Environmental responses to the 9.7 and 8.2 cold events at two ecotonal sites in the Dovre mountains, mid-Norway

Abstract

We found strong signals of two cooling events around 9700 and 8200 cal yrs. BP in lakes Store Finnsjøen and Flåfattjønna at Dovre, mid-Norway. Analyses included pollen in both lakes, and C/N-ratio, biomarkers (e.g. alkanes and br-GDGTs), and XRF scanning in Finnsjøen. The positions of these lakes close to ecotones (upper forest-lines of birch and pine, respectively) reduced their resilience to cold events causing vegetation regression at both sites. The global 8.2 event reflects the collapse of the Laurentide Ice Sheet. The 9.7 event with impact restricted to Scandinavia and traced by pollen at Dovre only, reflects the drainage of the Baltic Ancylus Lake. More detailed analysis in Finnsjøen shows that the events also caused increased allochtonous input (K, Ca), increased sedimentation rate, and decreased sediment density and aquatic production. br-GDGT-based temperatures indicate gradual cooling through the early Holocene. In Finnsjøen, ca. 3100 maxima-minima couplets in sediment density along the analyzed sequence of ca. 3100 calibrated years show the presence of varves for the first time in Norway. Impact of the 9.7 and 8.2 events lasted ca. 60 and 370 years, respectively. Pine pollen percentages were halved and re-established in less than 60 years, indicating the reduction of pine pollen production and not vegetative growth during the 9.7 event. The local impact of the 8.2 event sensu lato (ca 8420-8050 cal yrs. BP) divides the event into a precursor, an erosional phase, and a recovery phase. At the onset of the erosional phase, summer temperatures increased.

Abrupt Holocene climate shifts in coastal East Asia, including the 8.2 ka, 4.2 ka, and 2.8 ka BP events, and societal responses on the Korean peninsula

“…During the early Holocene, these short-term drying events likely recurred approximately every 1000 years in the study area. Many NH paleoclimate studies have reported similar shifts in early Holocene climate, for example, events centered at 9.8 ka 75,76 , 9.2 ka 77,78 , 8.2 ka 13,79 , 7.3 ka 80 , and 5.3 ka BP 81,82 .…”

Evidence for rapid paraglacial formation of rock glaciers in southern Norway from 10Be surface-exposure dating

“…The present-day uplift rate is 2–3 mm yr -1 (Dehls et al, 2000). Upper Ottadalen has been pine dominated since shortly after the deglaciation (Paus, 2010; Paus and Haugland, 2017), and pine grew at least up to 1270 m asl (present elevation) between 9.8 and 7.7 cal ka BP (Paus and Haugland, 2017; Paus et al 2019). The present-day pine-tree limit in the region is about 950 m asl.…”

Radiocarbon dating from Yuzhniy Oleniy Ostrov cemetery reveals complex human responses to socio-ecological stress during the 8.2 ka cooling event

“…An important point to highlight here is that the various model outcomes demonstrate that even small changes of only 1-2 °C can be highly significant for vegetation near climatic thresholds for plant communities and ecosystems in general 17,47,48 . As an apt point of comparison, the Little Ice Age of the fifteenth to nineteenth centuries had a significant historically attested impact on human, floral and faunal populations, particularly in northern Europe, including the disappearance of roe deer from Finland 56 , yet its magnitude was far less, and more variable, than that of the 8.2 ka event, being on average cooler by only ca.…”

“…While in the North Atlantic region the temperature decrease is reduced to 1-3 °C, this remains the largest climate downturn in the Holocene of the northern hemisphere. Yet details of the impact of the 8.2 ka cooling event on the environment are still debated, partly because its effects are highly dependent on the specific location and the resilience of individual ecosystems [43][44][45][46][47][48][49][50] .…”