Kinetic fractionation of the isotope composition of 18O, 13C, and of clumped isotope 18O13C in calcite deposited to speleothems. Implications to the reliability of the 18O and Δ47 paleothermometers

Kinetic fractionation of 18O and clumped isotopes 13C18O in calcite precipitated to speleothems in cave environments renders the paleo-climatic interpretation of these proxies difficult. Therefore a better understanding of the processes generating the isotope imprint is needed. A heuristic approach is taken to interpret recent data of the fractionations in a cave analogue experiment of calcite precipitation (Hansen et al. 2019) that shows a dependence on experimental precipitation rates, F. An expression, , is derived that is based on uni-directional irreversible precipitation and is valid for large F when the forward rate of precipitation dominates the backward rate of dissolution. In that derivation it is assumed that the kinetic constants of precipitation rates are different for the different isotopologues and that this is also true for their equilibrium concentrations ceq with respect to calcite. The constant, ε, is expressed by the kinetic fractionation where α denote the rate constants of precipitation for the rare and abundant isotopologues. The second constant, λ, is determined by the differing equilibrium concentrations of HCO3- isotopologues with respect to calcite and the pCO2 in the surrounding atmosphere. Fitting this expression to the experimental data one obtains the parameters ε and λ for different temperatures. Regarding these results the temporal evolution of 18δCaCO3 (t) and Δ47(t) is discussed for the experimental conditions and for cave environments. This has implications to the application of 1000lnα18 CaCO3-H2O as a paleo-thermometer. It shows the reason why so many differing calibrations have been reported. These results analogously can be applied also to clumped isotopes 13C18O and the calibration of the Δ47-thermometer with regard to speleothem calcite. In summary, a better understanding of the problems arising in the search for generally valid calibrations of 18O and Δ47 paleothermometers is presented.Key words: Calcium carbonate, 13C and 18O isotopes, clumped isotopes, kinetic fractionation between HCO3- and calcite, Δ47 paleothermometer.Kinetična frakcionacija izotopov 18O, 13C in izotopskega skupka 18O13C v sigah in zanesljivost paleotermometrov 18O in Δ47Kinetična frakcionacija 18O in skupka 13C18O v kalcitu, ki se kot siga odlaga v jamskih okoljih, dela težave pri interpretaciji paleoklime na osnovi teh proksijev. Zato potrebujemo boljše razumevanje procesov, od katerih je odvisen izotopski zapis v sigah. V tem delu s hevrističnim pristopom interpretiramo nedavno pridobljene podatke frakcionacij . Podatki, pridobljeni ob izločanju kalcita v pogojih, podobnih jamskim, kažejo, da na frakcionacijo bistveno vpliva hitrost izločanja kalcita (Hansen et al. 2019). V pogojih, ko je izločanje bistveno hitrejše od raztapljanja, velja zveza . Pri izpeljavi te enačbe upoštevamo, da so kinetične konstante izločanja in ravnotežna konstanta kalcita različne za različne izotopologe. Konstanto ε lahko izrazimo s kinetično frakcionacijo , kjer je α konstanta izločanja za redke oziroma večinske izotopologe. Drugo konstanto λ dobimo iz razlik ravnotežnih koncentracij izotopologov HCO3- glede na kalcit in na atmosferski pCO2 . S prilagajanjem izraza eksperimentalnim podatkom dobimo ε in λ pri različnih temperaturah. To omogoča obravnavo časovne odvisnosti 18δCaCO3 (t) in Δ47(t) pri eksperimentalnih pogojih in v jamskem okolju. Rezultati so pomembni za razumevanje uporabnosti paleotermometra 1000lnα18CaCO3-H2O in hkrati pokažejo na vzrok različnih kalibracij, kot jih zasledimo v literaturi. Rezultate lahko uporabimo tudi za izotopske skupke 13C18O in kalibracijo Δ47- za kalcitno sigo. Članek predstavi nov pogled na iskanje splošno veljavne kalibracije paleotermometrov 18O in Δ47.Ključne besede: kalcit, izotopa 13C in 18O, izotopski skupki, kinetična frakcionacij a med HCO3- in kalcitom, paleotermometer Δ47.

Isotope exchange between DIC in a calcite depositing water layer and the CO2 in the surrounding atmosphere : Resolving a recent controversy

Isotope exchange between DIC in a calcite depositing water layer and the CO2 in the surrounding atmosphere : Resolving a recent controvers

Problems in using the approach of Rayleigh distillation to interpret the 13C and 18O isotope compositions in stalagmite calcite

When calcite is precipitated from a water film on top of a stalagmite to its surface, the carbonate in the solution and consequently also the carbonate in the calcite deposited becomes enriched in the heavy isotopes 18O and 13C (Hansen et al. 2016; Dreybrodt & Scholz 2011; Romanov et al. 2008). This isotope signal is added to the isotope imprint resulting from climate variability. Therefore a physical model of the evolution of the isotope composition of carbonate in a water film, either flowing down the surface of the stalagmite at high drip rates or stagnant, when the drip rate is low, is necessary to discriminate the climate signal from the signal resulting from physical processes in the cave.Currently two models are proposed. In the first one (Scholz et al. 2009) one assumes that the isotope evolution can be described by a Rayleigh distillation process (Mook 2000) where during the entire process of precipitation the fractionation factor for carbon or oxygen, respectively remains constant. In another model one assumes that precipitation is a uni-directional non-equilibrium process, where the constants in the rate equations are slightly different for the light and the heavy isotope (Dreybrodt 2008; Dreybrodt & Scholz 2011). Results from these models have been compared for various scenarios by Scholz et al. (2009), Dreybrodt and Scholz (2011), Dreybrodt and Deininger (2014) and Dreybrodt and Romanov (2016). Differences of opinion clearly exist in the research community regarding which of these models best represents reality. In this letter I discuss the meaning of the Rayleigh equation for precipitation of calcite under equilibrium conditions and for precipitation of calcite governed by uni-directional rate equations

Implication to 13C, 18O, and clumped 13C18O isotope composition in DIC and calcite

Outgassing of CO2 from thin water layers of a solution of CaCO3 in an H2O -CO2 system plays a crucial role in the precipitation of calcite. Understanding the process of outgassing of CO2 during precipitation of calcite to the surface of stalagmites is important for the interpretation of isotope signals in the calcite deposited to the speleothem. There is, however, some confusion in the literature about the physics and chemistry of this process. Indistinct terms like forced, enhanced, rapid, intense, slow, increased, equilibrium and progressive outgassing are used widely in the literature to explain the impact on isotope composition of the calcite deposited. It is shown that in all the variety of conditions occurring in nature only two distinct processes of outgassing exist. 1. Diffusion controlled outgassing: In the first step, whenever a thin water layer of calcareous solution is present, either on the cave wall or on the surface of a stalagmite, molecular CO2 escapes within several seconds by physical diffusion and after about 40 seconds pH and DIC in the solution achieve chemical equilibrium with respect to the CO2 in the cave atmosphere. 2.) Controlled by precipitation: In the second step this supersaturated solution precipitates calcite, whereby for each unit CaCO3 deposited one molecule of CO2 is generated and escapes from the solution by molecular diffusion. This precipitation controlled outgassing is active during precipitation only. All variations of outgassing mentioned in the literature can be explained by one of these two types of outgassing. Furthermore it is shown that the first step of outgassing driven by diffusion has no influence on the isotope composition of the HCO3 - reservoir in the solution and consequently on that of calcite precipitated from it. The isotope composition of HCO3 for 13C as well as for 18O solely is determined by the second step of precipitation controlled outgassing. An experiment is presented proving that the amount of CO2 escaping from the solution during precipitation of calcite at any time is equal to the amount of calcite precipitated. The results are used for a critical application to the Δ47 clumped isotope thermometer that explains why in most stalagmites the calcite is not a good candidate to obtain correct temperatures at the time of its deposition.Key words: isotope, clumped isotope, speleothem, calcite, paleo- thermometer.Fizika in kemija razplinjanja CO2 pri odlaganju sige, s posebnim ozirom na signale izotopa 18O in izotopskega skupka 13C18O v raztopljenem organskem ogljiku in kalcituRazplinjanje CO2 iz tanke plasti raztopine sistema CaCO3 in H2O–CO2 je pomembno za izločanje kalcita in interpretacijo izotopskih signalov v odloženem kalcitu. V literaturi je precejšnja zmeda pri obravnavanju fizike in kemije procesa razplinjanja, saj raziskovalci uporabljajo različne izraze, kot so prisiljeno, poudarjeno, počasno, povečano in progresivno razplinjanje. V članku pokažem, da sta pri vseh različnih razmerah v naravi bistvena le dva procesa razplinjanja. 1) Difuzijsko razplinjanje: v prvem koraku molekularni CO2 v nekaj sekundah z difuzijo preide iz tanke plati vode, ki polzi ali po jamski steni ali po površini sige. Po približno 40 sekundah pH in raztopljeni organski ogljik v raztopini dosežeta ravnovesje z atmosferskim CO2. 2) Razplinjanje pri izločanju: v drugem koraku prenasičena raztopina izloča kalcit, pri čemer se za vsako odloženo molekulo CaCO3 iz raztopine sprosti molekula CO2, ki potem z difuzijo uide v jamsko atmosfero. S tema procesoma lahko pojasnimo vse druge načine razplinjanja, ki jih omenja literatura. Nato pokažem, da CO2, ki se razplini v prvem koraku, ne vpliva na izotopsko sestavo zaloge HCO3- v raztopini in zato tudi v izločenem kalcitu. Izotopska sestava HCO3- je tako za 13C in za 18O povsem določena z razplinjanjem med izločanjem kalcita. Ujemanje količine razplinjenega CO2 in izločenega kalcita pokažem tudi s poskusom. Rezultati omogočajo kritično obravnavo uporabe termometra na osnovi izotopskega skupka Δ47 in pojasnjujejo, zakaj kalcit ni primeren za določanje temperature v času izločanja.Ključne besede: izotop, izotopski skupek, siga, kalcit, paleo temperatura

Good for career-bad for science: Advice, how to optimize your career.: Observations and experiences in science factory by a last century scientist

The number of scientists and correspondingly the flood of publications explode. “Between 2008 and 2014, the number of scientific articles catalogued in the Science Citation Index of Thomson Reuters’ Web of Science grew by 23%, from 1.029,471 to 1.270,425. There were 7.8 million full-time equivalent researchers in 2013, representing growth of 21% since 2007” (UNESCO science report: towards2030,2015,http://uis.unesco.org/sites/default/ files/documents/unesco-science-report-towards- 2030-ex-sum-en.pdf). This has consequences to the rules of science production in the science factories. Publications are products that need marketing and the cash paid is a long list of publications and citations in journals of high impact factors that foster the career of authors. I have observed this during the last ten years and found that the following rules should be observed to support a successful career. All of the rules that I give below rest on true examples. The reader may judge whether these rules support the quality of science. My personal opinion is, they do not. Discussion in the community is urgently needed, but it will need a display of courage

Physics and Chemistry of Dissolution on Subaerialy Exposed Soluble Rocks by Flowing Water Films

The basic process active in the formation of subaerial features on karst rocks is chemical dissolution of limestone or gypsum by water films flowing on the rock surface. The dissolution rates of limestone and gypsum into thin films of water in laminar flow are given by F = α(ceq-c), where (ceq-c) is the difference of the actual concentration c in the water film and the equilibrium concentration ceq with respect to the corresponding mineral. Whereas for gypsum α is determined by molecular diffusion the situation is more complex for limestone. Experiments are presented, which show that for high undersaturation, c<0.3ceq, the rate law is F = α( 0.3ceq-c) ,and α becomes higher by about a factor of ten than for the rates at c>0.3ceq. These rate laws are used to calculate denudation rates on bare rock surfaces exposed to rainfall with differing intensity. The estimations are in reasonable agreement to field data. Starting from the experiments on the formation of Rillenkarren on gypsum performed by Glew and Ford (1980), we suggest a new relation between their length from the crest to the “Ausgleichsfläche” and the inclination of the rock surface. This is also applied to field data of Rillenkarren on limestone provided by J. Lundberg and A. Gines. In view of the many parameters influencing the formation of Rillenkarren these correlations can be considered as satisfactory

Regular stalagmites: The theory behind their shape

Under growth conditions constant in time stalagmites grow into an equilibrium shape, which is established, when all points of its surface are shifting by the same vertical distance during a time inter­val. Thereby is the recipitation rate in, is the calcium concentration of the supersatu­rated solution dripping to the apex of the stalagmite, and its equilibrium concentration with respect to calcite and the in the cave atmosphere. From these ingredients a numerical model of stalagmite growth into an equilibrium shape is presented. In this model one assumes idealistically that the water dripping to the apex flows continuously down the stalagmite, spreading out radially. By simple mass balance one finds that the equilibrium radius is , where is the volume of a drop and the drip interval. Furthermore numerical modeling repro­duces the vertical shifting of the stalagmite’s equilibrium shape. Finally an interesting similarity rule is found. If one scales two stalagmites of differing to the same size and chooses their growth axes as common axis and their apexes as common ori­gin, both show identical shapes. In other words regular stalag­mites are similar geometrically. This similarity rule is verified by digitizing the shapes of various natural stalagmites with di­ameters between 5 cm and 20 m. Within small natural varia­tions, the rescaled shapes are identical and close to the shape of the numerical model

Small-scale Terraces and Isolated Rimstone Pools on Stalagmites in Caves Exhibit Striking Similarity to Large-scale Terrace Landscapes at Hot Springs

We report on sinter terrace forms on the centimetre scale observed on the top and at the base of a stalagmite in Škocjanske jame (Škocjan caves). These exhibit connected rimstone dams, forming a net-like pattern with active water pools inside. The form is similar to those seen at the large travertine terraces, which form by precipitation of calcite from spring waters highly supersaturated with respect to calcite. In contrast to these patterns we have also found isolated sinter basins with dimensions of a few centimeter on stalagmite-like structures in the cave Dimnice, Slovenia. Similar basins a few meters wide are a tourist attraction in Pamukkale, Denizli, Turkey. The observed features have grown from supersaturated solutions of calcium carbonate in laminar flow. Large-scale landscapes originate under conditions of turbulent flow. Some ideas are presented why, in spite of the clear difference in flow, the shapes are similar on all scales