Modern limnology, sediment accumulation and varve formation processes in Lake Żabińskie, northeastern Poland: comprehensive process studies as a key to understand the sediment record

Reconstructions of paleoclimatic and paleoenvironmental data from sediment records require a thorough knowledge of the physical, chemical and biological factors that influence sediment-formation processes and signal preservation in lake sediments. Lake Żabińskie, an eutrophic hardwater lake located in northeastern Poland (Masurian Lake District), provides an unique environment for the investigation of processes that lead to the varve formation. During a two-year long observation period we investigated limnological and hydrochemical conditions within the water column, recent sediment fluxes and laminations preserved in the sediments of this lake to understand the relationship between the lake water properties and the sediment formation processes. We demonstrate that different mixing patterns may occur in Lake Żabińskie, from dimictic to meromictic depending on the meteorological conditions. Regardless of the water mixing pattern, the lake was stratified during much of the year which led to significant differences between surface and near-bottom water environments. The hypolimnion was characterized by higher conductivity and anoxic conditions with only short periods of better oxygenation, which created conditions ideal for the formation and preservation of biogenic varves. The material collected from the sediment trap revealed notable changes in sediment fluxes with characteristic spring maxima and, optionally, a second late fall maxima. Considerable variability was also observed for the fluxes of total organic carbon, biogenic silica and calcite. Microscopic investigation of the topmost sediments revealed a complex structure of the varves showing a distinct spring calcite lamina followed by several fine calcite laminae interbedded with diatom-rich laminae and, finally, by an organic-rich lamina with minerogenic admixtures deposited during winter. This seasonal variability was also reflected in the chemical composition inferred from high-resolution XRF measurements which allowed for the recognition of individual seasons within one varve. A characteristic annual succession of elemental composition followed a distinct pattern: spring was marked with a silica peak followed by a major calcium peak; during summer and fall minor calcium peaks occurred as well as maxima in iron and sulphur; winter was characterized by a peak in potassium. This study shows a remarkable potential of the sediment record from Lake Żabińskie as a high-resolution paleoenvironmental archive

Stratigraphy and components of annually laminated (varved) sediments

Annually laminated (varved) sediment sequences are regarded as one of the most important paleoenvironmental archives because they offer: - accurate „internal" age information in calendar years combined with - exceptional high temporal resolution down to a subannual timescale. This online varve image library shows different varve types, their seasonal sublaminae and successions as well as their components. This site is intended to summarize and distribute existing image information about varves, allow a better start of students and scientists to get acquainted with finely laminated sediment structures. Thin section preparation: There are two main techniques for impregnation of soft sediments: (1) acetone-water-resin exchange and (2) shock-freeze and freeze-dry technique. Each technique has certain advantages and disadvantages. Unless otherwise noted, all thin section presented were prepared using the shock-freeze and freeze-dry method adapted and modified from Lotter & Lemcke (1999). An expoy resin (Araldite2020) is used to impregnate the sediments. Standard techniques are then used to fabricate thin sections from the impregnated sediment slab applying rocksaw and grinding maschines, although some adaptation might be necessary of large-format thin sections (10 cm length). Imaging techniques: For macroscopic images we use a commercially available flatbed scanner with transparency unit and two sheets of polarizing foil. This foil can be bought on the internet (check e**y) or in stores supplying material for classroom experiments in physics. Microscopic images are taken by a Nikon D100 SLR camera mounted on an Olympus B50 microscope

Geochemical Dataset from a sediment core near Norderney, Wadden Sea (Germany)

The coastal area of the southern North Sea passed through several stages of development during the Holocene starting with swamps and bogs on Pleistocene sands. These were covered due to the rising sea-level by brackish and intertidal sediments with intercalated peat layers indicating repeated shoreline replacements. We analysed a 4.6 m-long sediment core recovered south of the island of Norderney (East Frisia, Germany) using a multiproxy approach. The record comprises a vertical stack of changing sedimentary facies, including a basal peat and a second peat layer intercalated between marine sediments, which provides a sedimentological record of local coastal evolution since 7000 cal. BP