The Taiwan coastal areas are facing predicted sea-level rise effects in the global climate change context. Better understanding of the mechanisms and forcing factors driving the geomorphological evolution of Taiwan's coastline is essential. We highlight the potential of small river estuaries as archives of coastal evolution and provide a paleo-environmental reconstruction of the Gangkou River estuary based on results from a combined methodological approach using geomorphological, sedimentological, and geochronological analyses. A consistent chronology was established by combining Optically Stimulated Luminescence (OSL) dating, as well as radiocarbon dating techniques. A distinct beach-rock layer allowed firm correlation of six investigated coastal profiles. Eustatic sea level change was identified as the primary coastal and estuarine landscape development forcing factor in the study area. Tectonic forcing could also be detected from the investigated sites, but has to be regarded as a subordinate secondary forcing factor. The Gangkou River estuary developed in the early Holocene at about 8 ka and was fully developed by the time the Holocene sea-level maximum was reached. With the sea-level dropping until modern times, estuarine zone relocation and a transition to terrestrial processes was initiated, leading to development of the current coastal dune system since about 2.5 ka. Major dune building phases correlate with the climate change associated with the Little Ice Age (LIA) event and stabilised towards recent times, which is in accordance with regional and over-regional coastal Aeolian records in Taiwan.

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<p>Previous study by Ho et al. (2017) proposed an evolutionary model of the Feng-Chuie-Sha (FCS) clifftop dunes in the Hengchun Peninsula, southeastern Taiwan. In this model, tectonic uplifting, eustatic sea-level falling and the fluctuations of the East Asian winter Monsoon during the late Holocene could be the major forcing factors to the development of the clifftop dune. However, the climbing dune at the bottom of the cliff has not been carefully investigated yet, as the climbing dune is an important link between the beach and the clifftop dune, in terms of aeolian sediment cascades. In this study, we aim to improve our understanding of the unique beach-climbing dune-clifftop dune system in the FCS, and to identify phases of the changing influence of geomorphological forcing factors during the Holocene. For the paleo-environmental reconstruction, a detailed chronological framework will be established by applying numerical dating techniques, such as radiocarbon and optically stimulated luminescence (OSL) dating. Landscape features and sedimentological successions were mapped in the field and samples were taken for high resolution grain size analyses. Preliminary results show that several carbonate-cemented thin layers of aeolian sediment were observed in the outcrop. Based on the sedimentological sequence, the thin layers in two sections can be correlated well. We interpret the correlated thin layers as palaeo-surfaces of the climbing dune, and they may indicate the pause time of sand accumulation. The slopes of the palaeo-surfaces gradually increase from the bottom to the top, demonstrating the morphological development of the climbing dune over time. As the OSL and radiocarbon dates of the outcrop section are still under processing, the accumulation periods and rates of the climbing dune and its relationship with the formation of the clifftop dune will be presented and discussed.</p><p>Ho, L., Lüthgens, C., Wong, Y., Yen, J., Chyi, S.(2017): Late Holocene cliff-top dune evolution in the Hengchun Peninsula of Taiwan: Implications for palaeoenvironmental reconstruction. Journal of Asian Earth Sciences 148, 13-30.</p>

<p>The change of barrier islands could be a precursor of coastal landscape evolution. The barrier islands on the coast of southwest Taiwan are continuing narrowing and landward moving in the past decades. The government has tried to install eight detached embankments to protect Dingtoue barrier island in 2001. In this study, we try to monitor the landform change by using UAV photogrammetry. Dingtoue barrier island is 1.3 km in length and with area of 30.5 ha. We have already conducted 4 campaigns of UAV photogrammetry between March 2018 and September 2019, and they can reveal the landscape of the end of summer and winter monsoon. We use Agisoft Metashape to process the aerial photos for acquiring the DEM and ortho-rectified image with the spatial resolution of 0.5 m and precision level of 0.04 m in both horizontal and vertical direction. We sub-divide Dingtoue barrier island into beach and sand dune zones for further analysis by using Arc GIS. The DEM of difference and areas will be obtained in beach and sand dune as well.</p><p>The results show that area of Dingtoue barrier island is increasing 5101.2 sq.m, while volume of Dingtoue barrier island is decreasing 26722.1 cu.m at the end of the 2018 summer monsoon. The beach part is increasing in both area and volume, while the sand dune part is decreasing in both area and volume. The northern part of the beach is extending to east and the sand dune zone is retreating to further east. The southern part of the beach is extending to west part, which is the sea in the past. Area of Dingtoue barrier island is increasing 719.4 sq.m, while volume of Dingtoue barrier island is increasing 36705.7 cu.m at the end of the 2018 winter monsoon. Area of the beach part is relative the same as the previous period be with some minor changes in the northern and southern part. The sand dune part is increasing in both area and volume. Area of Dingtoue barrier island is increasing 14616.2 sq.m while volume of Dingtoue barrier island is decreasing 23894.1 cu.m at the end of the 2019 summer monsoon. Areas of beach and sand dune are both increasing while volume of the sand dune is decreasing. The mid-part of the beach is occupied by sand dune and the beach is recovering to previous shape.</p><p>In general, Dingtoue barrier island is increasing 7% in area and is decreasing 13910.5 cu.m in volume between March 2018 and September 2019. The average surface lowering is 0.05 m in this period. The trend shows that typhoons will increase area of Dingtoue barrier island, but decrease volume. The winter will decrease area of Dingtoue barrier island but increase volume. So the main change of area is at the beach part and the main change of volume is at the sand dune part. From the installation of the eight detached embankments can stabilize Dingtoue barrier island by increasing area, and volume is decreasing during the summer period and increasing in the winter period.</p>

<p>This study reports a continuous microclimate monitoring carried out in Gorilla Cave、Beifeng Cave、Jingua Cave and Tienyu Cave(Kaohsiung, Taiwan) between June 2018 and August 2019. These limestone caves are located in the Mt. Shoushan, which is mainly composed of limestone and mudstone. This study tried to assess the recreational impacts to the microclimate of the caves by monitoring the CO<sub>2</sub>, temperature, humidity and barometric pressure, and provide effective management strategies. A monitoring station was set up at the middle of each cave. We also set up an auto-operated time-lapse camera at the entrance of the caves to record the numbers of tourists and their entering time and the durations in caves. As carbon dioxide in the limestone caves may have negative impact to both speleothems and visitors, our presentation focuses on the variations of CO<sub>2</sub> concentration in the caves.</p> <p>Daily and seasonal fluctuations of CO<sub>2</sub> concentration were observed. Monitoring data show that the concentration of carbon dioxide in the caves also changes significantly with the wet and dry seasons. The monthly average of the carbon dioxide concentration in the cave has a good correlation with rainfall and temperature, which means that the higher the temperature and humidity, the higher the carbon dioxide concentration in the cave. Besides, the difference between the day-night temperature change outside the cave and the temperature inside the caves also seems to affect whether the carbon dioxide inside the cave is easily dissipated or not. Especially when the temperature outside the cave at night is lower than the temperature inside the cave, the carbon dioxide concentration inside the cave often drops to the environmental background value (around 420 ppm). Therefore, the difference in air density caused by high and low temperature may be an important mechanism driving the gas exchange inside and outside the cave.</p> <p>Based on the monitoring results, we suggest that (1) The cave is open during the dry seasons from November to April. Although monitoring data indicate that the caves have gradually dried up in October, cave exploration activities have also become active. However, the period from wet to dry in the cave is theoretically the stage of cave rock development. Considering the continuous dripping in the cave at this time, in order to avoid disturbing the development of speleothems, it is recommended to close the caves until most of the caves are dry in November. (2) The caves are open daily from 8 am to 12 am, from 1 pm to 5 pm, with a break of an hour at noon. (3) There are one batch per hour and 8 batches per day to allow visitors enter the caves, and the stay time is limited to 1 hour. (4) The monitoring results also help us reasonably estimate the number of visitors in each batch, that is, Gorilla Cave is about 15 people, Tienyu Cave is 20 to 30 people, Beifeng Cave is about 20 people and Jingua Cave is 10 to 15 people.</p>