diﬀer starkly from the present (e.g., Lee et al. , 2008 ). Stable waterisotopes have been included in the hydrological cycle of various global atmospheric models, namely, GISS ( Jouzel et al. , 1987 ), ECHAM ( Hoﬀmann et al. , 1998 ), MUGCM ( Noone and Simmonds , 2002 ), CAM2.0 ( Lee et al. , 2007 ), LMDZ ( Bony et al. , 2008 ), CAM3.0 ( Noone and Sturm , 2010 ) and the atmosphere-ocean coupled model HadCM3 ( Tin- dall et al. , 2009 ). These models have been successfully used for simulating the present and paleoclimatic distributions of the stable isotopes in the global hydrological cycle. Charles et al. ( 1994 ) ﬁnd that changes in moisture transport and source regions for Greenland at the LGM may have produced an isotopic response independently of temperature changes. A similar result has also been found for shorter (millennial- scale) climate variations ( Liu et al. , 2012 ). Masson-Delmotte et al. ( 2006 ) show that a major part of Greenland and Antarctic coolings of the GCM simulations is caused by the prescribed local elevation increase due to ice sheets at the LGM. Werner et al. ( 2000 ) ﬁnd an increased seasonality in the annual cycle of precipitation over Green- land during the LGM, but not over Antarctica. Conventionally, the spatial slope over a region (the relationship between δ 18 O precip and temperature over a region) was as-
In future research, two main issues will have to be addressed in order to establish an appropriate description of the dependence of the non-equilibrium fractionation factor k on wind velocity (or, alternatively, to show in a more definite way that this dependence is negligible). First, more measurements of isotope ratios in atmospheric water vapor should be made available that al- low to test newly developed parameterizations of k. As isotope ratios in the evaporation flux cannot be measured directly, complex models, which include processes like the advection of water vapor (e.g. GCMs or the Lagrangian approach used here) have to be applied to compare theoretical predictions from a Craig-Gordon model with measurements. Second, more recent parameterizations of water evaporation from the ocean (see e.g. Fairall et al., 2003) might pro- vide the theoretical basis for the description of k. These parameterizations have the advantage that they are grounded on measurement data in a much stronger way than the mostly theoretical Brutsaert model applied by MJ79. However, they usually do not contain an explicit formulation of molecular diffusion, but subsume the properties of the diffusive surface layer in a parameter called moisture roughness length, which is then parameterized with an empirical equation. Ba- sically, the moisture roughness length can also be expressed in terms of a diffusion coefficient or Schmidt number (and thus calculated for the different waterisotopes) (cf. Liu et al., 1979; Brutsaert, 1982). But, owing to its empirical formulation, it is not straightforward to employ these more recent parameterizations of evaporation for the deduction of the isotope fractionation factor. In our opinion, this issue will have to be addressed with the help of a comprehensive ex- perimental (e.g. wind tunnel) study analyzing the dependence of the moisture roughness length on the Schmidt number, extending the work of Merlivat (1978a).
Over land surfaces two main processes exist which include a phase transition of water masses: evaporation and transpi- ration. Whereas isotope fractionation occurs during an evap- oration process, it is often assumed that the transpiration is a non-fractionating process (see Gat, 1996). Many of the presently existing GCMs enhanced with isotopes do not con- sider such difference between the evaporation and transpi- ration flux but simply assume that the whole evapotranspi- ration from land surface is a non-fractionating process (see, e.g., Hoffmann et al., 1998, for a more detailed discussion of this issue). So far, only very few GCM studies, e.g., Aleinov and Schmidt (2006), have started to investigate fractionation processes over land.
Abstract. In low-accumulation regions, the reliability of δ 18 O-derived temperature signals from ice cores within the Holocene is unclear, primarily due to the small climate changes relative to the intrinsic noise of the isotopic sig- nal. In order to learn about the representativity of single ice cores and to optimise future ice-core-based climate recon- structions, we studied the stable-water isotope composition of firn at Kohnen Station, Dronning Maud Land, Antarctica. Analysing δ 18 O in two 50 m long snow trenches allowed us to create an unprecedented, two-dimensional image charac- terising the isotopic variations from the centimetre to the 100-metre scale. Our results show seasonal layering of the isotopic composition but also high horizontal isotopic vari- ability caused by local stratigraphic noise. Based on the hor- izontal and vertical structure of the isotopic variations, we derive a statistical noise model which successfully explains the trench data. The model further allows one to determine an upper bound for the reliability of climate reconstructions conducted in our study region at seasonal to annual resolu- tion, depending on the number and the spacing of the cores taken.
respective storage can be lost during approximately 3.5 years (0.26 × 3.5 ≈ 1). Percentage enrichments suggested an average iso- topic enrichment during kettle hole flow-through of 28.10%. Thus, the regional mean water loss during the 2017 February –August period was likely to be approximately 26.00 –28.10%. Nitzsche et al. (2017) using the difference in LEL between a defined dormant and growth season in a similar method to the monthly LEL-based approach in present study proposed a regional water loss of 28.00% in both 2013 and 2014, advocating the findings of this study. More- over, Hayashi et al. (1998) found that summer evapotranspirative losses in Canadian prairie wetlands approximated 25.00% based on pan experiments, with a significant (75.00%) loss through infiltration and lateral, shallow groundwater flow to the sides of kettle holes in close agreement to findings of this study and again supportive of substantial lateral groundwater flow-through (Hayashi et al., 1998). The regional connection was already discussed by Kayler et al. (2018). They measured the isotopic signature along the Quillow stream. From upstream to downstream, the isotopic enrichment increases following the LEL of the kettle holes. There are over 1,100 kettle holes in the catchment. Due to the fact that the kettle holes are hydrologically connected to the shallow unconfined Weichsalien aquifers, the spatial isotopic pattern of the Quillow River discharge is affected. This takes place owing to the fact that a fraction of the streamflow discharge, recognized as base flow, is contributed by the shallow aquifer.
Stable isotopes in soil water and plant stem water (usually assumed to be xylem water) have been invaluable tools in elucidating ecohydrological interactions over the past decade (Penna et al., 2018). Earlier work by Ehleringer and Dawson (1992) and Ehleringer and Dawson (1992) explained the isotope content of xylem water in trees in terms of potential plant water sources. Building on that, Brooks et al. (2010) showed that the isotope characteristics of xylem water did not always correspond to bulk soil water sources as plant xylem water was fractionated and offset relative to the global meteoric water line (GMWL) compared to mobile soil water, groundwater and stream flow signatures. This led to the “Two Water Worlds” hypothesis which speculated that plant water was drawn from a “pool” of water that was “ecohydrologically separated” from the sources of groundwater recharge and stream flow (McDonnell, 2014). Research at some sites has found similar patterns of ecohydrologic separation (e.g., Goldsmith et al., 2012; Sullivan et al., 2016) and suggested it may be a ubiquitous characteristic of plant-water systems (Evaristo et al., 2015). Others have found that differences between plant water and mobile water may be limited only to drier periods (e.g., Hervé-Fernández et al., 2016; McCutcheon et al., 2017; Zhao et al., 2016), or may be less evident in some soil-vegetation systems (Geris et al., 2015). Direct hypothesis test- ing of potential processes that may explain the difference between the isotopic composition of xylem water and that of potential water sources has been advanced by detailed experiments in controlled environments, often involving the use of Bayesian mixing models which assume all potential plant water sources have been sampled (e.g., Stock et al., 2018). However, as field data become increasingly available from critical zone studies, more exploratory, inferential approaches can be insightful in terms of quantifying the degree to which xylem waterisotopes can or cannot be attributed to measured soil water sources (Amin et al., 2020).
mosses. A mentionable fractionation, which can explain the isotopic gap between Sphagnum biomass and N deposition, is not expectable in Sphagnum plants (Liu et al., 2013). Thus, the N supply for Sphagnum growth cannot mainly stem from direct atmospheric deposition, internal cycling processes are supposed to be much more important. The enriched N of atmospheric deposition is most likely immobilized by other organisms or processes, because isotope ranges of pore water were also significantly lower in both hollows and hummocks than values in atmospheric deposition (ρ<0.01)(Fig. 4.5, 4.6).
For ground water modelling and m odel calibration it is necessary to measure the ground wat er level. The location of observat ion wel ls shoul d be det ermined, so that as much as possible information on the ground water l evel can be achi eved. However the hydro- geological condi tions of t he cat chment area have t o be taken into account. Since there was no observation by Mongolian institutions or water suppliers in Darkhan we est ablished a new pi lot m onitoring system by i nstalling dat a l oggers i n unused l ocal abstraction wel ls. Here aut omatic dat a l oggers were used for a cont inuous m easurement of t he ground water lev el. Th e m easured d ata were m odified with the air pressure compensation and the sea level conversion.
Honduras is in Central America. Neighbour countries are Nicara- gua and El Salvador in the south and Guatemala in the west. The climate in Honduras is tropical. There is a dry season from No- vember to May and a rainy season from May to October. There is more rain in the north than in the south. 8.4 million people live in Honduras. 758.000 (= 9%) of them do not have clean water. The country is very poor, 29% of the population live on less than 2 US$ a day.
Estuaries have a prominent role in regulating material fluxes from land to sea (Crossland 2005), and the capacity of estuaries for reducing riverine nutrient loads to continental shelf seas has been appreciated as one of the most valuable functions of all global ecosystems (Costanza et al. 1997). According to current understanding of reactive nitrogen transport from land to sea, the estuaries of major rivers are thought to be sites of massive nitrate losses (Brion et al. 2004; Seitzinger et al. 2006), removing up to fifty per cent of reactive nitrogen(OsparCom 2000). In spite of its salient relevance as natural attenuation mechanism combating eutrophication of coastal seas and the intrinsic economic relevance of this specific ecosystem service, the cycling of nitrogen in contemporary estuaries is still subject to open questions. Most older studies are based on tidal input and output, which are prone to a large degree of uncertainty, or are based on mass fluxes alone, which is problematic when sources (e.g., nitrification) and sinks (assimilation and burial, denitrification) may be balanced. A few newer studies suggest that estuarine removal of reactive nitrogen may be significantly overrated, with estimates of removal efficiency ranging from ~5% in the Humber estuary (Jickells et al. 2000) to ~20% in the Rowley estuary (Tobias et al. 2003). More than concentration data alone, measurements of stable isotopes in reactive nitrogen species provide a powerful tool to assess internal turnover and sources in estuaries (Middelburg and Nieuwenhuize 2001; Sebilo et al. 2006). The combined use of δ 15 N-NO
To extract the isotope shift from the measurements of the individual isotopes, one must take into account that the absolute positions extracted in the ﬁtting routine are prone to changes or drifts in the laser frequency, the high voltage at the RFQ and the gas pressure inside the RFQ. Thus, the weighted averages of all 114 Cd reference scans directly preceding and succeeding the scan of the relevant isotope are calculated. Those two values are linearly interpolated in time to get the reference frequency at the moment of the measurement, which is then subtracted from the center of gravity of the isotope under investigation. All individual measurements of both runs are averaged, weighted with their statistical uncertainty, to get the ﬁnal isotope shift for each isotope. The results are presented in Tab. 4.3.
of the isotopes, surface ion sources (for elements with low work function like alkali metals), plasma ion sources (for elements with high ionization energies like noble gases) or resonant laser ionisation ion sources, RILIS, [Fed00] (in other cases) are used. For Mg, a three-step laser ionization was chosen, since it offers high efficiency (around 10 %) and in addition it gives high element selectivity [Koe03]. To allow efficient ionisation, enough light power has to be provided: pulsed lasers with a high repetition rate are used for this purpose. The laser light at the required frequencies is produced by dye lasers (including doubling or tripling of their frequencies) pumped by copper-vapour lasers with the repetition rate of 11 kHz. This rate is high enough to ensure that the probability of each atoms to be ionised in close to one. At the same time, the power allows to reach at least several percent of efficiency. The lasers are placed in a small laboratory inside the ISOLDE hall, and from there the laser beams are sent through a quartz window in the separator magnets straight into the hot cavity of the ion source.
Even though some of the scenarios can lead to a potential duration of well over 20 Myr, the timespan of escape is linked to the lifetime of the magma ocean. Once the magma ocean has completely solidified, it will no longer heat the atmosphere and the reaming water vapour will condense into liquid water when the critical water point has been reached (Odert et al. 2018; Elkins-Tanton 2012). And without H or O in the atmosphere no additional escape will happen. In regards to Mars an analysis of ancient zircons has shown that a magma ocean should have finished solidification after about 10 Myr (Bouvier et al. 2018), which would be around the 15 Myr mark in the results. The condensation timescale for Mars’ orbit is 0.1 Myr (Lebrun et al. 2013). As a result, the steam atmosphere should have condensed almost instantly upon magma ocean solidification. Of course, impacts could have kept parts of the surface molten or re-melted them during later times, especially impacts such as the giant impact 4430 Myr ago (Brasser & Mojzsis 2017). This would have caused further escape but with different EUV conditions.
cycle. First, we simulated the mean isotopic composition of the North American Ice Sheet (NAIS) during the past 120,000 years with a 2.5-dimensional thermomechanical ice-sheet model including ice δ 18 O as a passive tracer. This allowed us to estimate the changes in the magnitude and δ 18 O of the water flux exchanged between the NAIS and the Atlantic Ocean. Then, the water flux was used to force a zonally-averaged model of the Atlantic Ocean, as part of a coupled climate model of reduced complexity. The resulting changes of mean-ocean δ w , as well as δ w and δ c variations at different locations in the ocean were compared to the modeled NAIS ice volume, in order to investigate the possible phase differences due to ocean circulation. The simulated NAIS volume variations and the induced mean-ocean δ 18 O changes over the past 120,000 years indicated no significant time lag. However, locally the time lag in the ocean could reach up to 2000 years during glaciation, depending on the rate of deep-water formation. In contrast, the deglaciation signal was found to be practically simultaneous.
Several methods exist to perform direct measurements of lifetimes of excited states of nuclei. Some of them are based on the Doppler effect and allow to access lifetimes in the range from few femtoseconds to tens of nanoseconds [NSS79]. The technique used in this work is, however, the electronic fast timing, that provides access to a more limited range of lifetimes, but introduces less systematical errors. It relies on the accurate determination of the γ-ray detection time difference and it is thus subject to the combination of good timing and energy resolution and high efficiency of the detectors. Historically, plastic or BaF 2 scintillators (with very good timing resolution but very poor energy resolution) or germanium detectors (with very good energy resolution but very poor timing resolution) have been used. This restricted the applicability of the method to either very clean experiments in which the energy resolution was not crucial, or to experiments that aimed for the measurement of long lifetimes. However, the parallel development, in the last few years, of sophisticated electronic fast-timing methods [MGM89; Rég11] and the invention of novel γ-ray detectors with good timing resolution, good efficiency and good energy resolution [Loe+01] made the fast-timing spectroscopy of a large amount of nuclei, in the range from few nanoseconds down to tens of picoseconds, possible. Neutron-rich cerium isotopes are among these nuclei.
With this connection of PDR to EoS established, the study of the low-lying electric dipole strength promises great insight. As crucial aspects of the PDR have not been examined until now, this work is dedicated to the investiga- tion of the influence of shell effects on the PDR. Thus, focus of this work are nuclear structure aspects of the nuclei 50,52,54 Cr. This group of isotopes is distinguished from the thousands of known isotopes by a unique set of prop- erties. The chromium isotopic chain is the only one featuring stable isotopes below a neutron shell closure (in this case N = 28) as well as above, yet with natural abundances of several percent for each isotopes . The latter al- lows for the production of highly enriched and comparatively large amounts of target material, providing the necessary conditions for photon scattering experiments. Thus, as of today, the chromium isotopic chain is the only case, where the study of nuclear structure across a neutron shell closure (or indeed any shell closure, considering isotonic chains as well) can be performed with real photons as probes.
Inelastic proton scattering of 70,72,74 Ni and 76,78,80 Zn was performed at the RIBF facility of the RIKEN Nishina Center, Japan, as part of the first SEASTAR campaign. Radioactive isotopes were produced by the in-flight fission of a beam of 238 U ions incident on a 3 mm thick Beryllium target. After produc- tion, neutron-rich radioactive isotopes were selected and identified on an event-by-event basis using the BigRIPS separator. Selected isotopes of inter- est were focused onto the liquid hydrogen target of the MINOS device and γ-rays from inelastic (p, p ′ ) reactions were detected with the DALI2 array, consisting of 186 NaI crystals. Outgoing beam-like particles were identified using the ZeroDegree spectrometer. γ-rays produced in the reaction were Doppler corrected and the first 2 + and 4 + states in all the isotopes were identified. Detailed data analysis was performed including the implemen- tation of algorithms that discriminate events where more than one particle was present. Using detailed Geant4 simulations, exclusive cross-sections for inelastic proton scattering were obtained. Deformation lengths were deduced from the experimental cross-sections using the coupled-channel calculation code ECIS-97.
which was heated to 1200 K for 15 min to eliminate water contaminations. Then the various batches were pulverized in an agate mortar, pressed into pellets 15mm in diameter and reheated to 1200 K for 1 h. During the nal heating the pellets shrank slightly. Immediately after cooling, the actual samples were prepared by canning the pellets into air tight aluminum cylinders with 0.2 mm thick walls. Apart from the ve hafnium samples, a gold sample in an identical can was used for measuring the neutron ux. An empty can was mounted in the sample ladder for determining the sample-independent background. A graphite sample served for simulating the background due to scattered neutrons. The relevant sample parameters are compiled in Table 1, and the isotopic composition of the hafnium samples provided by IPPE Obninsk is listed in Table 2.