Abstract
Tokyo Bay is situated near the triple junction of the North America, Pacific, and Philippine Sea plates, where relative sea-level changes since the Last Glacial Maximum (LGM) have been strongly affected by subduction tectonics. In this study, 55 sea-level index points were extracted from the post-LGM incised valley fills beneath the lowlands north of Tokyo Bay and used to construct a detailed relative sea-level curve for the Early Holocene. Sea-level jumps were detected at 10.1–10.0, 9.2–9.1, and 8.9–8.7 ka, each of 2–7 m and each followed by an acceleration in the rate of sea-level rise. These paired phenomena are attributed to coseismic subsidence and an interseismic decrease in the rate of uplift, respectively. The Early Holocene sea-level changes in Tokyo Bay are characterized by remarkably short sea-level jumps of <100 years and accelerations in the rates of sea-level rise with relatively long durations of 200–800 years. After separating these tectonic effects from relative sea-level changes, sea-level jumps that have been hypothesized to be eustatic events, such as Meltwater Pulses 1C and 1D and the pre-8.2-ka event, were not identified based on a sea-level detection limit of 3 m, but a decrease in the rate of sea-level rise at 8.2 ka, which can be regarded as a global phenomenon, was verified in Tokyo Bay.
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