Tectonically-triggered sediment and carbon export to the Hadal zone

Rui Bao,Gerold Wefer,Negar Haghipour,Michael Strasser,Ann P. McNichol,Cameron McIntyre,Timothy I. Eglinton

doi:10.1038/s41467-017-02504-1

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.

Highlights

Sediments in deep ocean trenches may contain crucial information on past earthquake history and constitute important sites of carbon burial
In deep ocean trenches associated with subduction zones, organic matter (OM) derived from pelagic sedimentation may be augmented by sediment supply from the adjacent margin
Building on emerging knowledge of earthquake-triggered sediment remobilization processes gained from this recent earthquake, and the strong temporal constraints on prior similar events[25], the objectives of this study were to assess the role of sediment mobilization and lateral transport processes on the characteristics and 14C age of OM in hadal sediments, examine 14C age-depth profiles of hadal sediments in the context of episodic, event-driven sedimentation, and assess whether reliable OM-based 14C chronologies and age models can be established for carbonate biomineral-poor hadal zone sediments

Summary

Introduction

Sediments in deep ocean trenches may contain crucial information on past earthquake history and constitute important sites of carbon burial. In deep ocean trenches associated with subduction zones, OM derived from pelagic sedimentation may be augmented by sediment supply from the adjacent margin The latter, previously deposited and stored in upslope settings, may be supplied via background sedimentation processes (e.g., bottom and intermediate-depth nepheloid layer transport (BNL and INL)) or via more episodic gravity flows[20]. The application of the method is often limited due to low concentrations of target compounds Another approach uses a so-called ramped pyrolysis/oxidation (RPO) method in combination with carbon isotopic analysis of the CO2 evolved from thermal decomposition of the sedimentary OM15,23. When coupled with new methodologies that allow for high-throughput bulk sediment OC 14C determination[24], it may yield more robust constraints on sediment chronologies

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