Megathrust earthquake drives drastic organic carbon supply to the hadal trench

Abstract

The giant 2011 Tohoku-oki earthquake has been inferred to remobilise fine-grained, young surface sediment enriched in organic matter from the slope into the >7 km deep Japan Trench. Yet, this hypothesis and assessment of its significance for the carbon cycle has been hindered by limited data density and resolution in the hadal zone. Here we combine new high-resolution bathymetry data with sub-bottom profiler images and sediment cores taken during 2012–2016 in order to map for the first time the spatial extent of the earthquake-triggered event deposit along the hadal Japan Trench. We quantify a sediment volume of ~0.2 km3 deposited from spatially-widespread remobilisation of young surficial seafloor slope sediments triggered by the 2011 earthquake and its aftershock sequence. The mapped volume and organic carbon content in sediment cores encompassing the 2011 event reveals that this single tectonic event delivered >1 Tg of organic carbon to the hadal trench. This carbon supply is comparable to high carbon fluxes described for other Earth system processes, shedding new light on the impact of large earthquakes on long-term carbon cycling in the deep-sea.

Earthquake Impact on Active Margins: Tracing Surficial Remobilization and Seismic Strengthening in a Slope Sedimentary Sequence

“…This complements previous studies based on the composition of turbidites, which suggested earthquake-triggered remobilization of the upper 1-9 cm of slope sediments (McHugh et al, 2016;Moernaut et al, 2017). Furthermore, our results are in line with recent studies discussing the importance of earthquake shaking for transporting organic-rich surficial slope sediment to the hadal trench, forming an important contributor to the marine carbon cycle (Bao et al, 2018;Kioka et al, 2019;Mountjoy et al, 2018).…”

“…This could explain the continuity of turbidite paleoseismic records in several settings despite a scarcity of observed landslides (e.g., Goldfinger et al, ; Patton et al, ; Pouderoux et al, ) or lack of active sediment recharge on slopes (Goldfinger et al, ). Furthermore, seismically driven surficial remobilization has been suggested as an important process for carbon supply to the hadal zone (Kioka et al, ) due to the enhanced concentration of organic matter in surface sediments (Burdige, ). However, most studies on earthquake‐induced sediment transfer based their process assessment solely on the characterization of the final products, that is, the turbidite records in depositional basins (e.g., Ikehara et al, ; McHugh et al, ).…”

Event Stratigraphy in a Hadal Oceanic Trench: The Japan Trench as Sedimentary Archive Recording Recurrent Giant Subduction Zone Earthquakes and Their Role in Organic Carbon Export to the Deep Sea

“…The lower slope is steeper with an average gradient of ∼5 • (Kodaira et al, 2012;Koge et al, 2014). Active faulting along the subduction margin (Tsuru et al, 2002;Tsuji et al, 2013;Boston et al, 2017;Kodaira et al, 2017) forms a narrow mid-slope terrace at water depths of 4,000-6,000 m. The Japan Trench is characterized by the N-S to NNE-SSW trending horst-and-graben structures formed by flexural bending of the subducting Pacific plate, resulting in rough trenchfloor morphology with isolated trench-fill and graben-fill basins (Nakamura et al, 2013;Kioka et al, 2019). Our study area of the deep Japan Trench is bounded by the subducting Erimo and Daiichi-Kashima seamounts in the north and south, respectively (Cadet et al, 1987), constraining the trench to around 530 km long (Figure 1).…”

“…Hadal trenches are formed by the downward bending of oceanic crust in the plate subduction zone at 6-11 km water depths. As a result of the challenges in surveying and sampling in such great water depths, hadal trenches remain largely unexplored, yet they act as terminal sinks for sediment, organic carbon (OC) and even pollutants (Kioka et al, 2019;Peng et al, in press). The study of hadal trenches may allow to (i) unravel the history of subduction zone processes, including the world's largest earthquakes that occur in such subduction margin settings, and (ii) to investigate the deep-marine carbon cycle.…”

“…In the hadal Japan Trench, the AD 2011 Tohoku-oki earthquake remobilized young fine-grained surficial slope sediments enriched in organic matter, which was eventually deposited in the more than 7 km deep trench (Arai et al, 2013;Oguri et al, 2013;Strasser et al, 2013;Ikehara et al, 2016;McHugh et al, 2016;Kanamatsu et al, 2017;Bao et al, 2018;Kioka et al, 2019;Molenaar et al, 2019). Remarkably, the 2011 earthquake delivered >1 Tg (10 12 g) of OC to the Japan Trench between 36.0 • and 39.5 • N through the resedimentation of spatially widespread remobilization of surficial sediment with a total volume of ∼0.2 km 3 (Kioka et al, 2019). Moreover, several cores from the central part of the Japan Trench document evidence for event deposits related to surficial sediment remobilization triggered by older large earthquakes in the last few thousands of years, including the well-known AD 1454 Kyotoku and AD 869 Jogan earthquakes (Ikehara et al, 2016(Ikehara et al, , 2018Usami et al, 2018).…”