Salt pans as a new archaeological sea-level proxy: A test case from Dalmatia, Croatia

Reconstruction of paleo relative sea level (RSL) is based on multi-proxy disciplines including archaeology. Saltpans, like fish tanks which are considered a reliable method for acquiring RSL index points, are also anthropogenic intertidal facilities, used continuously in the Mediterranean from early antiquity. The Dalmatian shore contains a large number of preserved and historically dated ancient saltpans, now flooded by the rising sea, providing great potential for past RSL indication. The primary objective of this study is to develop a new holistic approach for producing high quality elevation measurements of the saltpan structures and estimating paleo RSL during the last 2 ka. The study combined aerial photo- grammetry of the site, bathymetry acoustics scanning, and underwater archaeological survey of the man- made structures, as well as sampling wood and mortar in situ where available. Evaluation of each site’s RSL and the functional height is based on the same assumptions and interpretations made for fish tanks, using elevation measurements on the top of the separation walls and the bottom of the sluice gates. In all the sites analyzed here, we achieved reliable digital surface models with continuous high- resolution data on the indicative structures with single centimeters level of accuracy. The study finds that during the 5th - 6th centuries, RSL was 92 ± 25 cm, increased to 62 ± 21 cm during the 7th - 11th centuries, and decreased to 104 ± 20 cm in the 14th century. Medieval RSL can be explained either by strong tectonic subsidence post 1300 AD or by fluctuations as observed in the East Mediterranean, which requires validation by further Medieval indicators.