Evidence for centennial scale sea level variability during the Medieval Climate Optimum (Crusader Period) in Israel, eastern Mediterranean

The current study provides evidence supporting a sea-level drop of up to about 50 ± 20 cm at the eastern coasts of the Mediterranean basin during the period AD 900–1300. The estimate is based on a variety of archaeological remains, mostly from the Crusader period, compared with other archaeological and biological proxies of sea level from the periods before and after. The Crusader low levels overlap the period known as the ‘Medieval Warm Period’ (MWP) or the ‘Medieval Climate Anomaly’ (MCA). On the basis of published data it appears that a positive North Atlantic Oscillation (NAO) phase coincided with a negative Southern Oscillation Index (SOI), the former affecting the temperature and freshwater flux in the Mediterranean Sea and most of its rivers, and the latter affecting the Nile outflow. Changes of 0.125 psu in salinity and 0.4 °C are estimated as upper limits for the change, and these are expected to cause a sea-level drop consistent in magnitude with the observed values. These provide the upper limit for a regional climate-forcing attribution of the observed sea level low. The possibility of crustal uplifts contributing to the observed changes is also discussed.