Stable isotope potential of Northern Vietnam stalagmites: A 51-cave survey with the Hendy test and U/Th analysis

Research Article| November 01, 2015 Are aragonite stalagmites reliable paleoclimate proxies? Tests for oxygen isotope time-series replication and equilibrium Matthew S. Lachniet Matthew S. Lachniet † Department of Geoscience, University of Nevada–Las Vegas, 4505 S. Maryland Parkway, Las Vegas, Nevada 89154, USA †matthew.lachniet@unlv.edu Search for other works by this author on: GSW Google Scholar Author and Article Information Matthew S. Lachniet † Department of Geoscience, University of Nevada–Las Vegas, 4505 S. Maryland Parkway, Las Vegas, Nevada 89154, USA †matthew.lachniet@unlv.edu Publisher: Geological Society of America Received: 07 Jul 2014 Revision Received: 15 Feb 2015 Accepted: 18 Mar 2015 First Online: 08 Mar 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 © 2015 Geological Society of America GSA Bulletin (2015) 127 (11-12): 1521–1533. https://doi.org/10.1130/B31161.1 Article history Received: 07 Jul 2014 Revision Received: 15 Feb 2015 Accepted: 18 Mar 2015 First Online: 08 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Matthew S. Lachniet; Are aragonite stalagmites reliable paleoclimate proxies? Tests for oxygen isotope time-series replication and equilibrium. GSA Bulletin 2015;; 127 (11-12): 1521–1533. doi: https://doi.org/10.1130/B31161.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract The use of aragonite stalagmites as paleoclimate proxies has become increasingly common because of their often exceptional uranium-series dating precision and fast growth rates, which allow near-annual climate resolution. However, aragonite is known to be susceptible to open-system behavior and may recrystallize to calcite under typical cave conditions. As a result, the fidelity of the oxygen isotopic variations preserved in aragonite stalagmites is not yet as firmly established as for calcite stalagmites, and few studies have investigated oxygen isotope replication and equilibrium with cave drip waters. I present new data and review findings from the literature that show that aragonite stalagmites may pass both the equilibrium and replication tests in some cases, but that other aragonites are clearly precipitated out of equilibrium with cave drip waters. As a case study, δ18O data for three exceptionally well-dated stalagmites from Juxtlahuaca Cave, Mexico, are presented. Two of the stalagmites are aragonite, and the third was measured on a diagenetically calcitized aragonite stalagmite. These results show that the modern aragonite precipitates in apparent oxygen isotopic equilibrium with drip waters, and the two aragonite speleothems replicate strongly over the past 530 yr, thus confirming a common paleoclimate signal. Observations of δ18O systematics in previously published aragonite stalagmite δ18O records from China and Belize show that at least two samples clearly precipitated modern aragonite out of isotopic equilibrium with cave drip waters. Because the equilibrium test only applies to modern precipitation for which temperature and drip-water δ18O values are known, both equilibrium and replication tests are required for confident interpretation of aragonite stalagmite δ18O time series, and studies that fail or do not attempt such tests should be considered cautiously. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Oxygen isotopic fractionation between drip water and speleothem calcite: A 10-year monitoring study, central Texas, USA

The assumption of oxygen isotope and major element equilibrium during prograde metamorphism was tested using staurolite‐grade pelitic schists that have undergone sequential porphyroblast growth and multiple episodes of recrystallization of matrix minerals and foliation development. Textural relationships are used to infer a metamorphic history that involves garnet growth followed by staurolite growth, with each porphyroblast growth event followed by at least one period of recrystallization of matrix minerals. Conventional geothermobarometry using Qtz–Grt–Pl–Ms–Bt ± St equilibria yields peak P–T conditions of c. 625 °C at 9–11 kbar, consistent with KMnFMASH petrogenetic grid predictions for stability of the assemblage Grt + St + Bt. Qtz–Grt oxygen isotope fractionations yield apparent temperatures of c. 590 °C and Qtz–St fractionations yield an apparent temperature of c. 595 °C. Diffusional modelling indicates that quartz isotopic compositions were reset by c. 30 °C via retrograde isotopic diffusional exchange with micas. The isotopic temperatures appear to be in excellent agreement with one another, and suggest oxygen isotope equilibrium was attained between garnet and staurolite at c. 625 °C. However, the agreement of Qtz–Grt and Qtz–Str isotopic temperatures is not consistent with petrographic observations (garnet grew before staurolite) and petrogenetic grid constraints that predict that garnet grows over a temperature interval of c. 525–550 °C. Given that: (i) oxygen diffusion rates in staurolite and garnet are slow enough to render an individual porphyroblast effectively closed to exchange after it forms; and (ii) matrix minerals are able to exchange isotopes via recrystallization during each period of deformation; garnet and staurolite could not have simultaneously achieved oxygen isotope equilibrium with each other or with minerals in the recrystallized matrix. Thus, the Qtz–Grt fractionations, which yield apparent temperatures that are in apparent agreement with peak metamorphic temperature and apparent temperatures for Qtz–St fractionations, cannot be fractionations resulting from equilibrium isotopic exchange. Instead, they are apparent fractionations between porphyroblasts formed at different temperature and times in the prograde P–T–D path, and quartz that recrystallized and exchanged with micas and plagioclase during several phases of deformation.

δ18O and δ13C values of modern brachiopod shells

The Kendrick brachiopods of Pennsylvanian age secreted low-Mg calcite shells with average SR2+ content of 1,140 ppm. The crinoids and rugose corals secreted intermediate-Mg calcite skeletons with average Sr2+ contents of 2,140 ppm and 1,770 ppm, respectively. Conversely, the Kendrick mollusks secreted aragonite shells which contain less than 1,000 ppm Mg2+. However, the average Sr2+ content (4,040 ppm for the cephalopods, 5,210 ppm for the gastropods, and 4,840 ppm for the pelecypods) is higher by a factor of about 2 over the average Sr2+ content of their Holocene counterparts. The brachiopods, gastropods, and pelecypods precipitated calcium carbonate in oxygen (average -4.5 ppt, ^dgr18O, PDB) and carbon (average +1.7 ppt, ^dgr13C, PDB) isotopic equilibrium with ambient Pennsylvanian seawater. The crinoids and rugose corals are light in both ^dgr13C and ^dgr18O by about 5 ppt, relative to isotopic equilibrium values. This isotopic depletion, as in the crinoids' modern counterparts, probably relates to the incorporation of isotopically light metabolic oxygen and carbon at the site of calcification. In contrast, the Kendrick cephalopods apparently precipitated shell aragonite in oxygen isotopic (-4.5 ppt) equilibrium with ambient seawater, whereas their carbon isotopic composition (+0.5 to -5.4 ppt) is controlled pos ibly by kinetic effects. The Fe2+ and Mn2+ contents of the fossil allochems and shale suggest that Kendrick seawater was slightly euxinic. In addition, the Na2+ content and oxygen isotopic composition indicate a slightly higher water temperature and hyposalinity for Kendrick seawater. Diagenetic alteration is limited to occlusion of pore spaces in the fossils and to compaction and cementation of the shale. This process probably occurred in the marine and/or submarine environment. End_of_Article - Last_Page 552------------

Oxygen isotopes in calcite grown under cave-analogue conditions

Sulfur isotopic effects in the disproportionation reaction of sulfur dioxide in hydrothermal fluids: implications for the δ34S variations of dissolved bisulfate and elemental sulfur from active crater lakes

The study of modern cave deposits forming under near isotopic equilibrium conditions can potentially help disentangle the processes influencing the oxygen isotope system and suitability of stalagmites as archives of past hydrological or thermal changes. We used cave monitoring to evaluate the impact of kinetic isotope fractionation and assess the conditions under which modern cave carbonates form in the Caumont cave and quarry system, located in Normandy, northwest France. Over 20 months, we collected climatological data, dripwater, and modern carbonate samples at 2–4-week intervals at three different stations inside the Caumont cave and quarry system. We find highly stable (10.4 ± 0.3°C – 11.3 ± 0.1°C) temperature in the deeper sections of the Caumont cave and quarry system. The temporal dynamics of δ18Odrip indicates that the drip water composition in Caumont reflects the original (though subdued) signal of precipitation, rather than the impact the seasonal to interannual cave air temperature has on isotopic fractionation. The monitoring reveals that δ13C of modern carbonate is influenced by prior carbonate precipitation that occurs during the summer season when evapotranspiration can minimize effective infiltration. Comparison of δ18O from dripwater and modern calcite, precipitated on glass plates and collected every two to four weeks, reveals that modern calcite forms near oxygen isotope equilibrium. A Hendy test on modern carbonate deposited on a stalagmite-shaped glass flask over 20 months confirms this finding because neither does δ13C increase with distance from the apex, nor are δ13C and δ18O positively correlated. We conclude that the δ13C signal in speleothems reflect summer (and longer-term) prior carbonate precipitation in response to effective infiltration dynamics, and that the δ18O signal likely reflects annual to multi-annual changes in the composition of precipitation above the cave.

Rapid isotopic equilibration, 16O2+18O2⇌ 216O18O, was observed upon contacting an equimolar mixture of (16O2+18O2) at 295 or 77 K with oxygen-deficient surfaces of pure and doped zinc oxides from which light was excluded at all stages. Kinetic expressions for opposing second-order reactions accurately described variations in mole fraction of 16O2, 16O18O and 18O2 in the gas phase during the approach to full isotopic equilibration at 295 or 77 K. Rate constants thereby derived for this R0-type exchange did not correlate with reported concentrations of conduction-band electrons for the zinc oxides, indicating that the rate-determining process for exchange was not collective-electron type charge transfer at the oxygen-deficient surfaces in the absence of illumination. Surfaces could be rendered inactive by extensive preoxidation in 16O2 at 650 K in the dark, but heating for 2 h periods in the dark under continuous evacuation restored activity to a progressively increasing extent at temperatures of 400–650 K. Preadsorption of H2O, H2 or (CH3)2CHOH at 295 K strongly inhibited activity. An explanation of the observed results is developed based on: (i) dissociative chemisorption at e–|Zncus sites on the oxygen-deficient surfaces; (ii) formation of triatomic oxygen surface intermediates; (iii) equilibration by reversible second-order reactions of O2 with these triatomic oxygen intermediates.

A critical question in radiometric dating of metamorphic rocks is whether minerals used to define internal isochrons have achieved isotopic equilibrium during a given metamorphic event, followed by preservation of the equilibrium afterward. A garnet peridotite at Zhimafang in the Sulu terrane of eastern China shows incongruent U-Pb, Rb-Sr, and Sm-Nd ages. Zircon SHRIMP U-Pb dating yielded an isochron age of 224 ± 8 Ma, pointing to zircon growth during Triassic UHP metamorphism. Two mineral assemblages gave consistent Rb-Sr internal isochron ages of 201 ± 4 and 205 ± 4 Ma, but much older Sm-Nd internal isochron ages of 376 ± 16 and 378 ± 24 Ma. Apparently, the Sm-Nd radiometric system fails to reequilibrate among the dated minerals during the Triassic UHP metamorphic event for the garnet peridotite. This result is confirmed by the state of oxygen isotope equilibrium (or disequilibrium) among the constituent minerals in the garnet peridotite. In particular, garnet is not in oxygen isotope equilibrium with any other of the analyzed minerals. The degree of oxygen isotope disequilibria among the other minerals varies from pair to pair. Oxygen isotope equilibrium is observed only between orthopyroxene and olivine for both samples and between phlogopite and clinopyroxene for one sample. It appears that the U-Pb, Rb-Sr, Sm-Nd, and O isotope systems in minerals of the garnet peridotite are in partial equilibrium during UHP metamorphism, i.e., equilibrium with respect to some isotopes and minerals, but not all. Based on available experimental diffusion data, our study of the combined U-Pb, Rb-Sr, Sm-Nd, and O isotope systems in the garnet peridotite demonstrates that the time scale for the UHP metamorphism and subsequent HP eclogite-facies recrystallization is possibly in the range of about 12 to 26 Ma, which was not long enough for the reequilibration of the Sm-Nd and O isotope systems, but just long enough for the reequilibration of the Rb-Sr isotope systems. Therefore, the rate of Sr diffusion in phlogopite (thus Sr isotope reequilibration between the mafic minerals) is constrained to be faster than rates of Nd and O diffusion in garnet (thus Sm-Nd and O isotope reequilibration between the same minerals) under conditions of subduction zone metamorphism.

Brachiopods recording seawater temperature—A matter of class or maturation?

Next to cetaceans and megafishes, freshwater turtles are the most iconic endangered freshwater species. A detailed questionnaire survey conducted with more than 100 individuals from fishing communities in northern Vietnam was used to investigate the current status of Southeast Asian turtles and provides new hope concerning the survival of Rafetus swinhoei, for which recent official records in the wild are limited to a single individual in Vietnam. The survey included the entire Vietnamese portion of the Da River in Hoa Binh and Son La provinces, as well as the Chu and Ma river system in Thanh Hoa Province, as they are the last sites where the world's rarest and largest Asian softshell turtle has been seen. The questionnaire, conducted in Vietnamese, focused on demographic details, fishing intensity and gear, the status of fishing grounds, and the frequency of interaction with turtles. The great majority of fishers could recognize different turtle species from photographs and describe their preferential breeding habitats; not all knew that they are protected. A few confirmed that more than once each year they still encounter freshwater turtles during their fishing activities. This survey provides detailed information on sites where freshwater turtles are still seen in northern Vietnam and broadens our hope that wild individuals of the extremely rare R. swinhoei may still be present in the remaining riparian wetlands of these biodiverse, dammed, and controlled river basins in North Vietnam.

In the Sm-Nd and Rb-Sr isotopic geochronology of metamorphic rocks, an important question is whether radiometric systems of mineral isochrons have achieved isotopic equilibrium during a given metamorphic event and preserved the equilibrium afterwards. An analogue to mineral chronometry is O isotope geothermometry. Because the rates of Sm-Nd, Sr and O diffusion in metamorphic minerals are comparable in many cases, the state of O isotope equilibrium between metamorphic minerals can provide a test for the validity of mineral Sm-Nd and Rb-Sr chronometers. In order to illustrate this applicability, O isotope geothermometry was carried out for Sm-Nd and Rb-Sr isochron minerals from ultrahigh-pressure (UHP) eclogites and gneisses at Shuanghe in the Dabie terrane of east-central China. Although the Sm-Nd isochrons give consistent Triassic ages of 213 to 238 Ma for UHP metamorphism, the Rb-Sr isochrons give Jurassic ages of 171 to 174 Ma for the same samples. O isotope geothermometry of the gneiss, eclogite and amphibolite minerals yields two sets of temperatures of 600 to 720 °C and 420 to 550 °C, respectively, corresponding to cessation of isotopic exchange by diffusion at about 225 ± 5 Ma during high pressure eclogite-facies recrystallization and at about 175 ± 5 Ma during amphibolite-facies retrogression. The preservation of Triassic Sm-Nd isochron ages, but the occurrence of Jurassic Rb-Sr isochron ages and the regular O isotope temperatures for the same samples, suggest that rates of Sr and O diffusion in such hydroxyl-bearing minerals as biotite and hornblende are faster than rates of Nd diffusion in garnet and Sr diffusion in phengite on the scale of a hand-specimen during the amphibolite-facies retrogression. While the mineral with slow diffusivity has exerted the primary control on the homogenization rate of initial isotope ratios among isochron minerals during retrograde metamorphism, the mineral with high parent/daughter ratio has exerted the principal control on the initiation of the mineral isochron clock in response to retrogression. Valid mineral isochrons can be expected to date the timing of metamorphic resetting only if the mineral with high parent/daughter ratio has a fast rate of radiogenic isotope diffusion during the metamorphic resetting.

This was the first study to assess improvements in accuracy related to ancillary data integration in Landsat 8 image classification since its launch in February 2013. Hoa Binh (northern Vietnam) is a mountainous province with natural forests at high elevations and planted forests on lower slopes. This study integrated a normalized difference vegetation index (NDVI) and digital elevation model (DEM) with the spectral bands of a Landsat 8 image to minimize the influence of shadows on image classification, distinguish between natural and planted forests, and produce a land cover map of Hoa Binh Province for forest inventory support. The image was geo-referenced to the projection of Vietnam (VN-2000) and digital numbers of bands 4 and 5 were converted to reflectance for the NDVI calculation. A DEM was generated from 1:50,000 topographic maps with 40-m contour intervals. A classification of accuracy was performed on a multisource dataset (bands 1–7, and 9, NDVI, and DEM) in comparison with results from a spectral image. The results indicated that user and producer accuracies increased by 14.36 and 11.29 % (natural forest), 7.27 and 10.33 % (regenerated forest), and 8.43 and 11.28 % (planted forest), respectively. Accuracies of identification of barren and agricultural lands, settlements, water bodies, and other classes increased insignificantly. Generally, overall accuracy improved by 5.23 % (from 84.51 to 89.74 %), and the kappa coefficient of the spectral classification was 0.72 compared with 0.86 for the ancillary classification. This study concluded that integration of DEM and NDVI data improved the accuracy of Landsat 8 image classification.

BackgroundVietnam, with its significant agricultural sector, large livestock population, rich biodiversity and close human-animal interactions, is highly vulnerable to zoonotic disease transmission. To better address this threat, representatives from the human, animal, and environmental health sectors in Vietnam worked together at two one health zoonotic disease prioritization (OHZDP) workshops to develop a list of priority zoonotic diseases for multisectoral one health collaboration in Hoa Binh and Lao Cai provinces in April 2024.MethodsWe modified the OHZDP process, developed by the U.S. Centers for Disease Control and Prevention (CDC), and utilized it to prioritize zoonotic diseases in Vietnam. This involved conducting defining prioritization criteria, developing specific questions with assigned weights for each criterion, and organizing two workshops with stakeholders.ResultThere were 25 participants in Hoa Binh's workshop (7 females and 18 males), and 27 participants in Lao Cai's workshop (9 females and 18 males). Following a discussion of tool outputs among experts, four zoonotic diseases were prioritized in Lao Cai province: Rabies, avian influenza, Streptococcus suis, and leptospirosis. In Hoa Binh province, three diseases were identified as priorities: Rabies, avian influenza, and Streptococcus suis.ConclusionRabies, avian influenza and Streptococcus suis were the three most prioritized diseases across the two provinces. This list can serve as a foundation for strengthening one health collaboration for disease prevention and control in these targeted provinces.