An experiment to assess the effects of diatom dissolution on oxygen isotope ratios

Smith, Andrew; Leng, Melanie J.; Swann, George E. A.; Barker, Philip A.; Mackay, Anson W.; Ryves, David B.; Sloane, Hilary J.; Chenery, Simon; Hems, Michael

doi:10.1002/rcm.7446

Cited by 17 publications

(23 citation statements)

References 30 publications

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“…With respect to naturally occurring processes, dissolution is a common feature of diatom silica diagenesis and the dissolution effect on δ 18 O silica values has not been well characterised to date. Experimental studies have indicated that diatom silica is isotopically homogenous and that δ 18 O silica values are not susceptible to dissolution effects . Similar conclusions were drawn by Moschen et al, although they did observe an increase in δ 18 O silica values under high pH conditions.…”

Section: Discussionsupporting

confidence: 81%

“…In the latter case, the sedimentary diatoms had lower δ 18 O silica values than the living diatoms, with sedimentary values falling upon the line defined by a series of lake surface sediment δ 18 O silica values across Europe . Partial dissolution of diatom frustules is one mechanism that may explain isotopic alteration during sedimentation; however, experimental studies suggest that the effects of dissolution upon diatom δ 18 O silica values are small to negligible, contrasting with experimental evidence using phytoliths . Conversely, the process of silica condensation has been frequently proposed to impart significant effects upon δ 18 O silica values .…”

Section: Introductionmentioning

confidence: 96%

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Post‐mortem oxygen isotope exchange within cultured diatom silica

Tyler

Sloane

Rickaby

et al. 2017

Rapid Comm Mass Spectrometry

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RationalePotential post‐mortem alteration to the oxygen isotope composition of biogenic silica is critical to the validity of palaeoclimate reconstructions based on oxygen isotope ratios (δ18O values) from sedimentary silica. We calculate the degree of oxygen isotope alteration within freshly cultured diatom biogenic silica in response to heating and storing in the laboratory.MethodsThe experiments used freshly cultured diatom silica. Silica samples were either stored in water or dried at temperatures between 20 °C and 80 °C. The mass of affected oxygen and the associated silica‐water isotope fractionation during alteration were calculated by conducting parallel experiments using endmember waters with δ18O values of −6.3 to −5.9 ‰ and −36.3 to −35.0 ‰. Dehydroxylation and subsequent oxygen liberation were achieved by stepwise fluorination with BrF5. The 18O/16O ratios were measured using a ThermoFinnigan MAT 253 isotope ratio mass spectrometer.ResultsSignificant alterations in silica δ18O values were observed, most notably an increase in the δ18O values following drying at 40–80 °C. Storage in water for 7 days between 20 and 80 °C also led to significant alteration in δ18O values. Mass balance calculations suggest that the amount of affected oxygen is positively correlated with temperature. The estimated oxygen isotope fractionation during alteration is an inverse function of temperature, consistent with the extrapolation of models for high‐temperature silica‐water oxygen isotope fractionation.ConclusionsRoutinely used preparatory methods may impart significant alterations to the δ18O values of biogenic silica, particularly when dealing with modern cultured or field‐collected material. The significance of such processes within natural aquatic environments is uncertain; however, there is potential that similar processes also affect sedimentary diatoms, with implications for the interpretation of biogenic silica‐hosted δ18O palaeoclimate records.

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Section: Discussionsupporting

confidence: 81%

Section: Introductionmentioning

confidence: 96%

Post‐mortem oxygen isotope exchange within cultured diatom silica

Tyler

Sloane

Rickaby

et al. 2017

Rapid Comm Mass Spectrometry

Self Cite

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“…However, we suppose differential dissolution to have a minor influence on the spatial variability of δ 18 O diatom at BT samples tackled in our study as these are (1) of similar age, (2) have been treated with wet chemistry at low temperatures, and (3) after preparation do not show any microscopical signs of dissolution effects, i.e. a low diatom dissolution index (Smith et al, 2016).…”

Section: Factors Explaining the Spatial Diatom Distributionmentioning

confidence: 98%

“…The study area is situated within the East Siberian continental temperate climate zone exhibiting taiga vegetation (boreal forests) and fragments of steppes and a predominant westerly wind system (Shahgedanova, 2002). The meteorological station in Yakutsk has recorded historical climate data (Gavrilova, 1993).…”

Section: Study Sitementioning

confidence: 99%

“…During counting of diatom valves, chrysophycean stomatocysts and Mallomonas were counted but not further taxonomically identified. Count numbers were used to estimate the chrysophyte cyst to diatom index (C : D) and Mallomonas to diatom index (M : D) relative to counted diatom cells (Smol, 1984;Smol and Boucherle, 1985). Diatom valve preservation was measured and calculated as the f -index (Ryves et al, 2001).…”

Section: Diatomsmentioning

confidence: 99%

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Spatial distribution of environmental indicators in surface sediments of Lake Bolshoe Toko, Yakutia, Russia

et al. 2019

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Abstract. Rapidly changing climate in the Northern Hemisphere and associated socio-economic impacts require reliable understanding of lake systems as important freshwater resources and sensitive sentinels of environmental change. To better understand time-series data in lake sediment cores, it is necessary to gain information on within-lake spatial variabilities of environmental indicator data. Therefore, we retrieved a set of 38 samples from the sediment surface along spatial habitat gradients in the boreal, deep, and yet pristine Lake Bolshoe Toko in southern Yakutia, Russia. Our methods comprise laboratory analyses of the sediments for multiple proxy parameters, including diatom and chironomid taxonomy, oxygen isotopes from diatom silica, grain-size distributions, elemental compositions (XRF), organic carbon content, and mineralogy (XRD). We analysed the lake water for cations, anions, and isotopes. Our results show that the diatom assemblages are strongly influenced by water depth and dominated by planktonic species, i.e. Pliocaenicus bolshetokoensis. Species richness and diversity are higher in the northern part of the lake basin, associated with the availability of benthic, i.e. periphytic, niches in shallower waters. δ18Odiatom values are higher in the deeper south-western part of the lake, probably related to water temperature differences. The highest amount of the chironomid taxa underrepresented in the training set used for palaeoclimate inference was found close to the Utuk River and at southern littoral and profundal sites. Abiotic sediment components are not symmetrically distributed in the lake basin, but vary along restricted areas of differential environmental forcing. Grain size and organic matter are mainly controlled by both river input and water depth. Mineral (XRD) data distributions are influenced by the methamorphic lithology of the Stanovoy mountain range, while elements (XRF) are intermingled due to catchment and diagenetic differences. We conclude that the lake represents a valuable archive for multiproxy environmental reconstruction based on diatoms (including oxygen isotopes), chironomids, and sediment–geochemical parameters. Our analyses suggest multiple coring locations preferably at intermediate depth in the northern basin and the deep part in the central basin, to account for representative bioindicator distributions and higher temporal resolution, respectively.

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