Abrupt climate change and early lake development – the Lateglacial diatom flora at Hässeldala Port, southeastern Sweden

Abstract

The fossil diatom record from the Hässeldala Port palaeolake, southeastern Sweden, offers an excellent opportunity to investigate how past climatic shifts influenced catchment conditions and early lake development. The record, dating to between 13 900 and 11 200 cal. a BP, covers a climatically dynamic period, starting with deglaciation followed by oscillations between warmer and colder climate states. The stratigraphical changes in the fossil diatom assemblages show a trend of less open‐water taxa and a successively more complex periphytic community as the lake shallows and the aquatic habitat structure develops. A diatom‐based reconstruction of lake water pH indicates a natural acidification trend early in the record from 13 900 to 12 500 cal. a BP. From 12 500 cal. a BP, coincident with the start of climate cooling, to 11 300 cal. a BP this trend is disrupted and lake waters become more alkaline. A cooler and drier climate most likely resulted in reduced soil organic matter build‐up as well as more frozen ground that impeded hydrological flow and decreased the input of dissolved organic matter and organic acids into the lake system. This study demonstrates the importance of the hydrological system as a link between terrestrial and aquatic ecosystems during early lake ontogeny.

The C20 highly branched isoprenoid biomarker – A new diatom-sourced proxy for summer trophic conditions?

“…The tephro-chronological framework of the site was established by Davies et al (2003Davies et al ( , 2004, whereas more recently, sediment geochemistry and fossil leaf stomata records have been investigated Steinthorsdottir et al, 2013). Temperature reconstructions based on midge and beetle stratigraphy were also produced (Whitehouse et al, unpublished results), while the diatom proxy records used here were recently presented by Ampel et al (2015).…”

“…A number of cores have been collected over the years and the present work refers to Core #5 collected in 2011, the new template core for Hässeldala Port (Steinthorsdottir et al, 2013;Ampel et al, 2015). The sequence is underpinned by a solid age-depth model, which has been lately updated (Steinthorsdottir et al, 2014).…”

“…A number (34) of samples (ca. 1 cm 3 ) were prepared for diatom analysis (Ampel et al, 2015). Diatoms were analysed according to standard procedures.…”

“…A minimum of 400 valves was identified in samples with a large number of fossil diatoms. Diatom abundance is expressed as a proportion (%) relative to the total number of assigned valves (Ampel et al, 2015). A diatom stratigraphy with four diatom assemblage zones (DAZs) was generated on the basis of the dendrogram produced by constrained incremental sum of squares using the TGView1.7.16 software (Grimm, 1991).…”

“…A diatom stratigraphy with four diatom assemblage zones (DAZs) was generated on the basis of the dendrogram produced by constrained incremental sum of squares using the TGView1.7.16 software (Grimm, 1991). For a detailed description of the diatom stratigraphy, the reader is referred to Ampel et al (2015).…”