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• Ballo, Eirik Gottschalk; D’Andrea, William J.; Høeg, Helge Irgens; Loftsgarden, Kjetil; Bajard, Manon Juliette Andree & Eckhardt, Sabine [Show all 10 contributors for this article] (2025). 2000 years of climate, environmental, and societal variability in southeastern Norway from the annually laminated sediments of Lake Sagtjernet. Quaternary Science Reviews. ISSN 0277-3791. 354. doi: 10.1016/j.quascirev.2025.109232. Full text in Research Archive Show summary

  Previous Common Era (i.e., the past 2000 years) climate reconstructions from Fennoscandia have focused on northern and central areas, with scarce data from the southern areas. Using varved sediments from Lake Sagtjernet in southeastern Norway, we developed a hydrogen isotope record from sedimentary leaf waxes (n-alkanes) as a proxy for hydrogen isotopes in precipitation, which we interpret as an indicator of temperature variability over the past 2000 years. The climate reconstruction provides high, decadal resolution for the period 360–770 CE, allowing critical evaluation during the Dark Ages Cold Period (around 300–800 CE) and a cooling during the 6th century, previously suggested as the coldest period of the Common Era. Our results reveal that the most rapid drop in temperature occurred from 536 to 545 CE (+74/-90 years), corresponding in time to the 536 and 540 CE volcanic eruptions. We also document an inferred cold interval that persisted from around 650 to 710 CE (+72/-90 years). While past studies have suggested prolonged cooling during the Dark Ages Cold Period, our findings show that, on average, the climate during 360–770 CE was similar to the Common Era average in the Lake Sagtjernet record. To explore socio-environmental interactions throughout the past 2000 years, we present a pollen-based environmental reconstruction and integrate it with archaeological evidence from around Lake Sagtjernet. These analyses reveal significant societal activities such as land clearing, cereal cultivation, and large-scale iron production, which drastically altered the landscape in the Viking Age (around 800–1050 CE) and the first half of the Norwegian Middle Ages (around 1050–1350 CE). Modern cultivation practices following the Black Death (1349–1350 CE) were first established around 1470 CE and increased continuously until around 1940 CE. Intensification of societal activities through the past millennium, including iron production and modern cultivation, occurred during both warmer (Medieval Climate Anomaly; 950–1250 CE) and colder (Little Ice Age; 1450–1850 CE) periods.

• Ballo, Eirik Gottschalk; Bajard, Manon Juliette Andree; Støren, Eivind & Bakke, Jostein (2023). Using microcomputed tomography (μCT) to count varves in lake sediment sequences: Application to Lake Sagtjernet, Eastern Norway. Quaternary Geochronology. ISSN 1871-1014. 75. doi: 10.1016/j.quageo.2023.101432. Full text in Research Archive Show summary

  Varved lake sediments are one of the most important natural archives that allow annual resolution paleoclimate reconstructions. Conventional varve counting techniques use thin sections to manually identify lamina. However, this technique is destructive, labour intensive and limited to a 2D representation of complex 3D features which may lead to misidentification of varve boundaries. This study presents the use of microcomputed tomography (μCT) scans in constructing varve chronologies, utilizing scanning resolutions of ∼50 μm (binned to ∼200 μm) for core sections up to 150 cm long. To evaluate this method, we cored and analysed Lake Sagtjernet in Eastern Norway — revealing a 593 cm-long sediment record of the past 10274 (+220/-329) years, with continuous laminations from 84 to 533 cm depth (75% of the sediments). Through limnological monitoring and microfacies analyses we demonstrate that the laminations are rare ferrogenic varves, with an annual deposition pattern comprised of seasonal changes in biogenic production superimposed on seasonal precipitates of iron and manganese hydroxides. The floating μCT-counted varve chronology presented here is the first non-glacial varve chronology in Norway and covers 4023 +113/-185 years. We find that μCT scans allow for a very fast and non-destructive way of counting varves with sufficient detail of varve boundaries. In the few sections where varve boundaries are too vague to resolve, we recommend using complimentary techniques such as thin sections in parallel. The varve chronology is in good agreement with the 95% confidence interval of the independent radiocarbon chronology based on 16 14C dates, and 210Pb and 137Cs activity peaks, indicating that the varve chronology can be equated to calendar age.

• Bajard, Manon Juliette Andree; Ballo, Eirik Gottschalk; Høeg, Helge Irgens; Bakke, Jostein; Støren, Eivind Wilhelm Nagel & Loftsgarden, Kjetil [Show all 11 contributors for this article] (2022). Climate adaptation of pre-Viking societies. Quaternary Science Reviews. ISSN 0277-3791. 278. doi: 10.1016/j.quascirev.2022.107374. Full text in Research Archive Show summary

  Understanding how the Viking societies were impacted by past climate variability and how they adapted to it has hardly been investigated. Here, we have carried out a new multi-proxy investigation of lake sediments, including geochemical and palynological analyses, to reconstruct past changes in temperature and agricultural practices of pre-Viking and Viking societies in Southeastern Norway during the period between 200 and 1300 CE. The periods 200–300 and 800–1300 CE were warmer than the 300–800 CE period, which is known as the “Dark Ages Cold Period”. This cold period was punctuated by century-scale more temperate intervals, which were dominated by the cultivation of cereals and hemp (before 280 CE, 420–480 CE, 580–700 CE, and after 800 CE). In between, cold intervals were dominated by livestock farming. Our results demonstrate that the pre-Viking societies changed their agricultural strategy in response to climate variability during the Late Antiquity.

• Schure, Anneke Theresia Maria ter; Bajard, Manon Juliette Andree; Loftsgarden, Kjetil; Høeg, Helge Irgens; Ballo, Eirik Gottschalk & Bakke, Jostein [Show all 12 contributors for this article] (2021). Anthropogenic and environmental drivers of vegetation change in southeastern Norway during the Holocene. Quaternary Science Reviews. ISSN 0277-3791. 270. doi: 10.1016/j.quascirev.2021.107175. Full text in Research Archive Show summary

  Uncovering anthropogenic and environmental drivers behind past biological change requires integrated analyses of long-term records from a diversity of disciplines. We applied an interdisciplinary approach exploring effects of human land-use and environmental changes on vegetation dynamics at Lake Ljøgottjern in southeastern Norway during the Holocene. Combined analysis of pollen and sedimentary ancient DNA (sedaDNA) metabarcoding of the sedimentary sequence of the lake describes the vegetation dynamics at different scales, and establishes a timeline for pastoral farming activities. We integrate this reconstruction with geochemical analysis of the sediments, climate data, archaeological evidence of local human settlement and regional human population dynamics. Our data covering the last 10,000 years reveals consistent vegetation signals from pollen and sedaDNA indicating periods of deforestation connected to cultivation, matching the archaeological evidence. Multivariate analysis integrating the environmental data from geochemical and archaeological reconstructions with the vegetation composition indicates that the vegetation dynamics at Lake Ljøgottjern were primarily related to natural processes from the base of the core (in ca. 8000 BCE, Mesolithic) up to the Early Iron Age (ca. 500 BCE–550 CE), when agricultural activities in the region intensified. The pollen signal reflects the establishment of a Bronze Age (ca. 1800–500 BCE) farm in the area, while subsequent intensification of pollen concentrations of cultivated plants combined with the first sedaDNA signals of cultivation and pastoralism are consistent with evidence of the establishment of farming closer to the lake at around 300 BCE. These signals also correspond to the intensification of agriculture in southeastern Norway in the first centuries of the Early Iron Age. Applying an interdisciplinary approach allows us to reconstruct anthropogenic and environmental dynamics, and untangle effects of human land-use and environmental changes on vegetation dynamics in southeastern Norway during the Holocene.

• Ballo, Eirik Magnus Gottschalk; Augland, Lars Eivind; Hammer, Øyvind & Svensen, Henrik (2019). A new age model for the Ordovician (Sandbian) K-bentonites in Oslo, Norway. Palaeogeography, Palaeoclimatology, Palaeoecology. ISSN 0031-0182. 520, p. 203–213. doi: 10.1016/j.palaeo.2019.01.016. Full text in Research Archive Show summary

  During the Late Ordovician, large explosive volcanic eruptions deposited worldwide K-bentonites, including the Millbrig and Deicke K-bentonites in North America and the Kinnekulle K-bentonite in Scandinavia. We have studied a classical locality in Oslo containing one of the most complete sections of K-bentonites in Europe. In a 53 m section of Sandbian age, we discovered 33 individual K-bentonite beds, the most notable beds being the Kinnekulle and the upper Grimstorp K-bentonite. Magnetic susceptibility (MS) measurements on two intervals show significant periodicity peaks interpreted as Milankovitch cycles and thus astronomically forced changes in sediment supply and composition. These cycles fit remarkably well with both the expected Milankovitch periodicities for the Ordovician as well as the radiometric ages presented in this study and may represent one of the most convincing demonstrations of Milankovitch cycles from the lower Paleozoic so far. Five of the K-bentonites have been dated by high-precision chemical abrasion-thermal ionization mass spectrometry (CA-TIMS) U-Pb zircon geochronology, where the Kinnekulle K-bentonite gives an age of 454.06 ± 0.43 Ma. We have integrated the new data and calculated an age model showing the sedimentation rates through the section and thereby the ages of each of the 33 K-bentonites. Using the age model, we further present a new age for the Sandbian-Katian stage boundary. The section in Oslo provides the highest resolution window into the Upper Ordovician K-bentonite succession so far and helps shed more light on the chronology of one of the most intense volcanic periods of the Paleozoic and the relationship with the global carbon cycle changes that followed.

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• Bajard, Manon Juliette Andree & Ballo, Eirik Gottschalk (2025). Den skjulte siden av norske innsjøer: naturlige arkiver forteller historien om klima, miljø og mennesker fra jernalder til middelalder. Full text in Research Archive Show summary

  Innsjøsedimenter kan sammenlignes med sidene i en historiebok, som kontinuerlig legger seg oppå hverandre og registrerer historien, dag etter dag, år etter år, i tusenvis av år. Alt som skjer i eller rundt innsjøen etterlater et spor på bunnen av innsjøen. Dette foredraget, basert på et nylig ferdigstilt forskningsprosjekt ved UiO, går gjennom bruken av norske innsjøsedimenter (Sagtjernet i Elverum og Ljøgottjern på Jessheim) til studere dynamikken mellom klima-, miljø- og samfunn i Sørøst-Norge gjennom de siste 2000 årene, med et spesielt fokus på perioden 300–800 e.Kr. I foredraget går vi gjennom resultatene fra Ljøgottjern og Sagtjernet. For å utforske historisk interaksjon mellom mennesker og miljø presenterer vi en miljørekonstruksjon basert på pollenavsetninger og integrerer dette med arkeologiske bevis fra området rundt innsjøene. Fra Ljøgottjern ser vi at temperaturvariasjon mellom 200 og 1300 e.Kr. indikerer en betydelig kaldere periode fra 300 til 800 e.Kr. sammenlignet med før (200–300 e.Kr.) og etter (800–1300 e.Kr.). Temperatursvingningene i denne kalde perioden påvirket jordbruksstrategiene rundt Ljøgottjern. Under varmere intervaller ble avlingsdyrking foretrukket, mens kaldere perioder førte til et skifte mot husdyrhold. Analysene fra Sagtjernet avslører betydelig aktivitet som rydning av land, kornproduksjon og storskala jernproduksjon, som dramatisk endret landskapet i vikingtiden (rundt 800–1050 e.Kr.) og første halvdel av den norske middelalderen (rundt 1050–1350 e.Kr.). Moderne dyrkningspraksis etter svartedauden (1349–1350 e.Kr.) ble første gang etablert rundt 1470 e.Kr. og økte kontinuerlig frem til rundt 1940 e.Kr. Vi ser videre en intensivering av menneskelig aktivitet gjennom det siste millennium, inkludert jernproduksjon og moderne dyrkning, som fant sted både i varmere og kaldere perioder.

• Ballo, Eirik Gottschalk (2022). Lipid biomarkers in Lake Sagtjernet, Norway. Full text in Research Archive
• Ballo, Eirik Gottschalk; Bajard, Manon Juliette Andree; Bakke, Jostein; Støren, Eivind Wilhelm Nagel; D'Andrea, William J. & Høeg, Helge Irgens (2022). Lake Sagtjernet hydrogen isotopes and pollen. Full text in Research Archive
• Swai, Violeth Charles; Kollsgård, Christine Tømmervik; Eilertsen, Vårin Trælvik; Braun, Carmen & Ballo, Eirik Gottschalk (2021). XRF core scanning for paleoclimate reconstructions. Full text in Research Archive
• Dijk, Evelien Van; Gundersen, Ingar Mørkestøl; Loftsgarden, Kjetil; Ballo, Eirik Gottschalk; Krüger, Kirstin & Iversen, Frode (2021). Can we link volcanic impacts on the climate to a change in society? Full text in Research Archive
• Schure, Anneke ter; Bajard, Manon Julietto Andree; Loftsgarden, Kjetil; Høeg, Helge Irgens; Ballo, Eirik Magnus Gottschalk & Bakke, Jostein [Show all 12 contributors for this article] (2021). Disentangling anthropogenic and environmental drivers of biological change in southeastern Norway during the Holocene. Full text in Research Archive
• Schure, Anneke ter; Bajard, Manon Julietto Andree; Loftsgarden, Kjetil; Høeg, Helge Irgens; Ballo, Eirik Magnus Gottschalk & Bakke, Jostein [Show all 12 contributors for this article] (2021). Anthropogenic and environmental drivers of biological change in southeastern Norway during the Holocene. Full text in Research Archive
• Bajard, Manon Julietto Andree; Ballo, Eirik Magnus Gottschalk; Høeg, Helge I.; Bakke, Jostein; Støren, Eivind N. & Loftsgarden, Kjetil [Show all 11 contributors for this article] (2021). Instability or adaptation of the pre-Viking society to the climate variability of the Late Antiquity? Full text in Research Archive Show summary

  Understanding how agricultural societies were impacted and adapted to past climate variations is critical to adapt to contemporary climate change and guaranty the food security. However, linking climate and change in the behaviour of a population are difficult to evidence. Here, we studied the climate variations of the period between 200 and 1300 CE and its impact on the pre-Viking and Viking societies in south Norway. We used a retrospective approach combining a multi-proxy analysis of lake sediments, including geochemical and palynological analyses, to reconstruct past changes in temperature and agricultural practices during the period 200-1300 CE. We associated variations in Ca/Ti ratio as a result of change in lake productivity with the temperature. The periods 200-300 and 800-1300 CE were warmer than the period between 300 and 800 CE, which is known as the “Dark Ages Cold Period” in the Northern Hemisphere. During this colder period, phases dominated by grazing activities (280-420 CE, 480-580 CE, 700-780 CE) alternated with phases dominated by the cultivation of cereals and hemp (before 280 CE, 420-480 CE, 580-700 CE, and after 800 CE). The alternation of these phases is synchronous of temperature changes. Cold periods are associated to livestock farming, and warmer periods to crop farming. This result suggests that when temperature no longer allowed crop farming, the food production specialized in animal breeding. The development of activities reached a maximum between 400 and 550 CE and a minimum between 680 and 800 CE, in agreement with archaeological findings. The Viking Age (800-1000 CE) started with an increase in temperature and corresponds to the warmest period between 200 and 1300 CE, allowing a larger development of the agriculture practices and society. Our results prove that the pre-Viking society adapted their agricultural practices to the climate variability of the Late Antiquity and that the Vikings expanded with climate warming.

• Ballo, Eirik Gottschalk; Bajard, Manon Juliette Andree; Bakke, Jostein & Støren, Eivind Wilhelm Nagel (2021). Using CT scans to count varves: Application to Lake Sagtjernet. Full text in Research Archive
• Ballo, Eirik Gottschalk; Bajard, Manon Juliette Andree; Bakke, Jostein & Støren, Eivind Wilhelm Nagel (2021). Using CT scans to count varves in Lake Sagtjernet. Full text in Research Archive
• Bajard, Manon Julietto Andree; Ballo, Eirik Magnus Gottschalk; Støren, Eivind Wilhelm Nagel; Bakke, Jostein; Høeg, Helge Irgens & Loftsgarden, Kjetil [Show all 8 contributors for this article] (2020). Volcanic Eruptions and their Impacts on Climate, Environment, and Viking Society in 500-1250 CE. Full text in Research Archive
• Bajard, Manon Julietto Andree; Ballo, Eirik Magnus Gottschalk; Støren, Eivind Wilhelm Nagel; Bakke, Jostein; Høeg, Helge Irgens & Loftsgarden, Kjetil [Show all 9 contributors for this article] (2020). Record of climate and environmental changes in a dead-ice lake close to Gardermoen told by a 10 000 years old freshwater fish and a Viking King. Full text in Research Archive Show summary

  We studied a six-meter long sediment sequence retrieved from the kettle lake Ljøgottjern, close to Oslo-Gardermoen Airport, to reconstruct environmental and climate changes during the last millennia. The lake is 18 m depth and located at 185 m a.s.l., under the maximum postglacial sea level. The largest burial mound of Northern Europe was built in the mid-6th century on the shore of this lake allegedly for King Rakni and makes this place ideal to study human-environment interactions in a paleo-perspective approach. Using a multi-proxy sedimentological analysis of this record, including 14C dating, paleo-secular variations, XRF and CT scans, and pollen, this study highlights different climate patterns throughout the Holocene. At the bottom of the core, a carbonated sandy-clayey layer with centimetric twigs overlays an organic rich black peaty-type layer, suggesting a continental environment. On top of that, a disturbed clay layer containing fish bones from a freshwater Carpinidae species was found. The fish could have been buried by the massive (70 cm) sandy carbonated deposit covering it. A sharp transition separates a clay cap on top of the deposit and the start of a finely laminated lacustrine sedimentation dated 9.3 ka cal. BP. The massive deposit could be associated to the outburst flood from the glacial lake Nedre Glomsjø dated 10-10.4 ka cal BP (Longva, 1984; Høgaas and Longva, 2016). A major change in the sedimentation occurred around 8 ka cal. BP, with darker sediments and a lower sedimentation rate. This change could be related to a warming climate and stabilization of the catchment by soil and forest development around the lake in the mid-Holocene. The sedimentation rate increased again between 2000 and 3000 years cal. BP as a result of the development of first human activities and major change in the vegetation (Høeg, 1997). We reconstructed temperature changes during the first millennia and compared it to societal dynamics. The period between 300 and 800 years cal. CE is colder than the period 800-1300 years cal. CE. After 1600 years cal. CE, an increase in erosion could be associated to the extension of the population and agriculture in Scandinavia and revealed a chronicle of the major floods in this area. The presence of freshwater fish older than 9,3 ka attests of their early and natural colonization of Scandinavian lakes. The comparison of this record with archaeological data will allow us to discuss socio-environmental dynamics following the deglaciation in the area. References: Smith, A.A. 2010. CO2 stor¬age. Journal of Sciences 32, 10-20. Høeg, H.I., 1997. Pollenanalytiske undersøkelser på Øvre Romerike : Ullensaker og Nannestad, Akershus fylke : Gardermoprosjektet, Varia (Universitetets oldsaksamling : trykt utg.). Universitetets oldsaksamling, Oslo. Høgaas, F., Longva, O., 2016. Mega deposits and erosive features related to the glacial lake Nedre Glomsjø outburst flood, southeastern Norway. Quat. Sci. Rev. 151, 273–291. https://doi.org/10.1016/j.quascirev.2016.09.015 Longva, O., 1984. Romeriksmjelen danna ved ein storflaum på Austlandet for vel 9000 år siden. Norges geologiske undersøkelse, Årsmelding 1984 8–11.

• Bajard, Manon Julietto Andree; Ballo, Eirik Magnus Gottschalk; Støren, Eivind Wilhelm Nagel; Bakke, Jostein; Høeg, Helge Irgens & Loftsgarden, Kjetil [Show all 9 contributors for this article] (2020). Tracing socio-environmental dynamics and climate changes in the period 300-1300 CE in Scandinavia from lake sediments. Full text in Research Archive Show summary

  Understanding large volcanic eruptions impacts on environments and societies is necessary to consider future climate and socio-environmental interactions. Lake sediments can record these dynamics on a continuous long time scale and include at the same time footprints from volcanic eruptions, climate changes and human activities. We analysed the sediments of Lake Ljøgottjern, located southeastern Norway. The largest burial mound of Northern Europe was built in the mid-6th century on the shore of this lake and makes this place an ideal site to study human-environmental interactions throughout the last millennia. Using a multi-proxy analysis of this sedimentary record, including 14C dating, geochemistry, as well as palynological data, we reconstructed temperature and socio-environmental changes in this area between 300 and 1300 CE (Common Era). We associated changes in Ca/Ti ratio with changes in temperature. The period between 300 and 800 CE was colder than the periods 200-300 and 800-1300 CE. Five abrupt cooling events seem to be linked to weakened positive NAO (North Atlantic Oscillation) phases, and two of them can also be linked to the two largest volcanic events of the period (i.e. the 536/540 CE double event, and 1257 CE eruption of Samalas). Palynological data indicate a decrease of the human activities and reforestation of the area in the 6th century. This abandonment is consistent with archaeological findings and could be related to the 536/540 cooling event. Very little activities are then recorded between 700 and 850 CE. Agricultural activities start again strongly in the Viking age with increase in temperature.

• Ballo, Eirik Magnus Gottschalk; Bajard, Manon Julietto Andree; Bakke, Jostein & Støren, Eivind Wilhelm Nagel (2019). Reconstructing climate and socio-environmental changes using lake sediments. Full text in Research Archive
• Ballo, Eirik Magnus Gottschalk; Bajard, Manon Julietto Andree; Bakke, Jostein & Støren, Eivind Wilhelm Nagel (2019). Reconstructing climate and socio-environmental changes using lake sediments. Full text in Research Archive
• Ballo, Eirik Magnus Gottschalk; Bajard, Manon Julietto Andree; Bakke, Jostein & Støren, Eivind Wilhelm Nagel (2019). Reconstructing climate and socio-environmental changes using lake sediments. Full text in Research Archive
• Ballo, Eirik Magnus Gottschalk; Bajard, Manon Julietto Andree; Støren, Eivind Wilhelm Nagel; Bakke, Jostein & Svensen, Henrik (2019). High-resolution lacustrine records of environmental changes in Scandinavia: a focus on the Migration period and the Viking age. Full text in Research Archive
• Ballo, Eirik Magnus Gottschalk; Bajard, Manon Julietto Andree; Støren, Eivind Wilhelm Nagel; Bakke, Jostein & Svensen, Henrik (2019). High-resolution lacustrine records of environmental changes in Scandinavia: a focus on the Migration period and Viking age. Full text in Research Archive
• Ballo, Eirik Magnus Gottschalk; Bajard, Manon Julietto Andree; Støren, Eivind Wilhelm Nagel; Bakke, Jostein & Svensen, Henrik (2019). High-resolution lacustrine records of environmental changes in Scandinavia: a focus on the Migration period and Viking age. Full text in Research Archive
• Ballo, Eirik Magnus Gottschalk; Bajard, Manon Julietto Andree; Støren, Eivind Wilhelm Nagel; Bakke, Jostein & Svensen, Henrik (2019). High-resolution lacustrine records of environmental changes in Scandinavia: a focus on the Migration period and Viking age. Full text in Research Archive
• Ballo, Eirik Gottschalk; Bajard, Manon; Bakke, Jostein & Svensen, Henrik Hovland (2025). Reconstructing climate, environmental and societal dynamics in southeastern Norway through the past 2000 years. Universitetet i Oslo. Full text in Research Archive Show summary

  One of the key challenges we face today is the changing climate and its environmental impacts, affecting all life on Earth. Examining historical human responses to climate crises provides insights into resilience and adaptability. Robust data is essential for studying past climate and environmental changes effectively. European climate records covering the past 2000 years reveal a prolonged cooling period, known as the Dark Ages Cooling Period (c. 300–800 CE), punctuated by a pronounced cooling in the mid-6th century. Studies show that these cold intervals are more complex and regionally varied than previously believed. In the 6th century in Norway, archaeological evidence points to crop failures, famine, farm abandonment and changes in social organization in some regions, while others experienced minimal impact during these cold periods. However, southeastern Norway lacks detailed high-resolution paleoclimate and paleoenvironmental reconstructions, limiting our ability to fully understand these events. This thesis aims to enhance understanding of climate, environmental, and societal dynamics in southeastern Norway over the past 2000 years, focusing on the Dark Ages Cold Period (c. 300–800 CE), through sediment analysis from Lake Sagtjernet and Lake Ljøgottjern in southeastern Norway. We introduce a μCT scan method for varve counting for Lake Sagtjernet, establishing the first varve chronology from a Norwegian lake, covering c. 4023 years. This chronology enables the first paleoclimate and paleoenvironmental reconstruction from Norwegian varved lake sediments. This reconstruction reveals 2000 years of temperature variability, highlighting a major cooling event—the largest in 2000 years—that aligns with the 6th century cooling event. However, sparse settlements in the first millennium complicate climate impact interpretation at Lake Sagtjernet, while the last millennium shows increased human activities during both warm and cold periods. Reconstructed temperatures between 200 and 1300 CE from Lake Ljøgottjern indicate a notably colder period from 300 to 800 CE, compared to the periods before (200–300 CE) and after (800–1300 CE), identified as the Dark Ages Cold Period. Temperature fluctuations within this cold period significantly influenced agricultural strategies at the more populated Lake Ljøgottjern. Warmer intervals favoring crop cultivation and colder intervals prompting a shift towards livestock farming, illustrating the impact of climatic conditions on societal development.

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