Isotopic Species Research Articles

Rotational Spectroscopy of Isotopologues of Silicon Monoxide, SiO, and Spectroscopic Parameters from a Combined Fit of Rotational and Rovibrational Data

Pure rotational transitions of silicon monoxide, involving the main ((28)Si(16)O) as well as several rare isotopic species, were observed in their ground vibrational states by employing long-path absorption spectroscopy between 86 and 825 GHz (1 ≤ J" ≤ 18). Fourier transform microwave spectroscopy was used to study the J" = 0 transition frequencies in the ground and several vibrationally excited states. The vibrational excitation of the newly studied isotopologues extend to between υ = 9 and 29 for (28)Si(17)O and (30)Si(16)O, respectively. Data were extended for some previously investigated species up to υ = 51 for the main isotopologue. The high spectral resolution allowed us to resolve the hyperfine structure in (28)Si(17)O caused by the nuclear electric quadrupole and magnetic dipole moments of (17)O for the first time, and to resolve the much smaller nuclear spin-rotation splitting for isotopic species containing (29)Si. These data were combined with previous rotational and rovibrational (infrared) data to determine an improved set of spectroscopic parameters of SiO in one global fit which takes the breakdown of the Born-Oppenheimer approximation into account. Highly accurate rotational transition frequencies for this important astronomical molecule can now be predicted well into the terahertz region with this parameter set. In addition, a more complete comparison among physical properties of group 14/16 diatomics is possible.

Isotopic analysis (C, N) and species composition of rodent assemblage as a tool for reconstruction of climate and environment evolution during Late Quaternary: A case study from Biśnik Cave (Częstochowa Upland, Poland)

Rodent remains are potentially a powerful tool in paleoecological reconstructions. Rodents are a worldwide group of mammals inhabiting all climatic zones, from arctic tundra to tropical forests. Some of their representatives have narrow ranges of environmental tolerance, while others have cosmopolitan distributions. Additionally, rodent remains are well preserved and numerous in cave sediments, and are easily identified to the species level.The species composition of rodent assemblage from the specific cave gives valuable data on ecosystem status around the site. Moreover, isotopic composition (C, N) of rodent remains provides information on some environmental factors, e.g. type of vegetation, soil activity, precipitation, and temperature.The material for this study was collected from the sediments of the Biśnik Cave (Poland). The cave is known from its sediment sequence deposited during the middle and late Pleistocene and Holocene, containing a rich collection of the Pleistocene fauna remains and archeological artifacts. The stratigraphy of the sediment sequence previously was based on archeological findings and several radiometric dates. In this study, we applied U–Th dating method to bone collagen, rodent tooth enamel, and cave bear tooth enamel. Finally, we revised the chronology of sediment sequence from the Biśnik Cave based on these new data.We found significantly higher variability of nitrogen and carbon isotopic composition in the lemming than in the common vole. However, both species show the same trends in isotopic composition of nitrogen in time. At the beginning of the record, δ15N values were relatively high, suggesting intensive soil activity and, indirectly, mild climate. After that, from a stratigraphic layer dated to the early Würm glaciation, lower δ15N values point to lower soil activity. Deterioration of ecosystem productivity and climate conditions were also confirmed by higher δ13C. This indicates lower canopy effect and suggests conversion of vegetation around the cave. The isotopic record suggests high instability of the environmental conditions during the Würm glaciations, with significantly warmer periods before and after the Last Glacial Maximum.

Laboratory rotational spectra of the dimethyl ether13C-isotopologues up to 1.5 THz

Context. Dimethyl ether is found in high abundance in the interstellar medium. Owing to its strong and dense spectrum throughout the entire microwave and terahertz regime, it contributes to the spectral confusion in astronomical line surveys. The great sensitivity of new observatories like ALMA enhances the need for reliable spectroscopic data, especially for isotopic species of abundant molecules. In addition, the study of the interstellar 12 C/13 C isotopic ratio can be used as a tracer of the formation process of a molecular species, and thus it gives insight into the chemical evolution of the observed region.Aims. The interpretation of astronomical observations depends on the knowledge of accurate rest frequencies and intensities. The objective of this work is to provide spectroscopic data for the two 13 C-isotopologues of dimethyl ether in the vibrational ground state.Methods. High-resolution rotational-torsional spectra of 12 CH3 O13 CH3 and (13 CH3 )2 O have been measured in the laboratory covering frequencies up to 1.5 THz. The analysis is based on an effective rotational Hamiltonian for molecules with two large-amplitude motions.Results. Predictions of the complete ground state rotational spectrum of dimethyl ether-13 C1 and -13 C2 up to 2 THz are presented with accuracies better than 1 MHz. Based on the laboratory work, transitions of 12 CH3 O13 CH3 dimethyl ether have been detected for the first time in a large submillimeter line survey of the high-mass star forming region G327.3-0.6 performed with the APEX telescope.

Vibration spectrum calculations of isotopic species of hydrogen sulfide using the discrete variable representation (DVR) method

In this work, a modified three-dimensional discrete variable representation (MDVR3D) program, which could be used to calculate the bound state vibration spectrum of some triatomic molecules is developed. The sine basis functions are chosen to define the DVR for the radial coordinates for this new program. Both the three-dimensional discrete variable representation (DVR3D) program and the MDVR3D program are used to calculate the vibration energy levels of the isotopic species of hydrogen sulfide (H232S, H233S, H234S, D232S, D233S, D234S, T232S, T233S, T234S). The calculated vibration energy levels from the MDVR3D program are consistent with the counterparts from the DVR3D program, which means that they are good procedures for calculating the bound state energy levels of the triatomic molecules and testing the quality of the potential energy surface (PES). The comparison of the experimental and theoretical vibration energy levels for the nine isotopic species of hydrogen sulfide molecule is made and shows good consistency. This work forms the basis for dealing with the rotational spectrum calculations and presents the first theoretical results for D233S, T232S, T233S, and T234S. Future spectrum observations are needed to compare with these new results.

The influence of the quantum nature of nuclei in high harmonic generation from H+2-like molecular ions

We study the full quantum dynamics of a simple molecular ion driven by an intense laser field. In particular we show that the quantum nature of the nuclear dynamics affects the emitted high harmonic generation (HHG) spectra, strongly reshaping the plateau region. In fact, it is evident that the characteristic flat trend is transformed into a descending trend, with the lower harmonics being two orders of magnitude more intense than the higher harmonics. We show that this effect is more pronounced in the lighter isotopic species of H2+ molecular ions and we also demonstrate that in this case the contribution to HHG from the antibonding electronic energetic surface is of the same order of magnitude as that from the bonding state.

Anomalous 13C Isotope Abundances in C3S and C4H Observed toward the Cold Interstellar Cloud, Taurus Molecular Cloud-1

We have studied the abundances of the (13)C isotopic species of C3S and C4H in the cold molecular cloud, Taurus Molecular Cloud-1 (Cyanopolyyne Peak), by radioastronomical observations of their rotational emission lines. The CCCS/(13)CCCS and CCCS/C(13)CCS ratios are determined to be >206 and 48 ± 15, respectively. The CC(13)CS line is identified with the aid of laboratory microwave spectroscopy, and the range of the CCCS/CC(13)CS ratio is found to be from 30 to 206. The abundances of at least two (13)C isotopic species of C3S are thus found to be different. Similarly, it is found that the abundances of the four (13)C isotopic species of C4H are not equivalent. The CCCCH/(13)CCCCH, CCCCH/C(13)CCCH, CCCCH/CC(13)CCH, and CCCCH/CCC(13)CH ratios are evaluated to be 141 ± 44, 97 ± 27, 82 ± 15, and 118 ± 23, respectively. Here the errors denote 3 times the standard deviation. These results will constrain the formation pathways of C3S and C4H, if the nonequivalence is caused during the formation processes of these molecules. The exchange reactions after the formation of these two molecules may also contribute to the nonequivalence. In addition, we have confirmed that the (12)C/(13)C ratio of some species are significantly higher than the interstellar elemental (12)C/(13)C ratio of 60-70. The observations of the (13)C isotopic species provide us with rich information on chemical processes in cold interstellar clouds.

Accurate High-N Rest Frequencies for CO+, an Ideal Tracer of Photon-Dominated Regions

The submillimeter-wave rotational spectra of CO(+), (13)CO(+) and C(18)O(+) in the v = 0 and 1 vibrational states were measured through a hollow cathode dc discharge in a cryogenic cell cooled to liquid nitrogen temperature. In addition, a few transitions of the main isotopic species have been measured between 1.1 and 1.3 THz. An updated isotopically invariant fit, including Born-Oppenheimer breakdown corrections, is presented: the derived set of independent molecular parameters, valid for all the isotopologues of the molecule included in the fit, allows to predict the rotational spectrum with calculated 1σ uncertainty of 280 kHz at 2 THz.

Millimeter-Wave Spectroscopy of S2Cl2: A Candidate Molecule for Measuring Ortho–Para Transition

S2Cl2 is a candidate for the observation of ortho-para transition. To estimate the ortho-para mixing in a hyperfine-resolved rotational state, pure rotational transitions were measured by millimeter-wave (mm-wave) spectroscopy using two different experimental set-ups. The transitions from the term value around 20 K was measured with a supersonic jet and those around 200 K were measured with a dry ice cooled gas cell. Several hundred peaks were assigned for the naturally abundant S2(35)Cl2 and S2(35)Cl(37)Cl isotopic species and the rotational molecular parameters including the fourth-order and sixth-order centrifugal distortion constants were determined. The hyperfine structures were partly resolved in some Q-branch transitions, which were well described with the hyperfine constants determined by FTMW spectroscopy in the centimeter-wave region. With the new rotational constants determined in our study and the previous hyperfine constants, it will be possible to obtain a more reliable ortho-para mixing ratio and to narrow down the possible candidate transitions in the mm-wave region for the observation of ortho-para transition.

Ab initio potential energy surface and predicted rotational spectra for the Ne–H2O complex

A new three-dimensional potential energy surface for the Ne-H2O complex was calculated using the coupled-cluster singles and doubles with noniterative inclusion of connected triples [CCSD(T)] with a large basis set supplemented with bond functions. The interaction energies were obtained by the supermolecular approach with the full counterpoise correction for the basis set superposition error. The CCSD(T) potential was found to have a planar T-shaped global minimum, two first-order saddle points, and a second-order saddle point. The global minimum is located at R = 3.23 Å, θ = 101.4°, and φ = 0.0° with a well depth of 64.14 cm(-1). The radial discrete variable representation∕angular finite basis representation method and the Lanczos algorithm were employed to calculate the rovibrational energy levels for four isotopic species (20)Ne-H2 (16)O, (22)Ne-H2 (16)O, (20)Ne-H2 (17)O, and (20)Ne-H2 (18)O. Rotational spectra within two internal rotor states, namely, the Σ(000) and Σ(101) states, were predicted. The average structural parameters of four Ne-H2O isotopomers on the two states were also calculated and analyzed.

Controlling the group velocity of colliding atomic Bose-Einstein condensates with Feshbach resonances

We report on a proposal to reduce the group velocity of a small ``laser'' Bose-Einstein condensate upon passing through a larger ``medium'' condensate of the same isotopic species in analogy to slowing of light passing through dispersive media. We make use of ultracold collisions near a magnetic Feshbach resonance, which gives rise to a sharp variation in scattering length with collision energy and thereby changes the group velocity. A generalized Gross-Pitaevskii equation is used to derive an expression for the group velocity in a homogeneous medium as well as for the spatial delay $\ensuremath{\delta}$, through a finite-sized medium BEC with a Thomas-Fermi density distribution. We predict a maximum reduction of the group velocity by a half, which physically corresponds to freely propagating Feshbach molecules. For typical narrow Feshbach resonances and a medium with number density ${10}^{15}$ cm${}^{\ensuremath{-}3}$, up to $85%$ of the lower bound can be achieved, making the effect experimentally observable. We also derive constraints on the experimental realization of our proposal.

Broadband Fourier transform rotational spectroscopy for structure determination: The water heptamer

Over the recent years chirped-pulse, Fourier-transform microwave (CP-FTMW) spectrometers have changed the scope of rotational spectroscopy. The broad frequency and large dynamic range make possible structural determinations in molecular systems of increasingly larger size from measurements of heavy atom (13C, 15N, 18O) isotopes recorded in natural abundance in the same spectrum as that of the parent isotopic species. The design of a broadband spectrometer operating in the 2–8GHz frequency range with further improvements in sensitivity is presented. The current CP-FTMW spectrometer performance is benchmarked in the analyses of the rotational spectrum of the water heptamer, (H2O)7, in both 2–8GHz and 6–18GHz frequency ranges. Two isomers of the water heptamer have been observed in a pulsed supersonic molecular expansion. High level ab initio structural searches were performed to provide plausible low-energy candidates which were directly compared with accurate structures provided from broadband rotational spectra. The full substitution structure of the most stable species has been obtained through the analysis of all possible singly-substituted isotopologues (H218O and HDO), and a least-squares rm(1) geometry of the oxygen framework determined from 16 different isotopic species compares with the calculated O–O equilibrium distances at the 0.01Å level.

Lyman-α photodesorption from CO2(ice) at 75 K: Role of CO2 vibrational relaxation on desorption rate

The photodesorption of CO2 from CO2(ice) at 75 K when irradiated by Lyman-α light is strongly mediated by vibrational relaxation of highly vibrationally excited molecules produced from the electronically excited CO2 state. A vibrationally hot molecule can either relax (major process) in the ice or desorb (minor process). We find that isotopically pure CO2 ices photodesorb least efficiently due to efficient vibrational tuning between molecules in the ice. Isotopically impure CO2 ices are more poorly vibrationally relaxed and hence photodesorb more efficiently. Mixed CO2-Xe ices are still more efficiently photodesorbed due to the dilution of CO2, which further reduces the rate of vibrational relaxation. Resonant interactions as well as phonon-assisted interactions contribute to vibrational relaxation efficiency in ices, and inversely to photodesorption efficiency. The vibrational lifetime of hot CO2 in its ice at 75 K is of order of 10(-15) s. These results indicate that under astronomical conditions, the rate of photodesorption will depend inversely on the rate of vibrational quenching in the ice, which is dependent on the abundance and distance of like oscillators from each other in the ice. In rather isotopically pure ices, the minority isotopic species will photodesorb more rapidly.

Theoretical Study of Triatomic Systems Involving Helium Atoms

The triatomic 4He system and its isotopic species \({^4{\rm He}_2^3{\rm He}}\) are theoretically investigated. By adopting the best empirical helium interaction potentials, we calculate the bound state energy levels as well as the rates for the three-body recombination processes: 4He + 4He + 4He → 4 He2 + 4He and 4He + 4He + 3He → 4He2 + 3He. We consider not only zero total angular momentum J = 0 states, but also J > 0 states. We also extend our study to mixed helium-alkali triatomic systems, that is 4He2X with X = 7Li, 23Na, 39K, 85 Rb, and 133Cs. The energy levels of all the J ≥ 0 bound states for these species are calculated as well as the rates for three-body recombination processes such as 4He + 4He + 7Li → 4 He2 + 7Li and 4He + 4He + 7Li → 4 He7Li + 4He. In our calculations, the adiabatic hyperspherical representation is employed but we also obtain preliminary results using the Gaussian expansion method.

Rotation and Rotation–Vibration Spectroscopy of the 0+–0– Inversion Doublet in Deuterated Cyanamide

The pure rotation spectrum of deuterated cyanamide was recorded at frequencies from 118 to 649 GHz, which was complemented by measurement of its high-resolution rotation-vibration spectrum at 8-350 cm(-1). For D2NCN the analysis revealed considerable perturbations between the lowest Ka rotational energy levels in the 0(+) and 0(-) substates of the lowest inversion doublet. The final data set for D2NCN exceeded 3000 measured transitions and was successfully fitted with a Hamiltonian accounting for the 0(+) ↔ 0(-) coupling. A smaller data set, consisting only of pure rotation and rotation-vibration lines observed with microwave techniques was obtained for HDNCN, and additional transitions of this type were also measured for H2NCN. The spectroscopic data for all three isotopic species were fitted with a unified, robust Hamiltonian allowing confident prediction of spectra well into the terahertz frequency region, which is of interest to contemporary radioastronomy. The isotopic dependence of the determined inversion splitting, ΔE = 16.4964789(8), 32.089173(3), and 49.567770(6) cm(-1), for D2NCN, HDNCN, and H2NCN, respectively, is found to be in good agreement with estimates from a simple reduced quartic-quadratic double minimum potential.

An investigation of the structure and large amplitude motions in the CH2F2⋯CO2 weakly bound dimer

The rotational spectrum of the weakly bound dimer CH2F2⋯CO2 has been measured using chirped-pulse and resonant cavity Fourier-transform microwave spectrometers in the frequency range 7–15GHz. Spectra for six isotopic species have allowed a determination of the structure for this complex, in which the fluorine atoms of the CH2F2 straddle the CO2 subunit with a C⋯CO angle of 71.3(4)°, and an M⋯C⋯C angle of ∼38° (where M is the center of mass of CH2F2). A doubling of all rotational transitions has been ascribed to rocking of the CH2F2 subunit between two equivalent positions via a C2v transition state, and this motion inverts the μc dipole moment component of the dimer. Analysis of the tunneling splittings with a coupled Hamiltonian gives an energy difference between the 0+ and 0− vibrational states of 115.1402(24) MHz in the parent isotopologue and use of a flexible 1-dimensional model provides an estimated barrier for this motion of ∼137(14) cm−1. Observed dipole moment components (μa=1.513(6) D, μb=0 D, μc=1.259(3) D, μtot=1.968(7) D) are consistent with the observed structure and with ab initio predictions.

Deuteration effect on the NH/ND stretch band of the jet-cooled 7-azaindole and its tautomeric dimers: Relation between the vibrational relaxation and the ground-state double proton-transfer reaction

Infrared spectra of NH and ND stretch bands of the 7-azaindole (7-AI) dimer and its tautomeric dimer are observed to investigate a deuteration effect on the spectra and also a ground-state double proton-transfer (DPT) reaction. We examined the three isotopic species for each dimers; undeuterated one (NH–NH) and one or two hydrogen atom(s) of the NH groups is deuterated ones (NH–ND and ND–ND, respectively). It is found that the ND stretch band profiles of the NH–ND and ND–ND tautomeric dimers are very similar with each other. This result is very distinct from the result of the comparison of the NH stretch band profiles of the NH–NH and NH–ND dimers in our previous paper. For a further discussion, we examined the deuteration effect in the case of the 7-AI dimer. It is found that band profiles of the NH stretch of the NH–NH and the NH–ND dimers and also the ND stretch of the NH–ND and the ND–ND dimers exhibit similar patterns, respectively. These facts indicates that the vibrational relaxation from the NH/ND stretch level of the dimer basically proceed within a monomer unit. The large deuteration effect of the NH stretch band profile observed previously is found to be characteristic of the tautomeric dimer. This behavior is related to a large anharmonicity of the potential energy surface originating from an existence of the double-proton transfer reaction barrier.

Determination of Inorganic Antimony Species Conversions during Its Speciation Analysis in Soil Using Isotope Dilution Techniques

A new method was developed in this work to account for inorganic Sb species interconversion during soil sample preparation and subsequent separation steps. The Sb(III) and Sb(V) concentrations at each investigated step in the analytical procedure were determined using species specific spikes (121Sb(III) with 81.18% and 123Sb(V) with 74.04% enrichment). The spiking of these enriched isotopes species solutions was done separately before soil sample extraction and before HPLC separation. Simply by subtracting the final concentration of each species done by on-line isotope dilution (ID) from its concentration at different stages of the analytical procedure done by species specific ID, the influence of each step on species transformation can be estimated. After optimization, the extraction procedure for inorganic Sb species 6% Sb(III) (1.3 RSD, n = 3) and 43.2% Sb(V) (2.9% RSD, n = 3) as percent of total Sb were detected in the examined soil sample using online ID. Using the above described methodology we found that there was no reduction of Sb(V) to Sb(III) during sample preparation or species separation. While about 9.3% of extractable Sb (4.6% of total) was converted from Sb(III) to Sb(V) during the extraction step, no conversion during HPLC separation step was observed. By compensating for Sb(III) transformation during the sample preparation step; the extractable Sb(III) and Sb(V) as percent of total Sb yielded 10.6% and 38.7%, respectively.

Effect of aromatic ring fluorination on CH⋯π interactions: rotational spectrum and structure of the fluorobenzene⋯acetylene weakly bound dimer

The rotational spectra for the normal isotopic species and for six (13)C singly substituted isotopologues (in natural abundance) of the fluorobenzene···acetylene (C6H5F···HCCH) weakly bound dimer have been measured in the 6.5-18.5 GHz region using chirped-pulse Fourier-transform microwave spectroscopy. The HCCH molecule interacts with the fluorobenzene via a CH···π contact and is determined to lie almost over the center of, and approximately perpendicular to, the aromatic ring, with an H···π distance (perpendicular distance from the H atom to the ring plane) of around 2.492(47) Å; a slight tilt of HCCH towards the para carbon atom of the fluorobenzene is evident. Binding energies of this complex and related benzene and fluorobenzene dimers obtained from the pseudodiatomic approximation are compared and indicate that fluorobenzene···acetylene lies among the more weakly bound of the complexes exhibiting some type of CH···π interaction.

A new ab initio intermolecular potential energy surface and predicted rotational spectra of the Kr−H2O complex

We report a new three-dimensional ab initio intermolecular potential energy surface for the Kr-H(2)O complex with the H(2)O monomer fixed at its experimental averaged structure. Using the supermolecular approach, the intermolecular potential energies were evaluated at the coupled-cluster singles and doubles level with noniterative inclusion of connected triples with the full counterpoise correction for the basis set superposition error and a large basis set including bond functions. The global minimum corresponding to a planar H-bond configuration was located at the intermolecular distance of 3.82 Å with a well depth of 169.98 cm(-1). In addition, two first-order and one second-order saddle points were also identified. The combined radial discrete variable representation∕angular finite basis representation method and the Lanczos algorithm were employed to calculate the rovibrational energy levels for 16 isotopic species of the Kr-H(2)O complexes. The rotational transition frequencies, structure parameters, and nuclear quadrupole coupling constants were also determined for the ground and first intermolecular vibrational excited states and are all in good agreement with the available experimental values.

Stable isotope values (δ18O & δ13C) of multiple ostracode species in a large Neotropical lake as indicators of past changes in hydrology

Modern lake hydrodynamics, ostracode species autecology, stable isotopes (δ18O and δ13C) of multiple ostracode species, ostracode taphonomy and sediment geochemistry were studied to improve interpretation of the late Pleistocene–early Holocene (∼24–10 ka) stable isotope record of ostracodes in sediment core PI-6 from Lago Petén Itzá, northern Guatemala. Oxygen and carbon stable isotopes in modern and fossil species assemblages of Lago Petén Itzá were used as indicators of changes in the balance between evaporation and precipitation, past lake level and carbon source. Ostracode taphonomy was used to detect past periods of strong currents, high-energy environments, and possible partial or full mixing of the lake. The modern lake water isotopic composition displays clear seasonal differences that are independent of lake level fluctuations. Modern benthic species displayed lower δ18O and δ13C values than nektobenthic species, with differences of 3.0‰ and 5.3‰, respectively. Valves of nektobenthic species display higher values of δ13C because these ostracodes live in shallower environments among abundant algae and aquatic plants, where productivity is high. The benthic species Limnocythere opesta Brehm, 1939 displayed the smallest average offset from δ18O water (+0.3‰) and the largest offset from δ13CDIC values (−4.1‰) among studied ostracode species. Nektobenthic species Heterocypris punctata Keyser, 1975 displayed the smallest difference relative to the δ13CDIC values (−0.1‰).Late Pleistocene–early Holocene climate conditions and water levels in Lago Petén Itzá can be summarized as follows: 1) high lake levels and cold conditions (Last Glacial Maximum [LGM], ∼24–19 ka), 2) fluctuating lake levels and cold conditions (Heinrich Stadial 1 [HS1], ∼19–15 ka), 3) high lake levels and warm and wetter conditions (Bølling-Allerød [BA], ∼15–13 ka), 4) low lake levels and dry conditions (Younger Dryas [YD], ∼13–11.5 ka) and 5) high lake levels and warm and wetter conditions (early Holocene, ∼11.5–10.0 ka). Average lake level fluctuation in Lago Petén Itzá during the late Pleistocene–early Holocene was as much as ∼25 m. Ostracode analyses suggest that the LGM was characterized by relatively low δ18O (+4.7 to +6.0‰), and δ13C values (−7.1 to −6.4‰) in ostracode valves, high inferred water depths and high percentages of broken adult and juvenile valves (>66%), suggesting a high-energy environment, strong currents, partial to full mixing, downslope transport, colder water temperatures and wetter conditions. An increase in the relative abundance of the benthic species L. opesta and higher numbers of broken valves suggest heavy precipitation events during the LGM (∼23.7, 21.7, 20.8 and 20.1 ka). HS1 was predominantly dry, but we identified times when lake levels were slightly higher, at the onset of the deglacial and a brief period (∼17–16 ka) between HS1b and HS1a. All studied climate proxies indicate wetter and warmer conditions and lake system stability during the BA. Lake levels dropped during the YD and gradually increased during the Preboreal and early Holocene. We demonstrate that modern and fossil ostracode isotopic signatures, species assemblages and taphonomy can be used together with physical and geochemical variables in Lago Petén Itzá sediments to make high-resolution inferences about late Pleistocene–early Holocene environmental changes in the lowland Neotropics.