Turbidity currents after the 2024 Noto Peninsula Earthquake and their environmental impacts on the Toyama Deep-Sea Channel in the Japan Sea

Abstract

Abstract The deep-sea environment before and after the 2024 Noto Peninsula Earthquake was investigated using a series of hydrographic and mooring observations in the Toyama Deep-Sea Channel (TDSC), Toyama Bay. Transient oxygen depletion was observed after the earthquake, and low-oxygen conditions in the TDSC persisted for at least 152 days after the mainshock. The concurrent increase in nutrient concentrations suggests organic matter decomposition in the TDSC. In addition, the turbidity (light transmittance anomaly) temporarily increased after the mainshock, suggesting advection or resuspension of particulate matters. Two turbidity current events were observed in March 30–31 and May 17–18 in the post-earthquake mooring observations at the thalweg, characterized by strong (> 16 cm s − 1 ), bottom-intensified downslope currents accompanied by transient temperature and turbidity increases. The observed turbidity currents were considered to be weaker and smaller than those at the mainshock. Although these turbidity current events correlated with meteorological disturbances, comparison of pre- and post-earthquake current conditions suggests that small-scale turbidity currents became more likely to occur after the mainshock. This study suggests that the mainshock on January 1, 2024 induced large-scale turbidity currents in the TDSC, transporting large volumes of organic-rich sediment to the deep sea from a shallow upstream region. As a result of the subsequent organic matter decomposition, transient oxygen depletion and nutrient increases were induced. In addition, small-scale turbidity currents frequently occurred after the mainshock. However, oxygen and turbidity returned to pre-earthquake conditions in June 2025 with decrease in small-scale turbidity current frequency.