Contrasting magnetic susceptibility trends in Holocene coastal strandplains of Saaremaa and Hiiumaa Islands, Estonia

Abstract Sedimentological signatures of hydrometeorological conditions along the eastern Baltic Sea coast include mineralogical anomalies, such as heavy-mineral concentrations (HMCs) of variable thickness and intensity, which contain ferrimagnetic (almost exclusively magnetite) fraction. We present the first sets of bulk volume magnetic susceptibility (MS) trends from coastal landforms in the western Estonian archipelago: Harilaid cuspate foreland (westernmost Saaremaa Island) and Tahkuna strandplain (northernmost Hiiumaa Island). Readings were conducted both in situ from trench walls and on core subsamples. Four compound beach-dune ridges (height: 2-3 m) at Harilaid formed within the past 300 years show a general increase in mean MS from 320-850 μSI with decreasing age, with peaks of 1,000-2,000 μSI below the crest (depth: ~0.3-0.6 m) likely related to contemporary wind acceleration over aggrading ridge crests. The highest mineralogical anomalies range from 2,000-5,500 μSI in historic dune sections and exceed 8,000 μSI along actively eroding upper berm segments, typical of HMCs generated by moderate storms. In contrast, at the Tahkuna site, Late Holocene beach ridges reveal substantially lower values: quartz-dominated dune lithosomes grade from 5-20 μSI downward to diamagnetically dominated (–1-7 μSI) beach facies. Values are higher (20-140 μSI) in historically reactivated parabolic dunes encroaching southward over this strandplain. MS anomalies are likely correlated with high-amplitude electromagnetic signal response in georadar records (70-300 MHz survey datasets) and provide useful information for optical luminescence sampling. Our study demonstrates that magnetic susceptibility trends provide useful means of rapidly assessing relative temporal changes in overall wave/wind climate, help identify discrete anomalies related to extreme events, and represent potentially quantifiable paleo-energy indices. Geological Society of America Abstracts with Programs. Vol. 52, No. 2, ISSN 0016-7592 doi: 10.1130/abs/2020SE-344004