- \n
- Large sedimentary landforms interpreted as \u201ccontourite drifts\u201d were discovered on the deep seafloor, at water depths greater than approximately 5,000 m, seaward of the Kuril Trench. These landforms are thought to have been formed by currents flowing close to the seafloor.<\/li>\n
- The study shows that large contourite drifts can form and be preserved even on the outer rise of an oceanic plate before it enters a subduction zone.<\/li>\n
- The findings identify a new target for investigating past deep-sea environments in the Northwest Pacific and demonstrate the importance of considering long-term sediment transport and redeposition by near-seafloor currents when interpreting stratigraphic records around ocean trenches, including records of past earthquakes.<\/li>\n<\/ul>\n
Summary<\/h4>\n
A research group including Hisashi Ikeda, a third-year doctoral student at the Graduate School of Sciences and Technology for Innovation, 911±¬ÁÏÍø¹ÙÍø; Assistant Professor Jih-Hsin Chang of the Institute of Oceanography, National Taiwan University; Researcher Ryo Nakanishi of the Research Institute of Geology and Geoinformation, Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology; and Director Toshiya Kanamatsu of the Volcanoes and Earthquakes Research Department, Japan Agency for Marine-Earth Science and Technology, has discovered large sedimentary landforms on the outer rise seaward of the Kuril\u2013Japan Trench system, off Hokkaido and northeastern Japan. These landforms are interpreted as having been formed by currents flowing close to the deep seafloor.
Such near-seafloor currents are known as \u201cbottom currents (Note 1)<\/sup>\u201d. Sediments transported and redeposited by bottom currents are called \u201ccontourites.\u201d Over long periods of time, the accumulation of contourites can form large sedimentary landforms known as \u201ccontourite drifts.\u201d Contourite drifts have been widely studied in regions such as the Atlantic Ocean, the Mediterranean Sea, and the Southern Ocean. However, their development and preservation on \u201couter rises,\u201d where an oceanic plate bends gently upward before entering a trench, have remained poorly understood.
The research group integrated seafloor bathymetric data, seismic reflection data used to investigate subsurface stratigraphic sections beneath the seafloor (Note 2)<\/sup>, sub-bottom profiler data used to image shallow strata immediately beneath the seafloor (Note 3)<\/sup>, and sediment core analyses. The results revealed two large sedimentary bodies on the Kuril Trench outer rise, with a combined area of approximately 12,000 km\u00b2. These bodies are interpreted to have formed through long-term sediment transport and redeposition by bottom currents.
The newly recognized sedimentary bodies may provide a new research target for investigating past deep-sea environments and changes in deep-ocean circulation in the Northwest Pacific. The study also indicates that, when interpreting sedimentary records around ocean trenches, it is important to consider not only deposits transported rapidly by earthquakes and tsunamis, but also the long-term redistribution of sediment by currents flowing near the seafloor. The paper was published online in the international journal Marine Geology on May 15, 2026.<\/p>\n![\"\"](\"https:\/\/ds27i1.cc.yamaguchi-u.ac.jp\/~www-yu\/english\/wp-content\/uploads\/sites\/4\/2026\/07\/26072901_en.png\")
Reference figure. Conceptual diagram showing the formation of a contourite drift. Bottom currents flowing close to the seafloor erode, transport, and redeposit fine-grained sediment. Seafloor relief, such as seamounts and slopes, creates areas where sediment is more likely to be eroded, bypassed, or accumulated. Over long periods of time, these processes can form contourite drifts.
<\/strong><\/p>\nBackground<\/h4>\n
On the deep seafloor, currents flowing close to the seabed can erode, transport, and redeposit fine particles such as mud, microfossil shells, and volcanic ash. These processes are among the important mechanisms that shape deep-sea morphology and stratigraphy. Contourite drifts are attracting attention as sedimentary archives that record changes in past ocean circulation and deep-sea environments.
Large contourite drifts have been studied mainly in the North Atlantic, South Atlantic, Mediterranean Sea, Southern Ocean, and Southwest Pacific. Contourite drifts have also been reported around subduction margins, but many of these studies have focused on areas inside the trench system or near the trench axis. In contrast, how large sedimentary landforms formed by bottom currents develop on the outer rise of an oceanic plate before subduction has not been sufficiently investigated.
Seaward of the Kuril Trench, the Pacific Plate bends upward before subduction, forming a broad outer-rise region. This area contains numerous seamounts and smaller topographic highs, resulting in complex seafloor morphology. In addition, deep waters originating around Antarctica reach the deep Northwest Pacific as part of the global ocean circulation system. When deep-ocean currents interact with seamounts and outer-rise topography, near-bottom flow can locally strengthen or change direction. As a result, sediment may be preferentially eroded, bypassed, or deposited in different areas. This study examined whether large sedimentary landforms formed by bottom currents are developed on the Kuril Trench outer rise.<\/p>\n![\"\"](\"https:\/\/ds27i1.cc.yamaguchi-u.ac.jp\/~www-yu\/english\/wp-content\/uploads\/sites\/4\/2026\/07\/26072902_en.jpg\")
Figure 1. Schematic overview of major contourite drift study areas and global deep-ocean circulation. Contourite drifts have previously been studied mainly in regions such as the North Atlantic, South Atlantic, Mediterranean Sea, Southern Ocean, and Southwest Pacific. In this figure, major previously studied regions are shown in blue, and the Kuril Trench outer-rise study area is shown in yellow.
<\/strong><\/p>\nStudy Details<\/h4>\n
The research group analyzed bathymetric and seismic reflection data acquired and archived by the Japan Agency for Marine-Earth Science and Technology (JAMSTEC). These data were combined with sub-bottom profiler data and sediment core samples collected during the MR24-02 and MR24-05 research cruises of the research vessel Mirai in 2024. This integrated approach allowed the group to investigate seafloor morphology, subsurface stratigraphic architecture, and sediment characteristics.<\/div>\n(1)Two large sedimentary bodies identified from seafloor morphology
The analysis revealed two large sedimentary bodies on the Kuril Trench outer rise. One is an elongated, tongue-shaped body adjacent to the northeastern side of Ryofu\u2013Daini Seamount and covers approximately 2,000 km\u00b2. The other is a larger sedimentary body extending to the southwest, covering approximately 10,000 km\u00b2. Elongated depressions occur around these bodies, and large-scale wavy bedforms are also present on the surface of the sedimentary bodies. These geomorphic features are interpreted to reflect the erosion, transport, and redeposition of sediment by bottom currents influenced by seafloor topography.<\/p>\n(2)Evidence from subsurface stratigraphy and sediment cores
Subsurface stratigraphic sections and sediment cores also provide evidence supporting formation by bottom currents. The subsurface sections show mounded geometries, asymmetric thickness variations, areas where sedimentary units thin laterally, and locally eroded or truncated parts. These features indicate that sediment was transported and accumulated over long periods of time under the influence of bottom currents.
The sediment cores consist mainly of diatomaceous mud and contain evidence of bioturbation, indicating that organisms mixed the sediment after deposition. Analyses of volcanic ash layers showed that the sedimentation rate on the top of the sedimentary body was approximately 2.9 times higher than that at a nearby depression site. This contrast suggests that fine-grained sediment was preferentially accumulated on the sedimentary body under the influence of bottom currents.<\/p>\n![\"\"](\"https:\/\/ds27i1.cc.yamaguchi-u.ac.jp\/~www-yu\/english\/wp-content\/uploads\/sites\/4\/2026\/07\/26072903_en.jpg\")
Figure 2. Large sedimentary landforms discovered on the Kuril Trench outer rise and evidence for their origin. A: Bathymetric map showing the two large sedimentary bodies, survey lines, and sediment core sites. B, C: Subsurface stratigraphic sections and their interpretations. The internal architecture of the sedimentary bodies shows mounded geometries, asymmetric thickness variations, and locally eroded or truncated parts, indicating sediment transport and accumulation by bottom currents. D: Shallow sub-bottom profile showing that the site on the sedimentary body and the site near the depression belong to the same shallow depositional system. E, F: Photographs and X-ray CT images of sediment cores.
<\/strong><\/p>\nSignificance<\/h4>\n
The significance of this study lies in demonstrating that bottom currents have transported sediment on a large scale and have contributed to the formation of seafloor morphology and subsurface stratigraphic architecture on the Kuril Trench outer rise. Previous studies around the Kuril and Japan trenches have focused mainly on earthquakes, tsunamis, submarine landslides, and plate subduction processes. This study shows that, in addition to these processes, persistent bottom currents flowing close to the seafloor over long periods of time can also play an important role in controlling sediment distribution and seafloor morphology around ocean trenches.
The results further show that large contourite drifts can form on the outer rise of an oceanic plate before subduction. This finding expands the range of geological settings in which contourite drifts can be recognized and studied.
The newly discovered sedimentary bodies may serve as a new geological archive for investigating how deep-ocean circulation in the Northwest Pacific has changed through time. The study also highlights the importance of considering bottom-current-related sediment transport when using trench-margin sedimentary records to investigate past earthquakes and tsunamis.<\/p>\nFuture Perspectives<\/h4>\n
A key future challenge is to establish a more detailed age framework for the strata composing the drifts. At present, their broad age interpretation is based on regional comparison with existing data from Deep Sea Drilling Project Site 436, located south of the Kuril Trench outer-rise study area. Future detailed analyses of sediment cores collected from multiple sites will allow the ages and sedimentary characteristics of the drift deposits to be constrained in greater detail. This will make it possible to investigate more specifically how deep-ocean circulation in the Northwest Pacific has changed over long timescales.
This discovery provides a new starting point for linking the deep-sea environmental history of the Northwest Pacific with the interpretation of sedimentary records around ocean trenches.<\/p>\nAcknowledgments<\/h4>\n
This study includes data and samples collected during the MR24-02 and MR24-05 research cruises of the research vessel Mirai, conducted as part of the JAMSTEC research project \u201cGeological Study of Paleo-Earthquakes and Tsunamis along the Kuril Trench.\u201d The authors sincerely thank the captains and crews of both cruises, all personnel who supported cruise operations, and the marine technicians who assisted with data acquisition. X-ray CT imaging of sediment cores was conducted through the cooperative research program of the Marine Core Research Institute, Kochi University (23A020, 24A002). The authors thank Dr. Yuka Kaiho of JAMSTEC for her assistance in using the JAMSTEC seismic survey database. The authors also thank Dr. Takeshi Ueno of the Atmosphere and Ocean Research Institute, The University of Tokyo, and Dr. Ken Ikehara of the Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology, for their valuable advice. This research was supported by the JST Support for Pioneering Research Initiated by the Next Generation program (JPMJSP2111), the 911±¬ÁÏÍø¹ÙÍø Fund, and the Kyoto University North Campus Equipment Analysis Hub.<\/p>\n
Paper Information<\/h4>\n
- \n
- Journal: Marine Geology<\/li>\n
- Volume and issue: Volume 498, August 2026<\/li>\n
- Article number: 107802<\/li>\n
- Title: Discovery of contourite drifts on the outer rise along the Kuril Trench, Northwest Pacific<\/li>\n
- Authors: Hisashi Ikeda1<\/sup>\uff0a, Jih-Hsin Chang2<\/sup>, Ryo Nakanishi3<\/sup>, Toshiya Kanamatsu4<\/sup>, Toshiya Fujiwara4<\/sup>, Kan-Hsi Hsiung4<\/sup>, Kiichiro Kawamura1<\/sup><\/li>\n
- \uff0aCorresponding author: 1<\/sup> 911±¬ÁÏÍø¹ÙÍø, 2<\/sup> National Taiwan University, 3<\/sup> National Institute of Advanced Industrial Science and Technology, 4<\/sup> Japan Agency for Marine-Earth Science and Technology<\/li>\n
- DOI: 10.1016\/j.margeo.2026.107802<\/li>\n
- URL: https:\/\/www.sciencedirect.com\/science\/article\/pii\/S002532272600099X<\/a><\/li>\n<\/ul>\n
Glossary<\/h4>\n
- \n
- Note 1. Bottom current: A current that flows close to the seafloor. Bottom currents can transport, erode, and redeposit mud and other fine-grained particles.<\/li>\n
- Note 2. Seismic reflection survey: A geophysical method that uses sound waves to investigate geological structures beneath the seafloor. This method can image subsurface structures over a wide area.<\/li>\n
- Note 3. Sub-bottom profiler: An acoustic instrument used to image shallow sedimentary layers immediately beneath the seafloor.<\/li>\n<\/ul>\n
<\/p>\n
Contacts<\/h4>\n
(research contacts)<\/div>\n- \n
- Division of Natural Sciences, Graduate School of Sciences and Technology for Innovation, 911±¬ÁÏÍø¹ÙÍø
Third-year doctoral student, Hisashi Ikeda
Email: e002wbv*yamaguchi-u.ac.jp (replace * with @)<\/li>\n - Division of Earth Sciences, Graduate School of Sciences and Technology for Innovation, 911±¬ÁÏÍø¹ÙÍø
Prof. Kiichiro Kawamura
E-mail: kiichiro*yamaguchi-u.ac.jp (replace * with @)<\/li>\n<\/ul>\n(media contact)<\/div>\n- \n
- Public Relations, 911±¬ÁÏÍø¹ÙÍø
E-mail: sh011*yamaguchi-u.ac.jp (replace * with @)<\/li>\n<\/ul>\n<\/div>\n<\/div>\n","protected":false},"featured_media":3308,"template":"","meta":[],"_links":{"self":[{"href":"https:\/\/ds27i1.cc.yamaguchi-u.ac.jp\/~www-yu\/english\/wp-json\/wp\/v2\/news\/3302"}],"collection":[{"href":"https:\/\/ds27i1.cc.yamaguchi-u.ac.jp\/~www-yu\/english\/wp-json\/wp\/v2\/news"}],"about":[{"href":"https:\/\/ds27i1.cc.yamaguchi-u.ac.jp\/~www-yu\/english\/wp-json\/wp\/v2\/types\/news"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/ds27i1.cc.yamaguchi-u.ac.jp\/~www-yu\/english\/wp-json\/wp\/v2\/media\/3308"}],"wp:attachment":[{"href":"https:\/\/ds27i1.cc.yamaguchi-u.ac.jp\/~www-yu\/english\/wp-json\/wp\/v2\/media?parent=3302"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}
- Public Relations, 911±¬ÁÏÍø¹ÙÍø
- Division of Natural Sciences, Graduate School of Sciences and Technology for Innovation, 911±¬ÁÏÍø¹ÙÍø
- \uff0aCorresponding author: 1<\/sup> 911±¬ÁÏÍø¹ÙÍø, 2<\/sup> National Taiwan University, 3<\/sup> National Institute of Advanced Industrial Science and Technology, 4<\/sup> Japan Agency for Marine-Earth Science and Technology<\/li>\n