17:15 〜 18:30
[MIS03-P03] Marine environmental changes affected by anthropogenic impacts based on XRF core scanner results in Tokyo Bay
The Tokyo Bay is one coastal area has heavily populated area in the drainage and its environment varied to be affected by the anthropogenic impacts during the last century. Previous studies discussed the environmental changes and its factors in Tokyo Bay such as eutrophication and pollution. This study reconstructed marine environment changes in Tokyo Bay based on variations of element contain in core sediments measured by XRF core scanner.
We collected four sediment cores by the gravity corer which has maximum core length of 150 cm in the offshore Shinagawa (TB01) and mouth of Tama river (TB06, 09, 13-2) in October 2020. These cores were measured the major and rear elements by XRF core scanner, Itrax (Cox Analytical Systems), set up at National Institute of Advanced Industrial Science and Technology (AIST, CS-49). These samples were measured in 30kV, 55mA and 10 seconds of exposure times using Molybdenum X-ray tubes at 1.0 mm intervals, respectively. All the XRF spectra were reevaluated by the Q-Spec software (version 15.1) to obtain individual element peak area. In order to reduce bias by matrix and closed-sum effects, the peak areas were normalized by the method of centered log-ratio(clr, Weltje and Tjallingii, 2008).
The collected cores were mainly consisted by silt. The TB01 and 06 cores showed the upper layer were darker than the lower and its boundaries were distinct. The TB09 showed dark color similar with the upper layer of TB01 and 06 through the core. The TB13-2 showed a dark color expected 10 cm of the surface and had plant and shell fragments concentrated layer. The Itrax results show that the clr values of Cr, Ni, Cu, Zn, Br and Y increase in these upper dark layers from the lower and the Si, Ca, Ti and Fe decrease in TB01 and 06. The profiles of these element in TB09 showed constant and same ranges of peak area with the upper layer of TB01 and 06. These results indicate that the upper dark layers contained more organic matters and metals than the lower affected by the eutrophication and pollution. On the other hand, the results of TB13-2 show the different patterns in the other cores which were almost constant and had some peaks. The site of TB13-2 was located at the mouth of Tama River. Therefore, the sedimentary process in TB13-2 was strongly influenced by the river discharge and the variations of element profiles indicated event layer caused by flood.
We collected four sediment cores by the gravity corer which has maximum core length of 150 cm in the offshore Shinagawa (TB01) and mouth of Tama river (TB06, 09, 13-2) in October 2020. These cores were measured the major and rear elements by XRF core scanner, Itrax (Cox Analytical Systems), set up at National Institute of Advanced Industrial Science and Technology (AIST, CS-49). These samples were measured in 30kV, 55mA and 10 seconds of exposure times using Molybdenum X-ray tubes at 1.0 mm intervals, respectively. All the XRF spectra were reevaluated by the Q-Spec software (version 15.1) to obtain individual element peak area. In order to reduce bias by matrix and closed-sum effects, the peak areas were normalized by the method of centered log-ratio(clr, Weltje and Tjallingii, 2008).
The collected cores were mainly consisted by silt. The TB01 and 06 cores showed the upper layer were darker than the lower and its boundaries were distinct. The TB09 showed dark color similar with the upper layer of TB01 and 06 through the core. The TB13-2 showed a dark color expected 10 cm of the surface and had plant and shell fragments concentrated layer. The Itrax results show that the clr values of Cr, Ni, Cu, Zn, Br and Y increase in these upper dark layers from the lower and the Si, Ca, Ti and Fe decrease in TB01 and 06. The profiles of these element in TB09 showed constant and same ranges of peak area with the upper layer of TB01 and 06. These results indicate that the upper dark layers contained more organic matters and metals than the lower affected by the eutrophication and pollution. On the other hand, the results of TB13-2 show the different patterns in the other cores which were almost constant and had some peaks. The site of TB13-2 was located at the mouth of Tama River. Therefore, the sedimentary process in TB13-2 was strongly influenced by the river discharge and the variations of element profiles indicated event layer caused by flood.