxes (note log scale)

Fig. 3

Relationship between fraction modern of bulk OC and height ratio of peak 1 to peak 2 in the RPO thermogram

Fig. 4

Chronology and radiocarbon characteristics of RPO thermal fractions of OM in sediment core GeoB 16431-1 for samples A–E. The samples’ labels are shown adjacent to right-hand Y-axis and in Fig. 3. Adjacent to the right-hand Y-axis are the thermal decomposition temperature intervals. The gray shading denotes the earthquake events. Their names and extents are marked by arrows on the left-hand Y-axis. The X-axis (top) indicates the ¹⁴C age (yr bp) of thermal decomposition fractions (the measurement error is smaller than the symbol)