Changes in Holocene relative sea-level and coastal morphology: A study of a raised beach ridge system on Samsø, southwest Scandinavia

Abstract

Changes in relative sea-level (RSL) during the Holocene are reconstructed based on ground-penetrating radar (GPR) data collected across a raised beach ridge system on the island of Samsø, Denmark. The internal architecture of the beach ridge and swale deposits is divided into characteristic radar facies. We identify downlap points interpreted to mark the transition from the beachface to the upper shoreface and, thus, sea-level at the time of deposition. This new data set shows that beach steps can be preserved and resolved in GPR reflection data. This is important, as downlap points identified at the base of the beach steps should be corrected for beach step height in order to be used as a marker of sea-level. Identification of beach steps in combination with observed changes in dips of the interpreted beachface reflections can give information about changes in the morphodynamic conditions of beach ridge progradation through time. The vertical levels of identified downlap points are combined with an age model based on optically stimulated luminescencedated samples to reconstruct RSL for the past c. 5000 years. Overall, the reconstruction shows that the period between c. 4800 and 3800 yr BP was characterized by relatively high RSL values around 2.3 m above DVR90 (Danish Vertical Reference 1990). A marked decrease in RSL of c. 1.3 m occurred between c. 3800 and 3600 yr BP at a rate of c. 5 mm/yr. After c. 3500 yr BP, the RSL curve shows a gradual decrease at a rate of c. 0.6 mm/yr.

Evolution of a large Baltic beach ridge plain (Neudarss, NE Germany): A continuous record of sea‐level and wind‐field variation since the Homeric Minimum

“…Hede et al . () report that the gradual decline in RSL since about 1500 BCE is overall parallel with a decline in temperature while the warm periods during the late Holocene, RWP and MWP, may be correlated with peaks in RSL.…”

Sedimentary indications and absolute chronology of Holocene relative sea‐level changes retrieved from coastal lagoon deposits on Samsø, Denmark

“…A complementary analysis of RSL index points was conducted on Holocene beach‐ridge deposits on Samsø covering the time period between 5.0 ka BP and the present (Nielsen & Clemmensen ; Hede et al . in press). In the lagoons, a clear transition from marine mud to marine sand was observed in most of the cores from Samsø and the existence of similar deposits has been described from nearby sites (Jacobsen ; Hede ).…”

“…; Hede et al . , in press), the timing and rates of RSL rise remain poorly understood. Coastal lagoons embedded in the moraine‐topography are commonly encountered along the coasts of central Denmark (Fig.…”

Coastal barrier stratigraphy for Holocene high-resolution sea-level reconstruction

“…The interface between the foreshore and the shoreface observed in GPR images has also been used and dated to infer sea-level trends2021434445. Some of these studies have focused on proving the reliability of this marker as a proxy of sea-level position by comparing recorded morphologies (morphology-slope of the reflections) with the present-day morphology of the foreshore and shoreface4346.…”

“…coastal wetland foraminifera, diatoms and pollen, coral reefs, sea-cave speleothems and archeological data, have reproduced sea-level histories over the last thousands of years for many regions worldwide12. Alternative proxies such as coastal barrier deposits have been also explored as potential indicators of sea-level change171819202122, showing promising results, which could be further explored.…”