Biogeochemical variability during the past 3.6 million years recorded by FTIR spectroscopy in the sediment record of Lake El'gygytgyn, Far East Russian Arctic

Abstract

Abstract.A number of studies have shown that Fourier transform infrared spectroscopy (FTIRS) can be applied to quantitatively assess lacustrine sediment constituents. In this study, we developed calibration models based on FTIRS for the quantitative determination of biogenic silica (BSi; n = 420; gradient: 0.9-56.5 %), total organic carbon (TOC; n = 309; gradient: 0-2.9 %), and total inorganic carbon (TIC; n = 152; gradient: 0-0.4 %) in a 318 m-long sediment record with a basal age of 3.6 million years from Lake El'gygytgyn, Far East Russian Arctic. The developed partial least squares (PLS) regression models yield high cross-validated (CV) R 2 CV = 0.86-0.91 and low root mean square error of crossvalidation (RMSECV) (3.1-7.0 % of the gradient for the different properties). By applying these models to 6771 samples from the entire sediment record, we obtained detailed insight into bioproductivity variations in Lake El'gygytgyn throughout the middle to late Pliocene and Quaternary. High accumulation rates of BSi indicate a productivity maximum during the middle Pliocene (3.6-3.3 Ma), followed by gradually decreasing rates during the late Pliocene and Quaternary. The average BSi accumulation during the middle Pliocene was ∼ 3 times higher than maximum accumulation rates during the past 1.5 million years. The indicated progressive deterioration of environmental and climatic conditions in the Siberian Arctic starting at ca. 3.3 Ma is consistent with the first occurrence of glacial periods and the finally complete establishment of glacial-interglacial cycles during the Quaternary.

Impact processes, permafrost dynamics, and climate and environmental variability in the terrestrial Arctic as inferred from the unique 3.6 Myr record of Lake El'gygytgyn, Far East Russia – A review

“…Ca and TIC contents in the Pliocene sediments point to the formation and deposition of calcite (CaCO 3 ) that was also confirmed by FTIRS (Meyer-Jacob et al, 2014;Wennrich et al, 2014;Fig. 8).…”

“…In combination with welloxygenated bottom-water conditions, as inferred from high Mn/Fe ratios, this environment resulted in a high seasonal primary production, which is reflected by high BSi accumulation rates ( Fig. 8) and larger planktonic diatom frustules during the interval 3.58-3.35 Ma Meyer-Jacob et al, 2014;Wennrich et al, 2014).…”

“…Although, very similar in visible sediment texture and colour, interglacial and interstadial/glacial sediments attributed to facies B exhibit remarkable differences in the geochemical composition and grain-size distribution. Interglacial periods are generally marked by an enhanced aquatic primary production visible in elevated BSi contents, Si/Ti ratios, and diatom concentrations (Cherapanova et al, 2007;Melles et al, 2012;Meyer-Jacob et al, 2014;Figs. 8, 11, 12).…”

“…Dark organic-rich layers with elevated TOC values within the reddish-brown laminated silt indicate the warmer conditions have promoted maximum primary production with an only incomplete organic matter decay. This is obvious in extraordinary high BSi contents and accumulation rates, Si/Ti ratios >0.8, peaks in diatom concentration and diversity, and highest dinosterol concentrations as a molecular biomarker for dinoflagellates (D'Anjou et al, 2013;Melles et al, 2012;Meyer-Jacob et al, 2014;Figs. 8, 11, 12).…”

“…In this perspective, the sediment sequence of Lake El'gygytgyn represents the first timecontinuous record of terrestrial Arctic climate change back to the time of the impact during the mid-Pliocene, a period often regarded as a potential analogue for the conditions expected for the end of the 21th century under persistent global warming (Brigham- Naish et al, 2009). Due to the high susceptibility of the lacustrine sedimentation to orbitally induced regional and global climate changes (e.g., Andreev et al, 2014;Francke et al, 2013;Melles et al, 2012;Meyer-Jacob et al, 2014;Wennrich et al, 2014), this longest terrestrial archive of the Arctic provides a unique window into the Pliocene/Pleistocene climatic evolution of Beringia on centennial to millennial time-scales.…”