The rapidly melting Totten Glacier of East Antarctica drains a basin containing ~3.5 m sea-level rise equivalent of ice, but the Totten Glacier dynamics and interaction with the Southern Ocean since the Last Glacial Maximum is not well understood. To better understand the response of the glacier to present and future climate changes, an accurate reconstruction of the retreat history of the Totten Glacier is needed. Hence, this study uses a multiproxy approach in analyzing beryllium isotopes, the first such record from this location, and grain size of a sediment core collected from the continental slope adjacent to Totten Glacier. The results, when evaluated together with nearby proxy records, reveal that the initial deglaciation of the Totten Glacier sector of the East Antarctic Ice Sheet began at ~18 ka BP. The rapid deglaciation from ~9 ka BP that followed is assumed to be caused by the intrusion of modified Circumpolar Deep Water to the grounding zone of the Totten Glacier. This intrusion may also be coupled with a weaker Antarctic Slope Current and southward shift of Antarctic easterlies. This result contributes to the body of knowledge regarding the dynamical response of marine-terminating glaciers to climate variability during the last deglaciation.

1. Otoliths have been widely studied as natural recorders of the entire life cycle of aquatic teleosts. Trace elements and stable isotope rations in otoliths are well understood and used as proxies of migration histories, however few elements have shown the potential to reconstruct the migration history of oceanodromous fish. 2. This study reports the first use of radiocarbon in otolith to reconstruct the horizontal migration history of fish. We analyzed three different stocks of walleye pollock Gadus chalcogrammus around Hokkaido, Japan. 3. Radiocarbon concentration from the outermost edge of otoliths showed a general consistency with seawater radiocarbon concentration of the sampling region, validating the application of otolith radiocarbon concentration to fish migration studies. Pollocks of all three stocks generally inhabited the nearby sampling area throughout their life cycle, though some pollocks of the Okhotsk and Japan Sea stocks respectively showed a possibility of migration between different sea regions. 4. This study confirmed a novel method using radiocarbon concentrations to reconstruct the migration history of marine teleost. Using the high sensitivity of otolith radiocarbon concentration observed in this study, it may be possible to detect fish migration with higher spatial resolution than previous studies using conventional proxies.

Infrequent megathrust earthquakes, with their complex cycles and rupture modes, require a high-resolution spatiotemporal record of tsunami inundations over thousands of years to provide more accurate long-term forecasts. The geological record suggests that Mw>8 earthquakes in the Kuril Trench occurred at intervals of several hundred years. However, uncertainties remain regarding the rupture zone, owing to the limited survey areas and chronological data. Therefore, we investigated the tsunami deposits in a coastal wetland of southeastern Hokkaido, Japan, to characterize the tsunamis that have originated from the Kuril Trench over the last 4000 years. On the Erimo coast, more than seven sand layers exhibited the common features of tsunami deposits, such as sheet distributions of several hundred meters, normal grading structures, and sharp basal contacts. According to numerical tsunami simulations, the 17th-century sand layer could be reproduced by using a multiple rupture zone model (Mw~8.8). We used high-resolution radiocarbon dating and tephras to correlate the tsunami deposits from the last 4000 years with those reported from regions ~100 km away. The tsunami history revealed here shows good agreement with histories of adjacent regions. However, the paleotsunamis reported to have occurred in regions > 200 km away include some events that differ from those in this study, which suggests a diversity of Mw>8 earthquakes in the Kuril Trench. We clarified the history and extents of earthquake-generated tsunamis along the southwestern end of the Kuril Trench, which were previously unknown. Our results provide a framework for magnitude estimations and long-term forecast of earthquakes.