Organic geochemical indicators have proven suitable to identify and characterize deposits of recent tsunamis, such as the 2011 CE Tōhoku-oki event, providing insights into erosional and transport processes of marine and terrestrial sediment inland (inundation) and offshore (backwash). However, lipid biomarkers have rarely been applied to historic and paleotsunami archives. We review lipid biomarkers suitable for paleotsunami research and present a case study using a targeted multi-compound approach on a geoslicer core from the Maita River Valley at Noda (Iwate Prefecture, Japan). At this site four paleotsunami deposits have previously been documented. In the analyzed samples, we quantified homologous series (n-alkanes, n-aldehydes, fatty acids), isoprenoids (pristane, phytane), terpenoids, diagenetically stable compounds (steranes, hopanes), and evaluated diagnostic ratios.All four paleotsunami sand layers show a coherent marine fingerprint relative to background sediment. This fingerprint is expressed by enrichment of short-chain homologues, C27 steranes and reduced C29/C27 sterane ratios, low pristane/phytane (≤0.7) with aquatic-sources clustering in the pristane/n-C17 vs phytane/n-C18 cross-plot, and lower sterane/hopane ratios. Terrigenous inputs are suppressed (lower long-chain homologues and TAR indices), while elevated OEP, CPI, and EOP ratios indicate rapid burial of relatively fresh plant waxes co-transported during inundation.These results demonstrate that lipid biomarkers preserve paleotsunami signatures for millennia and can refine source allocation, sediment transport pathways, and complement sedimentological approaches, by characterizing and reconstructing the inundation of paleotsunamis. Such multi-compound lipid biomarker approaches enable more robust paleotsunami detection and improve constraints for regional tsunami-hazard assessments.

The 2011 Tohoku-oki tsunami left a characteristic geochemical signature in the sediments of the Misawa harbor on the Aomori coastline (northern Japan), not only in vertical stratigraphy but also in lateral distribution. Suitable indicator compounds for the tsunami impact were used to identify and characterize the distribution of geochemical patterns within the harbor area. Specific compounds are illustrating the different emission sources and distribution during the 2011 tsunami. Petrogenic-derived markers, such as hopanes and polycyclic aromatic hydrocarbons, provide information about the tsunami-related destruction of facilities and technical material and the subsequent release of, for instance, oil and grease. Linear alkylbenzenes and diisopropylnaphthalene are used to identify sewage-derived contaminants released by the tsunami. Old burden markers such as dichlorodiphenyltrichloroethane and its metabolites or polychlorinated biphenyl signal erosion and rearrangement of contaminants present in the sediments prior to the tsunami. Distribution of the analyzed pollutant groups indicate the tsunami-related release through various emission sources and their potential origin. While petrogenic-derived pollutants revealed a significant local spread with hotspot formation near the release, sewage-derived compounds were widely distributed and originated from a diffuse source not necessarily located in the harbor area. In contrast to freshly released contaminants, old burden markers are characterized by erosion of contaminated pre-tsunami sediment, the remobilization of pollutants and subsequent deposition of these sediment-bound contaminants in the tsunami layer. The correlation between all pollutant groups by their preferred accumulation reveals that source-specific compounds show different emission sources but reveal also a topographical control of the pollutant distribution by the 2011 tsunami.

The 2011 Tohoku-oki tsunami released and mobilized many anthropogenic and natural organic compounds and, hereby, left a clear signature in its sedimentary remnants. In this study, a wide variety of organic marker substances were analyzed in 15 sediment profiles from the Aomori coast (Northern Japan). Total organic carbon (TOC) and fine grain fraction normalization have been tested with the wide dataset, and the already more frequently used TOC normalization was proven to be the more suitable one. Concentration profiles and specific ratios have been interpreted using two different approaches. Differentiation of marine and terrestrial matter characterized mixing processes due to the tsunami impact. Linking constituents to anthropogenic emission sources pointed not only to pollution revealed by the tsunami damages but also to dispersion processes, in particular erosion, transport, mixing and redeposition of particle-associated contaminants. Both approaches have been proved to identify unambiguously tsunamites in sedimentary archives and to reveal detailed insights into the tsunami-driven dispersion of particle-associated organic matter. Generally, the organic geochemical proxies as tested in this study can be reliably used to identify and characterize tsunami deposits in the sedimentary record. Finally, this strategy can be transferred to other locations affected by tsunamis for an in-depth characterization of the destruction and environmental changes induced by tsunami events.

Estimating paleotsunami frequency and size is an important requirement for assessing future tsunami risks. However, several issues such as ground soil erosion by subsequent tsunami waves and the preservation potential of tsunami deposits make it difficult to ascertain the paleotsunami history accurately based solely on tsunami deposits. This study demonstrates the importance of high-resolution and sequential dating to construct paleotsunami history. Those methods are sufficient to secure continuity of the geological record using calibrated C-14 ages. Along the Sanriku coast including our study area (Noda) at northern Japan, even though several paleotsunami studies have been conducted, the age correlation of tsunami deposits and paleotsunami history has not been reconstructed well because of the large variation in the estimated ages of tsunami deposits. After taking two core samples near the shore and at inland sites, we used them to confirm the continuity of geological records for 400-2700 years ago based on high-resolution and sequential dating results. Because historical records have documented the tsunami history during the last 400 years, we can construct a continuous paleotsunami history from 2700 years ago to the present without a missing event. Because one of our study sites is located inland, we were able to estimate the histories only of large tsunamis equivalent to the 1611 CE Keicho and 869 CE Jogan tsunamis; small tsunamis cannot be detected because those areas were not inundated. By combining these results with the paleotsunami history of surrounding areas, we reconstructed the paleotsunami history of widely comparable tsunami deposits on the northern to central Sanriku coast. Results showed that the paleotsunami histories can be correlated among sites. It is readily apparent that the tsunami interval is greater during the past 400 years than it was earlier along the Sanriku coast. Whereas earlier studies often estimated the ages of tsunami deposits based on results obtained only immediately above and immediately beneath the tsunami deposit, our results demonstrate the importance of high-resolution dating to avoid overlooking any tsunami deposit. Sequential dating is crucially important to correlate widely distributed tsunami deposits accurately. (C) 2022 Elsevier Ltd. All rights reserved.

Paleotsunami studies along the Pacific coast of Tohoku, northern Japan, have been considerably developed recently, particularly after the massive impact of the 2011 Tohoku-oki tsunami. Nevertheless, in the southernmost Shimokita Peninsula, studies pertaining to paleotsunami are underdeveloped, leading to a vague understanding of the tsunamigenic sources northward of the Tohoku region, along with incomplete hazard evaluation. Paleotsunami deposits in Shimokita can be related not only to the Japan Trench along the Sanriku coast but also to the Kuril trench along the Pacific coast of Hokkaido. In this study, we unveiled the paleotsunami history of Hachinohe in northern Tohoku. Using a combination of sedimentological, geochemical, paleontological, and mineralogical proxies, we characterized seven sand layers that dated from ca. 2700 to ca. 5500 yr BP based on radiocarbon (14C) ages as event deposits of marine origin. Sedimentological and paleontological evidence coupled with ground-penetrating radar imagery revealed a marsh environment comprising successive extinct ponds, controlling the depositional environment. Numerical modeling ruled out the possibility of storms as genetic sources, leading to the conclusion that the presence of event deposits with marine sediments in the study area would be associated with tsunami inundation episodes. Based on 14C dating, the mean frequency of recurrence of tsunamis is estimated as 384 years (320–450 yr, 95% confidence interval) and a coefficient of variation of 0.78 (0.68–0.99, 95% confidence interval). The previously recorded limited paleotsunami evidence and absence of an estimated recurrence interval in the Shimokita Peninsula reaffirm the importance of Hachinohe as a tsunami record site for the activity of both trenches.

On 26 May 1983 the Nihonkai-Chubu earthquake occurred off the western coast of Noshiro City, Akita Prefecture, Japan. The tsunami associated with this earthquake caused widespread damage to the northeastern coastal region of the Sea of Japan, including Akita Prefecture, and left behind sand and mud deposits. These deposits were first described in the 1990s, but have not been studied further. During December 2019 and January 2020, we conducted geological surveys to investigate post-1948 soil thinning in the pine-based coastal protective forests planted near Happo Town. A sand layer that thinned inland was observed in the soil at depths greater than 10 cm. Because the sand layer contained well-preserved fossil brackish–marine diatoms and exhibited a high bulk density, it is likely that the sand was transported inland from the coast. The sand layer was distributed from the coast to 150–270 m inland, but only within the coastal protective forest. By reference to historical records, we concluded that this sand layer was deposited by the 1983 tsunami, because this region could not have been reached by any event other than the tsunami produced by the Nihonkai-Chubu earthquake. We also observed another sand layer above the tsunami deposits, which may have been formed by Typhoon 9119 on 28 September 1991. Graphical Abstract

Identification of autochthonous, allochthonous, and reworked (derived fossil) taxa in diatom analyses is of fundamental importance for understanding how taphonomic processes affect diatom assemblages and for estimating paleoenvironments in coastal areas. To characterize modern and Neogene diatom assemblages, we surveyed the distributions of modern diatom assemblages and of Neogene fossil diatom assemblages in the Toberi River area, eastern Hokkaido, Japan. Then, on the basis of these results, we analyzed two cores collected near the Toberi River mouth and examined changes in the fossil diatom assemblages during the late Holocene. The results showed that not only allochthonous and extinct diatom taxa, but also extant taxa that have persisted over an extended geological time period, should be excluded when diatom assemblages are analyzed to reconstruct Holocene paleoenvironments in this area.

The 2011 Tohoku-oki tsunami had a destructive effect and impact on the coast of Japan. Coinciding with the inundation of vast coastal areas, the catastrophic event released many pollutants from damaged facilities but also remobilized sediment-bound residues. These environmental and depositional variations left a distinct signature in the sediment, both sedimentologically and geochemically. A wide variety of organic geochemical substances were detected in the sampled sediment profiles in Northern Japan (Misawa harbor, Futakawame and Oirase). Some compounds reflect the 2011 tsunami’s impact and may serve as possible indicators for further investigation of the inundation and backwash, sediment and pollutant distribution, and the preservation. For comparability, the tsunami samples and the respective over- and underlying layers (topsoil & soil) were analyzed. The selected compound groups differentiated the tsunami layer from the non-affected layers. Natural compounds, relocated by the tsunami, revealed an enrichment of short-chained n-alkanes as expressed by the terrigenous/aquatic ratio (TAR) and locally accumulated n-aldehydes pointing to an intensive mixing of marine and terrestrial material. Petrogenic pollutants, for instance hopanes, steranes, and polycyclic aromatic hydrocarbons (PAHs), illustrate a higher load in tsunami sediments as the result of damage of harbor facilities. Sewage-related compounds, such as linear alkylbenzene (LABs) and diisopropylnaphthalene (DIPN), were also enriched in the tsunami samples in contrast to the surrounding sites. Another compound group enriched in the tsunami deposits, are chlorinated pollution burdens by the backwash, such as DDX and polychlorinated biphenyls (PCBs), remobilized by erosion dominantly. The different environmental- and pollution-related compounds illustrate the suitability of geochemical markers as indicators to assess tsunami impact in 2011 Tohoku-oki tsunami affected sediments of Misawa harbor, Futakawame and Oirase in Northern Japan.

With a minimum of three reported waves, the 2011 Tohoku-oki tsunami’s destructive force caused massive damage along the northern Japanese Aomori coast. At Misawa the coastal control area was inundated up to 550 m inland and sandy sediment remnants can be traced to c. 350 m (c. 61–63% of the maximum inundation) from the shoreline. Linking the discovery of floatable plastic objects within a woody and organic layer to our analytical data lead to the detection of a yet undocumented woody-organic tsunami deposit first appearing on top of the sandy deposit but then reaching even further inland (approx. 69–72% of the max. inundation). By this observation our understanding of the documented part of the tsunami inundation may be improved. As a consequence, sand sheets of historic and paleo-tsunamis represent minimum estimates for the coastal inundation and underestimation may be reduced by addressing the woody and organic fraction of a tsunami’s inundation.

ABSTRACT Chiba, T. and Nishimura, Y., 2020. Using diatom assemblages to infer topographical changes from storm-induced sandbar breaching in Horokayanto Lagoon, Hokkaido, Japan. Journal of Coastal Research, 36(4), 720–731. Coconut Creek (Florida), ISSN 0749-0208. The sandbar of Horokayanto Lagoon, a sandbar-fronted lagoon on the coast of eastern Hokkaido, Japan, was partly breached, and the bottom was partly exposed during severe weather in June 2016. After the breach, the mean lagoon level fell to about 1.2 m above Tokyo Peil, equivalent to the height of the mean higher-high tide level. Field surveys were conducted on 2, 23, and 30 June 2016 to examine topographical changes in the Horokayanto area. Four diatom-assemblage groups were identified from samples collected during this fieldwork: marsh, emerged lagoon bottom, lagoon bottom, and seashore groups. The assemblages showed good consistency with the salinity and sediment properties at each location. The high-tide-level indicator Pseudopodosira kosugii was recognized in the emerged lagoon-bottom assemblage, together with freshwater–brackish and brackish–marine species. Living P. kosugii colonies had previously been recognized only in the lower reaches of the Obitsu River, Chiba Prefecture, Japan, although the species is widespread in Holocene sediments in Japan and other countries. Reworked Neogene diatoms were also detected in the assemblages. These diatoms were presumably derived from nearby Neogene basement rocks, such as the Taiki Formation, which were eroded by current inflow into the lagoon during the severe weather. During the period of emergence, seawater might have been transported into Horokayanto Lagoon by high waves generated by an atmospheric low-pressure system. Water pressure or moisture changes caused by the emergence, changes in light quantum density and ultraviolet rays, or changes in water quality, such as in salinity and pH, or a mixture of these factors, may have influenced the increase in abundance of P. kosugii.

The annual banded skeletons of reef corals potentially record past earthquakes events. We examined cores of five living Porites coral heads in Simeulue Island, Indonesia, near the epicenter of the 2004 Sumatra-Andaman and the 2005 Nias-Simeulue earthquakes. These sites showed 0.4-1.4 m of uplift. We measured skeletal strontium, magnesium, and calcium; carbon and oxygen isotopic ratios; and skeletal density, extension, and calcification rates, from 1994 to 2010. Coral geochemistry fluctuates more than are expected from strictly environmental causes; however, stress bands, reduced growth rates, and changed skeletal delta C-13 appear to reflect the tsunami and seismic uplift (the step change in skeletal delta C-13 results equated to 0.31 +/- 0.10 parts per thousand/m in response to the 2004 uplift and 0.23 +/- 0.03 parts per thousand/m to the 2005 uplift). (C) 2020 Elsevier Ltd. All rights reserved.

Abstract Nitzschia taikiensis sp. nov. is a brackish diatom species found in the Toberi River marsh, eastern Hokkaido, Japan. This species has characteristics similar to Nitzschia subamphioxoides Hustedt, which was originally described by Hustedt in 1959. In the present study, we conducted a comparative morphological analysis of N. taikiensis and N. subamphioxoides. The obtained results showed that they are different species. Sampling sites of N. taikiensis were located in salt marsh environments with very low salinity (1-5‰), acidic pH (5.2-5.9) and high mud content (95.0-97.5%). Identification of this species was relatively easy based on LM and SEM image analysis of its frustule features, such as the external form and stria density. This species has not been previously reported in Japan, which could be attributed to the reduction or loss of Japanese freshwater and salt marsh environments in the coastal areas, resulting from urban and industrial development.

Japan, more precisely, the eastern coastal areas of Honshu, are one of the most affected areas of tsunamis in the world. Major events within the last century were three Sanriki-oki tsunamis (1896, 1933, 1968), and the most recent 2011 Tohoku-oki tsunami, triggered by the 9.1 MW Tohoku-oki earthquake, which caused massive damage along the coastlines.The 2011 Tohoku-oki tsunami overtopped the coastal defense walls with waves of 6-10 m height along the shores of the Aomori Prefecture in Northern Japan. The inundation reached up to 550 m inland, however, sandy tsunami deposits are limited to 250 – 350 m of the total inundation distance. At the field site of Misawa Harbor the well-preserved identifiable tsunami remains show up to 18 cm thick sand layers with sedimentary features, such as fining upward sequences, mud caps and rip-up clasts. The sandy deposits were enclosed in the soil of the coastal protection forest. Along with the sedimentary record of the tsunami, the use of organic geochemical indicators can provide a better understanding of the extend and processes, such as the deposition of tsunami layers and the backwash, of the inundation by the 2011 Tohoku-oki tsunami. The devastating damages caused by the interaction of tsunami and earthquake released pollutants associated as biological and anthropogenic markers. These released pollutants give the tsunami deposit an unique geochemical signature, that is distinguishable from the background sedimentation. Organic-geochemical results reveal a strong increase of anthropogenic (polycyclic aromatic hydrocarbons, pesticides and chlorinated compounds) and a variation of biological markers (i.e. n-alkanes, fatty acids) in the 2011 tsunami deposit close to the fishery port. During the analysis of the samples, another variation of biomarker and anthropogenic marker were identified right below the soil layer of the current forest. This layer is as well distinguishable from the paleo-dune that marks the lowest sedimentological unit at the field site. This differentiation shows the likely impact of a historical Sanriki-oki tsunami (1896, 1933 or 1968). These organic geochemical results in combination with local eyewitness reports of the tsunamis and lead to the assumption that the sedimentary archive of the Aomori coastline contains and preserved at two or more tsunami events of the last century.The inclusion of organic geochemical markers to expand the characterizing and identifying proxies used in tsunami research are important to get a better understanding of the processes and deposition during tsunamis. Furthermore, this method can detect tsunami deposits beyond the visible recognizability of sedimentological identification of tsunami deposits and therefore can serve as a blue-print for historical and paleo-tsunami studies, as most of them only rely on visible sand deposits as marker for inundation distances from the beach. The high-resolution geochemical application can gain more information than standard techniques, like the identification of the “invisible” tsunami layer exceeding the limits of sandy deposits or the deposition in similar sedimentary textures, capturing a broader picture of the event.

Along the history, the Pacific coast of the Tohoku region has been characterized for facing a vast number of tsunamis associated with the highly active subduction of the Japan Trench. Most of the paleotsunami research has been focused on the south and central third of the Pacific coast of Tohoku, while in the northern third the number of this kind of studies is reduced; on the other hand, on the Pacific coast of Hokkaido paleotsunami research has been conducted to establish the recurrence linked to the Kuril trench (Minoura et al., 2013; Chagué-Goff et al., 2017; Inoue et al., 2017; Sawai, 2017). In Hachinohe, this type of research has not been done, being the results of Inoue et al., 2017 the closest at just 60 km southeastward and where the tsunami heights of the 2011 event were similar (Haraguchi & Iwamatsu, 2011). Because of this paleotsunami studies in Hachinohe are of enormous importance since its position could show tsunami activity related to both Kuril and Pacific trenches and its junction, where large tsunamigenic earthquakes have not been historically registered, hence, being this the primary objective of the present research. The study site marine terrace surface plain and km inland from the present shoreline; at the same time, this surface is positioned between the and rivers. We have identified eight sand layers, interbedded with mud and occasional tephra layers. Based on tephra analysis,