3. Generate results for comparison with those from all other Expedition 386 sites to explore spatiotemporal distribution of event deposits and the southern extent of sediment transport routed through the Ogawara submarine canyon to eventually develop a long-term record for giant earthquakes. Operations summaryBecause of very strong winds (>15 m/s) on 25 April 2021 at Site M0089, the decision was made to move the R/V Kaimei to Site M0084 in the northern Japan Trench focus area (Sites M0084 and M0085).Kaimei reached the site at 1430 h and multibeam echo sounder/subbottom profiler (MBES/SBP) surveys were carried out at Site M0084 from 1530 to 1645 h.Winds remained strong (>18 m/s) on the morning of 26 April, with wave heights of 3 m and 1.3 kt currents; the decision was made to delay GPC deployment until the winds dropped to <15 m/s.At 1200 h, the captain confirmed it was possible to maintain position under manual mode, and the go ahead was given to deploy the GPC.GPC operations started in Holes M0084A and M0084B with a 20 m GPC barrel string at 1230 h and were completed when the GPC system was recovered on deck at 1840 h.The deck crew and GPC operation team withdrew the core from the GPC assembly and cut it into 5 m segments.The Science Party cut the core into 1 m sections from 1900 to 2100 h.The GPC assembly was prepared for the next run at 2300 h.At 0000 h on 27 April, Kaimei began drifting to Site M0085, standing by at the site at 0200 h.Conditions were cold but calm (winds 8 m/s; wave height 1 m; <1.5 kt current).GPC preparations for Holes M0085A and M0085B with a 20 m barrel string began at 0600 h, and the GPC was recovered on deck at 1500 h.The deck crew and GPC operation team withdrew the core from the GPC assembly and cut it into 5 m segments.The Science Party cut the core into 1 m sections.Cutting was completed at 1610 h, and the GPC was made up for the next run at 2115 h.An MBES/SBP survey around Sites M0084 and M0085 commenced at 2115 h on 27 April and continued until 0700 h on 28 April.Conditions were warmer and calm (winds <3 m/s; <1.3 kt current; wave height <1 m).GPC operations started in Holes M0084C and M0084D with a 40 m GPC barrel string at 0700 h, and the GPC system was recovered on deck at 1500 h.The deck crew and GPC operation team withdrew core from the liner, and the Science Party sampled from section bottoms and cut core into 1 m sections from 1600 to 1930 h.GPC make up and preparation with a 40 m barrel was complete at 2130 h on 28 April, and MBES/SBP surveying around Sites M0084 and M0085 resumed at this time.MBES/SBP surveying around Sites M0084 and M0085 continued until 0445 h on 29 April and was suspended for 40 m GPC operations in Holes M0085C and M0085D.Conditions were overcast but calm (winds <5 m/s; <1.2 kt current; wave height <1 m).GPC operations started in Holes M0085C and M0085D with a 40 m core barrel string at 0600 h, and the GPC was recovered on deck at 1315 h.The GPC core bit was removed at 1400 h and the GPC was secured, but a rough weather forecast meant that withdrawing core was delayed.The ship began transit to a standby point off Miyako at 1400 h and arrived at 2300 h.Core from Holes M0085C and M0085D was withdrawn, and cores were cut into 5 and 1 m sections from 1130 to 1600 h on 30 April.The 40 m GPC assembly was made up at 2300 h, when the ship started the transit to Site M0083 (see Operations in the Sites M0083 and M0089 (Basin C2) chapter [Strasser et al., 2023d]).Kaimei returned to Site M0084 on 12 May at 0445 h.GPC operations started in Holes M0084E and M0084F using the 40 m core barrel string at 0800 h, and the GPC was recovered on deck at 1415 h.Conditions were calm (winds <4 m/s; wave height ~0.2 m) with a relatively strong current (~1.8 kt).The deck crew and GPC operation team withdrew the core from the liner, and the Science Party sampled from the section bottoms and cut the core into 1 m sections from 1430 to 1900 h.GPC make up and preparation with the 40 m barrel was complete at 2100 h on 12 May, and MBES/SBP surveying around Site M0084 commenced at 2100 h and continued until 0215 h on 13 May.

The delivery of organic carbon (OC) to the ocean's deepest trenches in the hadal zone is poorly understood, but may be important for the carbon cycle, contain crucial information on sediment provenance and event-related transport processes, and provide age constraints on stratigraphic sequences in this terminal sink. In this study, we systematically characterize bulk organic matter (OM) and OC signatures (TOC/TN, delta C-13, C-14), as well as those from application of serial thermal oxidation (ramped pyrolysis/oxidation) of sediment cores recovered along an entire hadal trench encompassing high stratigraphic resolution records spanning nearly 2000 years of deposition. We analyze two cores from the southern and northern Japan Trench, where submarine canyon systems link shelf with trench. We compare results with previously published data from the central Japan Trench, where canyon systems are absent. Our analyses enable refined dating of the stratigraphic record and indicate that event deposits arise from remobilization of relatively surficial sediment coupled with deeper erosion along turbidity current pathways in the southern and central study site and from canyon flushing events in the northern study site. Furthermore, our findings indicate deposition of predominantly marine OC within hemipelagic background sediment as well as associated with event deposits along the entire trench axis. This implies that canyon systems flanking the Japan Trench do not serve as a short-circuit for injection of terrestrial OC to the hadal zone, and that tropical cyclones are not major agents for sediment and carbon transfer into this trench system. These findings further support previous Japan Trench studies interpreting that event deposits originate from the landward trench slope and are earthquake-triggered. The very low terrestrial OC input into the Japan Trench can be explained by the significant distance between trench and hinterland (>180 km), and the physiography of the canyons that do not connect to coast and river systems. We suggest that detailed analyzes of long sedimentary records are essential to understand OC transfer, deposition and burial in hadal trenches. (C) 2021 The Author(s). Published by Elsevier B.V.

Understanding the impact of earthquakes on subaqueous environments is key for submarine paleoseismological investigations seeking to provide long-term records of past earthquakes. For this purpose, event deposits (e.g., turbidites) are, among others, identified and stratigraphically correlated over broad areas to test for synchronous occurrence of gravity flows. Hence, detailed spatiotemporal petrographic and geochemical fingerprints of such deposits are required to advance the knowledge about sediment source and the underlying remobilization processes induced by past earthquakes. In this study, we develop for the first time in paleoseismology a multivariate statistical approach using X-ray fluorescence core scanning, magnetic susceptibility, and wet bulk density data that allow to test, confirm, and enhance the previous visual and lithostratigraphic correlation across two isolated basins in the central Japan Trench. The statistical correlation is further confirmed by petrographic heavy grain analysis of the turbidites and additionally combined with our novel erosion model based on previously reported bulk organic carbon 14C dates. We find surficial sediment remobilization, a process whereby strong seismic shaking remobilizes the uppermost few centimeters of surficial slope sediment, to be a predominant remobilization process, which partly initiates deeper sediment remobilization downslope during strong earthquakes at the Japan Trench. These findings shed new light on source-to-sink transport processes in hadal trenches during earthquakes and help to assess the completeness of the turbidite paleoseismic record. Our results further suggest that shallow-buried tephra on the slope might significantly influence sediment remobilization and the geochemical and petrographic fingerprints of the resulting event deposits.

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.

Leg A SO251-1, Yokohama - Yokohama, 04.10.2016 - 15.10.2016, Leg B SO251-2, Yokohama - Yokohama, 18.10.2016 - 02.11.2016

Little is known about offshore tsunami deposits, although they have the potential to improve palaeotsunami reconstructions, especially in areas with limited preservation of onshore tsunami deposits. We analysed 44 sediment cores collected in 2012 at water depths of 14-30 m in Sendai Bay, north-eastern Japan, to identify the deposits of the 2011 Tohoku-oki tsunami with the aid of Cs-134 released from the Fukushima-Daiichi Nuclear Plant. The preserved tsunami deposits in the inner shelf are interbedded with very fine sand and mud, showing similar features to storm deposits. In the shoreface, a distinct layer of coarse sand overlies fine sand, appearing to have originated as beach sand transported offshore by the tsunami backwash. The coarse sand fades offshore around the boundary between the shoreface and inner shelf. Many of the core sites show evidence that surface sediment was reworked, probably by post-tsunami storm waves, suggesting that further reworking would make the ultimate preservation of the tsunami deposits unlikely. Copyright (C) 2015 John Wiley & Sons, Ltd.

We present differential bathymetry and sediment core data from the Japan Trench, sampled after the 2011 Tohoku-Oki (offshore Japan) earthquake to document that prominent bathymetric and structural changes along the trench axis relate to a large (similar to 27.7 km(2)) slump in the trench. Transient geochemical signals in the slump deposit and analysis of diffusive re-equilibration of disturbed SO42- profiles over time constrain the triggering of the slump to the 2011 earthquake. We propose a causal link between earthquake slip to the trench and rotational slumping above a subducting horst structure. We conclude that the earthquake-triggered slump is a leading agent for accretion of trench sediments into the forearc and hypothesize that forward growth of the prism and seaward advance of the deformation front by more than 2 km can occur, episodically, during a single-event, large mega-thrust earthquake.

A magnetic fabric analysis has been carried out on standard cube samples from one gravity and three multiple cores extracted from the Shiribeshi trough and Okushiri basin in the southern margin of the Japan sea north basin. It is aimed at tracing the flow path of turbidites that are assumed to have deposited in response to the 1993 Hokkaido-Nansei-oki earthquake. Magnetic remanence was used for reorientation to the geographic coordinates. Magnetomineralogical investigations including low-temperature magnetometry, magnetic hysteresis loops and isothermal remanent magnetization (IRM) acquisition experiments indicate that pseudo-single domain to multidomain magnetite is the principal magnetic carrier and is, therefore, capable of providing reliable anisotropy of magnetic susceptibility (AMS) palaeocurrent direction estimates. A well-developed near-horizontal magnetic foliation and minimum susceptibility axes lying close to vertical are recorded at all sites reflecting an original depositional fabric. Clearly defined magnetic lineation was observed at all sites and is considered to reflect the palaeocurrent direction. Down-core changes of susceptibility and key AMS parameters show good correspondence to occurrences of turbidite layers marking the increase of input of influx materials. In agreement with results from recent marine surveys and IZANAGI side-scan sonar images, an NNE transportation trend has been estimated for sediments at sites from the Shiribeshi trough with a possible depositing path initiating from the slope bounding the south and southeastern margin down to the trough floor. Similarly, a SSE palaeocurrent direction has been estimated for sediments from the Okushiri basin with evidence for a relatively strong transporting current flowing through the canyons along the steep slope bounding the north and northeastern margins of the basin. The present results agree with the view that slope failure is the most probable mechanism for the down-slope transport of the sand from the shelves and upper slopes down to floors of basins and troughs in the southern margin of the Japan sea north basin. They further support the ongoing assumption that the 1993 Hokkaido-Nansei-oki and other strong historical earthquakes together with associated tsunamis are the principal triggering forces for the down-slope mass gravitational transport and formation of turbidites in this seismically active area.

Rapid and drastic changes in radiolarian assemblages during the last 33 kyr were revealed in three sediment cores from the eastern and northeastern Japan Sea. Such changes occurred synchronously over the Sea according to the correlation by TL layers and AMS14C dating. On the basis of these bio-events, four radiolarian biozones were established : Ceratospyris borealis Interval Biozone (33 to 1514C kyr BP), Stylochlamydium venustum Interval Biozone (15 to 1214C kyr BP), Cycladophora davisiana Interval Biozone (12 to 10.514C kyr BP), and Larcopyle butschlii Interval Biozone (10.514C kyr BP to Present) . These radiolarian biozones are useful for correlating the upper Quaternary sediments in the Japan Sea, where carbonate fossils are poorly preserved below the calcium carbonate compensation depth (CCD) .

This paper proposes a method for a hierarchical network management system that is mainly used in large-scale networks. In this method, management information is extracted from the standard management protocol packets exchanged between a manager and network elements, and is provided for an integrated manager.