5:15 PM - 7:15 PM
[MIS23-P04] Depositional environment changes during the Holocene based on element properties off the mouth of Kinokawa River in Kiisuido Strait, Southwest Japan.
The Kiisuido Strait is located between Tokushima and Wakayama Prefectures and is connected to the Seto Inland Sea and the Pacific Ocean. The environment of the Kiisuido Strait is influenced by the inflow of Kuroshio water from the Pacific Ocean and the supply from the land. The Kii Channel is shallower than 60 m and was land during the last glacial period. To demonstrate the environmental changes of the Kiisuido Strait during the Holocene, this study collected core sediment (core length 346 cm) offshore of the mouth of the Kinokawa River, Wakayama Prefecture, used by gravity corer in December 2021.
The split sample of this core was measured element profiles with 5 mm interval using by XRF core scanner (ITRAX, Cox analytical system) and the subsampled were used for grain size by laser diffraction particle size analyze (LA960, Shimadzu) and concentrations of total organic carbon (TOC), total nitrogen (TN) and total sulfur (TS) by CHNS/O analyzer (Flash2000, Thermo Scientific). The age model of this core was estimated by AMS 14C and 210Pb and 137Cs dating.
The collected core was divided three units. The lower unit at the core depth of 346-275 cm was composited by poorly sorted fine sand-sand silt with 4 phi, middle unit at 275-89 cm depth by silty sand-sandy silt with 5-6 phi, and upper section above 89 cm depth by silt with 6-7 phi. The element profiles of Si, K Ti by XRF core scanner showed a decreasing toward the middle section from the lower, meanwhile Br increased. Profiles of Cu and Zn showed the increasing toward the core surface in the upper unit. The concentrations of TOC and TN were relatively lower in the lower unit and increased in the upper unit. The age model indicated 8.6-6.2 cal kyr BP in the lower unit, 6.1-0.1 cal kyr BP in the middle unit and after 0.1 cal kyr BP in the upper unit. The variation in the lower to middle unit suggested that decreasing of influence by hydrodynamic effect to seafloor with sea level change. These increasing trends of Cu, Zn and TOC in the upper unit suggested the anthropogenic impact in 20th century.
The split sample of this core was measured element profiles with 5 mm interval using by XRF core scanner (ITRAX, Cox analytical system) and the subsampled were used for grain size by laser diffraction particle size analyze (LA960, Shimadzu) and concentrations of total organic carbon (TOC), total nitrogen (TN) and total sulfur (TS) by CHNS/O analyzer (Flash2000, Thermo Scientific). The age model of this core was estimated by AMS 14C and 210Pb and 137Cs dating.
The collected core was divided three units. The lower unit at the core depth of 346-275 cm was composited by poorly sorted fine sand-sand silt with 4 phi, middle unit at 275-89 cm depth by silty sand-sandy silt with 5-6 phi, and upper section above 89 cm depth by silt with 6-7 phi. The element profiles of Si, K Ti by XRF core scanner showed a decreasing toward the middle section from the lower, meanwhile Br increased. Profiles of Cu and Zn showed the increasing toward the core surface in the upper unit. The concentrations of TOC and TN were relatively lower in the lower unit and increased in the upper unit. The age model indicated 8.6-6.2 cal kyr BP in the lower unit, 6.1-0.1 cal kyr BP in the middle unit and after 0.1 cal kyr BP in the upper unit. The variation in the lower to middle unit suggested that decreasing of influence by hydrodynamic effect to seafloor with sea level change. These increasing trends of Cu, Zn and TOC in the upper unit suggested the anthropogenic impact in 20th century.