Climatically induced cyclicity recorded in the morphology of uplifting Tihu coastal ridgeplain, Hiiumaa Island, eastern Baltic Sea

Abstract

Holocene relative sea level changes and palaeogeography of the uplifting Tihu ridge-swale beach system in the functionally tideless Baltic Sea were reconstructed using airborne LiDAR elevation data, ground-penetrating radar surveys, sedimentological proxies, recent models of Fennoscandian uplift due to glacial isostatic adjustment, and GIS-based terrain modelling. Considering that aeolian contribution to the ridge growth was relatively small and uniform along the studied profiles, it was possible to utilize an age estimation method based on terrain elevation and pre-determined RSL curves. The tested relative sea level curves converged around a linear trend during the past 7 ka, the rate of which (3.1–3.2 mm/a) is strongly correlated with relative-to-geoid uplift model output. We found that the Tihu system started to emerge from the sea ~5.4 ka ago. In its older part, it includes a complex of elevated barrier spits where both the isostatic uplift and gradual sediment aggradation due to longshore transport contributed to its nucleation and initial progradation. In its lower (younger) section, a forced progradation “staircase” of palaeocoastlines was formed in a regime of sediment deficit and low-energy hydrodynamic conditions. Analysis of near-cyclic occurrences of beach/foredune ridges and larger ridge sets within the Tihu ridgeplain revealed time intervals of enhanced storminess during 5.4–4.9, 4.8–4.5, 4.6–4.3, 4.1–3.8, 3.7–3.4, 3.2–2.9, 2.7–2.4, and 2.2–1.9 ka BP. Serving as a new independent proxy for past storminess and high sea level events in Estonia, these phases match well with some previous European Atlantic storminess reconstructions for Mid- to- Late Holocene.