Sea‐level markers identified in ground‐penetrating radar data collected across a modern beach ridge system in a microtidal regime

Abstract

Sea‐level rise has been related to global warming. The modern system on the northern coast of Anholt, Denmark, may well be analogous to other beach ridge systems formed in microtidal regimes and our results should have impact on estimation of past sea‐level variation. Ground‐penetrating radar data collected across the modern (<30 years old) berm, beach ridge and swale deposits resolve downlapping reflections interpreted to mark sea level at the time of deposition. Existing time series of sea‐level data constrain actual sea‐level variation. Nineteen readings of sea‐level markers made along our profile fluctuate within −0.42 and 0.57 m above present mean sea level, consistent with 95% of the sea‐level data. These fluctuations reflect tidal effects and meteorological conditions. Main data uncertainties are well‐known and the sea‐level markers may be identified with a high degree of confidence.

Review of some significant claimed irregularities in Scandinavian postglacial uplift on timescales of tens to thousands of years – earthquakes in Denmark?

“…But it will also apply to modern data, which is now available for Laesø. The same size of standard errors in the use of geological markers for slope measurements and for height measurements with respect to water level, are found in recent work by Nielsen and Clemmensen (2009). They observe similar large measurement scatter in modern data on Anholt, in the Kattegat Sea.…”

Insight into the late Holocene sea-level changes in the NW Atlantic from a paraglacial beach-ridge plain south of Newfoundland

“…Although care must be taken in the derivation of paleo-sea-level positions from depositional landforms due to challenges related to the chronologies and indicative meanings of individual deposits (Donnelly and Giosan, 2008), the potential of beach ridges to serve as markers of Holocene sea-level change has been widely demonstrated (Rodriguez and Meyer, 2006;Nielsen and Clemmensen, 2009;Pedersen et al, 2011;Tamura, 2012). These studies commonly rely on the upper shoreface/beachface facies contact in beach-ridge plains as a marker of past sea levels.…”

“…Several features of beach-ridge plains have been investigated for their potential use in sea-level reconstructions, including their elevation and morphology (Tanner and Stapor, 1971;Goy et al, 2003;Clemmensen and Nielsen, 2010), the internal architecture of the foreshore/upper shoreface interface (Tamura et al, 2008;Nielsen and Clemmensen, 2009;Hede et al, 2013), or the interface between wave-built facies and overlying aeolian deposits (van Heteren et al, 2000;Rodriguez and Meyer, 2006). Rodriguez and Meyer (2006) and Hede et al (2013) highlight that optimal sea-level markers require high preservation potential (protection again erosion or modification after deposition) and coincide with areas of high deposition rates and prograding shorelines.…”

“…Rodriguez and Meyer (2006) and Hede et al (2013) highlight that optimal sea-level markers require high preservation potential (protection again erosion or modification after deposition) and coincide with areas of high deposition rates and prograding shorelines. Although the choice and relevance of these markers are subject of debate, during the past decade, the elevation of the foreshore/upper shoreface interface as a marker of paleo-sea-level elevation has been used with broad success (Tamura et al, 2008;Nielsen and Clemmensen, 2009). However, this type of interface is limited in application, because it may be difficult to determine this horizon in the sedimentologic record.…”

Genesis and Evolution of A Beach-Ridge Plain Reflecting Relative Sea-Level Rise: A Case Study From Trab El Makhadha Gulf of Gabes, Southeastern Tunisia

“…Immediately seaward of the step, the sediments are typically fine grained and mark the transition to the foreshore across a low slope. Nielsen and Clemmensen (2009) interpret the internal sedimentary architecture of present coastal features, identified in ground-penetrating-radar data, as a proxy for the recent sea-level variation. Tamura et al (2008) reveal, from ground-penetratingradar profiles of Holocene beach deposits, that the lithologic boundary between geomorphic units of a beach profile is a marker of sea-level history.…”