H fractionation during the sublimation of water ice

Accepted Manuscript

D/H fractionation during the sublimation of water ice Christophe Lecuyer , Aurelien Royer , Franc¸ois Fourel , ´ ´ Magali Seris , Laurent Simon , Franc¸ois Robert PII: DOI: Reference:

S0019-1035(16)30184-1 10.1016/j.icarus.2016.12.015 YICAR 12303

To appear in:

Icarus

Received date: Revised date: Accepted date:

13 May 2016 4 November 2016 10 December 2016

Please cite this article as: Christophe Lecuyer , Aurelien Royer , Franc¸ois Fourel , Magali Seris , ´ ´ Laurent Simon , Franc¸ois Robert , D/H fractionation during the sublimation of water ice, Icarus (2016), doi: 10.1016/j.icarus.2016.12.015

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Highlights Sublimation of water ice was performed between -105°C and -30°C

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Sublimation produced isotopic fractionations in the range 0.969 to 1.123

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Below ≈ -50°C the water vapour is D-depleted relative to the residual ice

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Such D/H fractionations have impacts on the water cycle of terrestrial planets

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Sublimation cannot explain the D/H differences amongst Earth’s water and comets

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D/H fractionation during the sublimation of water ice

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Christophe Lécuyer1,*, Aurélien Royer1, François Fourel1, Magali Seris1,

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Laurent Simon2 and François Robert3

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Laboratoire de Géologie de Lyon, CNRS UMR 5276, University Claude

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Bernard Lyon 1, France 2

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Laboratoire d'Ecologie des Hydrosystèmes Naturels et Anthropisés, CNRS

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UMR 5023, University Claude Bernard Lyon 1, France

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Laboratoire de Minéralogie et Cosmochimie du Muséum, CNRS–MNHN UMR

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7202, Paris, France

*Corresponding author, also at Institut Universitaire de France.

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Abstract size: 172 words Full text size: 3,080 words

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1 Table; 5 Figures

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ACCEPTED MANUSCRIPT Keywords: water ice; sublimation; D/H; isotopic fractionation; comet

Abstract – Experiments of sublimation of pure water ice have been performed

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in the temperature range -105°C to -30°C and atmospheric partial pressures ranging from 10-6 to 10-1 mb. Sampling of both vapour and residual ice fractions has been performed with the use of a vacuum line designed for the extraction and

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purification of gases before the measurement of their D/H ratios. Sublimation was responsible for sizable isotopic fractionation factors in the range 0.969 to

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1.123 for temperatures lying between -105°C and -30°C. The fractionation factor

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exhibits a cross-over at temperatures around -50°C with the water vapour fraction being D-depleted relative to the residual ice fraction at T-50°C (ice-vapour

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= 0.969 to 0.995). This cross-over has implications for the understanding of the

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atmospheric water cycle of some terrestrial planets such as the Earth or Mars.

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The magnitude of deuterium enrichment or depletion between ice and water vapour cannot explain the differences in the D/H ratios amongst Jupiter comets and long–period comets families nor those that have been documented between Earth’s and cometary water.

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ACCEPTED MANUSCRIPT 1. Introduction

In Cosmochemistry, the D/H ratio is often used to trace the origin of water

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in solar system planets or asteroids (Ceccarelli et al., 2014; Jacquet and Robert, 2013; Ali-Dib et al., 2015). Clay minerals in the carbonaceous meteorites (chondrites) show a distribution of this D/H ratio ranging from 125 to 300 x10-6

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with a pronounced peak in the distribution around 150 x10-6 (in the following discussion this range will be referred to as the Chondritic distribution). Such a

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range is markedly different from (i) the protosolar hydrogen reservoir

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(D/H=20±5 x10-6) still constituting the atmospheres of the giant gaseous planets, (ii) cometary water (D/H ranging from 137 to 600 x10-6) or (iii)

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interstellar ice grains (D/H ≥ 950x10-6).

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The Chondritic distribution reflects the isotopic compositions of the water

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sources that have circulated in parent body meteorites during hydrothermal events that took place shortly after their accretion. The isotopic fractionation between clay minerals and water (5-10%), is negligible compared to the 300% variations defined by solar system planets and planetoïds. The origin of the

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ACCEPTED MANUSCRIPT Chondritic distribution remains unclear and no scientific consensus exists on this issue. The average D/H ratio of the Chondritic distribution is similar (within ±10%)

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to that of the Bulk Terrestrial Water Mantle (149±3 x10-6 including water buried in the deep mantle; Lécuyer et al., 1998; here after reported to as BTWM). It is thus generally accepted that the water on Earth reflects a mixture of several

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types of carbonaceous chondrites, added to the Earth during the final stages of its accretion. This scenario implies that the water actually forming the oceans condensed

in

the

protosolar

nebula

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regions

and

at

distances

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was

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commensurable with those where carbonaceous chondrites formed, i.e. between 3 and 10 A.U. In these regions the temperature was continuously lower than 190K

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and water existed as solid grains in the protosolar disk, eventually mixed with

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anhydrous minerals (Jacquet and Robert, 2013). The D/H ratios of water

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sublimated from 9 comets during their approach to the Sun, were measured spectroscopically (Hartog et al., 2011). These data show that the comets are systematically enriched in deuterium and show a clear isotopic heterogeneity whose origin is unknown. In two cases, the isotopic ratios were also measured by mass-spectrometers on board space missions and do not show any disagreement 6

ACCEPTED MANUSCRIPT with spectroscopic determination, excluding possible systematic bias between spectroscopic (comets) and spectrometric (meteorites) data. However, we wish to mention here that the geochemical mass spectrometers - through which the

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Chondritic distribution was established - have not been inter-calibrated with the on board space missions instruments. Since on average, comets show a D/H ratio that is a factor of 2 times higher than that of the BTWM, they cannot be the

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source of water on Earth.

However, it was argued that water vapour can be isotopically fractionated

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relative to the solid, during sublimation. If correct, (i) the measured D/H ratio in

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the vapour phase would not reflect the bulk D/H ratio of the comets and (ii) consequently, the statement regarding the impossibility of comets being the origin

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of water on Earth may be incorrect.

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In this paper we have examined this question experimentally. In these types of

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experiments, the possible sources of deuterium contamination of sublimating water are numerous. To overcome this central experimental issue, (1) we have used waters with D/H ratios lying in the terrestrial domain (i.e. D/H ≈ 150 x106

) to minimize the likelihood of possible contamination (this is a central issue

when using water isotopically labelled) and (2) we have measured precisely the 7

ACCEPTED MANUSCRIPT D/H ratio of both the sublimated and the residual ice in order to verify the isotopic mass balance between these two water fractions. The latter point (2) permits the elimination of all possible contamination artefacts. To emphasize our

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conclusions in this introduction, considering the large error bars on spectroscopic data, the cometary solid ice D/H ratio remains indistinguishable from that

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measured in its vapour phase (within ±10%).

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2. Experimental protocol

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2.1. Sublimation of water ice under vacuum

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P-T domains where sublimation of water ice takes place have been

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estimated by using the following integrated form of the Clausius–Clapeyron’s

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equation:

Ln(P0/P) = -∆ H/R.(1/T0 - 1/Tsub)

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(1)

ACCEPTED MANUSCRIPT P0 and T0 are the pressure (1013 mb) and temperature (100°C) of reference, P is the saturated vapour pressure at the temperature of sublimation Tsub, R (8.314 J.mol-1.K-1) is the universal constant of the ideal gases and ∆ H (51

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k.J.mol-1) is the enthalpy of sublimation of water ice. Accordingly, forty-one experiments of sublimation of pure water ice have been performed in the temperature range -105°C to -30°C and atmospheric

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partial pressures ranging from 10-6 to 10-1 mbar (Figure 1). Sampling of both vapour and residual ice fractions has been performed with the use of a vacuum

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line designed for the extraction and purification of gases before the measurement

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of their D/H ratios (Figure 2). Temperatures of sublimation were monitored using a temperature-controlled cryogenic trap (TCCP) fully operating in the

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range -190°C to -20°C. Temperature was modulated (±2°C) by using a thermal

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resistance heating wire, stored within a Pyrex™ chamber, in conjunction with an

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external isolated bath of liquid nitrogen. Heat transmission was ensured by use of an envelope of helium gas within the PyrexTM chamber. A sublimation experiment consisted of the sampling of 0.5 mL of water from an isotopically homogenous reservoir tank of 1 L of known D/H ratio (see section 2.2). As a first step, the sample was placed into a Pyrex™ glass sample 9

ACCEPTED MANUSCRIPT vessel, then connected to the vacuum line before being frozen with liquid nitrogen. Once the residual amount of air had been pumped, the water sample had been heated and quantitatively (i.e. with no possible loss) transferred to the

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TCCP by the use of a liquid nitrogen trap. A second step consisted of selecting a temperature of sublimation and collecting the generated water vapour in a second glass vessel during a given time. Transfer of water vapour from the TCCP to the

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glass vessel was facilitated by the use of a heat gun and a heating cable wrapping all the glass sections of the vacuum line (Figure 2). The same operation was

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repeated for the fraction of residual ice, it was vaporized using a heat gun then

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transferred to another Pyrex™ glass sample vessel by the use of a liquid nitrogen trap. Weights of both water fractions (the vapour and the ice fractions) were

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obtained by measuring the weight difference between the empty and water-

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bearing glass vessels with a Sartorius™ precision balance. Precision on these

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weight measurements was less than ±1% (Table 1; Figure 3). In a third step, aliquots of 0.5 L of both sublimated and residual ice fractions were pipetted into tin capsules. Those tin capsules were tightly sealed and placed into the automatic sample changer of an elemental analyzer coupled to an isotope ratio mass spectrometer for the determination of their D/H ratios (see section 2.2). A pump10

ACCEPTED MANUSCRIPT down time, which was achieved by rotary pumps complemented by an oil diffusion pump, of at least 3h is required to avoid any memory effect between

2.2) D/H measurements of water samples

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two sublimation experiments.

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For each sublimation experiment, both sublimated and residual ice fractions were analyzed for their D/H ratios. For each water sample, the DSMOW value

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corresponds to the average of five aliquots of 0.5 L. Those water aliquots were

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analyzed according to the protocol described by Morrison et al. (2001). The method is based on water reduction using a chromium-based reactor installed in a

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EuroEA3028-HTTM elemental analyser from Eurovector SpA (Milan-Italy). This

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elemental analyser has been upgraded with a EuroAS300 series liquid

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autosampler equipped with a 1μL 1BR-5 SGE syringe. The elemental analyser is connected online in continuous flow mode to an IsoPrime Isotopic Ratio Mass Spectrometer from IsoPrime UK Ltd (Cheadle-UK). The mass spectrometer is equipped with an electrostatic filter to prevent helium interferences on hydrogen mass 3 beams. The H3+ factor was calculated every day and was usually below 10 11

ACCEPTED MANUSCRIPT ppm/nA. The duration for each analytical run is approximately 300 s. Water samples collected from the vacuum line were pipetted into 13x32mm vials with butyl/Teflon sealed caps. When the volume of water collected from the

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sublimation experiment was too small special inserts had to be placed inside the vials to accommodate the specifications of the liquid autosampler. Five injections were performed from each vial of water from which the standard deviations

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reported in Table 1 were calculated. Hydrogen isotope ratios are reported relative to VSMOW in the ‰  unit, after scaling the raw data to the certified isotopic

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ratios of VSMOW2 and VSLAP2 (Werner and Brandt, 2001; Gröning et al.,

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2007) to which we also added aliquots of GISP former international standard (Gonfiantini, 1984; Hut 1987; Araguas-Araguas and Rosansk, 1995; Koziet et al.,

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1995). External reproducibility of such D/H measurements is between ±0.5‰ and

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±1‰ (2). The three types of waters which have been selected for the

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sublimation experiments have D values (‰ VSMOW) of -389.2±0.5‰ (Antarctic water), -70.3±0.8‰ (doubly distilled Rhône river water, Lyon, France) and -6.3±1.5‰ (evaporated distilled Rhône water).

3) Results and interpretation 12

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To validate the experimental protocol, we checked first the mass balance between the sublimated and residual ice D/H ratio, in order to check that the

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weighted sum of sublimated and residual ice fractions was as close as possible to the expected 100%. For the forty-one sublimation experiments, yields of water recovery range from 99.35% to 100.36% with a mean value of 99.96±0.21% (2)

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(Figure 3A). A temperature of -75°C was chosen to perform numerous (n = 26) sublimation experiments (Table 1) within a relatively large range of sublimation

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duration times (t = 30 s to 1680 s), resulting in a large range of sublimated water

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fractions (f = 7.1 to 33.5 %). It can be observed that the small variations in yields of water recovery had no impact on the D value of the water reservoir

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calculated by mass balance (Figure 3B), following equation (2):

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Dtotal≈ initial = [Xvapour]*Dvapour + [Yresidual ice]*Dresidual ice

(2)

with [Xvapour] + [Yresidual ice] = 1

The subscripts for D stand for the isotopic composition of the initial water, of the vapour and of the residual ice; X and Y for the relative fractions of 13

ACCEPTED MANUSCRIPT vapour and residual ice, respectively. The isotopic mass balance was also tested by comparing the D of the initial water reservoir to the D of the total water amount obtained by mass balance between the weight fractions and D of

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sublimated and residual ice fractions. During the complete batch of experiments, three waters of distinct D values were used to test whether the hydrogen isotope composition of the starting water could have some influence on the isotope

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partitioning between the sublimated and residual ice. Calculated D values obtained by mass balance are in agreement with the measured initial D values of

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water; that is -387±0.6‰ against -389.2±0.5‰ for the Antarctic water (Figure

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4A), -73.6±0.2‰ against -70.3±0.8‰ for the doubly distilled Rhône river water (Figure 4B), and -5.1±0.3‰ against -6.3±1.5‰ for the evaporated distilled

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Rhône water (Figure 4C). It must be also noted that these experiments

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performed within the vacuum chamber do not generate sizable standard

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deviations compared to the common analytical uncertainties (±1‰) associated with the measurement of D/H ratios in small water samples. These experimental data have also been used to calculate isotopic fractionation factors

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ACCEPTED MANUSCRIPT taking into account the mass balance between the fractions of sublimated and residual ice fractions:

 = Logf R + 1

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(3)

with f = mass fraction of water vapour (0 < f < 1), R the D/H ratio and

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the isotopic fractionation factor between ice and vapour:

 = (D/H)residual ice / (D/H)vapour

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Those calculated isotopic fractionation factors do not imply that processes of

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isotopic partitioning operating during these experiments obeyed the laws of

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equilibrium thermodynamics. In the framework of this study, they are mainly

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used to describe how D and H are distributed between the gaseous and solid phases during the sublimation of water ice. It is thus remarkable that the process

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of sublimation was responsible for sizable isotopic fractionations in the range 0.969 to 1.123 for temperatures lying between -105°C and -30°C (Figure 5A). The last observation, but not the least, is that the isotopic fractionation reversed at

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ACCEPTED MANUSCRIPT temperatures below approximately -50°C, with the water vapour fraction being D-depleted relative to the residual ice fraction ( = 0.969 to 0.995). The deuterium isotopic enrichment of the residual ice fractions relative to

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the sublimated water vapour has also been quantified by using the  notation as follows:

(4)

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ice-vapour = ([{Dice+1000}/{Dvapour+1000}] – 1) x103

The  values reveal that the D-enrichment and D-depletion of the gaseous and

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solid phases do not exceed 12% and 6%, respectively, in the temperature range of

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-105°C to -30°C explored in this study (Figure 5B).

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4) Discussion

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Our experiments show a D/H isotopic fractionation that took place

between water ice and water vapour during the process of sublimation (Figure 5). Although limited to few tens of per cents, this observation is significant, as no isotopic fractionation would be expected in a scenario where successive increments of the solid are removed to produce the vapour. Isotopic fractionation, 16

ACCEPTED MANUSCRIPT however, most likely operated in the boundary layer that might develop in the metastable domains of the water phase diagram; differences in diffusivity coefficients between the light and heavy molecules could explain the rather

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limited but measurable isotopic fractionations. Therefore, the isotopic fractionation between water ice and water vapour that took place during our sublimation experiments needs to be compared with

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those determined at or close to the thermodynamic equilibrium (Merlivat and Nief, 1967):

(5)

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103ln (ice–vapour) = -94.5 + 16.289(106.T-2)

For example, using equation (5) (with T in K), (ice-vapour) equals 1.199 at -30°C

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and 1.228 at -40°C, both significantly higher than our  values of 1.0546 and

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1.123, respectively.

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More recently, using a Picarro™ cavity ringdown spectrometer coupled to

a TC/EA IRMS, Ellehoj et al. (2013) performed D/H measurements to determine ice-vapour equilibrium fractionation factor α values in the range -40°C to 0°C. They established the following isotopic fractionation equation:

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ACCEPTED MANUSCRIPT Ln(ice–vapour) = 0.2133 – 0.2031.(103T-1) + 0.048888.(106.T-2)

(6)

Using equation (6) (T in K), ice-vapour equals 1.228 at -30°C and 1.274 at -40°C and once again, these are significantly higher than the  values determined

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during our experiments of water ice sublimation. It therefore suggests that, during our experiments, the isotopic exchange between ice and vapour is limited

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due to prohibitively slow rate of diffusivity of deuterium in ice. This has been recognized for a long time in the case of the evapouration of a water layer under a non-saturated atmosphere (Craig and Gordon, 1965).

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The observed D/H isotope fractionation between ice and vapour tends to

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reverse around -50°C (Figure 5). This could correspond to a change in the

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crystalline structure of water ice from the hexagonal (Ih) to the metastable cubic

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polymorph (Ic). Such phase transition is known to take place in the temperature

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range -140, -50 °C and in some cases up to -30 °C (Kuhs et al., 2012). The progressive decrease in the isotopic fractionation with temperature reflects the progressive decrease of the contribution of the isotopic exchange between solid and vapour (the vapour being enriched in deuterium) relative to the isotopic fractionation taking place during ice sublimation (the vapour being depleted in

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ACCEPTED MANUSCRIPT deuterium). This observed reversed isotopic fractionation in the domain of low temperatures has implications for the understanding of the surface water cycle. For example, it concerns the mechanism involved in ice cloud formation in the

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Earth's atmosphere (Riikonen et al., 2000; Murray et al., 2005; Murray and Bertram, 2006). According to Kuhs et al. (2012), cubic ice is dominant when droplets freeze at temperatures lower than -80 °C, these temperatures being

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relevant for clouds occurring in the polar stratosphere and those of the tropical tropopause. Sublimation of water ice also takes place in the most extreme cold

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regions of the Earth, such as the top of the highest mountains or in the central

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part of the Antarctic continent where sublimation of snow is a common phenomenon (e.g. Frezzotti et al., 2004). The knowledge of D/H fractionations

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between ice and vapour could also be applied to planets where prevailing surface

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temperatures are largely below zero such as on Mars where sublimation of water

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ice takes places at the South Pole (Byrne and Ingersoll, 2003; Titus et al., 2003).

5) Cosmochemical implications

In moderately to very cold (-80 to -190 °C) interplanetary environments, 19

ACCEPTED MANUSCRIPT ice Ic has been considered to be by far the most likely structure of solid water (e.g. Hobbs, 1974; Petrenko and Withworth, 1999). It has long been debated whether or not comets were critical contributors of water to the Earth (Bockelee-

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Morvan et al., 2015). The common assumption is to consider that these extraterrestrial icy objects have preserved for billions of years the D/H ratio of water they acquired in their formation region. Consequently, their potential

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critical role in the origin of water on Earth has been discarded by several authors (Lécuyer et al., 1998; Robert, 2006; Altwegg et al., 2015) as long–period and

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Jupiter family comets have D/H ratios about 2 times (e.g. Halley, Hale–Bopp and

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Hyakutake have D/H ratios of 316±34 x10-6, 320±120 x10-6 and 290±100 x10-6 respectively, for long period comets) and about 4 times (e.g. 67P/Churyumov-

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Gerasimenko 530±70 x10-6 for a Jupiter family comet) higher than those of

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present–day oceans (D/H = 155.7 x10-6) or the estimated BTWM (D/H = 149±3

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x10-6; Lécuyer et al., 1998). However, it has been shown recently that some

comets which belong to the Jupiter family, such as 103P/Hartley 2 (D/H = 161±0.24x10-6), have D/H ratios close to that of the Earth (Hartogh et al., 2011). The above considerations are valid under the condition that comets are able to preserve their primordial D/H ratios. 20

ACCEPTED MANUSCRIPT Fractionation up to 3500‰ has been reported during sublimation experiments of water ice mixed with several wt.% of micrometer size dust grains (Moores et al., 2012) with the vapour phase being depleted in Deuterium. The presently

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reported experiments were performed with pure water and thus did not attempt to reproduce this effect with dust. Moores et al. (2012) made the following observation; when ice is mixed with dust, the D/H ratio of the vapour decreases

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continuously with time, implying in turn that the D/H ratio of the ice reservoir also continuously decreases with time because of the removal of vapour enriched

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in Deuterium compared with ice. Although this kind of distillation is a potential

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option, in this mechanism, the first fractions of the sublimated vapour must exhibit a D/H ratio higher than that of the ice. This effect is not observable in

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the published data and additional experiments are needed to better understand

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the origin of this effect.

In the light of the results obtained in the course of our experiments, the

deuterium enrichment or depletion between the solid and gaseous water phases cannot explain the differences of D/H ratios both amongst comet families and also definitely not those that have been documented between the comets

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ACCEPTED MANUSCRIPT belonging to the Edgeworth–Kuiper belt and Earth’s water. In addition to any other considerations, for T < -50°C, the effect is in an opposite direction to account for the deuterium enrichment of cometary water vapour relative to

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BTWM, i.e. the vapour is depleted relative to the solid by 5%.

Acknowledgements – The authors thank J. Mortimer who edited the English of

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this manuscript. They are also grateful to two anonymous reviewers that helped us to improve the scientific content of this study. This study has been founded by

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the ERC Advanced Grant PaleoNanoLife (PI: F. Robert; 161764).

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Merlivat L., Nief G., 1967. Fractionnement isotopique lors des changements d’état

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solide-vapeur et liquide-vapeur de l'eau à des températures inférieures à 0°C. Tellus 19, 122–127.

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ACCEPTED MANUSCRIPT Murray, B.J., Knopf, D.A., Bertram, A.K., 2005. The formation of cubic ice under conditions relevant to Earth’s atmosphere. Nature 434, 202–205. Murray, B.J., Bertram, A.K., 2006. Formation and stability of cubic ice in water droplets. Phys. Chem. Chemical Physics 8, 186–192.

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Robert, F., 2006. Solar System Deuterium/Hydrogen ratio. In: Meteorites and the Early Solar System II. Arizona press; ed D. Lauretta & McSween Jr. H.Y. pp. 341-352. Titus, T.N., Kieffer, H.H., Christensen, P.R., 2003. Exposed water ice discovered near

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the south pole of Mars. Science 299, 1048–1051.

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Werner, R.A., Brandt, W.A., 2001. Referencing strategies and techniques in stable

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isotope ratio analysis. Rapid Communications in Mass Spectrometry 15, 501–519.

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Table 1: Hydrogen isotope compositions and weight fractions of waters produced during the experiments of sublimation in the temperature range 105°C to -30°C. Water type

Lyon DDW

-70.3

-30

4

0.496

PBS3-67

Evap. Lyon

-6.2

-35

3

0.499

PBS-16

Lyon DDW

-70.3

-40

4

-70.3

-55

-70.3

-55

PBS-31

Lyon DDW

-70.3

AC

PBS-24

-70.3

-55 -60

vapour)





0.5 12.76

21.1

0.1 99.68

-72.2

1.12257

117. 4

89.73

-14.6

0.5 10.15

82.1

0.6 99.88

-4.8

1.07804

98.1

0.496

67.00

-90.4

0.2 33.05

-38.3

0.8 100.05 -73.2

1.05456

57.3

4

0.494

13.71

-6.7

0.6 86.25

-81.2

0.3 99.95

-70.9

0.96669

8

0.496

72.31

-70.4

0.5 27.37

-81.9

0.3 99.68

-73.4

1.00037

1.75

0.495

41.82

-84.8

0.4 58.03

-63.4

0.2 99.85

-72.2

1.01797

23.4

2

0.495

13.42

-24.9

0.1 86.61

-85.1

0.2 100.03 -77.0

0.97623

61.7

ED

PT

PBS-20

Lyon DDW Lyon DDW Lyon DDW

CE

PBS-17

D(ice-

-86.2

86.91

M

PBS-15

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Experime nt#

Mass Volum Mass D of D of D of fracti Yield D e of fraction sublimat water Sublimati residual Sublimati on of of by on water of reservoi ed water S. water S. on time residu water mass reserv sublimat D. D. r (‰ temperat (‰ (‰ (min) al recove balan oir ed water VSMO VSMO ure (°C) VSMO water ry (%) ce (mL) (wt%) W) W) W) (wt%)

27

75.0 12.3

PBS-26 PBS-30 PBS-33 PBS-34 PBS-35 PBS-36 PBS-38 PBS-40 PBS-44

69.80

-68.3

0.4 30.09

-70.3

-65

4

0.496

7.77

-32.5

0.2 92.31

-70.3

-65

2

0.496

20.26

-55.0

0.4 79.97

-70.3

-65

1.33

0.496

15.10

-4.2

0.5 85.10

-70.3

-75

4

0.496

10.93

-34.8

-70.3

-75

16

0.497

20.22

-70.3

-75

0.75

0.495

-70.3

-75

16

-70.3

-75

-70.3

-75

-70.3

-75

-70.3

-75

-70.3 -70.3 -70.3

AC

PBS-49

Lyon DDW Lyon DDW Lyon DDW Lyon DDW Lyon DDW Lyon DDW Lyon DDW Lyon DDW Lyon DDW Lyon DDW Lyon DDW

0.496

-88.8

0.6 99.89

-74.4

0.99377

-78.3

0.4 100.07 -74.8

0.98439

-83.2

0.3 100.23 -77.7

0.98978

-84.7

0.3 100.20 -72.7

0.96366

0.3 89.10

-82.1

0.8 100.03 -76.9

0.98303

-16.6

0.1 79.81

-92.7

0.5 100.03 -77.4

0.96484

10.43

-19.0

0.4 89.54

-77.3

0.5 99.96

-71.1

0.97621

0.490

12.69

-36.9

0.9 87.66

-75.7

0.3 100.36 -71.1

0.98288

16

0.495

24.73

-14.9

0.3 74.90

-89.6

0.2 99.64

-70.8

0.95857

8

0.499

30.11

-29.4

0.3 69.51

-89.4

0.6 99.62

-71.0

0.96410

16

0.496

33.46

-36.5

0.4 66.89

-89.8

0.3 100.36 -72.3

0.96734

4

0.494

16.61

6.4

2.1 83.31

-90.5

0.6 99.92

-74.3

0.95581

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PBS-25

8

M

PBS-29

-65

ED

PBS-27

-70.3

PT

PBS-22

Lyon DDW Lyon DDW Lyon DDW Lyon DDW

-75

24

0.494

31.09

-24.1

2.5 68.75

-98.3

0.5 99.84

-75.1

0.95843

-75

12

0.494

19.47

-20.3

0.2 80.69

-86.3

0.7 100.16 -73.6

0.96797

-75

28

0.496

19.44

-30.4

0.4 80.64

-83.9

0.6 100.08 -73.6

0.97431

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PBS-21

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28

22.1 47.3 29.8 80.8 49.0 77.4 59.4 40.3 75.7 61.8 55.3 96.3 76.1 67.4 55.2

PBS2-55 PBS2-56 PBS2-57 PBS2-58 PBS2-59 PBS3-60 PBS3-61 PBS3-62 PBS3-63 PBS3-64

Evap. Lyon

PBS3-66

Evap.

0.497

23.32

-41.9

0.2 76.58

-82.7

0.3 99.91

-73.1

0.97932

-70.3

-75

8

0.496

21.48

-21.2

0.9 78.29

-88.6

0.1 99.77

-73.9

0.96654

-389.1

-75

4

0.463

17.49

-353.0

0.5 82.86

-392.2

0.4 100.35

-389.1

-75

24

0.505

26.64

-378.0

0.5 73.29

-389.8

0.6 99.93

-389.1

-75

0.5

0.501

9.56

-373.6

0.1 90.40

-388.0

0.3 99.95

-389.1

-75

8

0.499

17.08

-335.8

0.4 83.07

-398.1

0.3 100.15

-389.1

-75

16

0.498

22.52

-348.4

0.7 77.45

-398.1

0.7 99.97

-389.1

-75

20

0.498

20.39

-346.8

0.1 79.72

-397.5

0.3 100.11

-389.1

-75

12

0.500

21.64

-355.5

0.4 78.32

-395.9

0.3 99.96

-6.2

-75

20

0.492

24.11

-5.4

0.6 75.91

-5.6

0.5 100.02

-5.6

0.99941

-6.2

-75

24

0.499

18.35

58.8

0.7 81.59

-19.1

0.5 99.94

-4.8

0.96265

-6.2

-75

12

0.495

20.56

66.2

0.2 79.54

-23.4

0.6 100.10

-5.0

0.95553

-6.2

-75

16

0.500

21.53

29.2

0.2 78.58

-14.3

1.2 100.11

-5.0

0.97722

-6.2 -6.2

AC

-6.2

386.7 386.4 386.4 388.1 386.8 387.6 387.0

0.96704 0.98639 0.98934 0.95263 0.95678 0.95793 0.96505

-75

4

0.500

18.20

66.1

0.7 81.65

-21.3

0.5 99.85

-5.4

0.95877

-75

0.5

0.498

7.13

97.1

0.5 92.21

-12.9

0.4 99.35

-5.0

0.96253

8

0.499

18.11

55.6

0.4 81.64

-18.6

0.5 99.75

-5.2

0.96470

CE

PBS3-65

20

AN US

PBS2-54

-75

M

PBS2-53

-70.3

ED

PBS-52

Lyon DDW Lyon DDW Antarcti c Antarcti c Antarcti c Antarcti c Antarcti c Antarcti c Antarcti c Evap. Lyon Evap. Lyon Evap. Lyon Evap. Lyon Evap. Lyon

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PBS-51

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-75

29

42.5 68.8 60.7 18.9 23.0 93.9 76.2 77.5 62.7 -0.2 73.5 84.0 42.3 82.0 100. 3 -

Lyon

PBS-47

Lyon DDW

-70.3

-95

4

0.492

6.28

-30.7

0.1 93.37

-70.3

-95

28

0.496

5.61

-34.6

0.2 94.14

-70.3

-105

48

0.496

2.25

-41.2

AC

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PT

ED

M

PBS-45

Lyon DDW Lyon DDW

-76.8

0.2 99.66

-73.6

0.98493

-76.5

0.4 99.75

-74.0

0.98690

0.3 100.12 -73.3

0.99188

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PBS-46

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-

97.88

-73.9

70.3 47.5 43.5 34.1

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Figure captions:

Figure 1: P-T range of water ice sublimation experiments. This part of the water

31

ACCEPTED MANUSCRIPT phase diagram has been calculated according to Clausius–Clapeyron’s formula.

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See the text for further explanation.

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Figure 2: Schematic illustration of the vacuum line used to perform the sublimation

PT

experiments of water ice. (1) thermo-regulated cryogenic cold trap system, (2)

CE

Pyrex™ glass filled with 0.5 mL of initial water of known D/H ratio, (3) area

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where the sublimated water is collected in a Pyrex™ glass sample vessel by the use of a liquid nitrogen trap, (4) heating wire (dashed line) to remove adsorbed water within the vacuum line, and (5) secondary pumping system (oil diffusion pump) used to decrease the partial pressure down to 10-6 mbar inside the vacuum line.

32

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Figure 3: Results of mass balances between the fractions of sublimated and residual ice fractions obtained during the sublimation experiments.

33

ACCEPTED MANUSCRIPT A) Calculated yields (weighted sums of sublimated and residual ice fractions) of water transfer throughout the vacuum line for the forty-one experiments. B) Yields of water transfer as a function of the D values (‰ VSMOW) of the total

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water amount obtained by mass balance between the fractions and D of sublimated and residual ice. These results have been obtained for the twenty-six

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sublimation experiments performed at -75°C.

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Figure 4: D values (‰ VSMOW) of the total water amount obtained by mass balance between the fractions and D of sublimated and residual ice for the fortyone experiments depending on the initial D/H ratio of the water reservoir. A) D

35

ACCEPTED MANUSCRIPT = -389.2±0.5‰ (Antarctic water), B) D = -70.3±0.8‰ (double distilled Rhône river water, Lyon, France), and C) D = -6.3±1.5‰ (evaporated distilled Rhône

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water).

36

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Figure 5: D/H isotopic fractionation  and isotopic enrichment  (‰) between water ice and water vapour as a function of the temperature of sublimation (K). See definitions of (water ice-water vapour) and (water ice-water vapour) in the text.

37