Analyzing the triple oxygen isotope (Δ′17O) composition of carbonates and air CO2 can provide valuable information about Earth system processes. However, accurately measuring the abundance of the ...rare 17O‐bearing CO2 isotopologue using isotope ratio mass spectrometry presents significant challenges. Consequently, alternative approaches, such as laser spectroscopy, have been developed. Here, we describe an adaptable dual inlet system for a tunable infrared laser direct absorption spectrometer (TILDAS) that maintains stable instrumental conditions for subsequent sample and reference measurements. We report ∆′17O measurements on three types of samples: reference CO2, CO2 derived from the acid digestion of carbonates, and air CO2. The external repeatability (±1σ) for reference‐sample‐reference bracketing measurements is generally better than ±10 ppm, close to the average internal error of ±6 ppm. Our results demonstrate that laser spectroscopy is a capable technique for measuring triple oxygen isotopes with the precision required to resolve variations in the ∆′17O values of air CO2 and to use the ∆′17O of carbonates for paleothermometry.
Plain Language Summary
Tunable infrared laser direct absorption spectroscopy (TILDAS) is a technique that determines isotopologue abundances by shining a laser through the analyzed gas and measuring the amount of light absorbed. Laser spectroscopy is emerging as a competitive alternative to the more common isotope ratio mass spectrometry due to its ability to provide rapid and precise measurements of rare isotope ratios directly on CO2 gas. We present a cost‐effective dual inlet system for TILDAS to measure the triple oxygen isotope composition of carbonates and air CO2. Our setup maintains stable measurement conditions, for example, instrumental temperature, gas composition, pressure, and achieves external repeatability generally below ±10 ppm. Triple oxygen isotope measurements with such precision enable resolving variations in the 17O‐anomaly of air CO2 and using the ∆′17O values of carbonates for paleoenvironmental applications.
Key Points
An inlet system using inexpensive hardware and open‐source software was developed for tunable infrared laser absorption spectroscopy
Spectroscopic measurements of ∆′17O in CO2 can be negatively influenced by variable temperatures, uneven CO2 mixing, which were addressed
The external standard deviation of repeated ∆′17O measurements of CO2 from carbonates and air was better than 10 ppm
The new excess term of the triple oxygen isotope composition in meteoric water, expressed as ∆′17O, is conceived to track the component of kinetic fractionation in the water cycle, much like the ...traditional deuterium excess (d-excess) based on dual hydrogen and oxygen isotope compositions. Here, we use theoretical models to investigate the common and distinct features of variations in these two parameters that result from isotopic fractionation in each step of the water cycle. The objective is to demonstrate their different responses and sensitivities to hydroclimate processes and to explore an interpretive framework based on paired precipitation d-excess and ∆′17O data.
For oceanic evaporation as the first step of the water cycle, both models and observations suggest that the d-excess and ∆′17O of oceanic evaporation fluxes commonly respond to relative humidity as well as boundary-layer aerodynamics and isotopic gradients at the site of evaporation, reflecting similar moisture source information on short timescales. As the isotopic signal of oceanic vapor is transmitted to precipitation, d-excess and ∆′17O show distinct non-conservative behaviors in condensation and Rayleigh distillation, which result in decoupling between d-excess and ∆′17O in precipitation. This decoupling is particularly pronounced when the degree of distillation is small. Additionally, we develop a new model to show that the interaction between vapor mixing and distillation causes lower ∆′17O in precipitation than in the case of Rayleigh distillation without the presence of external vapor sources, whereas only minimal effects are observed in d-excess. Furthermore, we find that precipitation ∆′17O has a relatively higher sensitivity than d-excess to terrestrial evaporation-dominated moisture recycling and re-evaporation of raindrops in light rains. Finally, we develop stochastic model simulations to show that the idealized Rayleigh distillation model modified to incorporate the raindrop re-evaporation/equilibration and vapor mixing is sufficient to reproduce the observed patterns in the relationships among δ18O, d-excess, and ∆′17O in precipitation.
This forward-looking review built on the analysis of theoretical models highlights new opportunities in leveraging the joint information from precipitation d-excess and ∆′17O data to fingerprint water cycle processes at a range of spatiotemporal scales. However, we also emphasize the challenges associated with these complex and opaque tracers, which aggregate multiple fractionation steps within the water cycle. We suggest that site-specific, multiple-year 12 monthly means of paired precipitation d-excess and ∆′17O data are most useful to disentangle their complex controls. This effort will provide a mechanistic basis for future applications of triple oxygen isotope techniques in geological records for paleo-reconstructions.
Triple oxygen isotope compositions of authigenic minerals are an emerging tool for the reconstruction of fluid temperatures and the fluid isotopic composition. In this study, we analyzed euhedral ...authigenic quartz crystals from a halite deposit of the Upper Permian Zechstein evaporitic basin for their triple oxygen isotope composition using laser fluorination isotope ratio mass spectrometry. In the triple oxygen isotope space, additional information, such as the triple oxygen isotope composition of the ambient water, provides insights into equilibrium conditions during quartz formation that cannot be identified from δ18O alone. The triple oxygen isotope composition of authigenic quartz shows, that single oxygen isotope (δ18O) thermometry is not applicable for samples from evaporitic environments, where the fluids' δ18O deviates from dynamic oxygen isotope equilibrium. By combining the Craig and Gordon evaporation model with H2O – SiO2 triple oxygen isotope equilibrium fractionation, we reconstruct the formation temperature of authigenic quartz and the triple oxygen isotope composition of the marine-derived saline brine pore fluid in equilibrium with the quartz. We obtain temperatures of 90 to 130 °C that is interpreted as crystallization temperatures of microcrystalline quartz in pore fluid of halite during burial diagenesis. The triple oxygen isotope composition of authigenic quartz from evaporitic environments is suited as a geochemical tracer for fluid oxygen isotope compositions and ancient fluid or diagenetic temperatures.
The triple oxygen isotopic composition of gypsum mother water (gmw) is recorded in structurally bonded water in gypsum (gsbw). Respective fractionation factors have been determined experimentally for ...18O/16O and 17O/16O. By taking previous experiments into account we suggest using 18αgsbw-gmw=1.0037; 17αgsbw-gmw=1.00195 and θgsbw-gmw=0.5285 as fractionation factors in triple oxygen isotope space.
Recent gypsum was sampled from a series of 10 ponds located in the Salar de Llamara in the Atacama Desert, Chile. Total dissolved solids (TDS) in these ponds show a gradual increase from 23g/l to 182g/l that is accompanied by an increase in pond water 18O/16O. Gsbw falls on a parallel curve to the ambient water from the saline ponds. The offset is mainly due to the equilibrium fractionation between gsbw and gmw. However, gsbw represents a time integrated signal biased towards times of strong evaporation, hence the estimated gmw comprises elevated 18O/16O compositions when compared to pond water samples taken on site. Gypsum precipitation is associated with algae mats in the ponds with lower salinity. No evidence for respective vital effects on the triple oxygen isotopic composition of gypsum hydration water is observed, nor are such effects expected. In principle, the array of δ18Ogsbw vs. 17Oexcess can be used to: (1) provide information on the degree of evaporation during gypsum formation; (2) estimate pristine meteoric water compositions; and (3) estimate local relative humidity which is the controlling parameter of the slope of the array for simple hydrological situations. In our case study, local mining activities may have decreased deep groundwater recharge, causing a recent change of the local hydrology.
Abstract
This study demonstrates the potential of triple O-isotopes to quantify evaporation with recharge on a salt lake from the Atacama Desert, Chile. An evaporative gradient was found in shallow ...ponds along a subsurface flow-path from a groundwater source. Total dissolved solids (TDS) increased by 177 g/l along with an increase in δ
18
O by 16.2‰ and in δD by 65‰.
17
O-excess decreased by 79 per meg, d-excess by 55‰. Relative humidity (
h
), evaporation over inflow (
E
/
I
), the isotopic composition of vapor (
*
R
V
) and of inflowing water (
*
R
WI
) determine the isotope distribution in
17
O-excess over δ
18
O along a well-defined evaporation curve as the classic Craig-Gordon model predicts. A complementary on-site simple (pan) evaporation experiment over a change in TDS, δ
18
O, and
17
O-excess by 392 g/l, 25.0‰, and −130 per meg, respectively, was used to determine the effects of sluggish brine evaporation and of wind turbulence. These effects translate to uncertainty in
E
/
I
rather than
h
. The local composition of
*
R
V
relative to
*
R
WI
pre-determines the general ability to resolve changes in
h
. The triple O-isotope system is useful for quantitative hydrological balancing of lakes and for paleo-humidity reconstruction, particularly if complemented by D/H analysis.
Abstract Analyzing the triple oxygen isotope (Δ′ 17 O) composition of carbonates and air CO 2 can provide valuable information about Earth system processes. However, accurately measuring the ...abundance of the rare 17 O‐bearing CO 2 isotopologue using isotope ratio mass spectrometry presents significant challenges. Consequently, alternative approaches, such as laser spectroscopy, have been developed. Here, we describe an adaptable dual inlet system for a tunable infrared laser direct absorption spectrometer (TILDAS) that maintains stable instrumental conditions for subsequent sample and reference measurements. We report ∆′ 17 O measurements on three types of samples: reference CO 2 , CO 2 derived from the acid digestion of carbonates, and air CO 2 . The external repeatability (±1 σ ) for reference‐sample‐reference bracketing measurements is generally better than ±10 ppm, close to the average internal error of ±6 ppm. Our results demonstrate that laser spectroscopy is a capable technique for measuring triple oxygen isotopes with the precision required to resolve variations in the ∆′ 17 O values of air CO 2 and to use the ∆′ 17 O of carbonates for paleothermometry.
Plain Language Summary Tunable infrared laser direct absorption spectroscopy (TILDAS) is a technique that determines isotopologue abundances by shining a laser through the analyzed gas and measuring the amount of light absorbed. Laser spectroscopy is emerging as a competitive alternative to the more common isotope ratio mass spectrometry due to its ability to provide rapid and precise measurements of rare isotope ratios directly on CO 2 gas. We present a cost‐effective dual inlet system for TILDAS to measure the triple oxygen isotope composition of carbonates and air CO 2 . Our setup maintains stable measurement conditions, for example, instrumental temperature, gas composition, pressure, and achieves external repeatability generally below ±10 ppm. Triple oxygen isotope measurements with such precision enable resolving variations in the 17 O‐anomaly of air CO 2 and using the ∆′ 17 O values of carbonates for paleoenvironmental applications.
Key Points An inlet system using inexpensive hardware and open‐source software was developed for tunable infrared laser absorption spectroscopy Spectroscopic measurements of ∆′ 17 O in CO 2 can be negatively influenced by variable temperatures, uneven CO 2 mixing, which were addressed The external standard deviation of repeated ∆′ 17 O measurements of CO 2 from carbonates and air was better than 10 ppm
Atmospheric relative humidity is an important parameter affecting vegetation yet paleo-humidity proxies are scarce and difficult to calibrate. Here we use triple oxygen (δ17O and δ18O) and hydrogen ...(δD) isotopes of structurally-bound gypsum hydration water (GHW) extracted from lacustrine gypsum to quantify past changes in atmospheric relative humidity. An evaporation isotope-mass-balance model is used together with Monte Carlo simulations to determine the range of climatological conditions that simultaneously satisfy the stable isotope results of GHW, and with statistically robust estimates of uncertainty. We apply this method to reconstruct the isotopic composition of paleo-waters of Lake Estanya (NE Spain) and changes in normalized atmospheric relative humidity (RHn) over the last glacial termination and Holocene (from ∼15 to 0.6 cal. kyrs BP). The isotopic record indicates the driest conditions occurred during the Younger Dryas (YD; ∼12–13 cal. kyrs BP). We estimate a RHn of ∼40–45% during the YD, which is ∼30–35% lower than today. Because of the southward displacement of the Polar Front to ∼42°N, it was both windier and drier during the YD than the Bølling–Allerød period and Holocene. Mean atmospheric moisture gradually increased from the Preboreal to Early Holocene (∼11 to 8 cal. kyrs BP, 50–60%), reaching 70–75% RHn from ∼7.5 cal. kyrs BP until present-day. We demonstrate that combining hydrogen and triple oxygen isotopes in GHW provides a powerful tool for quantitative estimates of past changes in relative humidity.
•We present a new method for quantitative estimate of paleo-humidity changes.•Gypsum hydration water is used to infer the isotopic composition of paleo-lakes.•17O-excess and d-excess of the paleo-water can be determined.•An isotope-mass-balance model is used to quantify changes in RHn in the past.•The derived uncertainty in RHn can be as low as ±3% (1σ).
•Archean.•Pilbara Supergroup.•Interpillow carbonates.•Stable and radiogenic isotopes.•Trace elements.•Archean seawater.
Calcites hosted in the interpillow void spaces of extremely well preserved, ...3.47–3.12 Ga pillow lavas of the Archean Pilbara Craton, Australia, provide new geochemical insights into the composition of Archean seawater and its interaction with basaltic crust. We present a comprehensive dataset of major and trace elements, radiogenic 147Sm-143Nd, 87Rb-87Sr, and stable C-O isotopes for these calcites.
Based on their elemental composition and Post-Archean Australian Shale-normalized rare earth element and yttrium (REYPAAS) patterns, two types of calcites can be distinguished. Type I (n = 9) are coarse-grained calcites with elevated Mn concentrations (478–14,790 ppm) and high REY concentrations that match the basaltic host rock compositions. Petrographic textures in combination with geochemical data indicate precipitation from boiling seawater trapped between pillows during basalt eruption. Small light-REYPAAS depletions, only slightly super-chondritic Y/Ho (34.5–39.1), and low δ18O(VSMOW2) (9.25–16.66 ‰) suggest relatively high fluid-rock interactions of boiling seawater with the basaltic host rock. These characteristics are similar to those of interstitial carbonates found in modern mid-ocean ridge basalts. Type II carbonates (n = 6) are fine-grained, low-Mn (13.7–420 ppm) calcites that exhibit comparably high Sr concentrations (825–2,516 ppm) and anoxic modern seawater-like REYPAAS patterns, strong super-chondritic Y/Ho (39.1–55.8) and δ18O(VSMOW2) values of 9.10–13.18 ‰. These features hint to direct calcite precipitation from seawater within the degassing space with little fluid-rock interaction.
Almost all (Type I and Type II) of the calcites investigated here, combined with their respective host rocks, yield well-defined Sm-Nd isochron ages for the Apex (3,466 ± 23 Ma), Euro (3,365 ± 43 Ma), Honeyeater (3,187 ± 33 Ma), and Bradley (3,131 ± 24 Ma) formations. Only calcites from the Mt. Ada Basalt and their associated host rocks show a ∼ 100 Ma younger Sm-Nd isochron age (3,361 ± 22 Ma) compared to the U-Pb zircon age of formation.
Highly radiogenic initial Sr isotope compositions of the high-Mn calcites (Type I) and low Sr concentrations, suggest Sr remobilization for these calcites. In contrast, the low-Mn calcite (Type II) exhibit higher Sr concentrations and lower 87Sr/86Sr(i) of 0.7010–0.7011 at 3.34 Ga and 0.70137 at 3.12 Ga, suggesting increasing influence of crustal weathering on the composition of Paleoarchean seawater through time, and progressive decoupling from the Archean mantle (87Sr/86Sr(i) = 0.7003–0.7007).
Rationale
Determination of δ17O values directly from CO2 with traditional gas source isotope ratio mass spectrometry is not possible due to isobaric interference of 13C16O16O on 12C17O16O. The ...methods developed so far use either chemical conversion or isotope equilibration to determine the δ17O value of CO2. In addition, δ13C measurements require correction for the interference from 12C17O16O on 13C16O16O since it is not possible to resolve the two isotopologues.
Methods
We present a technique to determine the δ17O, δ18O and δ13C values of CO2 from the fragment ions that are formed upon electron ionization in the ion source of the Thermo Scientific 253 Ultra high‐resolution isotope ratio mass spectrometer (hereafter 253 Ultra). The new technique is compared with the CO2‐O2 exchange method and the 17O‐correction algorithm for δ17O and δ13C values, respectively.
Results
The scale contractions for δ13C and δ18O values are slightly larger for fragment ion measurements than for molecular ion measurements. The δ17O and Δ17O values of CO2 can be measured on the 17O+ fragment with an internal error that is a factor 1–2 above the counting statistics limit. The ultimate precision depends on the signal intensity and on the total time that the 17O+ beam is monitored; a precision of 14 ppm (parts per million) (standard error of the mean) was achieved in 20 hours at the University of Göttingen. The Δ17O measurements with the O‐fragment method agree with the CO2‐O2 exchange method over a range of Δ17O values of −0.3 to +0.7‰.
Conclusions
Isotope measurements on atom fragment ions of CO2 can be used as an alternative method to determine the carbon and oxygen isotopic composition of CO2 without chemical processing or corrections for mass interferences.
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