Abstract
PurposeIntact lake sediments reflect the development of terrestrial ecosystems. This development can be understood by decoding mineral and geochemical information of sedimentary archives. Therefore, we characterized a Holocene lake sediment core and revealed bulk to micro-scale variations via a combination of geochemical techniques and statistical methods.MethodsA 2.3 m sediment core was collected from Hotagen, a lake in west-central Sweden; a sediment sample was collected every 5 cm. A part of each sediment sample was kept untreated (named bulk) and another part was size-fractionated into < 4, 4–16, 16–64, and > 64 µm subsamples. Characterization was then made with respect to grain size distribution (GSD), physico-chemical parameters, geochemical properties, organic composition, and mineralogy. The sediments were investigated at bulk, micro-, and elemental scales using powder X-ray diffraction (XRD), diffuse reflectance infrared Fourier transform spectroscopy (DRIFT), and scanning electron microscopy coupled to energy-dispersive X-ray spectroscopy (SEM–EDX).ResultsThe deepest sediment was identified as glacial till dating back to the Late Pleistocene. The bulk sediments showed a clear distinction between 0–195 cm (unit 1, U1) and 200–225 cm (unit 2, U2) depths. Quartz and feldspar minerals decreased and organic matter and clay minerals increased from the till towards the lower limit of U1. The development in the sedimentary properties marked the transformation of the terrestrial ecosystem from glacier-covered land to vegetated areas. This development was also well reflected by the appearance of X-ray amorphous materials and the formation of distinct organo-mineral aggregates; chlorite was the predominant clay mineral in these aggregates. The geochemical variation between U2 and U1 sediments was further established by resolving the DRIFT spectral components through multivariate curve resolution alternating least square (MCR-ALS). The U1 sediments settled over a period of ~ 7500 years and showed comparable mineral, geochemical, and organic composition. However, the size-fractionated sediments, mainly < 4 µm, showed diverse mineral and geochemical composition. Indeed, these sediments were distinct by containing relatively higher amounts of X-ray amorphous materials and clay minerals, the latter had variable Na, Mg, and K contents.ConclusionThe combined use of geochemical and statistical approaches used in this study followed the mineral and geochemical development of sediments that had settled during the Late Pleistocene and Early Holocene Epochs. Finally, the U2 sediments marked the terrestrial ecosystem development that occurred during the late glaciation, deglaciation, and post-glaciation periods.Graphical abstract
Highlights
Lake sediments are recognized as storage zones for lithogenic and anthropogenic materials that are generated in catchments
The sediments were divided into two units with inflection points roughly at 200 cm based on X-ray diffraction (XRD) (Fig. 3b) and organic matter (OM) (Fig. 4a), and at 210 cm based on diffuse reflectance infrared Fourier transform spectroscopy (DRIFT) (Fig. 4c)
A 2.3 m sediment core collected from lake Hotagen, westcentral Sweden, revealed ~10,000 years of ecosystem development that occurred after the last glacial period
Summary
Lake sediments are recognized as storage zones for lithogenic and anthropogenic materials that are generated in catchments. These materials settle in lakes over long periods and form lacustrine archives (e.g., Schnurrenberger et al 2003; Kalis et al 2003). During the Late Pleistocene in Scandinavia, the Fennoscandian ice sheets eroded the landscape by plucking and abrasion, which resulted in fine clastic sediments. These fine sediments, as well as other clasts, rocks, and debris, were transported with glaciers and eventually settled when reaching lowland settings (Marshak 2011; Stroeven et al 2016). Primary producers facilitated weathering through the introduction of plant- and microbial-based organic acids
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