Origin and Genesis of coastal barriere systems. Case study from Rømø in the Danish Wadden Sea

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The Origin and Geneses of Coastal Barrier Systems

OBS - project

Introduction

We live in a geological period where the relative sea level is rising fast in many regions because of global warming. This fast rise of the sea level has large implications in coastal areas made up of soft sediments such as barrier coasts. Therefore, understanding the response of coastal barrier systems to sea level rise is important both from a scientific and from a practical point of view. Until very recently it has not been possible to date sandy barrier deposits directly. The new OSL method of dating quartz grains directly gives us a unique opportunity to establish a reliable chronology for coastal barrier systems. Therefore, we want to take advantage of this new method to date sandy barriers both in a transgressive system as the Wadden Sea and in a regressive system as the Jerup Beach ridge system in Vendsyssel. In this way we will be able to explain how sandy barrier coasts respond to changes in relative sea level. The investigations will be concentrated on the Holocene evolution of the Danish part of the Wadden Sea. Secondary we include investigations of the regressive system in Vendsyssel to better understand how sea level fluctuations influences the overall morphological and stratigraphic development of sandy coastal barriers.

Research objectives

We plan to investigate and hopefully answer the following basic research questions:

• What is the age of the Danish barrier islands Rømø, Mandø, Fanø, Skallingen and Langli as they appear today • Have the sandy barrier islands developed continuously along with the rising sea level in Holocene time or are the lateral barrier migration a discontinuous process. • Have periods with rapid and slowly rising relative sea level resulted in fundamentally different morphological responses of the barrier systems, and can fine-grained sediments deposited in the lagoon survive if the barrier island is eroded away for a longer period? • What is the timescale of the formation of beach ridges (embroynal barrier islands) on a shallow coastal plain experiencing a decreasing sea level?

Study sites

The study sites are the Danish Wadden Sea and the Holocene isostatically raised Jerup beach ridge plain north of Frederikshavn. The Jerup beach ridge plain is one of the largest beach ridge plains on a world scale. The first locality is chosen in order to establish a chronology for the formation of the Wadden Sea barrier islands following the transgression after the Weischelian glaciation. At this moment it has been chosen to limit the investigation to the Danish part of the Wadden Sea. The second locality is chosen in order to describe the rate of vertical and lateral migration of beach ridges on a strand plain subjected to a relative sea level fall owing to ongoing glacial rebound.