Climatic influence on the inter‐annual variability of late‐Holocene minerogenic sediment supply in a boreal forest catchment

Abstract

Processes controlling sediment yield vary over a range of timescales, although most process-based observations are extremely short. Lake sediments, however, can be used to extend the observational timescale and are particularly useful when annually laminated (varved) sediment is present. The sediment record at Kassjön (N. Sweden) consists of ~6400 varves, each 0·5-1 mm thick. Image analysis was used to determine grey-scale variation and varve thickness from which annual minerogenic accumulation rate (MinAR) (mg cm -2 year -1 ) was inferred for the period 4486 BC -AD 1900. MinAR varies on annual to centennial scales and mainly refl ects channel bank erosion by the infl ow streams. The mineral input refl ects the intensity of the spring run-off, which is dependent on the amount of snow accumulated during the winter, and hence MinAR is a long-term record of variability in past winter climate; other factors will be a variable response to catchment uplift, vegetation succession and pedogenesis. A major shift from low to high MinAR occurred ~250 BC, and peaks occurred around AD 250, 600, 1000, 1350 and 1650. Wavelet power spectrum analysis (confi rmed by Fourier analyses) indicated signifi cantly different periodicities throughout the period 4000 BC -AD 1700, including 275 years for the period 4000 BC -2900 BC, 567 years for the period 2901 BC -1201 BC, and 350 and 725 years for the period 1200 BC -AD 1700. The long-term, centennial scale variability (~350 years) may refl ect solar forcing (cf the 385-year peak in tree-ring calibrated 14 C activity) but interestingly, there is no obvious link to high frequency forcing, such as the North Atlantic Oscillation. The high resolution component of the record highlights the relevance of varved lake sediment records for understanding erosion dynamics in undisturbed forested catchments and their link to longterm climate dynamics and future climate change.

Lake and catchment response to Holocene environmental change: spatial variability along a climate gradient in southwest Greenland

“…The input of minerogenic sediment to lakes is controlled by relief and the intensity of runoff (Lamoureux and Gilbert 2004;Petterson et al 2010;Rubensdotter and Rosqvist 2003). In the Arctic, the timing of spring melt determines runoff (and hence particle movement) as rainfall intensity is often relatively low, even in coastal southwest Greenland for example, despite precipitation *500 mm year -1 .…”

“…The problem of climate inference is not helped by the number of single site studies that fail to consider regional variability and representativity. The problem is further exacerbated by the recognition that Neoglacial cooling, even in the absence of anthropogenic-driven land-cover change, causes substantial landscape degradation with increased erosional inputs and terrestrial carbon transfer from land to lakes (Andresen et al 2004;Leng et al 2012;McGowan et al 2008;Petterson et al 2010;Rubensdotter and Rosqvist 2003).…”

21st century climate change: where has all the geomorphology gone?

“…For instance, Petterson et al (2010) related the sedimentation records in lake varves for an undisturbed forest watershed to identify the range of variability in sedimentation processes. In turn, they bring to the fore a new concept: Historical Range of Variability (HRV).…”

“…Although HRV must necessarily remain a constructed concept (for instance, it requires us to specify the timescale over which that variability is determined, itself driven by the kind of methodological developments described above) it provides a template against which systematic impacts of climate variability and climate change can be judged. For instance, Petterson et al (2010) related the sedimentation records in lake varves for an undisturbed forest watershed to identify the range of variability in sedimentation processes. Layzell et al (2012) were able to combine a range of methods to quantify different types of Holocene river channel adjustment, including phases of deposition and incision.…”

Application of a method for detecting lamina characteristics in sediments for time series analysis: an example using a soft X-ray image of varves from the Hiruzenbara Formation

“…In some of these methods, however, problems associated with objectivity and reproducibility exist, and confirmation by the researcher through visual examination is required. In recent years, more objective identification and measurement of varves utilizing digital-image analyses have been applied (Cooper, 1997;Petterson et al, 1999;Prokoph and Patterson, 2004;Ojala and Saarinen, 2002;Ojala, 2004;Ojala and Alenius, 2005;Haltia-Hovi et al, 2007;Petterson et al, 2010). For example, Cooper (1997) summarized techniques of image analysis for laminated sediments.…”