Lithophyllum rims as biological markers for constraining palaeoseismic events and relative sea-level variations during the last 3.3 ka on Lopud Island, southern Adriatic, Croatia

Abstract

This study aims to discern the drivers of relative sea-level change at Lopud Island, distinguishing local tectonic from regional and global contributions. A detailed survey of sea-level markers ( Lithophyllum rims and tidal notches) allowed the distinction of a seismotectonically uplifted sector, approximately 1 km in length, along the southern coast of Lopud Island (Southern Adriatic). The established high-resolution algal rim geochronology based on 23 radiocarbon dates enables distinction between the Late Holocene transgression periods and the seismically triggered regression events. Consequently, we distinguish here local tectonic uplift and provide the first reconstruction of the assumed number, timing, and displacements of past seismic events. The most important uplift of around 0.42 ± 0.10 m occurred in 1667 CE Dubrovnik earthquake while the earlier one of 0.15 ± 0.10 m, occurred probably between ~800 CE and ~ 1100 CE. The uplift of this coastal segment was also evidenced in tidal notches which are today ~0.25 ± 0.15 m above mean sea-level. After correction for local coseismic displacements, the sea-level trends with full consideration of the available uncertainty were quantified using an Errors-In-Variables Integrated Gaussian Process model. The rates of RSL change vary between 0.2 and 0.7 mm/yr, with a mean of 0.4 mm/yr. The possibility of removing the local non-linear contribution, allows comparison of the obtained RSL curve with different glacio-isostatic model predictions. The obtained field based RSL records correspond well with the K33_j1b_WS9_6 model of Lambeck et al. (2011) . By distinguishing local non-linear RSL drivers (coseismic movements) from regional and global scale drivers we estimated a glacio-isostatic adjustment rate of ~0.34 mm/yr and a global common contribution of around 20 cm between 3.3 ka and 0.15 ka. This high-resolution study allows us to better approach the driving mechanisms of RSL change, thus providing new insight into the late Holocene sea-level history of this seismotectonically active sector of the Adriatic. Furthermore, this study reveals the precision of Lithophyllum rims in the studies of relative sea-level changes and demonstrates their potential in assessing palaeoearthquakes. • this study focuses on the most seismically active part of Croatia; • algal rims and tidal notches revealed coastal uplift of Lopud island; • the 1667 CE Dubrovnik earthquake was evidenced in the algal rim stratigraphy; • 23 new relative sea-level index points from the Adriatic cover the past 3.3 ka; • the drivers of relative sea-level change have been distinguished.