Linking silicon isotopic signatures with diatom communities

The use of silicon isotope ratios (expressed as delta Si-30) as a paleolimnological proxy in lacustrine systems requires a better understanding of the role of lake processes in setting the delta Si-30 values of dissolved Si (dSi) in water and in diatom biogenic silica (bSi). We determined the delta Si-30 of modern dSi (delta Si-30(dSi)) and bSi (delta Si-30(dSi)) in three lakes in Lassen Volcanic National Park (LAVO), California (USA), and produced diatom assemblage compositional data from the modern system and from sediment core samples. In the modern systems, we observe the largest magnitude diatom Si isotope fractionations yet reported, at -3.4 and -3.9 parts per thousand & nbsp; for Fragilaria dominated samples. Using statistical approaches designed to condense multivari-ate ecological data, we can deconvolve assemblage-specific Si isotope fractionations from the combined diatom assemblage delta Si-30 data. For example, samples dominated by generally deeper water euplanktic species have low delta Si-30(dSi) values (<-1.10 parts per thousand & nbsp;). Conversely, samples dominated by shallow water planktic or benthic periphyton have higher delta Si-30(dSi) values (>-0.14 parts per thousand & nbsp;). These data suggest that delta(30)Sii records from LAVO lakes reflect species specific Si isotope fractionations and thus act as pale-olimnological proxy for the aquatic-habitat of bSi production. Silicon isotope analysis should be coupled with diatom com-munity composition data and other geochemical proxies for the most robust paleolimnological interpretations. We also construct a Si mass-balance for Manzanita Lake based on elemental fluxes. Despite a short residence time of ~& nbsp;4 months, it is an efficient Si sink: about 30% of inflowing Si is retained in the lake sediments. An entirely independent Si isotope-based estimate agrees remarkably well. Burial fluxes of bSi derived from radiometrically dated sediment cores yield retention rates of about a factor of three higher, which might suggest groundwater is an important term in the lake Si budget. (C) 2022 The Authors. Published by Elsevier Ltd.& nbsp;& nbsp;

Automated summary

This study investigates the role of lake processes in determining the silicon isotope ratios of dissolved silicon and diatom biogenic silica in lakes. The research findings show species-specific fractionations of silicon isotopes in lakes, indicating the potential of using silicon isotopes as a paleolimnological proxy. Additionally, the study discusses the mass balance of silicon in lakes.