What hides in the beach sand? A multiproxy approach and new textural code to recognition of beach evolution on the southern and eastern Baltic Sea coast

Abstract

Sand beaches occur along the southern and eastern coasts of the Baltic Sea, and their sediments serve as an excellent archive of the past environment. In this study, we explore four beach locations in Poland and Latvia, taking a special interest in their sediments at the microscale. We determine sediment properties, potential extreme event records and type of transportation by applying grain-size analysis, and analysis of shape and character of sand grain surfaces under a binocular microscope and in a Camsizer M1 automated particle shape analyser, followed by statistical analysis. For a large dataset (of grains), the statistical approach reveals sediment grain characteristics that are hidden when looking at results in a traditional way. This approach allows a new textural code to be proposed that helps identify beach evolution and sedimentary environment conditions. Additionally, we define the threshold sphericity values for incidental storm records, and conversely, for long-lasting transportation and mature beach sediments, which are 0.8 and 0.9228, respectively. Both the textural code and threshold values can be utilised in sandy beach settings elsewhere. All in all, we detect (1) beaches with mature sediments that have experienced long-lasting transportation and reworking, (2) beaches and ancient beach ridges with medium sediment reworking and sediment mixing due to medium transport duration and pedestrian traffic, respectively, and (3) beaches that combine records of incidental storm events with grain inheritance from pre-Quaternary environments.