Browsing by Author "Yeung, Laurence Y."
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Item Atmospheric species concentrations and reaction rates relevant to N2 chemistry derived from WACCM-X model used in Yeung et al., Extreme enrichment in atmospheric 15N15N. Sci. Adv. 3, eaao6741 (2017)(Rice University, 2017) Yeung, Laurence Y.; Young, Edward D.; Earth, Environmental, and Planetary SciencesItem Clumped-Isotope Constraint on Upper-Tropospheric Cooling During the Last Glacial Maximum(Wiley, 2022) Banerjee, Asmita; Yeung, Laurence Y.; Murray, Lee T.; Tie, Xin; Tierney, Jessica E.; Legrande, Allegra N.Ice cores and other paleotemperature proxies, together with general circulation models, have provided information on past surface temperatures and the atmosphere's composition in different climates. Little is known, however, about past temperatures at high altitudes, which play a crucial role in Earth's radiative energy budget. Paleoclimate records at high-altitude sites are sparse, and the few that are available show poor agreement with climate model predictions. These disagreements could be due to insufficient spatial coverage, spatiotemporal biases, or model physics; new records that can mitigate or avoid these uncertainties are needed. Here, we constrain the change in upper-tropospheric temperature at the global scale during the Last Glacial Maximum (LGM) using the clumped-isotope composition of molecular oxygen trapped in polar ice cores. Aided by global three-dimensional chemical transport modeling, we exploit the intrinsic temperature sensitivity of the clumped-isotope composition of atmospheric oxygen to infer that the upper troposphere (effective mean altitude 10–11 km) was 6–9°C cooler during the LGM than during the late preindustrial Holocene. A complementary energy balance approach supports a minor or negligible steepening of atmospheric lapse rates during the LGM, which is consistent with a range of climate model simulations. Proxy-model disagreements with other high-altitude records may stem from inaccuracies in regional hydroclimate simulation, possibly related to land-atmosphere feedbacks.Item Effects of climate change on the movement of future landfalling Texas tropical cyclones(Springer Nature, 2020) Hassanzadeh, Pedram; Lee, Chia-Ying; Nabizadeh, Ebrahim; Camargo, Suzana J.; Ma, Ding; Yeung, Laurence Y.The movement of tropical cyclones (TCs), particularly around the time of landfall, can substantially affect the resulting damage. Recently, trends in TC translation speed and the likelihood of stalled TCs such as Harvey have received significant attention, but findings have remained inconclusive. Here, we examine how the June-September steering wind and translation speed of landfalling Texas TCs change in the future under anthropogenic climate change. Using several large-ensemble/multi-model datasets, we find pronounced regional variations in the meridional steering wind response over North America, but―consistently across models―stronger June-September-averaged northward steering winds over Texas. A cluster analysis of daily wind patterns shows more frequent circulation regimes that steer landfalling TCs northward in the future. Downscaling experiments show a 10-percentage-point shift from the slow-moving to the fast-moving end of the translation-speed distribution in the future. Together, these analyses indicate increases in the likelihood of faster-moving landfalling Texas TCs in the late 21st century.Item Experimental and modeling data used in Yeung et al., Extreme enrichment in atmospheric 15N15N. Sci. Adv. 3, eaao6741 (2017)(Rice University, 2017) Yeung, Laurence Y.; Young, Edward D.; National Science Foundation; Deep Carbon Observatory, Department of Energy; Earth, Environmental, and Planetary SciencesItem Extreme enrichment in atmospheric 15N15N(AAAS, 2017) Yeung, Laurence Y.; Li, Shuning; Kohl, Issaku E.; Haslun, Joshua A.; Ostrom, Nathaniel E.; Hu, Huanting; Fischer, Tobias P.; Schauble, Edwin A.; Young, Edward D.Molecular nitrogen (N2) comprises three-quarters of Earth’s atmosphere and significant portions of other planetary atmospheres. We report a 19 per mil (‰) excess of 15N15N in air relative to a random distribution of nitrogen isotopes, an enrichment that is 10 times larger than what isotopic equilibration in the atmosphere allows. Biological experiments show that the main sources and sinks of N2 yield much smaller proportions of 15N15N in N2. Electrical discharge experiments, however, establish 15N15N excesses of up to +23‰. We argue that 15N15N accumulates in the atmosphere because of gas-phase chemistry in the thermosphere (>100 km altitude) on time scales comparable to those of biological cycling. The atmospheric 15N15N excess therefore reflects a planetary-scale balance of biogeochemical and atmospheric nitrogen chemistry, one that may also exist on other planets.Item In Situ Quantification of Biological N2 Production Using Naturally Occurring 15N15N(American Chemical Society, 2019) Yeung, Laurence Y.; Haslun, Joshua A.; Ostrom, Nathaniel E.; Sun, Tao; Young, Edward D.; van Kessel, Maartje A.H.J.; Lücker, Sebastian; Jetten, Mike S.M.We describe an approach for determining biological N2 production in soils based on the proportions of naturally occurring 15N15N in N2. Laboratory incubation experiments reveal that biological N2 production, whether by denitrification or anaerobic ammonia oxidation, yields proportions of 15N15N in N2 that are within 1‰ of that predicted for a random distribution of 15N and 14N atoms. This relatively invariant isotopic signature contrasts with that of the atmosphere, which has 15N15N proportions in excess of the random distribution by 19.1 ± 0.1‰. Depth profiles of gases in agricultural soils from the Kellogg Biological Station Long-Term Ecological Research site show biological N2 accumulation that accounts for up to 1.6% of the soil N2. One-dimensional reaction-diffusion modeling of these soil profiles suggests that subsurface N2 pulses leading to surface emission rates as low as 0.3 mmol N2 m–2 d–1 can be detected with current analytical precision, decoupled from N2O production.Item Isotopic ordering in atmospheric O2 as a tracer of ozone photochemistry and the tropical atmosphere(Wiley, 2016) Yeung, Laurence Y.; Murray, Lee T.; Ash, Jeanine L.; Young, Edward D.; Boering, Kristie A.; Atlas, Elliot L.; Schauffler, Sue M.; Lueb, Richard A.; Langenfelds, Ray L.; Krummel, Paul. B.; Steele, L. Paul; Eastham, Sebastian D.The distribution of isotopes within O2 molecules can be rapidly altered when they react with atomic oxygen. This mechanism is globally important: while other contributions to the global budget of O2 impart isotopic signatures, the O(3P) + O2 reaction resets all such signatures in the atmosphere on subdecadal timescales. Consequently, the isotopic distribution within O2 is determined by O3 photochemistry and the circulation patterns that control where that photochemistry occurs. The variability of isotopic ordering in O2 has not been established, however. We present new measurements of 18O18O in air (reported as Δ36 values) from the surface to 33 km altitude. They confirm the basic features of the clumped-isotope budget of O2: Stratospheric air has higher Δ36 values than tropospheric air (i.e., more 18O18O), reflecting colder temperatures and fast photochemical cycling of O3. Lower Δ36 values in the troposphere arise from photochemistry at warmer temperatures balanced by the influx of high-Δ36 air from the stratosphere. These observations agree with predictions derived from the GEOS-Chem chemical transport model, which provides additional insight. We find a link between tropical circulation patterns and regions where Δ36 values are reset in the troposphere. The dynamics of these regions influences lapse rates, vertical and horizontal patterns of O2 reordering, and thus the isotopic distribution toward which O2 is driven in the troposphere. Temporal variations in Δ36 values at the surface should therefore reflect changes in tropospheric temperatures, photochemistry, and circulation. Our results suggest that the tropospheric O3 burden has remained within a ±10% range since 1978.Item Low oxygen and argon in the Neoproterozoic atmosphere at 815 Ma(Elsevier, 2017) Yeung, Laurence Y.The evolution of Earth's atmosphere on >106-yr timescales is tied to that of the deep Earth. Volcanic degassing, weathering, and burial of volatile elements regulates their abundance at the surface, setting a boundary condition for the biogeochemical cycles that modulate Earth's atmosphere and climate. The atmosphere expresses this interaction through its composition; however, direct measurements of the ancient atmosphere's composition more than a million years ago are notoriously difficult to obtain. Gases trapped in ancient minerals represent a potential archive of the ancient atmosphere, but their fidelity has not been thoroughly evaluated. Both trapping and preservation artifacts may be relevant. Here, I use a multi-element approach to reanalyze recently collected fluid-inclusion data from halites purportedly containing snapshots of the ancient atmosphere as old as 815 Ma. I argue that those samples were affected by the concomitant trapping of air dissolved in brines and contaminations associated with modern air. These artifacts lead to an apparent excess in O2 and Ar. The samples may also contain signals of mass-dependent fractionation and biogeochemical cycling within the fluid inclusions. After consideration of these artifacts, this new analysis suggests that the Tonian atmosphere was likely low in O2, containing ≤10% present atmospheric levels (PAL), not ∼50% PAL as the data would suggest at face value. Low concentrations of O2 are consistent with other geochemical constraints for this time period and further imply that the majority of Neoproterozoic atmospheric oxygenation occurred after 815 Ma. In addition, the analysis reveals a surprisingly low Tonian Ar inventory—≤60% PAL—which, if accurate, challenges our understanding of the solid Earth's degassing history. When placed in context with other empirical estimates of paleo-atmospheric Ar, the data imply a period of relatively slow atmospheric Ar accumulation in the Paleo- and Meso-Proterozoic, followed by extensive degassing in the late Neoproterozoic or early Cambrian, before returning to a relatively quiescent state by the Devonian. This two-step structure resembles that for the evolution of atmospheric O2, hinting at a common driving force from the deep Earth. Some caution is warranted, however, because still more enigmatic contaminations than the ones presented here may be relevant. Gases trapped in minerals may offer important constraints on the evolution of Earth's surface, climate, and atmosphere, but potential contaminations and other confounding factors need to be considered carefully before these records can be considered quantitative.Item Marine carbonate accumulation during the greenhouse climate of the Eocene(2021-04-28) Bhattacharya, Joyeeta; Yeung, Laurence Y.Major climatic transitions and aberrations accompanied by global carbon cycle perturbations are known to have occurred during the Eocene epoch, between 56-34 Ma. The warmest interval of the Cenozoic culminated during early Eocene, punctuated by multiple events of rapid injection of isotopically light carbon into the ocean-atmosphere system, e.g. Paleocene Eocene Thermal Maximum (PETM), ca. 56 Ma, which were preserved as negative carbon isotope excursions (CIEs) in the sedimentary record. The hothouse climate of early Eocene transitioned to a relatively cooler and less explored ‘warmhouse’ regime during middle-late Eocene, when multiple transient warming events occurred, which were at times associated with significant fluctuations in the oceanic carbonate saturation horizons. This study documents changes in carbonate dissolution indices and carbonate mass accumulation rate through the entire Eocene (56–34 Ma) at ODP Site 1209 on Shatsky Rise, north-central Pacific and ties it to a stable carbon and oxygen isotope record, which is stratigraphically correlated with the global benthic stack and equatorial Pacific CCD reconstruction of the Eocene, in order to explore the links between climate change, carbon cycling and marine carbonate accumulation. Our study finds a strong correlation between magnitude of CIEs and intensity of dissolution for early Eocene hyperthermal events which appears to significantly weaken for multiple dissolution events in middle-late Eocene, possibly indicating fundamental difference in their causal mechanism. As this study and multiple others in paleoceanography utilize bulk sediment carbon isotope (δ13C) records in Cenozoic chemostratigraphy; it is crucial to deconvolute the isotope signal of marine bulk sediments. Pelagic carbonates are ensemble of different components of varying proportion and distinct isotope composition; hence spatial and temporal co-variation of pelagic carbonate constituents is important to understand in order to make a comprehensive interpretation of bulk-δ13C records. In this part of the study, sediments from the late Paleocene-early Eocene interval (58-50 Ma), at ODP Site 1209 are dissected into size fractions to investigate how a temporally varying bulk carbonate ensemble influences the overall carbon isotope record. A set of 45 samples were examined for their bulk and size-fraction-specific δ13C and δ18O compositions. We find a significant increase in coarse-fraction abundance across PETM, driven by a changing community structure of calcifiers, modulating the size of CIE at Site 1209 and thus making it distinct from those recorded at other open-marine sites. These results highlight the importance of biogeography in marine stable-isotope record, especially when isotope excursions are driven by climate- and/or carbon-cycle changes. In addition, community composition changes will alter the interpretation of weight percent coarse fraction as a conventional proxy for carbonate dissolution. The next part of the work focusses on chemostratigraphy of the Lutetian-Bartonian stages of middle Eocene from sites on Tasman Sea, in the southwest Pacific, which represent a ‘warmhouse’ climate state: a transition from supergreenhouse/hothouse climate of early Eocene to the onset of polar glaciation and ‘coolhouse’ climate of Oligocene. Despite long-term cooling conditions in the background, middle Eocene was punctuated by at least one significant global warming and sea-floor carbonate dissolution event, referred to as the Middle Eocene Climate Optimum (MECO), ca. ~40.5 Ma. Over the last decade, studies from the Atlantic deep ocean sites have identified at least one other brief event of carbon cycle perturbation, during polarity chron 19R; referred to as Late Lutetian Thermal Maximum (LLTM). But its global extent remains unresolved. Our current work develops a stable isotope stratigraphy of middle Eocene sediments, precisely within the late Lutetian – early Bartonian stages from four different sites across Tasman Sea, two of which were drilled during IODP Expedition 371 (U1508C and U1509A) and two of which derive from field work in New Caledonia (the Sommet-Khian outcrop and the Cadart drill core). Here we identify long-term changes in carbon and oxygen isotope records, possibly related to 405 Ky eccentricity cycles; and present a δ13C-stratigraphic framework for the Tasman sea geochemical record in context of the global benthic stack. We also document the occurrence of LLTM (both in open- and marginal marine setting), which constitutes its first evidence from the Pacific, and hence corroborates its globally widespread occurrence. Also, we find the occurrence of MECO at Site U1509, consistent with its expression in the Southern Ocean. A positive carbon and oxygen isotope excursion along with emergence of pure carbonate system is documented in New Caledonia within NP16 biozone of middle Eocene; however, its global relevance remains elusive because of lack of reliable age datum. Ultimately this study provides evidence for a dynamic climate in middle Eocene and shows that marine sedimentary carbon isotopes constitute a robust and reliable tool for Cenozoic chemostratigraphic correlation.Item Stable isotope (C, N, O, and H) study of a comprehensive set of feathers from two Setophaga citrina(Public Library of Science, 2021) Deme, Samiksha; Yeung, Laurence Y.; Sun, Tao; Lee, Cin-Ty A.Oxygen, hydrogen, carbon and nitrogen stable isotopes were measured on a comprehensive sampling of feathers from two spring Hooded Warblers (Setophaga citrina) in Texas to evaluate isotopic variability between feathers and during molt. Isotopic homogeneity within each bird was found across all four isotopic systems, supporting the hypothesis that molt in these neotropical migrants is fully completed on the breeding grounds. This homogeneity suggests that the isotopic composition of a single feather is may be representative of the whole songbird. However, each bird was found to have one or two outlier feathers, which could signify regrowth of lost feathers after prebasic molt.Item Tracing oxygen cycling in the ocean by dissolved oxygen multi-isotopologues(2021-12-03) Li, Boda; Yeung, Laurence Y.Understanding the distribution and cycling of O2 is one of the core scientific questions in oceanography. The distribution of dissolved oxygen is influenced by physical, biochemical, and abiotic chemical processes. However, determining the relative importance of each mechanism in different environments remains difficult. This thesis utilizes the dissolved oxygen multiple isotopologues (16O16O, 16O17O, 16O18O, 17O18O, 18O18O), which participate biogeochemical cycling, advection, and diffusion as new direct tracers to constrain these processes. The theme of my first project is the oxygen production in the surface ocean, with a particular focus on the isotopic effects of gas exchange when the mixed layer is out of solubility equilibrium. Here we measured the kinetic and equilibrium fractionation factors for the four rare O2 isotopologues 16O17O, 16O18O, 17O18O, 18O18O relative to 16O16O in air-water gas transfer experiments. Moreover, we evaluate the possible effects of the updated fractionation factors on multiple isotopologue-based gross oxygen production (GOP) estimates and connect the observed air-water kinetic fractionation factors to dissolved-phase diffusive isotopic fractionation. Next, this thesis shifts the focus to the subsurface ocean, where uncertainties in transport flux and isotopic fractionation factors have long confounded the interpretation of the isotopic composition of dissolved oxygen. Therefore, we investigated the systematics of oxygen isotopologues in the subsurface Pacific using new data and a 2-D isotopologues-enabled isopycnal reaction-transport model. We measured multiple O2 isotopologues in the northeast Pacific, and compared them to previously published data. We find that transport and respiration rates constrained by O2 concentrations in the oligotrophic Pacific yield good measurement-model agreement across all O2 isotopologues when using a recently reported set of respiratory isotopologue fractionation factors. Estimated respiration rates range from 0.5 to 2.7 μmol/kg/yr for various isopycnal surfaces consistent with those previously inferred for the Atlantic. Lastly, this thesis attempts to address the mystery of puzzlingly low 17O/16O ratios observed for some subsurface low-oxygen samples. We resampled and remeasured the dissolved oxygen isotopologues at the San Pedro Ocean Time Series (SPOT) site, where low 17O/16O ratios were reported in previous studies. We find that this low ratio is caused by a typical analytical artifact, pressure baseline effect (PBE), which exhibits a non-linear behavior with the fraction of inert gas present in the analyte and can cause an overestimation of GOP at SPOT. A correction on these previously reported low 17O/16O ratios were applied to the GOP estimation model, in which we find that calculated GOP at SPOT can be overestimated by ~50 mmol O2/(m2d). Therefore, we underscore the necessity of a pre-purification process for insert gas removal during dissolved oxygen isotope measurements to avoid this potential PBE artifact.Item Tropospheric Ozone During the Last Interglacial(Wiley, 2022) Yan, Yuzhen; Banerjee, Asmita; Murray, Lee T.; Tie, Xin; Yeung, Laurence Y.The history of tropospheric O3, an important atmospheric oxidant, is poorly constrained because of uncertainties in its historical budget and a dearth of independent records. Here, we estimate the mean tropospheric O3 burden during the Last Interglacial period (LIG; 115 to 130 thousand years ago) using a record of the clumped isotopic composition of O2 (i.e., Δ36 values) preserved in Antarctic ice. The measured LIG Δ36 value is 0.03 ± 0.02‰ (95% CI) higher than the late pre-industrial Holocene (PI; 1,590–1,850 CE) value and corresponds to a modeled 9% reduction in LIG tropospheric O3 burden (95% CI: 3%–15%), caused in part by a substantial reduction in biomass burning emissions during the LIG relative to the PI. These results are consistent with the hypothesis that late-Pleistocene megafaunal extinctions caused woody and grassy fuels to accumulate on land, leading to enhanced biomass burning in the preindustrial Holocene.