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The multiexpedition Integrated Ocean Drilling Program/International Ocean Discovery Program (IODP) Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE) project was designed to investigate fault mechanics and seismogenesis along subduction megathrusts through direct sampling, in situ measurements, and long-term monitoring in conjunction with allied laboratory and numerical modeling studies. Overall NanTroSEIZE scientific objectives include characterizing the nature of fault slip and strain accumulation, fault and wall rock composition, fault architecture, and state variables throughout the active plate boundary system. Expedition 380 was the twelfth NanTroSEIZE expedition since 2007. Refer to Kopf et al. (2017) for a comprehensive summary of objectives, operations, and results during the first 11 expeditions. Expedition 380 focused on one primary objective: riserless deployment of a long-term borehole monitoring system (LTBMS) in Hole C0006G in the overriding plate at the toe of the Nankai accretionary prism. The LTBMS installed in Hole C0006G incorporates multilevel pore-pressure sensing and a volumetric strainmeter, tiltmeter, geophone, broadband seismometer, accelerometer, and thermistor string. Similar previous LTBMS installations were completed farther upslope at IODP Sites C0002 and C0010. The ~35 km trench–normal transect of three LTBMS installations will provide monitoring within and above regions of contrasting behavior in the megasplay fault and the plate boundary as a whole, including a site above the updip edge of the locked zone (Site C0002), a shallow site in the megasplay fault zone and its footwall (Site C0010), and a site at the tip of the accretionary prism (the Expedition 380 installation at Site C0006). In combination, this suite of observatories has the potential to capture stress and deformation spanning a wide range of timescales (e.g., seismic and microseismic activity, slow slip, and interseismic strain accumulation) across the transect from near-trench to the seismogenic zone. Expedition 380 achieved its primary scientific and operational goal with successful installation of the LTBMS to a total depth of 457 m below seafloor in Hole C0006G. The installation was conducted in considerably less time than budgeted, partly because the Kuroshio Current had shifted away from the NanTroSEIZE area after 10 y of seriously affecting D/V Chikyu NanTroSEIZE operations. After Expedition 380, the LTBMS was successfully connected to the Dense Oceanfloor Network System for Earthquakes and Tsunamis (DONET) in March 2018 using the remotely operated vehicle Hyper-Dolphin from the Japan Agency for Marine-Earth Science and Technology (JAMSTEC) R/V Shinsei Maru.

The multiexpedition Integrated Ocean Drilling Program/International Ocean Discovery Program (IODP) Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE) was designed to investigate fault mechanics and seismogenesis along subduction megathrusts through direct sampling, in situ measurements, and long-term monitoring in conjunction with allied laboratory and numerical modeling studies. Overall NanTroSEIZE scientific objectives include characterizing the nature of fault slip and strain accumulation, fault and wall rock composition, fault architecture, and state variables throughout the active plate boundary system. Expedition 380 was the twelfth NanTroSEIZE expedition since 2007. Refer to Kopf et al. (2017) for a comprehensive summary of objectives, operations, and results during the first 11 expeditions. Expedition 380 focused on one primary objective: riserless deployment of a long-term borehole monitoring system (LTBMS) in Hole C0006G in the overriding plate at the toe of the Nankai accretionary prism. The LTBMS installed in Hole C0006G incorporates multilevel pore pressure sensing and a volumetric strainmeter, tiltmeter, geophone, broadband seismometer, accelerometer, and thermistor string. Similar previous LTBMS installations were completed farther upslope at IODP Sites C0002 and C0010. The ~35 km trench-normal transect of three LTBMS installations will provide monitoring within and above regions of contrasting behavior in the megasplay fault and the plate boundary as a whole, including a site above the updip edge of the locked zone (Site C0002), a shallow site in the megasplay fault zone and its footwall (Site C0010), and a site at the tip of the accretionary prism (the Expedition 380 installation at Site C0006). In combination, this suite of observatories has the potential to capture stress and deformation spanning a wide range of timescales (e.g., seismic and microseismic activity, slow slip, and interseismic strain accumulation) across the transect from near-trench to the seismogenic zone. Expedition 380 achieved its primary scientific and operational goal with successful installation of the LTBMS to a total depth of 457 m below seafloor in Hole C0006G. The installation was conducted in considerably less time than budgeted, partly because the Kuroshio Current had shifted away from the NanTroSEIZE area after 10 y of seriously affecting D/V Chikyu NanTroSEIZE operations. After Expedition 380, the LTBMS was to be connected to the Dense Oceanfloor Network System for Earthquakes and Tsunamis in March 2018 using the remotely operated vehicle Hyper-Dolphin from the Japan Agency for Marine-Earth Science and Technology R/V Shinsei Maru.

The Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE) is a coordinated, multiexpedition International Ocean Discovery Program (IODP) drilling project designed to investigate fault mechanics and seismogenesis along subduction megathrusts through direct sampling, in situ measurements, and long-term monitoring in conjunction with allied laboratory and numerical modeling studies. The fundamental scientific objectives of the NanTroSEIZE drilling project include characterizing the nature of fault slip and strain accumulation, fault and wall rock composition, fault architecture, and state variables throughout the active plate boundary system. IODP Expedition 365 is part of NanTroSEIZE Stage 3, with the following primary objectives: (1) retrieval of a temporary observatory at Site C0010 that has been monitoring temperature and pore pressure within the major splay thrust fault (termed the “megasplay”) at 400 meters below seafloor since November 2010 and (2) deployment of a complex long-term borehole monitoring system (LTBMS) that will be connected to the Dense Oceanfloor Network System for Earthquakes and Tsunamis (DONET) seafloor cabled observatory network postexpedition (anticipated June 2016). The LTBMS incorporates multilevel pore pressure sensing, a volumetric strainmeter, tiltmeter, geophone, broadband seismometer, accelerometer, and thermistor string. Together with an existing observatory at Integrated Ocean Drilling Program Site C0002 and a possible future installation near the trench, the Site C0010 observatory will allow monitoring within and above regions of contrasting behavior of the megasplay fault and the plate boundary as a whole. These include a site above the updip edge of the locked zone (Site C0002), a shallow site in the megasplay fault zone and its footwall (Site C0010), and a site at the tip of the accretionary prism (Integrated Ocean Drilling Program Site C0006). Together, this suite of observatories has the potential to capture deformation spanning a wide range of timescales (e.g., seismic and microseismic activity, slow slip, and interseismic strain accumulation) across a transect from near-trench to the seismogenic zone. Site C0010 is located 3.5 km along strike to the southwest of Integrated Ocean Drilling Program Site C0004. The site was drilled and cased during Integrated Ocean Drilling Program Expedition 319, with casing screens spanning a ~20 m interval that includes the megasplay fault, and suspended with a temporary instrument package (a “SmartPlug”). During Integrated Ocean Drilling Program Expedition 332 in late 2010, the instrument package was replaced with an upgraded sensor package (the “GeniusPlug”), which included pressure and temperature sensors and a set of geochemical and biological experiments. Expedition 365 achieved its primary scientific and operational objectives, including recovery of the GeniusPlug with a >5 y record of pressure and temperature conditions within the shallow megasplay fault zone, geochemical samples, and its in situ microbial colonization experiment; and installation of the LTBMS. The pressure records from the GeniusPlug include high-quality records of formation and seafloor responses to multiple fault slip events, including the 11 March 2011 Tohoku M9 and 1 April 2016 Mie-ken Nanto-oki M6 earthquakes. The geochemical sampling coils yielded in situ pore fluids from the splay fault zone, and microbes were successfully cultivated from the colonization unit. The complex sensor array, in combination with the multilevel hole completion, is one of the most ambitious and sophisticated observatory installations in scientific ocean drilling (similar to that in Hole C0002G, deployed in 2010). Overall, the installation went smoothly, efficiently, and ahead of schedule. The extra time afforded by the efficient observatory deployment was used for coring in Holes C0010B–C0010E. Despite challenging hole conditions, the depth interval corresponding to the screened casing across the megasplay fault was successfully sampled in Hole C0010C, and the footwall of the megasplay was sampled in Hole C0010E, with >50% recovery for both zones. In the hanging wall of the megasplay fault (Holes C0010C and C0010D), we recovered indurated silty clay with occasional ash layers and sedimentary breccias. Some of the deposits show burrows and zones of diagenetic alteration/colored patches. Mudstones show different degrees of deformation spanning from occasional fractures to intervals of densely fractured scaly claystones of up to >10 cm thickness. Sparse faulting with low displacement (usually

Abundance and grazing impacts of krill, salps and herbivorous copepods were investigated in Antarctic waters along the 140°E meridian, south of Australia, during the summers of 2002 and 2003. North of the Southern Boundary of the Antarctic Circumpolar Current (SB-ACC), macrozooplankton comprised species of Salpa thompsoni and large herbivorous copepods, while the area south of the SB-ACC was numerically dominated by Euphausia superba or E. crystallorophias. North of the SB-ACC, the estimate of grazing impact revealed that krill, salps and copepods, Calanoides acutus, Calanus propinquus, Rhincalanus gigas and Metridia gerlachei, are able to remove a maximum of 37% of the total phytoplankton standing stock in early to midsummer, but grazing is negligible in late summer. The high grazing impact is attributed to the relatively high zooplankton abundance and low phytoplankton abundance. South of the SB-ACC, overall daily grazing impact of the three zooplankton groups was low and did not exceed 6% of the total phytoplankton standing stock throughout the investigation period. Present results indicate that the contribution of krill, salps and copepods varies seasonally as well as regionally across the SB-ACC. It seems that the carbon transport from surface to deep water by macro- and mesozooplankton in summer in this area is relatively large north of the SB-ACC but small south of the SB-ACC.

The Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE) program is a coordinated, multiexpedition drilling project designed to investigate fault mechanics and seismogenesis along subduction megathrusts through direct sampling, in situ measurements, and long-term monitoring in conjunction with allied laboratory and numerical modeling studies. The fundamental scientific objectives of the NanTroSEIZE drilling project include characterizing the nature of fault slip and strain accumulation, fault and wall rock composition, fault architecture, and state variables throughout the active plate boundary system. International Ocean Discovery Program (IODP) Expedition 365 will recover temporary monitoring instruments (a “GeniusPlug”) from previously drilled and cased Integrated Ocean Drilling Program Site C0010 and deploy a permanent long-term borehole monitoring system (LTBMS) in the same hole after deepening it to ~656 meters below seafloor (mbsf). These operations will complete preparations begun during Integrated Ocean Drilling Program Expedition 319 and continued during Integrated Ocean Drilling Program Expedition 332. This expedition will cover a period of 33 days, beginning on 26 March and ending on 27 April 2016. Site C0010 is located 3.5 km north of Integrated Ocean Drilling Program Site C0004 and was first drilled during Expedition 319. Operations during that expedition included drilling through the megasplay fault zone and into its footwall using logging while drilling (LWD), setting casing with screens spanning the fault zone, and installation of a simple temporary observatory (a “SmartPlug”) to monitor fluid pressure and temperature in the screened interval. Major lithologic boundaries as well as the location of the megasplay fault at ~407 mbsf were identified in LWD data and were used to select a depth interval spanning the fault for placement of the two screened casing joints. Three distinct lithologic packages were observed at Site C0010: slope deposits (Unit I, 0–182.5 mbsf), thrust wedge (Unit II, 182.5–407 mbsf), and overridden slope deposits (Unit III, 407 mbsf to total depth). During Expedition 332, the SmartPlug was recovered and replaced with an upgraded version, the GeniusPlug, which includes a set of geochemical and biological experiments housed in a 30 cm extension. This GeniusPlug will be recovered and replaced with a permanent LTBMS, which will be later linked to the Dense Oceanfloor Network System for Earthquakes and Tsunamis (DONET) submarine network. This Scientific Prospectus outlines the scientific rationale, objectives, and operational plans for Site C0010 and describes the contingency plan.