Disruptions in alongshore sediment transport on sedimentary shores of the Baltic Sea driven by changes in forcing wave fields

We address the impact of systematic changes in the wave directions to the magnitude and direction of wave-induced sediment transport along the southern and eastern sedimentary Baltic Sea shores. The analysis was performed using the CERC approach in terms of potential alongshore sediment transport based on SWAN-reconstructed wave time series forced by ERA5 winds for 1990–2021. The majority of transport is driven by waves approaching from one or two narrow (±15°) ranges of prevailing wave directions. These wave systems produce mostly >60% and in many locations up to 80–90% of the total transport. While either clockwise (CW) or counterclockwise (CCW) transport predominates in a part of the study area, many locations experience a delicate balance of transport under the impact of waves from the south-west and north-west and adjacent directions that generate CW and CCW transport. We show that the prevailing wave directions that drive most of the transport have not changed 1990–2021. Instead, the balance of waves from these directions has changed because of a systematic decrease in the frequency of waves from the north-west and adjacent directions. The overall intensity of transport driven by waves from these directions has considerably decreased in about 1/3 of the study area. The decrease rate of CW transport is up to 16,000 m 3 /yr. Such alterations infringe the balance or even direction of sediment transport in sectors affected by bi-directional wave patterns but usually only affect the magnitude of sediment transport in coastal sectors that develop under the impact of a single-peak wave system. • Prevailing wave directions driving most of sediment transport are identified. • Waves from SW and NW keep fragile balance of transport on the Baltic proper shores. • Significant changes have occurred in sediment transport across the study area. • The reason is a decrease in the frequency of waves from the north-west. • Changes in wave fields have varying impact across the study area.