The oxygen isotopic composition of phytolith assemblages from tropical rainforest soil tops (Queensland, Australia): validation of a new paleoenvironmental tool

Alexandre, Anne; Crespin, Julien; Sylvestre, Florence; Sonzogni, Corinne; Hilbert, David W.

doi:10.5194/cp-8-307-2012

Cited by 33 publications

(23 citation statements)

References 91 publications

(78 reference statements)

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Section: Imprint Of Changes In Atmospheric Rh On the 17 O-excess Of Pmentioning

confidence: 99%

“…Sharp et al (2016) and Alexandre et al (2012). Whereas Alexandre et al (2012) and Sharp et al (2016) Dodd and Sharp (2010) suggests that phytoliths formed in equilibrium with a water of isotope composition close to that of the bulk leaf water. This is additionally supported by the obtained averaged value of λ Phyto−LW (0.522 ± 0.001) close to the θ SiO 2 −water equilibrium value of 0.524 calculated for 25 • C from Sharp et al (2016).…”

Section: Imprint Of Changes In Atmospheric Rh On the 17 O-excess Of Pmentioning

confidence: 99%

“…In the wood, silica polymerizes in the secondary xylem supposedly unaffected by transpiration, in the form of Globular granulate phytolith types (Madella et al, 2005;Scurfield et al, 1974;ter Welle, 1976). These phytoliths make up more than 80 % of tropical humid forest and rainforest phytolith assemblages found in soils and sediments (Alexandre et al, 1997;Alexandre et al, 2012). Examination of the δ 18 O Phyto of rainforest assemblages showed correlations with the δ 18 O of precipitation (δ 18 O Pre ) and the atmospheric temperature (Alexandre et al, 2012).…”

Section: Introductionmentioning

confidence: 99%

“…These phytoliths make up more than 80 % of tropical humid forest and rainforest phytolith assemblages found in soils and sediments (Alexandre et al, 1997;Alexandre et al, 2012). Examination of the δ 18 O Phyto of rainforest assemblages showed correlations with the δ 18 O of precipitation (δ 18 O Pre ) and the atmospheric temperature (Alexandre et al, 2012). However, in this case, the use of δ 18 O Phyto did not further develop because it was applicable only to forested areas and humid climatic periods, which is a major drawback for paleoclimatic reconstructions.…”

Section: Introductionmentioning

confidence: 99%

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The triple oxygen isotope composition of phytoliths as a proxy of continental atmospheric humidity: insights from climate chamber and climate transect calibrations

et al. 2018

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Abstract. Continental atmospheric relative humidity (RH) is a key climate parameter. Combined with atmospheric temperature, it allows us to estimate the concentration of atmospheric water vapor, which is one of the main components of the global water cycle and the most important gas contributing to the natural greenhouse effect. However, there is a lack of proxies suitable for reconstructing, in a quantitative way, past changes of continental atmospheric humidity. This reduces the possibility of making model-data comparisons necessary for the implementation of climate models. Over the past 10 years, analytical developments have enabled a few laboratories to reach sufficient precision for measuring the triple oxygen isotopes, expressed by the 17 O-excess ( 17 O-excess = ln (δ 17 O + 1) -0.528 × ln (δ 18 O + 1)), in water, water vapor and minerals. The 17 O-excess represents an alternative to deuterium-excess for investigating relative humidity conditions that prevail during water evaporation. Phytoliths are micrometric amorphous silica particles that form continuously in living plants. Phytolith morphological assemblages from soils and sediments are commonly used as past vegetation and hydrous stress indicators. In the present study, we examine whether changes in atmospheric RH imprint the 17 O-excess of phytoliths in a measurable way and whether this imprint offers a potential for reconstructing past RH. For that purpose, we first monitored the 17 O-excess evolution of soil water, grass leaf water and grass phytoliths in response to changes in RH (from 40 to 100 %) in a growth chamber experiment where transpiration reached a steady state. Decreasing RH from 80 to 40 % decreases the 17 Oexcess of phytoliths by 4.1 per meg/% as a result of kinetic fractionation of the leaf water subject to evaporation. In order to model with accuracy the triple oxygen isotope fractionation in play in plant water and in phytoliths we recommend direct and continuous measurements of the triple isotope composition of water vapor. Then, we measured the 17 O-excess of 57 phytolith assemblages collected from top soils along a RH and vegetation transect in inter-tropical West and Central Africa. Although scattered, the 17 O-excess of phytoliths decreases with RH by 3.4 per meg/%. The similarity of the trends observed in the growth chamber and nature supports that RH is an important control of 17 O-excess of phytoliths in the natural environment. However, other parameters such as changes in the triple isotope composition of the soil water or phytolith origin in the plant may come into play. Assessment of these parameters through additional growth chambers experiments and field campaigns will bring us closer to an accurate proxy of changes in relative humidity.

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Section: Imprint Of Changes In Atmospheric Rh On the 17 O-excess Of Pmentioning

confidence: 99%

Section: Imprint Of Changes In Atmospheric Rh On the 17 O-excess Of Pmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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The triple oxygen isotope composition of phytoliths as a proxy of continental atmospheric humidity: insights from climate chamber and climate transect calibrations

et al. 2018

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“…Upon plant decay, part of the phytolith production can be incorporated into soils or sediments and preserved for as long as millions of years (Alexandre et al, 2011;Miller et al, 2012;Strömberg et al, 2013). These fossil phytolith assemblages can be used for reconstructing past vegetation and climate conditions via their morphological and geochemical signatures (Piperno, 2006;Alexandre et al, 2012). Phytoliths occlude small amounts of organic compounds, first evidenced by the production of carbon (C) and nitrogen (N) during dry ashing (Jones and Beavers, 1963).…”

Section: Introductionmentioning

confidence: 99%

New highlights of phytolith structure and occluded carbon location: 3-D X-ray microscopy and NanoSIMS results

et al. 2015

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Abstract. Phytoliths contain occluded organic compounds called phytC. Recently, phytC content, nature, origin, paleoenvironmental meaning and impact in the global C cycle have been the subject of increasing debate. Inconsistencies were fed by the scarcity of in situ characterizations of phytC in phytoliths. Here we reconstructed at high spatial resolution the 3-D structure of harvested grass short cell (GSC) phytoliths using 3-D X-ray microscopy. While this technique has been widely used for 3-D reconstruction of biological systems it has never been applied in high-resolution mode to silica particles. Simultaneously, we investigated the location of phytC using nanoscale secondary ion mass spectrometry (NanoSIMS). Our data evidenced that the silica structure contains micrometric internal cavities. These internal cavities were sometimes observed isolated from the outside. Their opening may be an original feature or may result from a beginning of dissolution of silica during the chemical extraction procedure, mimicking the progressive dissolution process that can happen in natural environments. The phytC that may originally occupy the cavities is thus susceptible to rapid oxidation. It was not detected by the NanoSIMS technique. However, another pool of phytC, continuously distributed in and protected by the silica structure, was observed. Its N / C ratio (0.27) is in agreement with the presence of amino acids. These findings constitute a basis to further characterize the origin, occlusion process, nature and accessibility of phytC, as a prerequisite for assessing its significance in the global C cycle.

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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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The oxygen isotopic composition of phytolith assemblages from tropical rainforest soil tops (Queensland, Australia): validation of a new paleoenvironmental tool

Cited by 33 publications

References 91 publications

The triple oxygen isotope composition of phytoliths as a proxy of continental atmospheric humidity: insights from climate chamber and climate transect calibrations

The triple oxygen isotope composition of phytoliths as a proxy of continental atmospheric humidity: insights from climate chamber and climate transect calibrations

New highlights of phytolith structure and occluded carbon location: 3-D X-ray microscopy and NanoSIMS results

Post‐mortem oxygen isotope exchange within cultured diatom silica

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