Abstract
Diatom-rich sediment in a small subarctic lake (Lake 850) was investigated in a 9400 cal. yr BP sediment record in order to explore the impact of Holocene climate evolution on silicon cycling. Diatom stable silicon isotopes ([Formula: see text]) and biogenic silica (BSi) indicate that high BSi concentrations in sediment throughout the Holocene are associated with a lighter Si isotope source of dissolved silica (DSi), such as groundwater or freshly weathered primary minerals. Furthermore, higher BSi concentrations were favoured during the mid-Holocene by low detrital inputs and possibly a longer ice-free period allowing for more diatom production to occur. The diatom [Formula: see text] signature shows a link to changes in regional climate and is influenced by length of diatom growth period and hydrological fluctuations. Lighter Si isotopic values occur during the mid-Holocene, when climate is inferred to be more continental and drier, with pronounced seasonality. In contrast, a heavier Si isotopic signature is observed in the early and late Holocene, when oceanic influences are thought to be stronger and the climate wetter. The [Formula: see text] values have generally lighter signatures as compared with other studies, which supports a light DSi source.
Highlights
In natural waters silicon is primarily present in the dissolved form as silicic acid H4SiO4, called dissolved Si (DSi), which originates from the weathering of primary minerals
The Holocene environmental changes in the catchment, such as increases in treeline recorded by other proxies, are not reflected in δ 30SiBSi
Diatom production, species composition and changes in the relative proportions of DSi sources driven by climate forcing influence the δ 30SiBSi
Summary
In natural waters silicon is primarily present in the dissolved form as silicic acid H4SiO4, called dissolved Si (DSi), which originates from the weathering of primary minerals. Rivers and lakes act as a sink for DSi in the global silicon cycle, where lakes store the DSi primarily as diatoms (Frings et al, 2014b), which are unicellular siliceous algae. Diatom production and dissolution are partly controlled by the sensitivity of diatoms to DSi concentration (Hamm et al, 2003; Yool and Tyrrell, 2003), and both processes – production and dissolution – influence changes in lake DSi (Panizzo et al, 2017). Fossil diatoms in lake sediment are used as an archive of environmental history and can be used for unravelling changes in silicon cycling as a result of their high preservation potential. BSi concentration in lake sediments is affected by diatom preservation (Panizzo et al, 2016; Ryves et al, 2003). Low detrital input can result in high sediment BSi concentration (Conger, 1942; Zahajská et al, 2021b)
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