Using Annual Resolution Pollen Analysis to Synchronize Varve and Tree-Ring Records

Martin Theuerkauf,Tobias Scharnweber,Anja Prager,Almut Mrotzek,Eike Engelbrecht,Michael Hupfer,Nadine Dräger

doi:10.3390/quat2030023

Abstract

Fossil wood and varved lake sediments allow proxy analysis with exceptionally high, (sub-)annual resolution. Both archives provide dating through ring and layer counting, yet with different accuracy. In wood, counting errors are small and can be eliminated through cross-dating because tree-rings show regionally synchronous patterns. In varved sediments, counting errors are larger and cross-dating is hampered by missing regional patterns in varve parameters. Here, we test whether annual pollen analysis is suited to synchronize varve records. To that end, annual pollen deposition was estimated in three short cores from two lakes in north-eastern Germany for the period 1980–2017 CE. Analysis has focused on Fagus sylvatica and Picea abies, which show the strongest annual variations in flowering (mast). For both tree taxa, annual flowering variations recorded by forest and pollen monitoring are well represented in varved lake sediments, hence indeed allow us to synchronize the records. Some pollen mast events were not recognized, which may relate to sampling uncertainties, redeposition or regional variations in flowering. In Fagus sylvatica, intense flowering limits wood growth in the same year. Peaks in pollen deposition hence correlate with minima in tree-ring width, which provides a link between varved lake sediments and fossil wood.

Highlights

Laminated lake sediments, like tree-ring records, are invaluable archives for palaeoecological and palaeoclimatological research with annual or even seasonal resolution
Such time-sensitive applications rely on accurate dating, ideally to the year, which is commonly achieved in tree-ring but not in varve studies
Intense flowering and seed production require a substantial amount of resources, so that in mast years fewer resources are available for radial growth, and even less when mast years coincide with summer droughts [23]. This effect is visible as an inverse correlation between mast years and ring-width chronologies [24]. We explore whether such a relationship is recognizable between annual pollen deposition and tree-ring width

Summary

Introduction

Laminated (varved) lake sediments, like tree-ring records, are invaluable archives for palaeoecological and palaeoclimatological research with annual or even seasonal resolution. The study of multiple sites along climate gradients and comparison with other accurately dated, high resolution proxies from, e.g., ice cores or tree-ring studies, has the potential to explore leads and lags of climate and environmental change. Such time-sensitive applications rely on accurate dating, ideally to the year, which is commonly achieved in tree-ring but not in varve studies. Intra-annual density fluctuations may be mistaken for annual ring boundaries, so-called false rings [2] Such counting errors can be Quaternary 2019, 2, 23; doi:10.3390/quat2030023 www.mdpi.com/journal/quaternary

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