Sedimentary and geomorphic responses to changes in rate of sea-level rise: Holocene marine transgression of Dogger Bank, North Sea

Abstract

<p>Coastal landforms such as barriers are crucial in protecting coastlines and reducing the rate of erosion and retreat. Sea-level rise threatens to change the baseline in which such landforms exist, therefore changing sediment fluxes and hydrodynamics at coastlines. Understanding the stability of landforms under changing conditions is crucial to protect and mitigate against the influence of future sea-level rise on coastal infrastructure, ecology and populations. By studying past periods of sea-level rise with rates similar to those projected for the future, we can begin to understand how coastlines may evolve over the next few centuries.</p><p>Dogger Bank, in the southern North Sea, experienced marine transgression during the Early Holocene. Over a period of 800 years, sea level rose by 7-8 m. This rate of ~10 mm/yr is similar to that projected within the next century. Our study area is located on the southeastern side of the former Dogger Bank island. Between 9.5 and 8.7 ka BP, two phases of coastal barriers were present, retreating with different mechanisms at different time periods due to antecedent topographic changes and evolving hydrodynamics. Barrier phase A was drowned in place due to a low-angle topography and little reworking of the barrier. Barrier phase B retreated by continuous overstepping, which occurred due to a higher-angle topography and an increase in wave energy. Complete inundation of the study area occurred by 8.7 ka, with the barrier phase B first becoming an isolated barrier, then breaking down completely. The subsequent wave ravinement transitioned the landform from barrier to offshore sand bar. At this time, the rate of sea-level rise had increased to as much as 20 mm/yr during the pre-8.2 ka sea-level jump, causing the final barrier breakdown and inundation of Dogger Bank. The coastal morphology in the study area is now buried beneath up to 20 m of shallow marine sand, deposited as the dominant tidal current transported sediment from west to east.</p><p>The unique landform preservation at Dogger Bank allows unprecedented spatial and temporal resolution into the investigation of coastal response to sea-level rise. This study adds evidence to the growing body of work that sea-level rise is the driver of, but not necessarily the controlling factor in, barrier retreat mechanism. Furthermore, a rarely-preserved landform, the isolated barrier, is presented. The results of the study provide valuable insights into the transition from coastal to fully marine during transgression of low-relief coastal areas, which provides an analogue for future sea-level rise scenarios.</p>