Between the North Atlantic Oscillation and the Siberian High: A 4000-year snow accumulation history inferred from varved lake sediments in Finland

Abstract

Clastic-organic varved sediments from the boreal Lake Kalliojärvi, Central Finland, record changes in snow accumulation for more than 4000 years. The varve record was reconstructed using digital image analysis from 4132 varve yr BP to present with 2.2% counting error and is supported by paleomagnetic data. Two laminae are identified in a typical varve structure: (1) the minerogenic lamina, which accumulates during spring as a result of catchment erosion triggered by spring floods and (2) the organic lamina, which is composed of allochthonous and autochthonous organic matter that accumulates during summer, autumn, and winter. The minerogenic influx is related to variations in snow accumulation and follows the different phases of the North Atlantic Oscillation (NAO). Decreased snow accumulation is related to a weakened NAO phase. Thus, the minerogenic influx record provides additional information about NAO variation. The Fe/Mn ratio is related to changes in redox conditions at the lake floor. The oxygen availability in the lake floor depends on the duration of the ice cover during winter. Strengthened Siberian High (SH) causes colder autumn and winter temperatures and therefore leads to extended duration of ice cover. Fe/Mn can be considered as a proxy for SH. The sediment record suggests pronounced, generally positive but strongly fluctuating NAO phase, from ca. 4100 to 3200 varve yr BP. Periods of strengthened SH are observed at 3900–3600, 1900–1500, and 1200–750 varve yr BP. Our study suggests that NAO and SH operate individually, are not clearly linked, and do not entirely block each other.

Holocene interaction of maritime and continental climate in Central Europe: New speleothem evidence from Central Germany

“…The second reconstruction used to test the concept of a shifting climate boundary is a multi-element proxy record of DSM input from lake SS1220 (DSMSS1220) in southwestern Greenland (Olsen et al 2012). The DSM record is the sum of Sr, Zn and Ti counts observed in the lake sediment profile, in a similar fashion as proposed by Saarni et al (2016), and is used here to infer NAO conditions.…”

Differential North Atlantic control of winter hydroclimate in late Holocene varved sediments of Lake Kortejärvi, eastern Finland

“…; Saarni et al . ). Sediment supply from upstream lakes during snow‐melt floods is most likely negligible for detrital layer formation, due to trapping of the transported material in the preceding basin.…”

“…; Ojala & Alenius ; Saarni et al . ). Therefore, enhanced winter snow accumulation causing more intense spring floods probably contributed to thicker snow‐melt layers in KJ sediments.…”

“…; Saarni et al . , b). These diverse forcing mechanisms point to modifying influences of different lake‐catchment characteristics on snow‐melt layer formation that need further investigation.…”

Arctic hydroclimate variability during the last 2000 years – current understanding and research challenges

“…However, it is also possible that part of these deviations arise from varying sensitivity of the proxies to different seasons. While most of the studied proxy records likely represent hydroclimatic variations during summer, at least four of the records indicating relatively drier LIA (Luoto and Helama, 2010;Berntsson et al, 2015;Saarni et al, 2016) may actually reflect climatic and environmental factors attributable to boreal winter/spring phenomena, such as flooding, erosion, stream flow. In boreal settings, an outstanding peak in runoff is generally attained during the spring season.…”