Anthropogenic and climate signals in late-Holocene peat layers of an ombrotrophic bog in the Styrian Enns valley (Austrian Alps)

Wolfgang Knierzinger,Ruth Drescher-Schneider,Andreas Limbeck,Felix Horak,Daniela Festi,Lukas Brunnbauer,Simon Drollinger,Klaus-Holger Knorr,Michael Wagreich

doi:10.5194/egqsj-69-121-2020

Abstract

Abstract. Using peat bogs as palaeoenvironmental archives is a well-established practice for reconstructing changing climate and anthropogenic activity in the past. In this paper, we present multi-proxy analyses (element geochemistry, pollen, non-pollen palynomorphs, stable Pb isotopes, humification, ash content) of a 500 cm long, 14C-dated peat core covering the past ∼5000 years from the ombrotrophic Pürgschachen Moor in the Styrian Enns valley (Austrian Alps). Early indications of low settlement and agricultural activity date to ∼2900 cal BCE. An early enrichment of Cu was found in peat layers corresponding to the late Copper Age (∼2500 cal BCE). These enrichments are attributed to Cu mining activities in the Eisenerz Alps. More pronounced increases in cultural indicators (cultivated plants, shrubs, herbs, charcoal) in the pollen record and enrichments of trace metals suggest significant human impact in the vicinity of Pürgschachen Moor in the middle Bronze Age (∼1450–1250 cal BCE), in the late Bronze Age (∼1050–800 cal BCE) and in the period of the late La Tène culture (∼300 cal BCE–1 cal CE). The greater part of the Iron Age and the Roman imperial period are each characterized by a general decline in anthropogenic indicators compared to previous periods. Distinct enrichments of Pb and Sb in the sample that corresponds to ∼900 cal CE are attributed to medieval siderite mining activity in the immediate vicinity of Pürgschachen Moor. The results of this interdisciplinary study provide evidence that strong, climate-controlled interrelations exist between the pollen record, the humification degree and the ash content in an ombrotrophic environment. Human activity, in contrast, is mainly reflected in the pollen record and by enrichments of heavy metals. The study indicates a dry period in the region of the bog around ∼1950 cal BCE.

Highlights

1.1 Peat bogs as geochemical and palaeoenvironmental archivesIn recent years, several multi-proxy studies of bogs, involving elemental, isotopic, and palynological and/or plant macrofossil analyses, have gained in significance, enabling relatively accurate interpretations and quantifications of human impact in the past (e.g. Bindler, 2003; De Vleeschouwer et al, 2007; van der Knaap et al, 2011; Segnana et al, 2019; von Scheffer et al, 2019)
Varying ash contents in peat bogs have been linked to climate changes in two ways: on the one hand, the ash content is affected by a varying dust flux due to climate variations and human land-use change, which directly influence the amount of mineral matter in the bog (Pratte et al, 2017)
After first indications of low settlement (∼ 2900 cal BCE) and mining activity (∼ 2500 cal BCE) in the region in the late Copper Age, a reduction in human presence in the early Bronze Age is suggested by a lack of evidence in the geochemical and palynological records

Summary

Introduction

1.1 Peat bogs as geochemical and palaeoenvironmental archivesIn recent years, several multi-proxy studies of bogs, involving elemental, isotopic, and palynological and/or plant macrofossil analyses, have gained in significance, enabling relatively accurate interpretations and quantifications of human impact in the past (e.g. Bindler, 2003; De Vleeschouwer et al, 2007; van der Knaap et al, 2011; Segnana et al, 2019; von Scheffer et al, 2019). Ombrotrophic (rain-fed) peat bogs are solely dependent on precipitation and isolated from the direct influence of rivers, springs or groundwater. Such bogs provide excellent archives for reconstructing past atmospheric fluxes and environmental conditions (Martínez-Cortizas et al, 1999; De Vleeschouwer, 2010; Drexler et al, 2016). With respect to the Alpine region during the Holocene, palaeoenvironmental studies have mainly concentrated on the reconstruction of environmental conditions and past human impact in the Western Alps and western parts of the Eastern Alps (e.g. Büntgen et al, 2005; Nicolussi et al, 2005; Festi et al, 2014; Segnana et al, 2019). Few data exist regarding areas in the eastern foothills of the Alpine main ridge in eastern Austria (e.g. Drescher-Schneider, 2003; Schmidt et al, 2006; Boch et al, 2009; Huber et al, 2010)

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