Winter climate signal in boreal clastic-biogenic varves: a comprehensive analysis of three varved records from 1890 to 1990 AD with meteorological and hydrological data from Eastern Finland

Abstract

Clastic-biogenic varves are widely used for reconstructing past climate: in boreal environments, the accumulation of minerogenic clasts on the lake floor is generally considered a proxy for past variations in spring floods reflecting previous winter conditions. However, the physical mechanisms behind this winter climate sensitivity and the influence of catchment type on the varve formation are not fully investigated.Here, we present a winter climate record inferred from the clastic laminae of three lakes located on the region of fine-grained tills in eastern Finland spanning from AD 1890 to 1990. The minerogenic varve data is compared with instrumental meteorological and hydrological time series in order to investigate the physical link between winter and spring climate and minerogenic matter accumulation. Our analyses reveal that the climate-catchment mechanisms operating in the region of fine-grained tills in eastern Finland differ crucially from previously described climate catchment interactions on sand moraine-dominated catchments in central Finland. Usually the maximum river discharge in spring controls the clastic lamina formation. However, in contrast to earlier boreal varve records from central Finland, the clastic lamina formation in the studied region correlates negatively with spring temperatures and winter precipitation. This could be an artefact of varying catchment dynamics but also related to the regional climate. The lakes surrounded by catchments characterized by fine-grained tills are more sensitive to cold and dry winters. The differences in the sensitivity of varve characteristics to climate, highlights the importance of understanding the catchment dynamics in detail in order to better understand climatic forcing.

Ultra-High-Resolution Monitoring of the Catchment Response to Changing Weather Conditions Using Online Sediment Trapping

“…According to the measurements at the study site in February of 2016-2018, the oxygen concentration in bottom waters was 8.1, 4.2, and 4.4 mg/L, respectively. Thus, with its size, catchment, and water characteristics, Savilahti Bay resembles the previously reported Finnish lakes with annually laminated sediments [4,9,15,21,23].…”

“…Annually laminated (varved) sediments have shown their importance in paleoclimatological and environmental studies [1][2][3]. A high temporal resolution up to subannual scale allows robust dating [1] as well as investigation of past hydroclimatic and temperature variability, even in a season-specific manner [4][5][6][7]. Varves, formed as a consequence of seasonal cycles in sediment availability and production [2], are highly dependent on catchment characteristics and environmental conditions [2,8].…”

“…Varves, formed as a consequence of seasonal cycles in sediment availability and production [2], are highly dependent on catchment characteristics and environmental conditions [2,8]. This leads to their sensitivity in reflecting changes in climatic conditions over time in different climatic zones [9][10][11][12][13] and underlines the need to understand each varve record with respect to their individual catchment and climate characteristics [2,4]. Understanding the detailed mechanisms that mediate hydroclimatic changes in sedimentary records is critical for paleoclimatic and environmental interpretations [2,4,14,15].…”

“…This leads to their sensitivity in reflecting changes in climatic conditions over time in different climatic zones [9][10][11][12][13] and underlines the need to understand each varve record with respect to their individual catchment and climate characteristics [2,4]. Understanding the detailed mechanisms that mediate hydroclimatic changes in sedimentary records is critical for paleoclimatic and environmental interpretations [2,4,14,15]. Understanding of the process is further gained by using sediment trap monitoring, which reveals seasonal changes in sedimentary material in detail [14][15][16][17][18].…”

“…Thus, the influences of short-term meteorological and hydrological events on flux rate changes are not recorded, but are addressed on the scale of weeks. Furthermore, wind and frost formation, which are obscured by the more dominant forcing factors, have been suggested to influence sediment accumulation [4,[21][22][23], but so far have been addressed using indirect evidence and statistical approaches. Using seasonal trap monitoring, these questions are difficult to answer, because other erosional events, such as spring floods or numerous rainy days, have dominated the sedimentation.…”