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Earthquake-regulated carbon cycle in the hadal trenches

Tectonically-triggered sediment and carbon export to the Hadal zone

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Sediments in deep ocean trenches may contain crucial information on past earthquake history and constitute important sites of carbon burial. We found that the 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.

Reference:

Bao, R., Strasser, M., McNichol, A. P., Haghipour, N., McIntyre, C., Wefer, G., & Eglinton, T. I. (2018). Tectonically-triggered sediment and carbon export to the Hadal zone. Nature Communications 9, 121. https://doi.org/10.1038/s41467-017-02504-1

Earthquake-enhanced dissolved carbon cycles in ultra-deep ocean sediments

1Earthquake-enhanced dissolved carbon cycles in ultra-deep ocean sediments
Hadal trenches are unique geological and ecological systems located along subduction zones. Earthquake-triggered turbidites act as efficient transport pathways of organic carbon (OC), yet remineralization and transformation of OC in these systems are not comprehensively understood. Here we measure concentrations and stable- and radiocarbon isotope signatures of dissolved organic and inorganic carbon (DOC, DIC) in the subsurface sediment interstitial water along the Japan Trench axis collected during the IODP Expedition 386. We find accumulation and aging of DOC and DIC in the subsurface sediments, which we interpret as enhanced production of labile dissolved carbon owing to earthquake-triggered turbidites, which supports intensive microbial methanogenesis in the trench sediments. The residual dissolved carbon accumulates in deep subsurface sediments and may continue to fuel the deep biosphere. Tectonic events can therefore enhance carbon accumulation and stimulate carbon transformation in plate convergent trench systems, which may accelerate carbon export into the subduction zones.

Reference:

Chu, M., Bao, R.*, Strasser, M., Ikehara, K., Everest, J., Maeda, L., Hochmuth, K., Xu, L., McNichol, A., IODP 386 scientists.  (2023). Earthquake-enhanced dissolved carbon cycles in ultra-deep ocean sediments. Nature Communications 14, 5427. https://doi.org/10.1038/s41467-023-41116-w