Cryptotephra quantification in lake sediments: Two workflows developed for sites with distant Laacher See tephra fallout

Cryptotephra research has emerged as a major tool for determination of the age of sediments and unraveling the relationship between past volcanic events and their environmental impacts. Lacustrine deposits are particularly important for continental tephra research. Lakes provide relatively stable environments conducive to the long-term preservation of (crypto)tephra layers, forming valuable continental cryptotephra archives. While studies on fingerprinting of marine tephras and peat samples are more common, the identification and quantification of cryptotephra within lacustrine records remains an underexplored area.    
In this study, we introduce innovative workflows for the quantification of cryptotephra, particularly in lake sediments with distant Laacher See tephra fallout, which represents the most important stratigraphic marker in late-glacial deposits in Central Europe. Our approach initiates with the identification of potential cryptotephra positions and thickness of the deposits, accomplished through the integration of magnetic susceptibility (MS), X-ray fluorescence (XRF), and computer tomography (medical- and micro-CT) to precisely delineate the extent of the cryptotephra layer within the sediments. The subsequent step evaluates presence and identifies the source of the present cryptotephra layer. This is accomplished using scanning electron microscopy (SEM) and polarizing microscopy to visually confirm the presence of cryptotephra and investigate its geochemical fingerprint, enabling linkage to a specific volcanic eruption.    
The key element of our study are methods for quantifying cryptotephra glass shards within sedimentary records. Shard extraction using stepwise flotation with heavy liquids and quantification using standardized markers and a polarizing microscope provides a robust, straightforward laboratory-based technique. Additionally, we offer an innovative, software-based alternative that combines TIMA analysis on thin sections with customized image analysis to study the area fraction of the glass phase, its depth-dependent variation, particle density with a focus on clustering behavior, depth-dependent particle count, total particle count, and particle size distribution within the glass phase.    
The significance of both methods lies in the efficiency and precision of cryptotephra quantification, enabling a deeper understanding of shard concentration, depth-dependent shard distribution, as well as multi-site comparison of shard influx within continental cryptotephra deposits.