Magnetic and geochemical signatures of flood layers in a lake system

Abstract

River floods holds the capasity to erode and transport sediments that are deposited whenever the discharge is reduced. In catchments that are subjected to repeated flooding, downstream lakes can therefore contain a record of past events across multiple timescales. High-resolution core scanning analyses, such as X-ray fluorescence (XRF) scanning and magnetic susceptibility (MS) provide data that are frequently used to detect flood layers in soft sediment archives, such as lakes, fjords and ocean basins. Deposits of past floods also can potentially reveal information about the evolution of flood events as well as source area.Here we explore ways in which subtle variability in high-resolution data can be utilized and subsequently vetted by high-precision measurements in order to delineate the copious information that can be extracted from soft sediment records. By combining magnetic hysteresis measurements and first-order reversal curves (FORCs) with inductively coupled plasma optical emission spectrometer (ICP-OES) measurements of chemical elements on 36 samples, questions about flood dynamics and variability are raised, and also sources of noise in high-resolution scanning techniques are discussed. Specifically, we show that a lake flood record from Southern Norway containing 92 floods distributed over 10,000 years can be subdivided into two groups of floods that were generated either by spring snow melting, intense summer rainstorms, or a combination of both. The temporal evolution of this pattern shows a marked shift toward spring floods around 2000 years ago compared to the earlier part of the record.Various approaches have been employed in order to detect flood layers in lake sediments. These include high-resolution measurements such as X-ray fluorescence (XRF) scanning [e.g., Czymzik et al., 2013; Swierczynski et al., 2013; Wilhelm et al., 2016], magnetic susceptibility [e.g., Støren et al., 2010; Arnaud et al.,

New flood frequency estimates for the largest river in Norway based on the combination of short and long time series

“…Nonstationarity is typically identified as quasi-cyclic flood-rich and flood-poor periods (for European studies, see e.g. Brázdil et al, 2005;Glaser et al, 2010;Hall et al, 2014;Jacobeit et al, 2003;Kundzewicz, 2012;Mudelsee et al, 2004;Swierczynski et al, 2013), where the flood-rich period may last for 50-60 years (e.g. Glaser et al, 2010).…”

“…This major climate shift recorded in Europe is noteworthy because the flood seasonality is different across such a large area for many reasons, including the varying altitudinal differences. In high-lying areas in Austria (north of the Alps, Swierczynski et al, 2013) and in the central Alps (Switzerland and northern Italy, Wirth et al, 2013), floods start to increase, as in eastern Norway, rapidly just after 4000 years ago and remain on average high until 2000 years ago. Studying the relative distribution of floods in Norway, Støren et al (2012) suggest that the long-term trends in the floods are dependent on changes in the distribution of winter precipitation related to semi-permanent shifts in atmospheric circulation patterns and that an anomalously strong meridional component in the atmospheric circulation pattern is linked to floods in eastern Norway.…”

A quick and low‐cost technique to identify layers associated with heavy rainfall in sediment archives during the Anthropocene

“…Sakaguchi et al, 2006). In the absence of long-term records of meteorological data or river monitoring, sediment deposition in lakes may provide powerful archives for reconstructing the sequence of significant detrital deposits generated in response to heavy storms (Støren et al, 2016;Wirth et al, 2013). So far, the majority of studies reconstructing precipitation based on sedimentary sequences were conducted on very long time periods (Holocene to millennial scales), and they were generally carried out in mountainous environments (Navratil et al, 2012;Vannière et al, 2013;Wilhelm et al, 2013).…”

“…With most of these methods, it remains difficult to have access to high resolution information without conducting expensive, destructive and/or time-consuming analyses. After the visual description of the sequences (Soutar & Crill, 1977), these classical measurements include particle size (Arnaud et al, 2002), magnetic susceptibility (Osleger et al, 2009;Støren et al, 2016), geochemistry (Hodell et al, 2010), organic matter content (Simonneau et al, 2013;Ishii et al, 2017), colour (Debret et al, 2010) or density (Wheatcroft et al, 2006;St-Onge et al, 2012). These latter density measurements are often used for characterizing sediment cores (St-Onge et al, 2007).…”

“…CT-Scan presents a clear advantage for detecting and describing high resolution sedimentary facies and structures within sedimentary records (Fortin et al, 2013;Foucher et al, 2014). This technique was already shown to be useful for detecting highresolution cyclicity in sediment cores (e.g paleoclimate oscillation: St-Onge and Long, 2009), instantaneous deposits (Fouinat et al, 2017;Richardson et al, 2018), correlation with changes in particle size (Boespflug et al, 1995), the quantification of biogenic structures (Rosenberg et al, 2007) or again to track flood deposits using a multiproxy approach (Støren et al, 2016).…”