5:15 PM - 6:45 PM
[SCG48-P35] The submarine sedimentary environment around the Tokara Islands suggested by surface sediment distribution
Keywords:Tokara Islands, submarine sediment, sedimentology
GSJ, AIST conducted marine geological surveys around the Tokara Islands located in the northern part of Nansei-Shoto region from FY2020 to FY2022. We obtained surface sediment samples on seven cruises (GB21-1, -2, and -3, GB22-1 and -2, KH-22-2, and KH-23-1).
The Tokara Strait, a geomorphic boundary separates the Northern and Central Ryukyu Islands. Numerous volcanic islands and submarine volcanoes are distributed, although the land area is small. It is also a meandering area where the Kuroshio Current passes through the islands from the East China Sea to the Pacific Ocean, raising many potential geoscientific issues. Therefore, detailed geological surveys on the Tokara Strait give us important information for solving these geoscientific issues.
According to data from more than 260 sediment samples and seafloor photographs acquired at a resolution of about 10 km in this area, sediments around the Tokara Islands consist mainly of volcaniclastic and biogenic materials. The sedimentation rate of muddy sediments estimated from core samples is around 10 to 20 cm/kyr, which is slightly lower than in other surrounding areas such as Okinawa Trough. The region off Tokara Islands has a small land area that is the source of the inflow of terrestrial material. The production of adherent organisms in the shallow areas below the Arikozoic layer is also low. As a result, the submarine area off the Tokara Islands is considered to have a relatively poor sediment inflow. The major sources of sediment inflow, especially sandy sediments, are mainly composed of volcanic materials from islands and submarine volcanoes scattered throughout the area, redeposition from sedimentary rock outcrops distributed in the northern part of the area, and biological production in the ocean surface layer.
Rocky bottom and gravelly sediments are widely distributed around topographic highs such as sea spurs and knolls, and sandy sediments showing bedforms such as ripples are widely distributed around the islands, mainly in the 300 to 700 m depth range. Based on the geographic and bathymetric distribution of transport and erosion areas and the distribution of bottom current directions indicated by ripples, the submarine sediments off the Tokara Islands are thought to be influenced by the Kuroshio Current, which meanders in this area and passes from the East China Sea to the Pacific Ocean. However, the influence of the Kuroshio Current is very complicated because the current velocity increases and the direction of the current changes with the passage of the islands, and because the sediment supply is small and traces of the bottom current of the low sea level period can be left on the surface.
The Tokara Strait, a geomorphic boundary separates the Northern and Central Ryukyu Islands. Numerous volcanic islands and submarine volcanoes are distributed, although the land area is small. It is also a meandering area where the Kuroshio Current passes through the islands from the East China Sea to the Pacific Ocean, raising many potential geoscientific issues. Therefore, detailed geological surveys on the Tokara Strait give us important information for solving these geoscientific issues.
According to data from more than 260 sediment samples and seafloor photographs acquired at a resolution of about 10 km in this area, sediments around the Tokara Islands consist mainly of volcaniclastic and biogenic materials. The sedimentation rate of muddy sediments estimated from core samples is around 10 to 20 cm/kyr, which is slightly lower than in other surrounding areas such as Okinawa Trough. The region off Tokara Islands has a small land area that is the source of the inflow of terrestrial material. The production of adherent organisms in the shallow areas below the Arikozoic layer is also low. As a result, the submarine area off the Tokara Islands is considered to have a relatively poor sediment inflow. The major sources of sediment inflow, especially sandy sediments, are mainly composed of volcanic materials from islands and submarine volcanoes scattered throughout the area, redeposition from sedimentary rock outcrops distributed in the northern part of the area, and biological production in the ocean surface layer.
Rocky bottom and gravelly sediments are widely distributed around topographic highs such as sea spurs and knolls, and sandy sediments showing bedforms such as ripples are widely distributed around the islands, mainly in the 300 to 700 m depth range. Based on the geographic and bathymetric distribution of transport and erosion areas and the distribution of bottom current directions indicated by ripples, the submarine sediments off the Tokara Islands are thought to be influenced by the Kuroshio Current, which meanders in this area and passes from the East China Sea to the Pacific Ocean. However, the influence of the Kuroshio Current is very complicated because the current velocity increases and the direction of the current changes with the passage of the islands, and because the sediment supply is small and traces of the bottom current of the low sea level period can be left on the surface.