Palaeowinds and depositional conditions from Holocene loess in Sweden and Finland

The nature of deglacial and Holocene wind regimes in Fennoscandia is debated, as is the degree to which wind‐blown loess deposits exist in the region. Loess deposits in Fennoscandia are often relatively thin, discontinuous and less well‐sorted than typical loess, and questions remain over the degree of their post‐depositional reworking and the impact on absolute age estimates. In situ loess deposits in the region would have the potential to constrain dust‐transporting wind regimes during loess deposition. Here we address this using detailed mapping, grain size and anisotropy of magnetic susceptibility (AMS) analyses. The study introduces the first application of AMS to loess in Fennoscandia, to test (i) the degree of reworking of Fennoscandian loess, (ii) the nature of dust‐transporting winds, and (iii) their correspondence to associated source deposits and dune fields. We extend previously known loess distributions and assess the degree to which depositional and post‐depositional processes are recorded in the sedimentary fabrics. Our results highlight widespread physical disturbance, pedogenesis, slope and subaqueous deposition in the many loess deposits in the region, which impacts their suitability for reliable age dating. Despite this, we demonstrate that in situ and non‐reworked loess also exists in the region. The combination of the loess distribution and its aeolian AMS fabrics, alongside grain size and deposit thickness changes, indicates loess deposition under prevailing N‐NE winds. This contrasts with N‐NW winds inferred from the form of nearby parabolic dunes. While published luminescence ages from Swedish loess are at times Middle or even Late Holocene in age, we propose that these may be underestimates due to widespread reworking of loess shown in our post‐depositional AMS fabrics. We therefore conclude that Swedish‐Finnish loess was deposited on hills under a predominant northeasterly, anticyclonic synoptic‐scale wind regime occurring in the presence of the decaying Fennoscandian Ice Sheet during deglaciation. By contrast, the form of dunes in nearby valley bottom dune fields is likely affected by aeolian reworking under dominant westerly winds redirected at the surface by valley topography later in the Holocene, while the loess deposits remained in place.