Anna Pint

Sediment Transport and Hydrodynamic Parameters of Tsunami Waves Recorded in Onshore Geoarchives

ABSTRACT Brill, D.; Pint, A.; Jankaew, K.; Frenzel, P.; Schwarzer, K.; Vött, A., and Brückner, H., 2014. Sediment transport and hydrodynamic parameters of tsunami waves recorded in onshore geoarchives. In regions with a short historical tsunami record, the assessment of long-term tsunami risk strongly depends on geological evidence of prehistoric events. Whereas dating tsunami deposits is already well established, magnitude assessment based on remaining sedimentary structures is still a major challenge. In this study, two approaches were applied to deduce transport processes and hydrodynamic parameters of tsunami events from onshore deposits found in the coastal plain of Ban Bang Sak, SW Thailand: (1) The maximum offshore sediment source was determined using granulometry, geochemistry, mineralogy and foraminifera of the tsunamites, and reference samples from various marine and terrestrial environments, and (2) the onshore flow velocities and flow depths of associated tsunami waves were estimated by means of sedimentation modelling. In the case of the Indian Ocean tsunami (IOT) of 2004, modelled flow velocities of 3.7 to 4.9 m/s, modelled onshore flow depths of up to 5.5 m, and a sediment source from offshore areas shallower than a 45-m water depth—including littoral sediments transported as bedload and suspended load from the shallow subtidal zone—are in agreement with quotations based on survivor videos and posttsunami surveys. For a 500- to 700-year-old predecessor, comparable flow velocities and flow depths of 4.1 to 5.9 m/s and 4.0 to 7.5 m, respectively, were modelled, indicating a similar magnitude as the IOT 2004. Comparable values of maximum transport distance and depth of wave erosion were also found. In the case of three older tsunami candidates, dated to 1180 to 2000 cal BP, the deposits indicate partly similar source areas with water depths of less than 45 m and partly shallower source areas restricted solely to the beach. Whereas the former tsunamis are interpreted as events similar to 2004, the latter are more likely storms or tsunamis of a lower magnitude.

Ostracod fauna associated with Cyprideis torosa – an overview

The ostracod Cyprideis torosa (Jones) tolerates a wide range of salinity from fresh to brackish water-transition to hyperhaline values. The species often dominates ostracod assemblages in oligohaline and hyperhaline waters. For a more precise determination of controlling ecological factors, mainly the salinity, the accompanying ostracod fauna needs to be investigated. In oligohaline inland water bodies of humid climates, C. torosa is associated with tolerant non-marine ostracods. In coastal lagoons the mostly very low-diversity ostracod assemblages are characterized by brackish taxa accompanying C. torosa. In saline lakes of arid climatic zones non-marine and brackish species occur together, but brackish ostracods frequently dominate the assemblages. Monospecific occurrences of C. torosa are realized mainly in hypersaline environments. Examples are given that represent typical ostracod taxa that co-occur with C. torosa.

Salinity-dependent sieve pore variability in Cyprideis torosa: an experiment

Salinity-dependent sieve pore variability in Cyprideis torosa (Jones) is tested and confirmed through a culture experiment investigating valves from a salinity range between 0.6 and 14.8. In contrast to results from a previous study, the proportion of sieve pore shapes shows a slight offset at higher values probably caused by relatively lower calcium concentrations in our microcosms. Besides ion concentration, salinity variability and ion composition are assumed to be driving factors for sieve pore shapes, as for the case of noding in Cyprideis torosa. Despite some limitations in using sieve pore shapes as a proxy in quantitative salinity reconstructions in athalassic water bodies, an application for detecting trends and salinity changes in fossil associations and for quantitative reconstructions in marginal marine waters is feasible and adds a valuable salinity proxy, especially for the oligohaline to mesohaline salinity range.

New occurrences of Cyprideis torosa (Crustacea, Ostracoda) in Germany

Living Cyprideis torosa (Jones, 1850) was found in Germany along the North Sea coast and on some islands, within the Baltic Sea and in coastal waters near the Baltic Sea, but also in some inland natural and anthropogenic saline waters. The natural inland waters were probably colonized by birds because this species was found only in permanent saline shallow lakes that provide resting places for migrating birds. Information on the fossil and Recent record and on the biology of C. torosa and its accompanying ostracod fauna is discussed.

Late Quaternary salinity variation in the Lake of Siebleben (Thuringia, Central Germany) – Methods of palaeoenvironmental analysis using Ostracoda and pollen

We test several methods of ostracod-based palaeoenvironmental reconstruction using indicator species approach, mutual ecological/climatic range methods, transfer functions, modern analogue technique and morphological variation within Cyprideis torosa in reconstructing the site evolution of a late Quaternary small lake basin in Thuringia, Central Germany. Sediment sections containing a diverse ostracod fauna were studied and compared with those from modern water bodies of Thuringia. Palynological investigations were executed to reconstruct the environmental conditions in the catchment area and for a obtaining a biostratigraphical framework. The brackish water ostracod Cyprideis torosa as well as the foraminifer Haplophragmoides indicate phases of saline groundwater influence, fed by salt bearing sediments of the Triassic basement. The accompanying freshwater ostracod fauna, however, reflects only low variations of salinity and temperature. Environmental changes in salinity, temperature and ecological stability indicated by microfossils and pollen are caused by an interplay of climatic shifts and the local geological and hydrological setting.