Holocene Hydroclimate Variability in Central Scandinavia Inferred from Flood Layers in Contourite Drift Deposits in Lake Storsjön

Abstract

Despite the societal importance of extreme hydroclimate events, few palaeoenvironmental studies of Scandinavian lake sediments have investigated flood occurrences. Here we present a flood history based on lithological, geochemical and mineral magnetic records of a Holocene sediment sequence collected from contourite drift deposits in Lake Storsjön (63.12 • N, 14.37 • E). After the last deglaciation, the lake began to form around 9800 cal yr BP, but glacial activity persisted in the catchment for~250 years. Element concentrations and mineral magnetic properties of the sediments indicate relatively stable sedimentation conditions during the Holocene. However, human impact in the form of expanding agriculture is evident from about 1100 cal yr BP, and intensified in the 20th century. Black layers containing iron sulphide appear irregularly throughout the sequence. The increased influx of organic matter during flood events led to decomposition and oxygen consumption, and eventually to anoxic conditions in the interstitial water preserving these layers. Elevated frequencies of black layer occurrence between 3600 and 1800 cal yr BP reflect vegetation changes in the catchment as well as large-scale climatic change. Soil erosion during snowmelt flood events increased with a tree line descent since the onset of the neoglacial period (~4000 cal yr BP). The peak in black layer occurrence coincides with a prominent solar minimum~2600 cal yr BP, which may have accentuated the observed pattern due to the prevalence of a negative NAO index, a longer snow accumulation period and consequently stronger snowmelt floods.

Geochemical and sedimentological responses of Arctic glacial Lake Ilirney, Chukotka (Far East Russia) to palaeoenvironmental change since ~ 51.8 ka BP

“…The most prominent visual feature of the transition to LUIV sediments is the appearance of FeeMn laminations. High Fe within laminations corresponds with pyrite (FeS 2 ), confirmed by the observance of arsenopyrite (FeAsS) within XRD samples and by colour change of laminations during core opening resulting from oxidation (Labuhn et al, 2018). The origin of FeeMn laminations has been discussed by several authors.…”

“…Redox laminations thus support the interpretation of suboxic conditions at the sediment-water interface. The sporadic appearance of vivianite concretions within LUIV, a further proxy of suboxic sediment conditions, that is often associated with organic material, may reinforce this hypothesis (Asikainen et al, 2007;Labuhn et al, 2018;Rothe et al, 2016). Vivianite however may also form during post-depositional secondary diagenetic processes and therefore may not be contemporaneous with the sediment water interface conditions at the time of deposition (Rothe et al, 2016).…”

“…Redistribution of shoreline sediments was also likely hampered through reduced wave-activity under the lake ice cover. Reduced sedimentation rates during this period likely contributed to the absence of FeeMn laminations in the sediments as redox layers need to be buried to prevent dissolution under anoxic conditions (Labuhn et al, 2018;Odegaard et al, 2003;Prokopenko et al, 2001). Physicochemical proxies verify cold, deteriorated environmental conditions with high physical weathering, evidenced by very high K/Ti values by 37 (±3) ka BP, associated with increased minerogenic input of feldspars within the clay and very fine silt fraction.…”

Cyclic preservation of Fe/Mn-redox fronts in sediments of an oligotrophic, ventilated deep-water lake (Lago Fagnano, Tierra del Fuego)

“… Enhanced mass accumulation rate of settling organic matter, due to higher biological productivity and/or increased influx, would lead to stronger oxygen consumption in the sediment. Floods carrying high amounts of organic matter were suggested to trigger this mechanism in Lake Storsjön (Sweden), where black organic-rich layers were preserved in the sediments that are enriched in Fe sulphides (Labuhn et al, 2018). In Lago Fagnano, peaks in the inc/coh ratio from XRF data (Figs.…”

Paleoecological assessment of cladoceran community dynamics in two subarctic peatlands

“…AD. This time period corresponds to late Holocene climate cooling, which is characterized by intensified flooding in northern Scandinavia (Labuhn et al 2018) and increasing water levels in Finnish Lapland lakes due to high effective moisture (Seppä and Birks 2001;Korhola et al 2005). During wet conditions, the strong spring floods would have induced coalescence of multiple flarks resulting in larger pools with higher potential to harbor a more diverse cladoceran community (DiFonzo and Campbell 1988; Fig.…”