Driving processes of relative sea-level change in the Adriatic during the past two millennia: From local tectonic movements in the Dubrovnik archipelago (Jakljan and Šipan islands) to global mean sea level contributions (Central Mediterranean)

Abstract

New high-resolution relative sea-level (RSL) proxy data obtained from Lithophyllum rims in the Adriatic allow us to distinguish major local, regional and global RSL driving processes during the past two millennia. RSL change on the Elafiti islands in the Dubrovnik archipelago (Southern Adriatic) has been significantly affected by local tectonic contributions, which vary spatially and increase southeastwards from Jakljan to Grebeni. Consequently, the RSL change on northwestward islands, Jakljan and Šipan, is still dominantly driven by linear regional glacio-isostatic adjustment (GIA) processes estimated at ~0.34 mm/yr. However, GIA effects are occasionally cancelled out by local, non-linear coseismic uplifts of small magnitude and by variations in the global mean sea level (GMSL). Thus the rapid fall in GMSL of 0.26 mm/yr offset the GIA effects between approximately ~1000–1250 cal AD, resulting in temporal hiatuses in algal rim formation. After ~1800 cal AD, GIA rates were significantly amplified by GMSL rise, which exceed 0.9 mm/yr at Jakljan and Šipan and goes up to 1.4 mm/yr at Koločep and Grebeni, confirming the acceleration of RSL rise over the past two hundred years. The new GMSL records from the northern and southern Adriatic, allow us to reconstruct the first high-resolution GMSL curve for the Adriatic. We show that GMSL variability is in-phase with solar activity during the last two millennia, acting on cycles of ~350, 220 and 100-yrs. We also show that increased GMSL fall, which stopped the formation of algal rims around ~1000 and ~ 1600 cal AD, coincides with the global reduction in radiative forcing associated with the Oort and Maunder minima, with a drop in sea surface temperature (SST) and with increased salinity. Thus, our analyses revealed a consistent periodicity between the Adriatic GMSL signal, solar forcing, SST and salinity, with the most important cycle being the 350-year Great Solar Cycle.