[M-IS08] Geopark

[MIS08-04] Re-evaluation of Lake Ichinome-gata with global significance: Toward collaboration between geopark and university

*Takuto Ando¹, Takahiro Suzuki¹, Takeshi Hayashi², Hiroto Kajita³, Atsuki Nagata³, Koji Umeda³ (1.Faculty of International Resource Sciences, Akita University, 2.Faculty of Education and Human Studies, Akita University, 3. Faculty of Science and Technology, Hirosaki University)

Keywords:Geopark, Oga Peninsula, Lake Ichinome-gata, Sediment trap, varve

The Oga Peninsula is a well-known area for geological research due to its numerous exposed outcrops that record the history since the expansion of the Sea of Japan. These outcrops belong to the Oga Peninsula-Ogata Geopark, which is part of the Japan Geopark. The Megata volcanic group, which includes Toga Bay, is located in the western part of this geopark. This study focuses on Lake Ichinome-gata as a maar lake, belonging to this volcanic group. Lake Ichinome-gata is famous for the deposition of xenoliths including peridotite. In addition, the anoxic water mass expands in the bottom layer of Lake Ichinome-gata due to the deeper compared to short widths associated with the geomorphic character of the maar lake, and the annual layer (varve) is preserved in the bottom sediments. Microscopic observations of lake sediment cores from Lake Ichinome-gata indicate that the varve consists of light and dark layers rich in diatom remains and terrestrial material, respectively (Yamada et al., 2018). One of a group of haptophytes that synthesize alkenones, lipids whose composition changes with water temperature, is inhibited in this lake. Therefore, it has the potential to reconstruct annual or seasonal water temperature from sediment cores, which is rare around the world. Sediment cores have been used for research, and most of the monthly observations have focused on hydrological studies (Kusano & Hayashi, 2015). However, the monthly survey of sedimentological and biogeochemical observations, which are important for understanding the depositional process of varve sediments, had not been conducted. We formed a new team from Akita University and Hirosaki University, and started a two-year monthly survey from the end of April last year, after obtaining the permission under the permission of government. Part of this research was supported by the 2023 Akita Geopark Research Grant.
During and after the monthly survey, we measured the water temperature in the depth direction and the concentrations of suspended sediments and nutrients, and analyzed environmental DNA and biomarkers (lipids), and observed the plankton community with a microscope for water samples. The sediment trap is installed at the center of the lake to collect sediments for flux measurement, microscopic observation, elemental analysis, and macromolecular analysis. Furthermore, we collected surface sediments every month and several core samples. The results of these samples will be presented in detail in other sessions of this conference. In this presentation, we will mainly discuss the importance of future scientific researches for the geopark and the relationship between geoparks and universities.