scholarly journals Kinetic fractionation of the isotope composition of 18O, 13C, and of clumped isotope 18O13C in calcite deposited to speleothems. Implications to the reliability of the 18O and Δ47 paleothermometers

2019 ◽  
Vol 48 (3) ◽  
Author(s):  
Wolfgang Dreybrodt
Keyword(s):  
Isotope Composition ◽  
Clumped Isotope ◽  
Kinetic Fractionation

scholarly journals Leaf scale quantification of the effect of photosynthetic gas exchange on Δ47 of CO2

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Getachew Agmuas Adnew ◽  
Magdalena E. G. Hofmann ◽  
Thijs L. Pons ◽  
Gerbrand Koren ◽  
Martin Ziegler ◽  
...  
Keyword(s):  
Gas Exchange ◽  
Isotope Composition ◽  
Diffusion Flux ◽  
Leaf Water ◽  
Back Diffusion ◽  
Ambient Conditions ◽  
Photosynthetic Gas Exchange ◽  
O Isotope ◽  
Clumped Isotope ◽  
Kinetic Fractionation

AbstractThe clumped isotope composition (Δ47, the anomaly of the mass 47 isotopologue relative to the abundance expected from a random isotope distribution) of CO2 has been suggested as an additional tracer for gross CO2 fluxes. However, the effect of photosynthetic gas exchange on Δ47 has not been directly determined and two indirect/conceptual studies reported contradicting results. In this study, we quantify the effect of photosynthetic gas exchange on Δ47 of CO2 using leaf cuvette experiments with one C4 and two C3 plants. The experimental results are supported by calculations with a leaf cuvette model. Our results demonstrate the important roles of the Δ47 value of CO2 entering the leaf, kinetic fractionation as CO2 diffuses into, and out of the leaf and CO2–H2O isotope exchange with leaf water. We experimentally confirm the previously suggested dependence of Δ47 of CO2 in the air surrounding a leaf on the stomatal conductance and back-diffusion flux. Gas exchange can enrich or deplete the Δ47 of CO2 depending on the Δ47 of CO2 entering the leaf and the fraction of CO2 exchanged with leaf water and diffused back to the atmosphere, but under typical ambient conditions, it will lead to a decrease in Δ47.

Fractionation of clumped isotopes of CO2 during photosynthesis

2021 ◽  
Author(s):  
Getachew A. Adnew ◽  
Magdalena E.G. Hofmann ◽  
Thijs L. Pons ◽  
Gerbrand Koren ◽  
Martin Ziegler ◽  
...  
Keyword(s):  
Gas Exchange ◽  
Carbon Cycle ◽  
Isotope Composition ◽  
Diffusion Flux ◽  
Carbonic Anhydrase Activity ◽  
Clumped Isotopes ◽  
Photosynthetic Gas Exchange ◽  
O Isotope ◽  
Clumped Isotope ◽  
Kinetic Fractionation

<p>Stable isotope (δ<sup>13</sup>C and δ<sup>18</sup>O) and mole fraction measurements of CO<sub>2</sub> are used to constrain the carbon cycle. However, the gross fluxes of the carbon cycle, especially photosynthesis and respiration, remain uncertain due to the challenging task of distinguishing individual flux terms from each other. The clumped isotope composition (Δ<sub>47</sub>) of CO<sub>2</sub> has been suggested as an additional tracer for gross CO<sub>2</sub> fluxes since it depends mainly on temperature but not on the bulk isotopic composition of leaf, soil and surface water, unlike δ<sup>18</sup>O of CO<sub>2</sub>.</p><p>In this study, we quantify the effect of photosynthetic gas exchange on Δ<sub>47</sub> of CO<sub>2</sub> using leaf cuvette experiments with two C<sub>3</sub> and one C<sub>4</sub> plants and discuss challenges and possible applications of clumped isotope measurements. The experimental results are supported by calculations with a leaf cuvette model. Our results demonstrate how the effect of gas exchange on Δ<sub>47</sub> is controlled by CO<sub>2</sub>-H<sub>2</sub>O isotope exchange (using plants with different carbonic anhydrase activity), and kinetic fractionation as CO<sub>2</sub> diffuses into and out of the leaf (using plants with different stomatal and mesophyll conductance). We experimentally confirm the previously suggested dependence of Δ<sub>47</sub>­­ on the stomatal conductance and back-diffusion flux.</p>

Combined clumped isotope measurements resolve kinetic biases in carbonate formation temperatures

2020 ◽  
Author(s):  
David Bajnai ◽  
Weifu Guo ◽  
Niklas Löffler ◽  
Katharina Methner ◽  
Emilija Krsnik ◽  
...  
Keyword(s):  
High Precision ◽  
Dissolved Inorganic Carbon ◽  
Isotope Composition ◽  
Coral Skeletons ◽  
Carbonate Formation ◽  
Devils Hole ◽  
Kinetic Effects ◽  
Clumped Isotope ◽  
Kinetic Fractionation ◽  
Geologic Record

<p>Reaction kinetics involved in the precipitation of carbonates can introduce large scatter and inaccuracies in the temperatures derived from their <em>δ</em><sup>18</sup>O and ∆<sub>47</sub> values. Advances in mass spectrometry instrumentation recently enabled high-precision analysis of the <sup>18</sup>O–<sup>18</sup>O clumping in carbonate minerals (<em>∆</em><sub>48</sub>), despite the relatively low natural abundance of <sup>12</sup>C<sup>18</sup>O<sup>18</sup>O, the main isotopologue contributing to the <em>∆</em><sub>48</sub> signal (1). Measurements of <em>∆</em><sub>48</sub>, when combined with <em>∆</em><sub>47,</sub> can yield additional insights into kinetic effects and the carbonate formation environment (2).</p><p>Here we report high-precision <em>∆</em><sub>47</sub> and <em>∆</em><sub>48</sub> values of speleothem carbonates, modern coral skeletons, a brachiopod, and a belemnite. We constrained equilibrium in <em>∆</em><sub>47</sub> vs <em>∆</em><sub>48</sub> space by anchoring empirically derived <em>∆</em><sub>47</sub> vs temperature and <em>∆</em><sub>48</sub> vs temperature relationships to a Devils Hole mammillary calcite, known to be precipitated at extremely slow rates at a constant 33.7(±0.8) °C and water oxygen isotope composition. Our results, compared to theoretical predictions, provide the most substantial evidence to date that the isotopic disequilibrium commonly observed in speleothems and scleractinian coral skeletons is inherited from the dissolved inorganic carbon pool of their parent solutions. Data from an ancient belemnite imply it precipitated near isotopic equilibrium and confirm the warmer-than-present temperatures at Early Cretaceous southern high latitudes. The presence of similar kinetic departure in a brachiopod but not in a belemnite suggests that the current discrepancy between belemnite and brachiopod-based temperature estimates in the geologic record is most likely related to a greater kinetic bias in the isotopic composition of brachiopod shells.</p><p>We demonstrate that the combined clumped isotope method makes it possible to identify carbonates that did not precipitate in thermodynamic equilibrium from their parent water. Our results highlight the potential that the combined clumped isotope analyses hold for accurate paleoclimate reconstructions and the identification of the kinetic fractionation processes dominant in carbonate (bio)mineralisation.</p><p>(1) Fiebig et al. (2019), https://doi.org/10.1016/j.chemgeo.2019.05.019</p><p>(2) Guo, W. (2020), https://doi.org/10.1016/j.gca.2019.07.055</p>

scholarly journals Reconstruction of drip-water δ<sup>18</sup>O based on calcite oxygen and clumped isotopes of speleothems from Bunker Cave (Germany)

2013 ◽  
Vol 9 (1) ◽  
pp. 377-391 ◽  
Author(s):  
T. Kluge ◽  
H. P. Affek ◽  
T. Marx ◽  
W. Aeschbach-Hertig ◽  
D. F. C. Riechelmann ◽  
...  
Keyword(s):  
Variation Method ◽  
Clumped Isotopes ◽  
New Approach ◽  
Drip Water ◽  
The Holocene ◽  
Water Composition ◽  
Kinetic Isotope ◽  
Cave Drip Water ◽  
Clumped Isotope ◽  
Kinetic Fractionation

Abstract. The geochemical signature of many speleothems used for reconstruction of past continental climates is affected by kinetic isotope fractionation. This limits quantitative paleoclimate reconstruction and, in cases where the kinetic fractionation varies with time, also affects relative paleoclimate interpretations. In carbonate archive research, clumped isotope thermometry is typically used as proxy for absolute temperatures. In the case of speleothems, however, clumped isotopes provide a sensitive indicator for disequilibrium effects. The extent of kinetic fractionation co-varies in Δ47 and δ18O so that it can be used to account for disequilibrium in δ18O and to extract the past drip-water composition. Here we apply this approach to stalagmites from Bunker Cave (Germany) and calculate drip-water δ18Ow values for the Eemian, MIS3, and the Holocene, relying on independent temperature estimates and accounting for disequilibrium. Applying the co-variation method to modern calcite precipitates yields drip-water δ18Ow values in agreement with modern cave drip-water δ18Ow of −7.9 ± 0.3‰, despite large and variable disequilibrium effects in both calcite δ18Oc and Δ47. Reconstructed paleo-drip-water δ18Ow values are lower during colder periods (e.g., MIS3: −8.6 ± 0.4‰ and the early Holocene at 11 ka: −9.7 ± 0.2‰) and show higher values during warmer climatic periods (e.g., the Eemian: −7.6 ± 0.2‰ and the Holocene Climatic Optimum: −7.2 ± 0.3‰). This new approach offers a unique possibility for quantitative climate reconstruction including the assessment of past hydrological conditions while accounting for disequilibrium effects.

scholarly journals Marine temperatures underestimated for past greenhouse climate

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Madeleine L. Vickers ◽  
Stefano M. Bernasconi ◽  
Clemens V. Ullmann ◽  
Stefanie Lode ◽  
Nathan Looser ◽  
...  
Keyword(s):  
Surface Waters ◽  
Isotope Composition ◽  
Stable Oxygen Isotopes ◽  
Greenhouse Climate ◽  
Temperature Reconstructions ◽  
Stable Oxygen ◽  
Clumped Isotope ◽  
Earth’S Climate ◽  
Extinct Group

AbstractUnderstanding the Earth’s climate system during past periods of high atmospheric CO2 is crucial for forecasting climate change under anthropogenically-elevated CO2. The Mesozoic Era is believed to have coincided with a long-term Greenhouse climate, and many of our temperature reconstructions come from stable isotopes of marine biotic calcite, in particular from belemnites, an extinct group of molluscs with carbonate hard-parts. Yet, temperatures reconstructed from the oxygen isotope composition of belemnites are consistently colder than those derived from other temperature proxies, leading to large uncertainties around Mesozoic sea temperatures. Here we apply clumped isotope palaeothermometry to two distinct carbonate phases from exceptionally well-preserved belemnites in order to constrain their living habitat, and improve temperature reconstructions based on stable oxygen isotopes. We show that belemnites precipitated both aragonite and calcite in warm, open ocean surface waters, and demonstrate how previous low estimates of belemnite calcification temperatures has led to widespread underestimation of Mesozoic sea temperatures by ca. 12 °C, raising estimates of some of the lowest temperature estimates for the Jurassic period to values which approach modern mid-latitude sea surface temperatures. Our findings enable accurate recalculation of global Mesozoic belemnite temperatures, and will thus improve our understanding of Greenhouse climate dynamics.

Towards disentangling climatic and tectonic changes of southernmost Africa using strontium isotope stratigraphy and clumped isotope thermometry

2021 ◽  
Author(s):  
B. Linol ◽  
I. Montañez ◽  
A. Lombardo ◽  
D. Kuta ◽  
D. Upadhyay ◽  
...  
Keyword(s):  
South Africa ◽  
Sea Level Rise ◽  
Sea Level ◽  
Secondary Ion Mass Spectrometry ◽  
Isotope Composition ◽  
Tectonic Activity ◽  
Elemental Ratios ◽  
Strontium Isotope Stratigraphy ◽  
Clumped Isotope ◽  
Global Sea Level

Abstract Upper Cretaceous-Cenozoic marine sequences preserved between 30 and 350 masl across southern South Africa record a complex history of climatic and tectonic changes. In this study, we measure the strontium (Sr) isotope composition of fossil shark teeth, echinoderms, corals and oyster shells to chronostratigraphically constrain the ages of these sequences. The method requires careful petrographic screening and micro-drilling of the samples to avoid possible alteration by diagenesis. To assess palaeoenvironmental effects in the shells we measured the Mg/Ca elemental ratios and O isotope values using electron microprobe analysis (EMPA) and secondary ion mass spectrometry (SIMS). In addition, we employed carbonate clumped isotope thermometry to test palaeotemperatures reconstruction. The analysis of recent to modern stromatolites by clumped isotopes yields an average temperature of 20.2°C, in agreement with present day observations. The fossil oyster shells suggest a warmer (23.0°C) seawater palaeotemperature, possibly due to major deglaciation and sea-level rise during the Neogene. We also find that transgressions occurred above 200 to 350 m elevation during: 1) the Campanian-Maastrichian (~75 Ma); 2) the mid-Oligocene (32 to 26 Ma); and 3) the Messinian-Zanclean (6 to 5 Ma). These three episodes are linked to well-known variations in global sea level and regional tectonic processes that could have affected the continental margin differently. The most recent transgression coincides with a maximum global sea-level rise of ~50 m at ca. 5.3 Ma, and a worldwide plate kinematic change around 6 Ma, which in Eurasia led to the closure of the Mediterranean Sea. In the Eastern Cape of South Africa, the new dates of analyzed oyster shells constrain a minimum uplift rate of ca. 150 m/Myr during this tectonic activity. The results have important implications for robust calibration of relative sea level in southern Africa.

Clumped Isotope Paleothermometry: Principles, Applications, and Challenges

2012 ◽  
Vol 18 ◽  
pp. 101-114 ◽  
Author(s):  
Hagit P. Affek
Keyword(s):  
Isotope Composition ◽  
Isotope Analysis ◽  
Atomic Scale ◽  
Clumped Isotopes ◽  
Temperature Dependent ◽  
Deep Time ◽  
Diagenetic Alteration ◽  
Carbonate Formation ◽  
Rare Isotopes ◽  
Clumped Isotope

Clumped isotopes geochemistry measures the thermodynamic preference of two heavy, rare, isotopes to bind with each other. This preference is temperature dependent, and is more pronounced at low temperatures. Carbonate clumped isotope values are independent of the carbonate δ13C and δ18O, making them independent of the carbon or oxygen composition of the solution from which the carbonate precipitated. At equilibrium, it is therefore a direct proxy for the temperature in which the carbonate mineral formed. In most cases, carbonate clumped isotopes record the temperature of carbonate formation, irrespective of the mineral form (calcite, aragonite, or bioapatite) or the organism making it. The carbonate formation temperatures obtained from carbonate clumped isotope analysis can be used in conjunction with the δ18O of the same carbonate, to constrain the oxygen isotope composition of the water from which the carbonate has precipitated. There are, however, cases of deviation from thermodynamic equilibrium, where both clumped and oxygen isotopes are offset from the expected values. Such carbonates must be characterized and calibrated separately. For deep-time applications, special care must be paid to the preservation of the original signal, in particular with respect to diagenetic alteration associated with atomic scale diffusion that may be undetectable by common tests for diagenesis.

scholarly journals Oxygen isotope composition of the Phanerozoic ocean and a possible solution to the dolomite problem

2018 ◽  
Vol 115 (26) ◽  
pp. 6602-6607 ◽  
Author(s):  
Uri Ryb ◽  
John M. Eiler
Keyword(s):  
Oxygen Isotope ◽  
Isotope Exchange ◽  
Isotope Composition ◽  
Temporal Variations ◽  
Oxygen Isotope Exchange ◽  
Diagenetic Alteration ◽  
Isotope Studies ◽  
Dolomite Problem ◽  
Clumped Isotope

The18O/16O of calcite fossils increased by ∼8‰ between the Cambrian and present. It has long been controversial whether this change reflects evolution in the δ18O of seawater, or a decrease in ocean temperatures, or greater extents of diagenesis of older strata. Here, we present measurements of the oxygen and ‟clumped” isotope compositions of Phanerozoic dolomites and compare these data with published oxygen isotope studies of carbonate rocks. We show that the δ18O values of dolomites and calcite fossils of similar age overlap one another, suggesting they are controlled by similar processes. Clumped isotope measurements of Cambrian to Pleistocene dolomites imply crystallization temperatures of 15–158 °C and parent waters having δ18OVSMOWvalues from −2 to +12‰. These data are consistent with dolomitization through sediment/rock reaction with seawater and diagenetically modified seawater, over timescales of 100 My, and suggest that, like dolomite, temporal variations of the calcite fossil δ18O record are largely driven by diagenetic alteration. We find no evidence that Phanerozoic seawater was significantly lower in δ18O than preglacial Cenozoic seawater. Thus, the fluxes of oxygen–isotope exchange associated with weathering and hydrothermal alteration reactions have remained stable throughout the Phanerozoic, despite major tectonic, climatic and biologic perturbations. This stability implies that a long-term feedback exists between the global rates of seafloor spreading and weathering. We note that massive dolomites have crystallized in pre-Cenozoic units at temperatures >40 °C. Since Cenozoic platforms generally have not reached such conditions, their thermal immaturity could explain their paucity of dolomites.

Rapid and Precise Carbon Dioxide Clumped Isotope Composition Analysis by Tunable Infrared Laser Differential Absorption Spectroscopy

2020 ◽  
Author(s):  
David Nelson ◽  
Zhennan Wang ◽  
David Dettman ◽  
Barry McManus ◽  
Jay Quade ◽  
...  
Keyword(s):  
Carbon Dioxide ◽  
Stable Isotope ◽  
Absorption Spectroscopy ◽  
Isotope Ratio ◽  
Continuous Wave ◽  
Isotope Composition ◽  
Infrared Laser ◽  
Composition Analysis ◽  
Differential Absorption ◽  
Clumped Isotope

&lt;p&gt;Carbon dioxide clumped isotope thermometry is one of the most developed applications of the geochemistry of multiply substituted isotopologues. The degree of heavy isotope clumping (e.g., &lt;sup&gt;16&lt;/sup&gt;O&lt;sup&gt;13&lt;/sup&gt;C&lt;sup&gt;18&lt;/sup&gt;O) beyond an expected random distribution can be related to the temperature of calcite precipitation. This provides an independent temperature estimate that, when combined with carbonate &amp;#948;&lt;sup&gt;18&lt;/sup&gt;O values, can constrain paleowater &amp;#948;&lt;sup&gt;18&lt;/sup&gt;O values. However, the use of isotope ratio mass spectrometry (IRMS) to do these measurements remains relatively rare because it is time-consuming and costly. We have developed an isotope ratio laser spectrometry method using tunable infrared laser differential absorption spectroscopy (TILDAS) and describe our latest results using both gaseous carbon dioxide samples and CO&lt;sub&gt;2&lt;/sub&gt; derived from carbonate minerals. The TILDAS instrument has two continuous wave lasers to directly and simultaneously measure four isotopologues involved in the &lt;sup&gt;16&lt;/sup&gt;O&lt;sup&gt;13&lt;/sup&gt;C&lt;sup&gt;18&lt;/sup&gt;O equilibrium calculation. Because each isotopologue is independently resolved, this approach does not have to correct for isobaric peaks. The gas samples are trapped in a low volume (~250 ml) optical multi-pass cell with a path length of 36 meters. Raw data are collected at 1.6 kHz, providing 96,000 peak-area measurements of each CO&lt;sub&gt;2&lt;/sub&gt; isotopologue per minute. With a specially designed sampling system, each sample measurement is bracketed with measurements of a working reference gas, and a precision of 0.01&amp;#8240; is achieved within 20 minutes, based on four repeated measurements. The total sample size needed for a complete measurement is approximately 15 &amp;#956;mol of CO&lt;sub&gt;2&lt;/sub&gt;, or 1.5 mg of calcite equivalent. TILDAS reported &amp;#8710;&lt;sub&gt;16O13C18O&lt;/sub&gt; values show a linear relationship with theoretical calculations, with a very weak dependence on bulk isotope composition. The performance of the TILDAS system demonstrated in this study is competitive with the best IRMS systems and surpasses typical IRMS measurements in several key respects, such as measurement duration and isobaric interference problems. This method can easily be applied more widely in stable isotope geochemistry by changing spectral regions and laser configurations, leading to rapid and high precision (0.01&amp;#8240;) measurement of conventional stable isotope ratios and &amp;#948;&lt;sup&gt;17&lt;/sup&gt;O in CO&lt;sub&gt;2&lt;/sub&gt; gas samples.&lt;/p&gt;

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