@article{SpallanzaniKogaCichyetal.2022, author = {Spallanzani, Roberta and Koga, Kenneth T. and Cichy, Sarah B. and Wiedenbeck, Michael and Schmidt, Burkhard C. and Oelze, Marcus and Wilke, Max}, title = {Lithium and boron diffusivity and isotopic fractionation in hydrated rhyolitic melts}, series = {Contributions to mineralogy and petrology}, volume = {177}, journal = {Contributions to mineralogy and petrology}, number = {8}, publisher = {Springer}, address = {New York}, issn = {0010-7999}, doi = {10.1007/s00410-022-01937-2}, pages = {17}, year = {2022}, abstract = {Lithium and boron are trace components of magmas, released during exsolution of a gas phase during volcanic activity. In this study, we determine the diffusivity and isotopic fractionation of Li and B in hydrous silicate melts. Two glasses were synthesized with the same rhyolitic composition (4.2 wt\% water), having different Li and B contents; these were studied in diffusion-couple experiments that were performed using an internally heated pressure vessel, operated at 300 MPa in the temperature range 700-1250 degrees C for durations from 0 s to 24 h. From this we determined activation energies for Li and B diffusion of 57 +/- 4 kJ/mol and 152 +/- 15 kJ/mol with pre-exponential factors of 1.53 x 10(-7) m(2)/s and 3.80 x 10(-8) m(2)/s, respectively. Lithium isotopic fractionation during diffusion gave beta values between 0.15 and 0.20, whereas B showed no clear isotopic fractionation. Our Li diffusivities and isotopic fractionation results differ somewhat from earlier published values, but overall confirm that Li diffusivity increases with water content. Our results on B diffusion show that similarly to Li, B mobility increases in the presence of water. By applying the Eyring relation, we confirm that B diffusivity is limited by viscous flow in silicate melts. Our results on Li and B diffusion present a new tool for understanding degassing-related processes, offering a potential geospeedometer to measure volcanic ascent rates.}, language = {en} } @article{VossBookhagenSachseetal.2020, author = {Voss, Katalyn A. and Bookhagen, Bodo and Sachse, Dirk and Chadwick, Oliver A.}, title = {Variation of deuterium excess in surface waters across a 5000-m elevation gradient in eastern Nepal}, series = {Journal of hydrology}, volume = {586}, journal = {Journal of hydrology}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0022-1694}, doi = {10.1016/j.jhydrol.2020.124802}, pages = {17}, year = {2020}, abstract = {The strong elevation gradient of the Himalaya allows for investigation of altitude and orographic impacts on surface water delta O-18 and delta D stable isotope values. This study differentiates the time- and altitude-variable contributions of source waters to the Arun River in eastern Nepal. It provides isotope data along a 5000-m gradient collected from tributaries as well as groundwater, snow, and glacial-sourced surface waters and time-series data from April to October 2016. We find nonlinear trends in delta O-18 and delta D lapse rates with high-elevation lapse rates (4000-6000 masl) 5-7 times more negative than low-elevation lapse rates (1000-3000 masl). A distinct seasonal signal in delta O-18 and delta D lapse rates indicates time-variable source-water contributions from glacial and snow meltwater as well as precipitation transitions between the Indian Summer Monsoon and Winter Westerly Disturbances. Deuterium excess correlates with the extent of snowpack and tracks melt events during the Indian Summer Monsoon season. Our analysis identifies the influence of snow and glacial melt waters on river composition during low-flow conditions before the monsoon (April/May 2016) followed by a 5-week transition to the Indian Summer Monsoon-sourced rainfall around mid-June 2016. In the post-monsoon season, we find continued influence from glacial melt waters as well as ISM-sourced groundwater.}, language = {en} } @article{ApaesteguiCruzVuilleetal.2018, author = {Apaestegui, James and Cruz, Francisco William and Vuille, Mathias and Fohlmeister, Jens Bernd and Carlo Espinoza, Jhan and Sifeddine, Abdelfettah and Strikis, Nicolas and Guyot, Jean Loup and Ventura, Roberto and Cheng, Hai and Edwards, R. Lawrence}, title = {Precipitation changes over the eastern Bolivian Andes inferred from speleothem (delta O-18) records for the last 1400 years}, series = {Earth \& planetary science letters}, volume = {494}, journal = {Earth \& planetary science letters}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0012-821X}, doi = {10.1016/j.epsl.2018.04.048}, pages = {124 -- 134}, year = {2018}, abstract = {Here we present high-resolution delta O-18 records obtained from speleothems collected in the eastern Bolivian Andes. The stable isotope records are related to the regional- to large-scale atmospheric circulation over South America and allow interpreting changes in delta O-18 during the last 1400 yr as a function of changes in precipitation regimes over the southern tropical Andes. Two distinct phases with more negative delta O-18 values, interpreted as periods of increased convective activity over the eastern Andean Cordillera in Bolivia are observed concomitantly with periods of global climate anomalies during the last millennium, such as the Medieval Climate Anomaly (MCA) and the Little Ice Age (LIA) respectively. Changes in the Bolivian delta O-18 record during the LIA are apparently related to a southward displacement of the Intertropical Convergence Zone (ITCZ), which acts as a main moisture driver to intensify convection over the tropical continent. During the MCA, however, the increased convective activity observed in the Bolivian record is likely the result of a different mechanism, which implies moisture sourced mainly from the southern tropical Atlantic. This interpretation is consistent with paleoclimate records further to the north in the tropical Andes that show progressively drier conditions during this time period, indicating a more northerly position of the ITCZ. The transition period between the MCA and the LIA shows a slight tendency toward increased delta O-18 values, indicating weakened convective activity. Our results also reveal a non-stationary anti-phased behavior between the delta O-18 reconstructions from Bolivia and northeastern Brazil that confirms a continental-scale east-west teleconnection across South America during the LIA.}, language = {en} } @article{SchildgenHoke2018, author = {Schildgen, Taylor F. and Hoke, Gregory D.}, title = {The topographic evolution of the central andes}, series = {Elements : an international magazine of mineralogy, geochemistry, and petrology}, volume = {14}, journal = {Elements : an international magazine of mineralogy, geochemistry, and petrology}, number = {4}, publisher = {Mineralogical Society of America}, address = {Chantilly}, issn = {1811-5209}, doi = {10.2138/gselements.14.4.231}, pages = {231 -- 236}, year = {2018}, abstract = {Changes in topography on Earth, particularly the growth of major mountain belts like the Central Andes, have a fundamental impact on regional and global atmospheric circulation patterns. These patterns, in turn, affect processes such as precipitation, erosion, and sedimentation. Over the last two decades, various geochemical, geomorphologic, and geologic approaches have helped identify when, where, and how quickly topography has risen in the past. The current spatio-temporal picture of Central Andean growth is now providing insight into which deep-Earth processes have left their imprint on the shape of the Earth's surface.}, language = {en} } @article{NguyenLeDuyNguyenVietDuHeidbuecheletal.2019, author = {Nguyen Le Duy, and Nguyen Viet Du, and Heidb{\"u}chel, Ingo and Meyer, Hanno and Weiler, Markus and Merz, Bruno and Apel, Heiko}, title = {Identification of groundwater mean transit times of precipitation and riverbank infiltration by two-component lumped parameter models}, series = {Hydrological processes}, volume = {33}, journal = {Hydrological processes}, number = {24}, publisher = {Wiley}, address = {Hoboken}, issn = {0885-6087}, doi = {10.1002/hyp.13549}, pages = {3098 -- 3118}, year = {2019}, abstract = {Groundwater transit time is an essential hydrologic metric for groundwater resources management. However, especially in tropical environments, studies on the transit time distribution (TTD) of groundwater infiltration and its corresponding mean transit time (mTT) have been extremely limited due to data sparsity. In this study, we primarily use stable isotopes to examine the TTDs and their mTTs of both vertical and horizontal infiltration at a riverbank infiltration area in the Vietnamese Mekong Delta (VMD), representative of the tropical climate in Asian monsoon regions. Precipitation, river water, groundwater, and local ponding surface water were sampled for 3 to 9 years and analysed for stable isotopes (delta O-18 and delta H-2), providing a unique data set of stable isotope records for a tropical region. We quantified the contribution that the two sources contributed to the local shallow groundwater by a novel concept of two-component lumped parameter models (LPMs) that are solved using delta O-18 records. The study illustrates that two-component LPMs, in conjunction with hydrological and isotopic measurements, are able to identify subsurface flow conditions and water mixing at riverbank infiltration systems. However, the predictive skill and the reliability of the models decrease for locations farther from the river, where recharge by precipitation dominates, and a low-permeable aquitard layer above the highly permeable aquifer is present. This specific setting impairs the identifiability of model parameters. For river infiltration, short mTTs (<40 weeks) were determined for sites closer to the river (<200 m), whereas for the precipitation infiltration, the mTTs were longer (>80 weeks) and independent of the distance to the river. The results not only enhance the understanding of the groundwater recharge dynamics in the VMD but also suggest that the highly complex mechanisms of surface-groundwater interaction can be conceptualized by exploiting two-component LPMs in general. The model concept could thus be a powerful tool for better understanding both the hydrological functioning of mixing processes and the movement of different water components in riverbank infiltration systems.}, language = {en} } @article{RohrmannStreckerBookhagenetal.2014, author = {Rohrmann, Alexander and Strecker, Manfred and Bookhagen, Bodo and Mulch, Andreas and Sachse, Dirk and Pingel, Heiko and Alonso, Ricardo N. and Schildgen, Taylor F. and Montero, Carolina}, title = {Can stable isotopes ride out the storms? The role of convection for water isotopes in models, records, and paleoaltimetry studies in the central Andes}, series = {Earth \& planetary science letters}, volume = {407}, journal = {Earth \& planetary science letters}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0012-821X}, doi = {10.1016/j.epsl.2014.09.021}, pages = {187 -- 195}, year = {2014}, language = {en} } @article{KahmenDawsonViethetal.2011, author = {Kahmen, Ansgar and Dawson, Todd E. and Vieth, Andrea and Sachse, Dirk}, title = {Leaf wax n-alkane delta D values are determined early in the ontogeny of Populus trichocarpa leaves when grown under controlled environmental conditions}, series = {Plant, cell \& environment : cell physiology, whole-plant physiology, community physiology}, volume = {34}, journal = {Plant, cell \& environment : cell physiology, whole-plant physiology, community physiology}, number = {10}, publisher = {Wiley-Blackwell}, address = {Hoboken}, issn = {0140-7791}, doi = {10.1111/j.1365-3040.2011.02360.x}, pages = {1639 -- 1651}, year = {2011}, abstract = {The stable hydrogen isotope ratios (delta D) of leaf wax n-alkanes record valuable information on plant and ecosystem water relations. It remains, however, unknown if leaf wax n-alkane delta D values record only environmental variation during the brief period of time of leaf growth or if leaf wax n-alkane delta D values are affected by environmental variability throughout the entire lifespan of a leaf. To resolve these uncertainties, we irrigated Populus trichocarpa trees with a pulse of deuterium-enriched water and used compound-specific stable hydrogen isotope analyses to test if the applied tracer could be recovered from leaf wax n-alkanes of leaves that were at different stages of their development during the tracer application. Our experiment revealed that only leaf wax n-alkanes from leaves that had developed during the time of the tracer application were affected, while leaves that were already fully matured at the time of the tracer application were not. We conclude from our study that under controlled environmental conditions, leaf wax n-alkanes are synthesized only early in the ontogeny of a leaf. Our experiment has implications for the interpretation of leaf wax n-alkane delta D values in an environmental context, as it suggests that these compounds record only a brief period of the environmental variability that a leaf experiences throughout its life.}, language = {en} } @article{KienelPlessenSchettleretal.2013, author = {Kienel, Ulrike and Plessen, Birgit and Schettler, Georg and Weise, Stephan and Pinkerneil, Sylvia and Boehnel, Harald and Englebrecht, Amy C. and Haug, Gerald H.}, title = {Sensitivity of a hypersaline crater lake to the seasonality of rainfall, evaporation, and guano supply}, series = {Fundamental and applied limnology : official journal of the International Association of Theoretical and Applied Limnology}, volume = {183}, journal = {Fundamental and applied limnology : official journal of the International Association of Theoretical and Applied Limnology}, number = {2}, publisher = {Schweizerbart}, address = {Stuttgart}, issn = {1863-9135}, doi = {10.1127/1863-9135/2013/0405}, pages = {135 -- 152}, year = {2013}, abstract = {The hypersaline crater lake and its catchment on seabird island Isabel (Pacific, off Mexico) was studied to explore the influence of strong seasonal variations in rainfall/evaporation and guano contribution on its limnology. The hypersaline lake water (HSW, 78 \%) is up to 2.2-times enriched in inert ions relative to mean seawater. Rainfall during summer dilutes the HSW to form a less saline rainwater body (RWB) above a chemolimnion between 2 and 4 m water depth. The RWB is inhabited first by diatoms and ostracods followed later on by cyanobacteria and ciliates. Evaporation of > 1.5 m depth of lake water over the dry season increases the salinity of the RWB until the water column becomes isohaline at HSW concentrations in the late dry season. Differences in the stable isotope composition of water and primary producers in RWB and HSW reflect this development. Introduction of seabird guano and the decrease of salinity fuel a high primary production in the RWB with higher delta(CDIC)-C-13 and delta(13)Corg of particulate organic matter than in the HSW. The high N supply leads to high delta N-15 NH4 values (+ 39 \% in the HSW) as the consequence of ammonia volatilization that is strongest during guano maturation and with evaporative salinity increase from the HSW. Precipitation of carbonate (calcite and aragonite) from the RWB and the HSW is hindered by the high concentration of guano-derived P. This inhibition may be overcome with evaporative supersaturation during particularly dry conditions. Carbonate may also precipitate during particularly wet conditions from the dilute RWB, where the P-concentration is reduced during an active phytoplankton production that raises the pH. Differences in the stable isotope signatures of carbon and oxygen in HSW and RWB (+ 5 \% delta(CDIC)-C-13 and -3 \% d18OH2O) suggest the processes of carbonate precipitation can be distinguished based on the isotope signature of the carbonates deposited. Changes in the lake system are indicated when lower temperatures and higher rainfall in the 2006 wet season introduced more and less mature guano to the lake. The lower pH was accompanied by lower ammonia volatilization and carbonate precipitation as indicated by an increased concentration of NH4, Ca, Sr and DIC, while delta H-2, delta(NNH4)-N-15, and salinity were lower. According to our results, the observed sediment laminations should reflect the introduction of catchment material (including guano) with runoff, the RWB plankton production, and the carbonate precipitation in relation to its origin and seasonality.}, language = {en} }