A1 Refereed original research article in a scientific journal
Disruption of boreal lake circulation in response to mid-Holocene warmth; evidence from the varved sediments of Lake Nautajärvi, southern Finland
Authors: Lincoln, Paul; Tjallingii, Rik; Kosonen, Emilia; Ojala, Antti; Abrook, Ashley, M.; Martin-Puertas, Celia
Publisher: Elsevier
Publication year: 2025
Journal: Science of the Total Environment
Journal name in source: The Science of the total environment
Journal acronym: Sci Total Environ
Article number: 178519
Volume: 964
ISSN: 0048-9697
eISSN: 1879-1026
DOI: https://doi.org/10.1016/j.scitotenv.2025.178519
Web address : https://doi.org/10.1016/j.scitotenv.2025.178519
Self-archived copy’s web address: https://research.utu.fi/converis/portal/detail/Publication/485165800
Future climate projections are expected to have a substantial impact on boreal lake circulation regimes. Understanding lake sensitivity to warmer climates is therefore critical for mitigating potential ecological and societal impacts. The Holocene Thermal Maximum (HTM; ca 7-5 ka BP) provides a valuable analogue to investigate lake responses to warmer climates devoid of major anthropogenic influences. Here, we analyse the micro-X-ray core scanning profiles (μ-XRF) of the annually laminated (varved) sediments from Lake Nautajärvi (NAU-23) in southern Finland to elucidate changes in lake circulation and sedimentation patterns. Principal component analysis (PCA) identifies two key components in the geochemical data associated with the nature of the sediments, i.e. detrital vs organic sedimentation (PC1), and hypolimnetic oxidation (PC2). Our findings reveal that during the HTM, the lake became more sensitive to changes in oxygenation and mixing intensity. These changes were triggered by a warmer climate, which increased organic matter and redox sensitive metal solute concentrations in the water column, strengthening lake stratification and weakening dimictic circulation patterns. Superimposed on HTM weakened circulation are distinct phases of increased oxidation and iron-rich varve formation that do not happen when the background conditions are cooler (i.e. the early and late Holocene). This is driven by temporary strengthening of the mixing regime in response to climatic variability and storminess cycles across southern Scandinavia. These findings demonstrate that whilst warmer conditions weaken boreal lake circulation regimes, they can also make them increasingly vulnerable to short term oscillations in prevalent climatic conditions and weather patterns, which could have significant impacts on lake water quality and aquatic ecosystems. These findings underscore the non-stationary nature of lake sensitivity to short-term climatic variability and emphasize the potential for similar shifts to occur under future warming scenarios.
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Funding information in the publication:
This study was funded by the UKRI Medical Research Council through a Future Leaders Fellowship held by C.Msingle bondP, contributing to the research project DECADAL: Rethinking Palaeoclimatology for Society (MR/W009641/1). The authors wish to thank Saija Saarni who assisted with core extraction from Nautajärvi, and Alice Carter-Champion and Laura Boyall who have engaged in valuable discussions with the authors on lake sedimentation processes, XRF analyses and the final code structure included in the supplementary information.