Search

Clumped isotope data from carbonated apatite from in vivo and in vitro samples are presented to refine the relationship between mineral growth temperature and carbonate clumped isotopic composition (Δ47). Δ47, δ18O and δ13C data were obtained from phosphoric acid digestion (T = 110 °C) of chemically untreated teeth from an African elephant, Greenland sharks, sand tiger sharks and synthetic apatites. These data cover a temperature range between 1 °C and 80 °C and enlarge the calibration dataset presented in Wacker et al. (2016) by a factor of five. Taxon-specific analyses of tooth enamel(oid) and dentine reveal that both tissues show identical Δ47 values even though the content of organic matter differs by an order of magnitude. The following Δ47 temperature calibration for (bio)apatite is derived (R2 = 0.9924, p-value Δ 47 C D E S 110 = 0.0325 ( ± 0.0012 ) × 10 6 / T 2 + 0.2137 ( ± 0.0124 ) ( w i t h T i n K a n d Δ 47 i n ‰ ) This calibration becomes indistinguishable from a reprocessed empirical calibration of calcite made in the same laboratory if a difference of the acid fractionation factors (AFF) of 0.110‰ between 25 °C and 110 °C is considered. The measured AFF for bioapatite matches the one that is extrapolated from experimental data on calcite and aragonite. The oxygen isotope fractionation between structural carbonate in the synthesized carbonated hydroxylapatites (CHAP) and water between 7 °C and 80 °C closely follows the temperature dependence for the calcite-water system. It is described by the following (CHAP-water) equation (R2 = 0.997, p-value 1000 l n ( α C H A P - w a t e r ) = 17.23 ± 0.59 × 10 3 × T - 1 - 27.28 ( ± 1.73 ) ( w i t h T i n K ) Both calibrations are applied to shark teeth from a modern Greenland shark and a fossil megatooth shark (Carcharodon megalodon) specimen to reconstruct the apparent Δ47-based habitat temperature of C. megalodon (19 ± 4 °C) and the oxygen isotopic compositions of seawater.

Significance Clumped and stable isotope data of paleosol carbonate and fossil tooth enamel inform about paleoenvironments of Early Pleistocene hominins. Data on woodland- vs. grassland-dominated ecosystems, soil temperatures, aridity, and the diet of Homo rudolfensis and Paranthropus boisei ca. 2.4 Ma show that they were adapted to C3 resources in wooded savanna environments in relatively cool and wet climates in the Malawi Rift. In contrast, time-equivalent Paranthropus living in open and drier settings in the northern East African Rift relied on C4 plants, a trend that became enhanced after 2 Ma, while southern African Paranthropus persistently relied mainly on C3 resources. In its early evolutionary history, Homo already showed a high versatility, suggesting that Pleistocene Homo and Paranthropus were already dietary generalists., New geochemical data from the Malawi Rift (Chiwondo Beds, Karonga Basin) fill a major spatial gap in our knowledge of hominin adaptations on a continental scale. Oxygen (δ18O), carbon (δ13C), and clumped (Δ47) isotope data on paleosols, hominins, and selected fauna elucidate an unexpected diversity in the Pleistocene hominin diet in the various habitats of the East African Rift System (EARS). Food sources of early Homo and Paranthropus thriving in relatively cool and wet wooded savanna ecosystems along the western shore of paleolake Malawi contained a large fraction of C3 plant material. Complementary water consumption reconstructions suggest that ca. 2.4 Ma, early Homo (Homo rudolfensis) and Paranthropus (Paranthropus boisei) remained rather stationary near freshwater sources along the lake margins. Time-equivalent Paranthropus aethiopicus from the Eastern Rift further north in the EARS consumed a higher fraction of C4 resources, an adaptation that grew more pronounced with increasing openness of the savanna setting after 2 Ma, while Homo maintained a high versatility. However, southern African Paranthropus robustus had, similar to the Malawi Rift individuals, C3-dominated feeding strategies throughout the Early Pleistocene. Collectively, the stable isotope and faunal data presented here document that early Homo and Paranthropus were dietary opportunists and able to cope with a wide range of paleohabitats, which clearly demonstrates their high behavioral flexibility in the African Early Pleistocene.

Geochemical records from incremental carbonate archives, such as fossil mollusk shells, contain information on climate and environmental change at the resolution of days to decades (e.g. Schöne and Gillikin, 2013; Ivany, 2012). These high-resolution paleoclimate data, providing snapshots of past climate change on a human scale, complement more conventional reconstructions on a geological timescale of thousands to millions of years. Recent innovations in geochemical techniques such as high-resolution trace element and clumped isotope analyses provide the unique potential to improve the accuracy and resolution of these high-resolution climate reconstructions in the near future (see e.g. de Winter et al., 2020a; b; Caldarescu et al., 2021). However, to be able to make the most out of these new techniques requires a more detailed understanding of the timing and mechanisms of mollusk shell growth as well as the relationship between environment and shell chemistry on daily to weekly timescales.The UNBIAS (UNravelling BIvAlve Shell chemistry) project combines investigations on lab-grown modern bivalve shells with reconstructions based on fossil shell material from past greenhouse periods in an attempt to improve our understanding of short-term temperature variability in warm climates. Samples from cultured shells labeled with a novel trace element spiking method are used to calibrate accurate temperature reconstructions from bivalve shells using the state-of-the-art clumped isotope method. As a result, we present a temperature calibration of clumped isotope measurements on aragonitic shell carbonates. New statistical routines are developed to accurately date microsamples within shells relative to the seasonal cycle (ShellChron; de Winter, 2020) and to strategically combine these microsamples for seasonal reconstructions of temperature and salinity from fossil shells (seasonalclumped, de Winter et al., 2020c; de Winter, 2021). We present the first results of this integrated seasonal reconstruction approach on fossil bivalve shells from the Pliocene Warm Period and Late Cretaceous greenhouse of northwestern Europe as well as an outlook on future plans within the UNBIAS project. ReferencesCaldarescu, D. E. et al. Geochimica et Cosmochimica Acta 294, 174–191 (2021).de Winter, N. J. ShellChron v0.2.8: Builds Chronologies from Oxygen Isotope Profiles in Shells. (2020).de Winter, N. J. seasonalclumped v0.3.2: Toolbox for Seasonal Temperature Reconstructions using Clumped Isotope Analyses. (2021).de Winter, N. J. et al. Paleoceanography and Paleoclimatology 35, e2019PA003723 (2020a).de Winter, N. J. et al. Nature Communications in Earth and Environment (in review; 2020b) doi:10.21203/rs.3.rs-39203/v2.de Winter, N., Agterhuis, T. & Ziegler, M. Climate of the Past Discussions 1–52 (2020c) doi:https://doi.org/10.5194/cp-2020-118.Ivany, L. C. The Paleontological Society Papers 18, 133–166 (2012).Schöne, B. R. & Gillikin, D. P. Palaeogeography, Palaeoclimatology, Palaeoecology 373, 1–5 (2013).

It has recently been shown that the clumped isotopic composition (Δ47) of carbonate-bearing hydroxyapatite (CHAP) from teeth and bones reveals important information about the body temperature of vertebrates (Eagle et al., 2010, 2011). In this study we reinvestigate the temperature dependence of Δ47 in CHAP, extending the temperature range from 2 to 59 °C. In addition, the effects of chemical pre-treatment of CHAP on its bulk and clumped isotopic composition are studied. CHAP is best reacted with phosphoric acid at 90 to 110 °C minimizing the potential of evolved CO2 or reaction intermediates to re-equilibrate with traces of water in the acid environment. Reaction at 110 °C ensures that digestions of CHAP samples are complete within 60 min. We determined a Δ47 ⁎ 90–110 value of 0.032 ± 0.008‰ that is - within errors - indistinguishable from a Δ47 ⁎ 90–110 value of 0.019 ± 0.007‰ received for aragonite. For tooth enamel pre-treated with H2O2 lower Δ47 values, and higher δ18O and δ13C values were measured than for pre-treated tooth dentine. In addition, similar trends were observed for pre-treated dentine and bone material: higher Δ47 values, and lower δ18O and δ13C values were determined compared to untreated samples. A new tentative clumped isotope temperature calibration based on a synthetic apatite, untreated tooth enamel of an African elephant and enameloid from teeth of a Greenland shark is presented using a reaction temperature of 110 °C. It follows the equation: Δ47 = 0.0320 (± 0.0022) × 106/T2 + 0.1977 (± 0.0259) (Δ47 in ‰ and T in K). The slope of this regression line is identical to those previously obtained from 90 °C digestions of calcite and/or aragonite in several laboratories (e.g., Henkes et al., 2013; Wacker et al., 2014; Defliese and Lohmann, 2015). The Δ47 data of untreated enamel(oid) samples reacted at 90 °C closely match a Δ47-1/T2 relationship for calcite that was made at the same digestion temperature (Wacker et al., 2014). These preliminary results suggest that calcite calibrations made at a reaction temperature of 90 °C might be directly applicable to CHAP samples to determine their formation temperatures.

Eocene hyperthermals are among the most enigmatic phenomena of Cenozoic climate dynamics. These hyperthermals represent temperature extremes superimposed on an already warm Eocene climate and dramatically affected the marine and terrestrial biosphere, yet our knowledge of temperature and rainfall in continental interiors is still rather limited. We present stable isotope (δ18O) and clumped isotope temperature ( Δ 47 ) records from a middle Eocene (41 to 40 Ma) high-elevation mammal fossil locality in the North American continental interior (Montana, USA). Δ 47 paleotemperatures of soil carbonates delineate a rapid +9/−11 °C temperature excursion in the paleosol record. Δ 47 temperatures progressively increase from 23 °C ± 3 °C to peak temperatures of 32 °C ± 3 °C and subsequently drop by 11 °C. This hyperthermal event in the middle Eocene is accompanied by low δ18O values and reduced pedogenic carbonate concentrations in paleosols. Based on laser ablation U/Pb geochronology of paleosol carbonates in combination with magnetostratigraphy, biostratigraphy, stable isotope, and Δ 47 evidence, we suggest that this pronounced warming event reflects the Middle Eocene Climatic Optimum (MECO) in western North America. The terrestrial expression of northern hemisphere MECO in western North America appears to be characterized by warmer and wetter (sub-humid) conditions, compared to the post-MECO phase. Large and rapid shifts in δ18O values of precipitation and pedogenic CaCO3 contents parallel temperature changes, indicating the profound impact of the MECO on atmospheric circulation and rainfall patterns in the western North American continental interior during this transient warming event.

The topography of the present-day Washington Cascades impacts atmospheric circulation and precipitation patterns in the Pacific Northwest, introducing a pronounced orographic rain shadow in the lee of the mountain range. The temporal development of Cascade topography, however, remains largely unconstrained for the early Cenozoic. Based on coupled carbonate clumped isotope (Δ47) and oxygen isotope (δ18O) measurements we reconstruct δ18O values of Eocene groundwater (δ18Owater) in the Chumstick basin (central Washington), today located in the Cascade rain shadow. Δ47 (paleo)thermometry indicates a systematic change in basin burial temperatures from 110°C to 70°C depending on burial depth in the basin. These data are in good agreement with low-T thermochronological and vitrinite reflectance data, and further constrain the basin burial and exhumation history. In concert with field observations, microstructural analysis, and δ18O values of the analyzed carbonates, we suggest that the Δ47 temperatures and δ18O values reflect open-system carbonate cement recrystallization in meteoric-derived groundwaters during early burial diagenesis. Assuming open-system behavior, reconstructed mean δ18Owater values of ~ −7‰ (middle Eocene) to −9‰ (late Eocene/early Oligocene) are consistent with a low-elevation origin of the corresponding meteoric waters that permeated the sandstone/conglomerate members of the Eocene sedimentary units. In light of the paleogeographic setting of the Chumstick basin, the reconstructed δ18Owater values agree well with Pacific-derived moisture that did not experience strong rainout. The absence of a rain shadow effect therefore permits only moderate Eocene/Oligocene elevations at least for the southern part of the Washington proto-Cascades.

Preventing the inclusion of oxygen bearing compounds from the organic fraction of skeletal tissues is often considered key to obtaining faithful δ18O measurements of the mineral fraction, which are widely used across the archaeological, forensic and geochemical sciences. Here we re-explore the contentious issue of organic removal pretreatments by establishing how different silver phosphate preparation methods perform in producing pure silver phosphates with a faithful biogenic isotopic signal. We then compare this baseline performance to a pretreatment based approach. Our results show that anion exchange purification combined with slow precipitation of silver phosphate consistently produces silver phosphates of high purity without prior pretreatment. Rapid precipitation protocols without additional purification, while effective and time-efficient for low organic samples such as enamel, suffer from the inclusion of substantial amount of organic matter in silver phosphates from bone or dentine samples. However, despite substantial organic contamination in such samples, δ18O values do not necessarily show substantial shifts. Further study is needed to clarify the reason for this, but for now the use of an anion exchange based protocol represents the most cautious approach to processing bone and dentine samples and we recommend its use for such samples. Confirming previous work we find H2O2 pretreatment to be only partially effective at removing higher amounts of organic matter. Both H2O2 and NaOCl pretreatments show unpredictable side effects on δ18O values of both bones and inorganic samples. We additionally find no indication that the presence of organic material hinders the dissolution of bioapatite samples.

As conceptual model for a cloud a system is considered which is open for condensate mass transport and subject to internal processes such as cloud microphysical transformation and vertical condensate transport. The effects of microphysical processes are represented in parameterized form and the system is divided into two layers to account for the vertical structure. The evolution is mathematically described in terms of four coupled nonlinear ODEs; the prognostic variables are the mass concentrations of cloud water as well as precipitation condensate in each of the layers. In the absence of vertical velocity the evolution in the lower layer is triggered by the evolution in the upper layer. In the presence of an upwind, the dynamics in both layers is mutually coupled. Depending on the chosen parameter values up to four steady states are found. When varying the parameter upwind velocity, three regimes are distinguished: For week upwind the long-term evolution is steered by the external sources; for stronger upwind the cloud condensate is blown out of the cloud in the final state and does not contribute to formation of precipitation; for intermediate upwind multiple steady state solution branches arise which characterize the transition between those two regimes.

The Quadrature Method of Moments (QMoM) is applied to a one-dimensional test case for sedimentation of raindrops. Comparison of the results with a reference spectral method exhibits discrepancies (“step patterns”) that must be considered as modeling artifacts. As the QMoM has been demonstrated to be effective and accurate in various contexts, the origin of these artifacts is investigated and found to be related to the transport of the quadrature abscissas. Further test cases are considered to examine the influence of different initial conditions on the development of the modeling artifacts. The study shows that these artifacts are inherent to the application of QMoM in pure sedimentation context.

We present the first universal calibration of the clumped isotope thermometer for calcites of various mineralizing types. These are an eggshell of an ostrich, a tropical bivalve, a brachiopod shell, cold seep carbonate, and three foraminifera samples that grew between 9 and 38 C. CaCO3 was digested at 90 C using a common acid bath. Considering a difference in phosphoric acid fractionation factors between reaction at 25 and 90 C of 0.069& (Guo et al., 2009), the function between growth temperature T and the excess of 13 C– 18 O bonds in the evolved CO2 is expressed by a linear regression between 1/T 2 and absolute D47 (R 2 = 0.9915)

This study deals with the comparison of numerically and experimentally determined collision kernels of water drops in air turbulence. The numerical and experimental setups are matched as closely as possible. However, due to the individual numerical and experimental restrictions, it could not be avoided that the turbulent kinetic energy dissipation rate of the measurement and the simulations differ. Direct numerical simulations (DNS) are performed resulting in a very large database concerning geometric collision kernels with 1470 individual entries. Based on this database a fit function for the turbulent enhancement of the collision kernel is developed. In the experiments, the collision rates of large drops (radius > 7.5μm$> 7.5\,\text{\textmu{}m}$) are measured. These collision rates are compared with the developed fit, evaluated at the measurement conditions. Since the total collision rates match well for all occurring dissipation rates the distribution information of the fit could be used to enhance the statistical reliability and for the first time an experimental collision kernel could be constructed. In addition to the collision rates, the drop size distributions at three consecutive streamwise positions are measured. The drop size distributions contain mainly small drops (radius < 7.5μm$< 7.5\,\text{\textmu{}m}$). The measured evolution of the drop size distribution is confronted with model calculations based on the newly derived fit of the collision kernel. It turns out that the observed fast evolution of the drop size distribution can only be modeled if the collision kernel for small drops is drastically increased. A physical argument for this amplification is missing since for such small drops, neither DNSs nor experiments have been performed. For large drops, for which a good agreement of the collision rates was found in the DNS and the experiment, the time for the evolution of the spectrum in the wind tunnel is too short to draw any conclusion. Hence, the long-time evolution of the drop size distribution is presented in a submitted paper by Riechelmann et al.

In numerical weather prediction models, parameterisations are used as an alternative to spectral modelling. One type of parameterisations are the so-called methods of moments. In the present study, two different methods of moments, a presumed-number-density-function method with finite upper integration limit and a quadrature method, are applied to a one-dimensional test case (‘rainshaft’) for drop sedimentation. The results are compared with those of a reference spectral model. An error norm is introduced, which is based on several characteristic properties of the drop ensemble relevant to the cloud microphysics context. This error norm makes it possible to carry out a quantitative comparison between the two methods. It turns out that the two moment methods presented constitute an improvement regarding two-moment presumed-number-density-function methods from literature for a variety of initial conditions. However, they are excelled by a traditional three-moment presumed-number-density-function method which requires less computational effort. Comparisons of error scores and moment profiles reveal that error scores alone should not be taken for a comparison of parameterisations, since moment profile characteristics can be lost in the integral value of the error norm.

RATIONALE The kinetic nature of the phosphoric acid digestion reaction enables clumped isotope analysis of carbonates using gas source isotope ratio mass spectrometry (IRMS). In most laboratories acid digestions are performed at 25°C in sealed vessels or at 90°C in a common acid bath. Here we show that different Δ47 results are obtained depending on the digestion technique employed. METHODS Several replicates of a biogenic aragonite and NBS 19 were reacted with 104% H3PO4 in sealed vessels at 25°C and at 90°C using a common acid bath. The sample size varied between 4 mg and 14 mg. Purification methods that are standard for clumped isotope analyses were applied to the evolved CO2 before measuring the abundances of masses 44 to 49 relative to a reference gas by IRMS. RESULTS A systematic trend to lower and more consistent Δ47 values is observed for reactions at 25°C if the sample size is increased. We suggest that secondary re-equilibration of evolved CO2 or reaction intermediates with free water molecules preferentially occurs for relatively small samples (4–7 mg), finally yielding elevated Δ47 values compared with >7 mg aliquots. In contrast, no such sample size effect on Δ47 values is observed for carbonates that are digested at 90°C using the common acid bath. CONCLUSIONS The determination of Δ47 values of carbonate samples smaller than 7 mg becomes more precise and accurate if digestions are performed at 90°C. Based on our results we propose that the difference in phosphoric acid fractionation factor between 25°C and 90°C is 0.07‰ for both calcite and aragonite. Copyright © 2013 John Wiley & Sons, Ltd.

RATIONALE The measurement of the abundances of minor isotopologues by mass spectrometry requires correction of subtle non-linearities in the mass spectrometer that cause deviations in the relationship between actual and measured isotope ratios. Here we show that negative backgrounds on the Faraday cups recording the minor ion beams are the cause of the observed non-linearities in the measurement of CO2 isotopologues, and propose a new correction procedure for clumped isotope measurements. METHODS We carefully investigated the cause of non-linearity effects in the measurement of the abundance of 13C18O16O, a minor isotopologue of CO2 with m/z 47, on two different mass spectrometers. By using gases of different composition with close to stochastic and with non-random distribution of isotopes we demonstrate that the apparent dependence of the excess abundance of the isotopologue of m/z 47 on the bulk isotopic composition of CO2 is due to a background interference that is linearly dependent on the partial pressure of the gas in the source of the mass spectrometer. CONCLUSIONS Background determination with gas flowing into the source of the mass spectrometer is necessary for accurate clumped isotope measurements of CO2. Background corrections can be performed accurately if the slit width of the m/z 44 Faraday cup significantly exceeds that of the one for m/z 47, using a correlation between m/z 44 signal intensity and the corresponding minimum in m/z 47 background. We propose two new correction schemes that reduce the time-consuming measurement of gases of different bulk isotopic compositions. These findings may also be relevant for the measurement of other rare isotopologues by mass spectrometry. Copyright © 2013 John Wiley & Sons, Ltd.

In the early 1980s, Germany started a new era of modern Antarctic research. The Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research (AWI) was founded and important research platforms such as the German permanent station in Antarctica, today called Neumayer III, and the research icebreaker Polarstern were installed. The research primarily focused on the Atlantic sector of the Southern Ocean. In parallel, the German Research Foundation (Deutsche Forschungsgemeinschaft, DFG) started a priority program ‘Antarctic Research’ (since 2003 called SPP-1158) to foster and intensify the cooperation between scientists from different German universities and the AWI as well as other institutes involved in polar research. Here, we review the main findings in meteorology and oceanography of the last decade, funded by the priority program. The paper presents field observations and modelling efforts, extending from the stratosphere to the deep ocean. The research spans a large range of temporal and spatial scales, including the interaction of both climate components. In particular, radiative processes, the interaction of the changing ozone layer with large-scale atmospheric circulations, and changes in the sea ice cover are discussed. Climate and weather forecast models provide an insight into the water cycle and the climate change signals associated with synoptic cyclones. Investigations of the atmospheric boundary layer focus on the interaction between atmosphere, sea ice and ocean in the vicinity of polynyas and leads. The chapters dedicated to polar oceanography review the interaction between the ocean and ice shelves with regard to the freshwater input and discuss the changes in water mass characteristics, ventilation and formation rates, crucial for the deepest limb of the global, climate-relevant meridional overturning circulation. They also highlight the associated storage of anthropogenic carbon as well as the cycling of carbon, nutrients and trace metals in the ocean with special emphasis on the Weddell Sea. DFG/SPP/1158

In common cloud microphysics parameterization models, the prognostic variables are one to three moments of the drop size distribution function. They are defined as integrals of the distribution function over a drop diameter ranging from zero to infinity. Recent works (by several authors) on a one-dimensional sedimentation problem have pointed out that there are problems with those parameterization models caused by the differing average propagation speeds of the prognostic moments. In this study, the authors propose to define the moments over a finite drop diameter range of [0, Dmax], corresponding to the limitation of drop size in nature. The ratios of the average propagation speeds are thereby also reduced. In the new model, mean particle masses above a certain threshold depending on Dmax lead to mathematical problems, which are solved by a mirroring technique. An identical, one-dimensional sedimentation problem for two moments is used to analyze the sensitivity of the results to the maximum drop diameter and to compare the proposed method with recent works. It turns out that Dmax has a systematic influence on the model’s results. A small, finite maximum drop diameter leads to a better representation of the moments and the mean drop mass when compared to the detailed microphysical model.

A weather episode, characterized by the passage of synoptic disturbances, is investigated for Dronning Maud Land, Antarctica. Due to the sparsity of observations, information about the spatial and temporal distribution of precipitation at high resolution can be gained only by modelling. The simulations presented here are performed with the high-resolution, non-hydrostatic weather forecast COSMO Model with a horizontal mesh size of 7 km. The comparison with observations at four stations shows that the simulation captures the general meteorological conditions well, while a warm bias and a weak daily cycle are found in near-surface temperatures. With regard to precipitation, the timing relates well to the observations; the amount of precipitation, however, is that of an extreme event and possibly overestimated in some regions. The horizontal distribution of precipitation is dominated by topographic effects. The simulations show the general decrease of precipitation toward the interior, as seen in the accumulation climatology, however, the decrease is not monotonous. For example, in the simulations horizontal structures such as precipitation bands of some 100 km width appear on the plateau, which can only be resolved by models with mesh sizes of 10 km or less.

It is well known that a subtle nonlinearity can occur during clumped isotope analysis of CO2 that - if remaining unaddressed - limits accuracy. The nonlinearity is induced by a negative background on the m/z 47 ion Faraday cup, whose magnitude is correlated with the intensity of the m/z 44 ion beam. The origin of the negative background remains unclear, but is possibly due to secondary electrons. Usually, CO2 gases of distinct bulk isotopic compositions are equilibrated at 1000 °C and measured along with the samples in order to be able to correct for this effect. Alternatively, measured m/z 47 beam intensities can be corrected for the contribution of secondary electrons after monitoring how the negative background on m/z 47 evolves with the intensity of the m/z 44 ion beam. The latter correction procedure seems to work well if the m/z 44 cup exhibits a wider slit width than the m/z 47 cup. Here we show that the negative m/z 47 background affects precision of dual inlet-based clumped isotope measurements of CO2 unless raw m/z 47 intensities are directly corrected for the contribution of secondary electrons. Moreover, inaccurate results can be obtained even if the heated gas approach is used to correct for the observed nonlinearity. The impact of the negative background on accuracy and precision arises from small imbalances in m/z 44 ion beam intensities between reference and sample CO2 measurements. It becomes the more significant the larger the relative contribution of secondary electrons to the m/z 47 signal is and the higher the flux rate of CO2 into the ion source is set. These problems can be overcome by correcting the measured m/z 47 ion beam intensities of sample and reference gas for the contributions deriving from secondary electrons after scaling these contributions to the intensities of the corresponding m/z 49 ion beams. Accuracy and precision of this correction are demonstrated by clumped isotope analysis of three internal carbonate standards. The proposed correction scheme can be easily applied if the slit width of the m/z 49 Faraday cup is bigger than that of the m/z 47 cup.

Raindrops in warm clouds grow faster than predicted by classical cloud models. One of the possible reasons for this discrepancy is the influence of cloud turbulence on the coagulation process. In Part I (Siewert et al., 2014) of this paper series, a turbulent collision kernel has been derived from wind tunnel experiments and direct numerical simulations (DNS). Here we use this new collision kernel to investigate the influence of turbulence on coagulation and rain formation using two models of different complexity: a one-dimensional model called RAINSHAFT (height as coordinate) with cloud microphysics treated by a spectral bin model (BIN) and a large-eddy simulation (LES) model with cloud microphysics treated by Lagrangian particles (a so called Lagrangian Cloud Model, LCM). Simulations are performed for the case of no turbulence and for two situations with moderate and with extremely strong turbulence. The idealized 0- and 1-dimensional runs show, that large drops grow faster in the case turbulence is taken into account in the cloud microphysics, as was also found by earlier investigations of other groups. For moderate turbulence intensity, the acceleration is only weak, while it is more significant for strong turbulence. From the model intercomparison it turns out, that the BIN model produced large drops much faster than the LCM, independent of turbulence intensity. The differences are larger than those due to a variation in turbulence intensities. The diverging rate of formation of large drops is due to the use of different growth models for the coagulation process, i.e. the quasi-stochastic model in the spectral BIN model and the continuous growth model in LCM. From the results of this model intercomparison it is concluded, that the coagulation process has to be improved in future versions of the LCM. The LES-LCM model was also applied to the simulation of a single 3-D cumulus cloud. It turned out, that the effect of turbulence on drop formation was even smaller as the turbulence within the cloud was weaker than prescribed in the idealized cases. In summary, the use of the new turbulent collision kernel derived in Part I does enhance rain formation under typical turbulence conditions found in natural clouds but the effect is not very striking. © 2015 The authors. DFG/SPP/1276 DFG/ET 8/14 DFG/WA 1334/8 DFG/BE 2081/10

Ice particles are considered in prevalent cloud microphysical parametrisation schemes in a simplified way by assigning them certain fixed forms, whereas in the atmosphere they occur in various different shapes. In this study, the sensitivity of cloud and precipitation properties to the selected interpretation of the ice particle shape is investigated with the help of simulations of a wintertime weather episode using the mesoscale weather forecast model ‘Lokal–Modell’ of the DWD. The results show that the interpretation of the particular ice particle type has a clear impact on the local surface precipitation rates while the area mean surface precipitation is only slightly affected. Most striking, however, is the influence on the simulated masses of cloud water in the atmosphere. To avoid the prescription of a fixed ice particle shape, a parametrisation variant is presented to account for the variation of ice particles' shape according to their growth history.

The local mass balance equations of cloudy air are formulated for a model system composed of dry air, water vapor, and four categories of water condensate particles, as typically adopted for numerical weather prediction and climate models. The choice of the barycentric velocity as reference motion provides the most convenient form of the total mass continuity equation. Mass transfer across the earth’s surface due to precipitation and evaporation causes a nonvanishing barycentric vertical velocity ws and is proportional to the local difference between evaporation rate and rain plus snow rate. Hence ws vanishes only in the special situation that evaporation and precipitation balance exactly. Alternative concepts related to different reference motions are reviewed. However, the choice of the barycentric velocity turns out to be advantageous for several reasons. The implication of the nonvanishing total mass transport across the earth’s surface is estimated from model simulations for two extreme weather situations: a polar cold air outbreak and a tropical cyclone. While the effect is small in the first case, it is important in the latter. The large precipitation rates in the tropical cyclone case cause a loss of atmospheric mass, which corresponds to a vertical velocity at the surface larger than −20 mm s−1, and an instantaneous drop in pressure, which if sustained for 6 h, would correspond to about 49 hPa; this demonstrates the necessity of using the correct formulation of the mass balance in simulation models for moist air.

The paper focuses on a comparison of solutions of the budget equations for specific moments of a hydrometeor size distribution, simplified to the problem of pure drop sedimentation, as following from models with a one-moment or a two-moment parameterization of microphysical processes and from a reference model based on spectral treatment of sedimentation. The solutions for the transient vertical profiles of liquid water content show remarkable differences in their spatial structure: starting from an idealized, discontinuous initial profile in form of a square wave, shock and rarefaction waves evolve in the parameterized models, while the reference solution describes a smooth distribution. These principle differences follow from the fact, that the budget equations for the moments in the parameterized models are of the form of quasi-linear advection equations, with the decisive nonlinearity arising from the parameterization relation for the sedimentation flux, whereas the reference solution follows from a linear partial differential equation. Hence, the quasi-linear shock effects have to be interpreted as a mathematical artifact of the parameterization assumptions. The differing evolution of the liquid water profiles finds expression in remarkable differences in the time series of surface precipitation rate for the spectral and parameterized models.

Atmospheric CCN-humidity spectra (describing the CCN-number concentration as function of supersaturation) are derived as the integral over given particle size distributions. In that concept the finite boundary, representing the limiting activated particle size, results from the critical values of the Kohler-curve. As utilization of this general outcome different representative aerosol size distributions of the power law type as well as the log-normal type are chosen for case studies which are compared to empirical results. The dependency on temperature of the limiting activated particle size is shown to provide a non-negligible influence on the number of activated particles.

The kinetic nature of the phosphoric acid digestion reaction enables clumped isotope analysis of carbonates using gas source isotope ratio mass spectrometry (IRMS). In most laboratories acid digestions are performed at 25°C in sealed vessels or at 90°C in a common acid bath. Here we show that different Δ47 results are obtained depending on the digestion technique employed.Several replicates of a biogenic aragonite and NBS 19 were reacted with 104% H3 PO4 in sealed vessels at 25°C and at 90°C using a common acid bath. The sample size varied between 4 mg and 14 mg. Purification methods that are standard for clumped isotope analyses were applied to the evolved CO2 before measuring the abundances of masses 44 to 49 relative to a reference gas by IRMS.A systematic trend to lower and more consistent Δ47 values is observed for reactions at 25°C if the sample size is increased. We suggest that secondary re-equilibration of evolved CO2 or reaction intermediates with free water molecules preferentially occurs for relatively small samples (4-7 mg), finally yielding elevated Δ47 values compared with7 mg aliquots. In contrast, no such sample size effect on Δ47 values is observed for carbonates that are digested at 90°C using the common acid bath.The determination of Δ47 values of carbonate samples smaller than 7 mg becomes more precise and accurate if digestions are performed at 90°C. Based on our results we propose that the difference in phosphoric acid fractionation factor between 25°C and 90°C is 0.07‰ for both calcite and aragonite.

The measurement of the abundances of minor isotopologues by mass spectrometry requires correction of subtle non-linearities in the mass spectrometer that cause deviations in the relationship between actual and measured isotope ratios. Here we show that negative backgrounds on the Faraday cups recording the minor ion beams are the cause of the observed non-linearities in the measurement of CO(2) isotopologues, and propose a new correction procedure for clumped isotope measurements.We carefully investigated the cause of non-linearity effects in the measurement of the abundance of (13)C(18)O(16)O, a minor isotopologue of CO(2) with m/z 47, on two different mass spectrometers. By using gases of different composition with close to stochastic and with non-random distribution of isotopes we demonstrate that the apparent dependence of the excess abundance of the isotopologue of m/z 47 on the bulk isotopic composition of CO(2) is due to a background interference that is linearly dependent on the partial pressure of the gas in the source of the mass spectrometer.Background determination with gas flowing into the source of the mass spectrometer is necessary for accurate clumped isotope measurements of CO(2). Background corrections can be performed accurately if the slit width of the m/z 44 Faraday cup significantly exceeds that of the one for m/z 47, using a correlation between m/z 44 signal intensity and the corresponding minimum in m/z 47 background. We propose two new correction schemes that reduce the time-consuming measurement of gases of different bulk isotopic compositions. These findings may also be relevant for the measurement of other rare isotopologues by mass spectrometry.

The mathematical representation of the mass continuity equation and a boundary condition for thevertical velocity at the earth’s surface is re-examined in terms of its dependence on the frame ofreference velocity. Three of the most prominent meteorological examples are treated here: (a) thebarycentric velocity of a full cloudy air system, (b) the barycentric velocity of a mixture consisting ofdry air andwater vapour and (c) the velocity of dry air. Although evidently the physical foundation holdsindependently of the choice of a particular frame, the resulting equations differ in their mathematicalstructure: In examples (b) and (c) the diffusion flux divergence that appears in the corresponding massequation of continuity should not be omitted a priori. As to the lower boundary condition for the normalcomponent of velocity, special emphasis is placed on the net mass transfer across the earth’s surfaceresulting from precipitation and evaporation. It is shown that for a flat surface, the reference verticalvelocity vanishes only in case (c). Regarding cases (a) and (b), the vertical reference velocities aredetermined as functions of the precipitation and evaporation rates. They are nonzero, and it is shownthat they cannot generally be neglected. DOI: 10.1034/j.1600-0870.2003.00019.x

This chapter summarises mesoscale modelling studies, which were carried out during the ACSYS decade until 2005. They were aiming at the parameterisation and improved understanding of processes in the Arctic boundary layer over the open ocean and marginal sea ice zones and over the Greenland ice sheet. It is shown that progress has been achieved with the parameterization of fluxes in strong convective situations such as cold-air outbreaks and convection over leads. A first step was made towards the parameterization of the lead-induced turbulence for high-resolution, but non-eddy resolving models. Progress has also been made with the parameterization of the near-surface atmospheric fluxes of energy and momentum modified by sea ice pressure ridges and by ice floe edges. Other studies brought new insight into the complex processes influencing sea ice transport and atmospheric stability over sea ice. Improved understanding was obtained on the cloud effects on the snow/ice surface temperature and further on the near-surface turbulent fluxes. Finally, open questions are addressed, which remained after the ACSYS decade for future programmes having been started in the years after 2005.

Common parametrization models for cloud microphysical processes use condensate mass density and/or particle number density as prognostic properties. However, other moments of the particle size distribution can likewise be chosen for prediction. This study deals with parametrization models with one and two, respectively, prognostic moments for the sedimentation of drop ensembles. The spectral resolving model defines the reference solution. The evolution of the vertical profiles of liquid water content, drop number density and rain rate strongly depend on the choice of the prognostic moments in the parametrization models. In models with a single prognostic moment, its vertical profile is copied by all other moments. The moment of most physical pertinence is recommended for prediction. In models with two prognostic moments, the vertical profiles of all moments differ. The orders of the prognostic moments should be chosen close to the order of moments of highest relevance. Otherwise large errors occur. For example, comparison of modelled versus observed radar reflectivity (6th moment with respect to diameter) does not tell much about the quality of other properties if reflectivity is diagnosed from for example, number density and mass density. Furthermore, mass conservation is fulfilled only if mass density is forecasted.

[1] The maximum effect of open leads within sea ice on the near-surface atmospheric temperature is estimated using a 1D atmospheric model coupled with a thermodynamic snow/sea ice model. The study is restricted to clear-sky conditions during polar night. The model is initialized with a typical wintertime atmospheric temperature profile. Results are analyzed at different integration times corresponding to different fetches over the fractured sea ice as a function of wind speed and sea ice concentration A. The results demonstrate that for A > 90% small changes in the sea ice fraction have a strong effect on the near-surface temperature. A change by 1% causes a temperature signal of up to 3.5 K. A threshold value of about 4 m s−1 for the 10-m wind speed divides the air-ice interaction process into a weak-wind and strong-wind regime.

[1] The effect of the choice of ice particle type in the parameterization of cloud microphysics on the simulated cloud and precipitation properties is investigated. Generalized parameterization equations for riming and deposition rates as well as sedimentation fluxes are given. Simulation studies with a mesoscale numerical weather prediction model for a two-dimensional flow over a hill show that the fields of condensate content and precipitation strongly depend on the interpretation of the sedimenting ice particles as e.g., graupel or unrimed aggregates. A parameterization model to account for the variation of particle attributes due to riming is presented.

Monatswerte der Sonnenscheindauer an 11 Stationen des sudwestdeutschen Raumes aus der Zeit 1890–1977 werden mit Hilfe von statistischen Methoden untersucht. Die Analyse der zeitlichen Schwankungen erfolgt anhand von 11- bis 30jahrigen gleitenden Mitteln, Haufigkeit und Ausmas von Extremwerten, Variationskoeffizient und relativer interannueller Variabilitat. Die Sonnenscheindauer hat gegenuber den Werten um 1900 in allen Jahreszeiten zugenommen; in den letzten Jahren ist wieder ein abnehmender Trend erkennbar. Die 30jahrig gleitenden Variabilitatsmase erreichen im Sommer- und Wintertertial ihr Minimum um 1930.

The irreversible H2O-transfer between a drop and moist air is described on the basis of the diffusion model for condensational drop growth. Depending on the chosen form of the flux-gradient relationship to approach the irreversible vapour diffusion flux, distinct equations for the growth rate follow, all of which are equally in accord with thermodynamics. They differ in the formulation of the driving force and in the choice of the relevant moisture variable as well as in the correction term due to thermal effects. Considering all assumptions entering the approaches of the condensational drop growth rate, arguments are provided that the most relevant form of the growth equation should be that depending linearly on the mass fraction of water vapour in air as representative moisture variable.

The application of the theory of non-equilibrium thermodynamics to phenomena of cloud micro-physics has been examined for the example of mass growth of atmospheric water drops due to vapour diffusion and condensation. A materially and energetically closed heterogeneous system composed of a drop phase and a surrounding dry air-water vapour mixture is assumed as appropriate basic model in order to treat the concomitant theoretical aspects (comprising description of the individual growth rate, variation of moist air temperature, and drop surface conditions) in dependency on the central criteria of irreversibility. Owing to this, a main object of our theory is the thorough derivation of the budget equations of thermal energy and entropy representing, respectively, the first and second law of thermodynamics. Physically, these principles, associated with the peculiar thermodynamic behaviour of coexisting atmospheric drops and vapour, embody a suitable theoretical frame for the line of reasoning. The dominant position is owned by the production rate of entropy, a bilinear form of thermodynamic forces and fluxes. The occasion arises to postulate adequate non-equilibrium laws for the irreversible transport of matter and heat. With regard to the entropy rate of change and the thermodynamic situation in the drop-moist air model, one is left with the option to consider several alternative postulates for the fluxes and, hence, several equivalent parameterizations of the growth rate of drops. Four such approaches in accord with the thermodynamic context are discussed. As each of them depends on the surface temperatures of drops, it is expedient to complete the growth equations by a separate treatment of these micro-state variables. Practical scaling arguments for these internal thermodynamic parameters reveal that a suitable reduced form of the energy budget for the isolated drop-moist air-model system can be assumed. As a consequence, the droplet surface temperature becomes a diagnostic parameter which can be eliminated from the growth equation.