Characteristics of wave-built sedimentary archives in Buor Khaya Bay (71°N/130°E), Siberian Arctic, Russia.

Prograded sequences of beach deposits preserve valuable paleoenvironmental information on the long-term variability of the (wave-) climate forcing driving centennial to millennial coastal evolution. Buor Khaya Bay, NE Siberian Arctic, is located at the transition between the Verkhoyansk mountain range and the Arctic Ocean and is one of the few places along the Russian arctic coast, where wide beach-ridge systems exist. Two field sites in Buor Khaya Bay were visited during an expedition in August 2017 in order to obtain baseline information to assess the potential of the systems for the reconstruction of Holocene sea level and past sea-ice extent. The inner parts of the bay are ice-free for three to four months during the short boreal summer. The wave forcing of the system is hence a function of the duration of ice-free conditions and fetch across the open sea surface. Both systems are composed of several sets of beach ridges composed of sand- to cobble-sized shales of local origin. The morphological arrangement of landforms and the characteristics of the beach deposits evidence (1) extensive periods of continuous progradation, and (2) unconformities with changes in ridge orientation suggesting fluctuations in the directional components of energy supply and sediment delivery. The project is at an early stage of investigation and we present first insights into a new and promising area of investigation. Work will be continued in summer 2018

Indication of Holocene sea-level stability in the southern Laptev Sea recorded by beach ridges in north-east Siberia, Russia

The rapid warming of the Arctic may affect the stability of coastal geomorphological systems. Prograded sequences of wave-built deposits, so-called beach-ridge systems, preserve a proxy record of the long-term variability in the drivers of coastal evolution. Information on relative sea level (RSL), climate forcing and sediment supply can be reconstructed from these archives. Buor Khaya Bay is one of the few places along the Siberian Arctic coast where wide beach-ridge systems exist. A previously undescribed field site was surveyed in order to obtain information on the geomorphological processes along the modern shoreline under the current environmental conditions, and the characteristics of the Holocene beach-ridge deposits (e.g., elevation, sediment and age). Our data show that the system formed under storm wave/surge conditions. The beach ridges prograded ca. 1100 m between 6200 and 2600 cal yr BP, with only minor variations in surface elevation. This suggests a continuous and high sediment supply and similar storm wave run-up heights during that time. This relationship is interpreted as indicating RSL stability at a similar-to-present elevation during the period of beach-ridge formation. The hiatus in coastal progradation is concurrent with a deteriorating climate (cooling) in the Laptev Sea area and our data hence suggest increased rates of coastal change during periods of warmer climate conditions. Our study illustrates the potential of coastal sedimentary archives to provide a more complete view of the forcing, resilience and long-term evolution of unconsolidated Arctic coasts in a changing environment