Evolution of Lisbon riverine area (Portugal) using multi-proxy analysis on sediments collected on the northern margin of the Tagus estuary

The Tagus estuary is one of the larger estuaries of Europe (area of c.325km2). Lisbon is located in the northern margin of the estuary and despite the long diachrony of its occupation since the Palaeolithic, the city was founded during the Iron Age and grown continuously since then. The riverine front, containing archaeological evidences of occupation since the Iron Age, and clearly modified during the Roman Period, was successively enlarged at the end of the Middle Age by the construction of landfills, conquering area to the river that was used since then for the development of maritime-related activities and others. In 2014 a 7.5m-long core was collected from sediment below the landfill (-1m MSL) during the re-arrangement works of Ribeira das Naus (a Lisbon downtown riverine street built-up on a landfill constructed in the 1940¿s) in an area used as a dock - Doca da Caldeirinha - between the 18th and the 20th centuries. According to bibliography, the area was strongly affected by the 1755 earthquake and related tsunami. Several environmental proxies, combined with 14C dating, were analyzed at vertical high resolution. The sediment is essentially composed by mud (>90% of fine particles) with ca. 9% of organic matter and ca. 4% of CaCO3. ¿13C values are around -25¿, reflecting estuarine conditions. Sediments have accumulated between 2000 cal BP and 1362 cal BP, evidencing high sedimentation rates (SR) in this area during the Roman Period. SR were extrapolated using Clam 2.2 software and values of 0.9 cm yr-1 (-8.5m to -5.7m MSL; 2000 cal BP to 1600 cal BP) and 1.9-2cm yr-1 (-5.7m to -1m MSL; 1600 cal BP to 1362 cal BP) were determined. The high SR can result from both natural and anthropic causes; however, changes on the sedimentary pattern of the Tagus estuary over the last 2000 years are mainly due to human impact. The pollen record preserved in the core attests the existence of open landscape vegetation between 2000 cal BP and 1362 cal BP with the occurrence of h