Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | , 3 D slopes, δ , L. Schröder ). The full cycle 3 1 − 1.1 m yr 1 km, with the reduced ac- ± O) were measured along the < D and 17O-excess/ 17 δ , M. Scheinert δ 4 O and 18 δ , S. Popov 1 D, 6910 6909 δ , V. Lipenkov 3 1 , L. Eberlein 1,2 This discussion paper is/has beenPlease under refer review to for the the corresponding journal final The paper Cryosphere in (TC). TC if available. Climate and Environmental Research Laboratory, Arctic and Antarctic Research Institute, St. Petersburg State University, 33–35, 10thTechnische line Universität Dresden, VO, 199178 Institut St. für Petersburg, PlanetarePolar Russia Geodäsie, Marine 01062 Geological Dresden, Research Germany Expedition, 24 Pobedy st., 198412 Lomonosov, Russia of the dune driftmulation is and thus isotopic aboutdrilled composition 410 in years. are Since the supposed the mega-dunetwo to spatial area parameters. drift We anomalies would simulated with exhibit of a verticala the snow the profile non-climatic non-climatic accu- dune, of 410 variability, snow an isotopic using yearprofile composition ice the cycle with is core such of data then these compared ontained with the from the a dune real core size vertical drilledsimilar. in and profile the The of velocity. mega-dune obtained snow This area. results isotopic We artificial note arefrom composition that ice discussed ob- the cores in two drilled terms profiles beyond are of the very interpretation mega-dune areas. of data obtained we conclude that thedune spatial area variability could of be explained thedata, by snow post-depositional we isotopic snow modifications. composition estimated Using in the the the GPR apparent mega- dune drift velocity (4.6 2 km profile across thesurements and mega-dune GPR ridge survey. It accompanied isand shown by that isotope precise the content GPS spatial variability covaries altitude ofchanges with mea- snow by accumulation the one surface order slope. of The magnitude accumulation within rate the regularly distance cumulation at the leeward slopebetween of the the dunes. dune At and theof increased same accumulation a time, in the dune the accumulation wave hollow tion, rate (22 mm averaged which we) over suggests the corresponds length no wellcompared additional with to the wind-driven the value snow surroundingcorrelation obtained sublimation with plateau. the at in The snow Vostok the accumulation. snow Sta- Analyzing mega-dunes dxs/ isotopic composition is in negative Abstract We present the results30 km of to glaciological the investigations east from58th, in Vostok 59th the Station and (central 60th mega-dune East Russian area Antarctica) Antarcticaccumulation implemented Expedition located rate during (January and 2013–January the isotope 2015). content Snow ( The Cryosphere Discuss., 9, 6909–6936,www.the-cryosphere-discuss.net/9/6909/2015/ 2015 doi:10.5194/tcd-9-6909-2015 © Author(s) 2015. CC Attribution 3.0 License. Non-climatic signal in ice corelessons records: from Antarctic mega-dunes A. Ekaykin and A. Turkeev 1 38 Beringa st.,2 199397, St. Petersburg, Russia 3 4 Received: 11 November 2015 – Accepted: 3Correspondence December to: 2015 A. – Ekaykin Published: ([email protected]) 17 December 2015 Published by Copernicus Publications on behalf of the European Geosciences Union. 5 20 25 15 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | erent parts of the ff 6911 6912 (Black and Budd, 1964; Frezzotti et al., 2002b; 1 . − 2 The first observations of relationship between the ice sheet surface topography (sur- In 1988 Swithinbank suggested to call such waves “mega-dunes” (Swithinbank, The first dedicated ground survey of mega-dunes was madeSince the 1980s by the mega-dunes are Frezzotti observed with the use of the satellite methods Since then such surface undulations have been observed in di The precipitated snow is not simply re-distributed in the mega-dune area. Indeed, it The Antarctic glaciology has gained a lot from implementing the ground penetrating drift velocity ranges from 4 to 25 myr tribute the snow withmulation the on increased the accumulation convexities inconfirmed (Black the and in concaves Budd, and a 1964). reducedEkaykin number This accu- et relationship of al. (2002), has studies, Frezzotti beenpari et e.g. et later al. Anschütz al. (2007), (2004), Fujita et Richardson etalso et al. al. shown al. (2011), (2007), that (1997), Hamilton Rotschky the (2004), Dadicface, et Kas- dunes et al. which are (2004). al. does not These studies not stagnant, (2013), thus have but allow maintaining rather the their drift snow dynamical across to the equilibrium. simply ice The fill sheet estimates in sur- of the the hollows dunes’ between horizontal the dunes face slope) and snow accumulation rate have shown that the dunes strongly redis- (Albert et al., 2004; Alberti2000; and Frezzotti Biscaro, et 2010; al., Arcone 2002b),length et of which al., 2–5 form 2012b; km, the Fahnestock the et system amplitude al., of 2–8 m, parallel and ridges the with length the of the wave- ridges of up to 100 km. occupying in total about 500 000 km 1988) based on their similarityconventionally to used to the describe desert the sand specific mega-dunes. dunes At observed present in this central term East is Antarctica et al. (2002b). It was shown,of in the particular, that dunes snow where is removed specifictrast, from erosional snow the type leeward accumulation slopes of is snow,by increased “glaze the surface”, on depositional is the types formed. of windward In the slopes con- snow that microrelief. are characterized (Alberti and Biscaro, 2010; Fahnestock et1988), al., which 2000; Scambos has et revealed al., that 2012; these Swithinbank, snow features are widely presented in Antarctica Antarctic continent – inschütz Adelie et al., Land 2006; (Pettre EisenLand et (Gow et and al., al., Rowland, 2005), 1986), 1965; Enderbyb), Whillans, Dronning Queen Land 1975), Maud Mary (Fujita Victoria Coast et Land Land (Dolgushin, (Frezzotti al.,(Black (An- 1958; et 2002), and Vladimirova al., and Budd, Marie 2002a, Ekaykin, 1964; Byrd 2014), Goodwin, Wilkes 1990) Land – or, simply speaking, almost everywhere. Van der Veen et al., 1999; Whillans, 1975). extent of the mega-dune fieldsof and glaze the surfaces continent (that area), occupyaccount in where total for snow more correct drift than estimate processes 10 % Scambos of are et the intensified, al., must Antarctic 2012; be surface Zwally et taken mass al., into balance 2015). (Das et al., 2013; is widely recognized that the wind-drivensnow sublimation mass-balance is an (Bintanja important and part2012) Reijmer, of removing 2001; the surface Lenaerts from 20 etmega-dunes al., to this 2010; 75 % figure Thiery of may et precipitation increase al., (Frezzotti to et 85 % al., (Frezzotti 2004, et 2007). al., In 2004).Thus, the the wide 1 Introduction Mega-dunes are one of theThe most first intriguing reports and on spectacular thesheet existence phenomena was of in made the Antarctica. soon huge after wavesinterior on the during the the beginning surface IGY of of (Dolgushin, theused the 1958), extensive at Antarctic although exploration that ice the of time. term the “mega-dunes” Antarctic was not yet structures in the central Antarcticamega-dunes, outside they the are “classical” characterized mega-dunefaces) areas. by and Similar persistent to increased zones accumulation. ofglaze The snow surfaces disturbed erosion is stratigraphy (glaze found thatstructures sur- at marks have been the the persistent for buried depths tens of more thousands than of years 2000 (Arcone m, et al., which 2012a, suggests b). that these radar (GPR) techniquein (Eisen mega-dune et al., areas2005; 2008). (Anschütz Frezzotti et The et al., 2002a). GPR al., In survey particular, 2006; this has allowed Arcone discovering also the et mega-dune-like been al., made 2012a, b; Eisen et al., 5 5 25 20 15 10 10 25 20 15 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | O). 17 δ D, which is 2 orders of δ O) in 42 snow surface sam- O and 18 18 δ δ D, δ analyzer. For this, each sample was D and i δ O and 0.2 ‰ for 18 δ 6914 6913 ect the isotopic content of the deposited snow, ff analyzer. Our working standard (VOS), measured after every 5 samples, was i ect the snow chemistry (Mahalinganathan et al., 2012). In October 2015 we also measured 17O-excess values in the samples collected In January 2015 we also drilled a 20 m borehole in pointThe MD00 concentration of (Fig. heavy 1). water In isotopes the ( ob- In January 2014 and January 2015 the stakes were revisited, and the repeated mea- In the summer seasons of 58th, 59th and 60th Russian Antarctic Expeditions (RAE), The strong post-depositional metamorphosis of snow in the mega-dunes has to mod- Physical properties of snow in the mega-dune areas have been studied by Albert Chemical properties of the mega-dune snow were considered in very few studies ff during the 59th RAE using a Picarro L2140- ples taken in 58thmeasured at and Climate 59th and Environmental RAE,L2120- Research as Laboratory (CERL) well using as a Picarro in 183 samples from MD00 core, was magnitude less than the natural variabilityand of thus the satisfactory snow isotopic for composition the (see purposes below) of the study. made of the light2, Vostok GISP snow and andrandomly SLAP-2. calibrated chosen The against samples was reproducibility the 0.04 ‰ IAEA of for standards results VSMOW- defined by re-measurements of measured 15 times inmeasurements. the Every high-precision 3 mode samples we and measured we the took VOS standard an previously average calibrated of the last 10 tained firn core we measuredanalysis with snow a density resolution and of took 10 samples cm. for stable water isotope snow accumulated during 2 yearswere taken (January again 2013–January for 2015). chemical and The isotopic snow analyses. samples surements of their heights and surface snow density allowed obtaining the amount of 2 Data and methods 2.1 Glaciological and stable water isotopeIn data January 2013accumulation-stake profile the was established perpendicular Vostok tototal mega-dune the number of mega-dune stakes crest. area was The 21stakes was (named was MD00 visited about to MD20), 100 m, the forsamples distance and of between the the the adjacent upper total firstfor 1.5 length the m time. of concentration of of the snow The the profile were stable also was water isotopes taken 1983 m ( near (Fig. each 1). stake The to be analyzed 2013–2015, we carried out complexlocated glaciological investigations about in 30 the km mega-dune to area analyze the the East spatial from distribution Russian of Vostok the Station snow (Fig. isotope 1). content In in this the paper mega-dunes. we to complex surface topography doeswhich a cause a poor correlationonly of a isotopic short profiles obtained distanceHowever, in (Benoist no two et systematic points separated al., study by been 1982; of conducted Ekaykin up snow et to isotopic now. al., composition 2014; in Karlöf the et mega-dunes al., 2006). has ify its stable waterNeumann et isotope al., properties 2005). (Courville It is et also al., known 2007; that Frezzotti irregular et snow redistribution al., by 2002b; wind due (Dixon et al., 2013). Ita is noted that the surface slope may, at least in the coastal areas, et al. (2004), Courville et al.particular, (2007), the Gregory et snow al. erosion (2014), Severinghaus zonessnow et of (depth al. mega-dunes (2010). hoar) In are characterized representedplace by by in increased coarse-grained snow air under permeability.composition near-zero The of accumulation processes help taking gas toIt trapped understand in is the the suggested datacurrently ice that on existing isotopic core low-accumulation in air highly the mega-dunetimes bubbles permeable areas, (Dreyfus (Severinghaus snow had et et al., large zones, 2010). extent al., similar in 2010). Antarctica to in that the glacial 5 5 25 20 15 10 20 15 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | . 1 − . 1 erential solution from − ff erences of 2.9 cm (at 160 ff erences at track crossovers. ff 6915 6916 Below we present the results of the glaciological investigations in the Vostok mega- The GPR equipment was installed on 2 sledges towed by a ski-doo. The route of the The main problem in the processing and interpretation of the GPR data is the di- In Fig. 2 we showed the GPR registration recorded along the glaciological profile The wavelength of the Vostok mega-dunes are about 1.9 km, and the amplitude (the All the data discussed in this paper is presented in Table 1. Therefore the Bernese GPS Software 5.1 (Dach et al., 2007) was used to process the dune area (Fig. 3). crossover points) for trackWith K58B a and RMS 2.4 ofthe cm 7.7 absolute (at cm precision 9 at ofpropagation crossover 5159 a to points) crossovers single about for between 5.4 kinematic cm. track the surface height K58C. two according tracks2.3 to we the can variance estimate GPR data During the austral summer fielduary season 2013) of the the 58th GPRthe Russian profiling Antarctic mega-dune was Expedition area. performed (Jan- The towas 200 MHz applied. study GSSI the SIR10B snow-firn GPR layer with structure “5106 of 200 MHz” antenna (MD00-MD20). 3 Results The mega-dune formation isprevailing related wind to direction (SPWD) a (Frezzotti sharp etnot al., increase an 2002b). of The exception, the Vostok mega-dunes as icewhere are sheet they the slope form SPWD in leeward changesthe the from closest from vicinities the near of eastern zero Vostok shore Station or the of even wind the negative is Lake values blowing uphill) Vostok, (interestingly, to in about 1.6 mkm elevation change between the1.2 dune m, i.e. crest they and are the relativelystudies. small nearest compared windward to hollow) those reported is in about the above mentioned GPR profiling was the same withGPR the profiles geodetic were observations. obtained In (Fig. total,obtained 1), about along though 80 the km in glaciological of this the profile paper (points we MD00-MD20 only in use Fig. theelectric 1). 2 km properties section of the mediaused where the the electromagnetic model waves published aretime-section by propagating. (Fig. We Popov 2) and Eberlein intowave speed (2014) the we to depth used transform section. the the firn To calculate radio-echo density data the measured vertical in MD00 electromagnetic core. Crossovers inside one track imply an internal RMS of the di The latter figure generallymega-dunes agrees only develop with where the the SPWD Frezzotti is et from al. 1 (2002) to 1.5 conclusion mkm that the GPS and GLONASS observations.used As two reference local receivers stations at Vostok for stationtwo this in reference a network distance stations of solution less at we thanRussian the 50 research km coast and stations additional with Progress baselineAustralian and lengths Station a of station Casey). about of Afterwe 1350 the reducing km estimated global the (near the IGS-network the antenna accuracy near positions the by to calculating the the snow height surface di 2.2 GNSS positioning The absolute altitude and locationusing was the determined geodetic with high GPS accuracy technique. along the profile two kinematic GNSS profiles (K58B and K58C) as a combined di against VSMOW-2, GISP and SLAP-2values (taking of, into correspondingly, 0, account 22 that andexcess they 0 have value per 17O-excess of meg; Schoenemann VOS et wasof al., the found 2013). 17O-excess to The values 17O- be of 0 individual per samples was meg, 8 similar per to meg. SLAP. The reproducibility 5 5 25 20 25 15 10 20 15 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | ‰ 0.2 / − 0.2 ‰ − erent post- ff 0.38, is not statistically − erence between snow surface ff cient, D, dxs and 17O-excess) of the ffi δ 0.5 to 16 cm of snow (or from − D slopes (ratios between the standard de- δ 6918 6917 ) is slightly higher than that measured at Vostok stake 3 − D) with the magnitude of about 20 ‰ and the wavelength δ D and 17O-excess/ δ ). 3 − We explain this behavior of the snow isotopic composition by di During the field-works we also did not observe big di The spatial variability of the accumulation rate covaries well with the surface slope: An alternative explanation of negative spatial relationship of isotopic composition and We may use the isotopic data to determine which mechanism, “post-depositional” or The observed dxs/ The surface snow density does not show any distinct spatial variability (Fig. 3d). The In Fig. 3a–c we show the isotopic composition ( significant due to theobserved in small the number closest of vicinitycomposition points). of correspond Vostok, A to where very the positivethe spatial similar negative smaller anomalies anomalies spatial picture of scale of was isotopic (Ekaykin snow previously et accumulation, al., 2002). though on upper 1.5 m of snow sampledin twice snow near isotopic each point content of ( our profile. One can see a wave depositional alteration of the initial isotopicin composition the of low- snow and precipitation high-accumulation deposited is zones characterized of the by mega-dunes. “a Indeed,(Frezzotti the long, et erosion multiannual, al., zone steep 2002b,topes temperature-gradient p. due metamorphism” 8). to Thus, strong post-depositional thether modification facilitated snow by (Town the here et increased al., should permeability2004). 2008) of be We that the may enriched may snow speculate in be in that such fur- incharacterized heavy locations by the (Albert iso- a mega-dunes et very described al., strong by modificationtransformation Frezzotti of et should the al. snow be (2002b), physical even properties, stronger the than isotopic in the Vostok dunes. snow accumulation was suggested bycrystals Ekaykin are et smaller and al. wind (2002).by speed Since wind is in comparing higher, winter this tomega-dunes the snow snow the snow could proportion precipitated be of easier in summer re-distributed summer. snow If is larger so, than in“re-distributional” in the the (or accumulation erosion both) zone. zone iscomposition mainly of in responsible the the for mega-dune the area. anomaly of the snowviations isotopic of the smoothed profiles shown in Fig. 3a–c) are, correspondingly, similar to that of the mega-dune.composition There is and a accumulation negative covariation rate between snow (correlation isotopic coe the smaller is the slope,the the previous higher observations is (Anschütz et accumulation al., (Fig. 2006). 3f and e), in accordance with character in leeward and windward slopesnot of demonstrate the the dunes dominance (Fig. of 4).in the The erosion the glaze zone surface, accumulation does and zone, no asmega-dune big field. reported sastrugi are by observed Frezzotti et al. (2002b) for the Victoria Land network (0.33 gcm mean snow density (0.355 gcm to 58 mmwe according tothat the reported surface by snow Frezzotti et density,lation Fig. al. over 3d). (2002b) the This (from 1 range 7 duneat is to wavelength the larger 35 is mm). than Vostok The 22 stake mm, meanthe network which annual mega-dune (23 is accumu- mm). area very If was similar thethat the to precipitation same, the over rate then accumulation the at our mega-dunesublimation Vostok result (Frezzotti station areas does et and the al., not in 2004). support accumulation the is observation reduced due to the wind-driven 3.1 Accumulation rate and isotopic contentDue of to snow the in subsequent mega-dunes measurementsthe mega-dunes, of we the were heights able to ofand define the the January stakes snow 2015 accumulation established between (Fig. across Januarysnow 3e). 2013 build-up. In One accordance may with clearly thethe previous see snow studies the is (see regular the removed review from spatialthe in locations variability Introduction), dunes) with of and the the deposited increaseddunes where and surface the windward slope side slope (leeward of is sidemulation the decreased of changes dunes). by or In an a inversed order distance (hollow of of between magnitude, few hundred from meters the accu- 5 5 25 10 15 20 25 20 10 15 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | D slopes reported δ ‰ (Landais et al., 2012). / . 1 − , so the real dune drift velocity 1 ‰ (Ekaykin et al., 2016). During − / ‰ and 0.4 permeg / 6919 6920 0.1 ‰ ‰ and 0.4 permeg , and the correction to the dune drift velocity due to − 1 / − 0.2 ‰ − . However, the ice is moving almost in parallel with the dune . With this velocity a dune drift by 1 wavelength in about 1 1 − − . This corresponds very well with the value reported by Frezzotti ‰. During the post-depositional changes of the snow isotopic com- 1 / − 1.1 myr ± In the GPR profile taken across the mega-dunes (Fig. 2), we see several distinct Thus we may conclude that the mixing of the summer and winter precipitation in dif- We should also note that the 17O-excess values positively covariate with the accu- We chose 3 fold hinges (the summit of crests and two lowest points ofAs the pointed fold by Arcone et al. (2005), the apparent dune drift velocity observed in the For this, we first need to date each IRH. We used the density profile obtained from Let us simulate such an oscillation that we would see in a core drilled at MD00 point. may trace its drift in time. the MD00 core and the average snow accumulation rate in the mega-dune area in order internal reflection horizons (IRH).subtracting For these 7 of depths them fromaltitude we the of defined each ice the IRH depths sheet (Fig. (Table elevation, 1) 3g). we and, Thus could we define can the see absolute the buried surfaces of our dune and oratory experiments, not in natural conditions, so the 17O-excess/ At present we doexcess not values, know or if it thisthe positive suggests mega-dune covariation area. another is mechanism caused that by creates errors isotopic in3.2 the anomalies 17O- in Mega-dune drift We used thecalculate GPR the data velocity of to the dunes reconstruct drift. the previous positions of the dunes, and to ferent proportions cannot explain thein variability of the snow mega-dune isotopic area, compositionnificantly observed since smaller. The the post-depositional variability factorisotopic of would composition better 17O-excess in explain and the the mega-dunes, of observed butbe snow dxs still too the strong. would Note, variability however, be of that 17O-excess the sig- seems data to of Ekaykin et al. (2016) were obtained in lab- mulation rate (Fig. 3c andif e), the though snow one isotopic would composition expect variability a is negative covariation due in to case the post-depositional processes. there may be underestimated. real dune velocity is higherice than flow the velocities observed in one. this According region to do Richter not et exceed al. 2 myr (2013), the ice movement shouldwe be need close not to real, zero,calculations but too. we the Finally, use for resultant the the apparent dune dune purposes velocity velocity of observed of our 4.6 by3.3 myr study GPR, so in Non-climatic temporal the oscillation further related toWhen the the mega-dune dune drift drifts, therate spatial and anomalies in isotopic snow compositionnow physical are located properties, accumulation at drifting the accordingly.isotopic leeward For side composition, example, of about the the 300 pointcreased dune years MD00, accumulation with ago and reduced was lower accumulation in heavymega-dune and the isotope area, enriched content. hollow he If between would one seetions dunes drills a in with an snow quasi-periodic in- ice accumulation (with and core the isotopic in period composition the of related 410 to years) the oscilla- dune drift. dips) to traceof the 4.6 dune drift. On average, the410 dune years. is drifting upwind with theGPR images rate is a combination of the real dune velocity and the ice movement, and the crests (from north-west tothe south-east). MD profile So, is the close projection to of 0 myr the ice speed vector on to calculate the depth-ageuppermost function IRH and marks determine the the surface– age of 530 the of years dune each ago. about IRH 130 years (Fig. ago, 3g). and The the lowermost could be up to 6.6 myr et al. (2002b), 5 myr the seasonal cycle ofparameters the are related isotopic by composition slopes of snow precipitation at Vostok, these and 0.9 permeg position these slopes are 5 5 25 20 10 15 20 25 10 15 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 6922 6921 usive smoothing due to the increased ventilation of the snow ff In Dronning Maud Land the ice cores drilled in relatively short distance oneIn from general, in low-accumulation sites signal-to-noise ratio in both snow accumulation Even the vicinities of the main domes cannot be considered as “dune-safe”. Indeed, In the case of MD00 core we know that the “signal” we see is mostly related toIndeed, a it dune is commonly understood that a mega-dune area is an unsuitable placeAs to an example we may mention the South Pole Station region that is not a mega- In Fig. 5d we also showed by the blue line the real isotopic profile from the MD00 In our simulations we do not take into account that the mega-dune snow may ex- In Fig. 5a we showed a temporal variability of snow accumulation (blue) and isotopic Combining the dune-related and climatic components, we obtain the expected tem- 420 ‰. Neither climatic record, nor the isotopic profile from the mega-dunes (Fig. 5a) another demonstrate opposite200 trends years in (Oerter et the al.,climatic snow 2000), factors. accumulation which may rates be over considered the as the past influencerate of and the isotopic non- composition2014). is The very noise, small, relatedprocesses, being to is the of larger snow the than re-distribution order the by of climatic wind 0.2 signal and/or (Ekaykin even post-depositional at et the al., centennial scale. This means topography (Benoist et al., 1982). the study of theDome snow C isotopic showed composition a profile very in low two neighboring signal-to-noise cores ratio drilled likely at related to the local ice sheet ical amplitude of few metersder and Veen wavelength et of al. severalsnow kilometers (1999) hills – and see are Fig. Fig. notstructures 2 8 are elongated, in in not but Van Hamilton stationary, but rather (2004).non-climatic slowly round variability change Unlike of their in the snow locations, shape. accumulation mega-dunes, whichfew rate The causes these thousand with temporal authors the years. period suggest Very of similar(Eisen these several et structures hundred al., or are 2005) observed and around in West the Antarctica Kohnen (Arcone Station et al., 2005). drift, but how canice one cores? separate the climatic signal from non-climatic variabilitydrill in ice real for climaticdune studies, fields but are it free does from not non-climatic, mean “relief-related” that variability. thedune locations area, outside but the detailed mega- topographic survey shows mega-dune-like features with a typ- to an ice core isotopicmega-dune profile. area We and calculated compared an it artificial with the ice real core ice isotopic core profile isotopic in profile. the − demonstrate such highsimulations. isotopic value, this is why we could not4 reproduce it Discussion in – our non-climatic variability inIn ice the cores previous sections wenificant demonstrated spatial that variability the in snowexplain the isotopic this mega-dune composition variability, area, and has suggested then sig- a explained possible how mechanism this to “dune-related” signal is transferred column. In this case the isotopic profile could becore. substantially One smoothed. can see aof good resemblance the between MD00 them, core. except for Indeed, the at very bottom the part depth of 20 m the core has isotopic composition of perience enhanced di (Fig. 5a), this is why itprofile is is essentially presented non-linear. The in resultingoscillations Fig. simulated are vertical 5d compressed isotopic by due redaccumulation to is line. the higher, In they low the are accumulation stretched. upper rate, part and of deeper, the when profile the the isotopic composition (red) that should beTo seen construct in these point curves, MD00 we when simplyby the divided the dune the above crosses distance mentioned of this velocity of each point. thevariability point dune in in drift. Fig. Vostok We 3a region also and showed over in e Note the Fig. that same 5a the the time climatic amplitudes interval of (Ekaykin the et both al., components 2014) are inporal similar. purple. variability of snow isotopic compositiona in vertical MD00 isotopic (Fig. 5b). profile Then usingtion we takes the transform into depth-age it account to the function significant presented dune-related in variability in Fig. snow 5c. accumulation This rate func- 5 5 25 20 15 10 25 20 15 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | m 6 to 10 3 years in the low 4 –10 3 m (micro-relief) and from 10 1 to 10 6924 6923 2 − erent hypothesis. For example, in a short distance one erent in terms of snow accumulation rate, isotopic com- ff ff . This allowed us to simulate the temporal variability of the 1 − The logistic operations in Antarctica were provided by Russian Antarctic 1.1 myr ± , the range of “meso-dunes” (Eisen et al., 2008; Ekaykin et al., 2002). It is 3 to 10 1 This study was completed at the expense of the grant of Russian Science Foundation (project In the future studies we plan to investigate the spatial variability of chemical content, The influence of snow topography on snow accumulation is known and to large extent Using the GPR data, we were able to trace the drift of the dunes and to calculate Using the examples published in literature we suggest that similar non-climatic oscil- We also suggest that the mega-dunes are a unique environment that provides the In this paper we present the results of the field works carried out during three Antarc- 14-27-00030). are grateful to Anna Kozachek andWe Diana also Vladimirova thank (CERL) Achille for Zirizzotti thegia, and high-quality Rome, Stefano isotopic Italy) Urbini data. for (Istituto providing Nazionale the di GPR Geofisica equipment. e Vulcanolo- the concentration of microparticlesVostok mega-dune and area. other compounds in theAcknowledgements. surface snow inExpedition. the We personally thank Vitaly Zarovchatskiy for his help in the field works. The authors can find locations absolutely di position, physical and (likely)post-depositional chemical processes, properties, to which modeletc. could glacial be conditions used (Severinghaus to et study al., the 2010) necessary conditions to test di understood on the spatial scale from 10 their velocity, 4.6 lations in snow accumulation ratetica, and even beyond isotopic the composition mega-dune are fields. widespread in Antarc- accumulation area (which comprises mostmore of the than East one Antarctica ice (Arthern core et should al., be 2006)) investigated for each location. snow isotopic composition that wouldof be the observed mega-dune in across a thisthe given point. snow point isotopic Then due composition we to with comparedmega-dune the the this cite. passing We real artificial showed isotopic vertical that data profile the from of two a profiles firn are very core similar. drilled in the (mega-dunes and continental scale). However, very10 little is known about the scale from likely that the driftsnow of isotopic the composition meso-dunes and accumulation causes rateto the with non-climatic mechanisms a period temporal similar of oscillations to fewstudies of tens those of of years this described due phenomenon in are this needed. paper for the mega-dunes. Further 5 Conclusions The ice cores arethis priceless will source hold of true numerouslimitations even and despite is diverse the paleo-climatic related unavoidable data, limitations. toon and One relatively a of short high the time most levelareas. scales important of (years The to noise main millennia), whichleads reason especially contaminates to in of snow the the this low-accumulation re-distribution climaticpost-depositional noise due processes. signal is to wind a activity, complex which snow/ice is sheet furthertic complicated topography summer by that seasons the in theof vicinity large of snow Vostok relief Station. forms, Westrate mega-dunes, mainly on that deal the the with snow leeward the isotopic sides influence and composition. of We increased the demon- concentration dunes of arealteration heavy characterized of water by the molecules snow reduced likely isotopic accumulation mulate due content. more In to snow opposite, post-depositional that windward is sides enriched of in the light dunes water accu- isotopes. that to study climatic variability with the periods less than 10 5 5 25 20 15 10 10 15 25 20 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 6926 6925 N: potential for a gas-phase climate proxy, Quaternary Sci. 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D.: Snow accumulation and surfaceGow, topography A. in J. the and katabatic Rowland, zone R.: of On the eastern Gregory, relationship S. of A., snow accumulation Albert, to M. surface R., topography and Baker, I.: Impact of physical properties and accumulation Hamilton, G. S.: Topographic control of regional accumulation rate variability at South Pole and 5 5 10 15 20 25 30 15 25 10 20 30 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | O 17 δ , Rapid Commun. Mass ect of atmospheric water ff 5 46 89 8 11 10 14 11 12 17 14 15 19 179 17 19 24 10 18 209 19 12 26 8 13 27 14 108 12 15 14 17 149 27 16 8 3 12 26 12 14 15 15 17 17 18 23 19 25 excess 1316 6 7 919 10 1216 11 13 1513 11 16 1313 11 18 13 18 15 11 20 13 15 20 17 13 14 25 16 18 25 14 16 17 1912 15 17 18 28 16 18 5 28 17 28 815 28 11 1310 14 10 10 16 14 15 16 24 18 17 19 24 29 − − − − − − − − − − − − − − − − O 17 O dxs 17O- 1st 2nd 3rd 4th 5th 6th 7th 18 O and 56.04 14.0 56.3756.30 13.1 55.76 14.1 56.97 13.3 55.97 14.3 13.8 56.3657.49 15.1 57.94 15.2 57.29 16.5 57.02 16.3 57.47 15.0 14.7 57.2756.32 15.556.08 14.0 055.17 13.4 954.62 12.8 355.51 11.9 12 7 11.9 56.04 2 1356.72 12.8 14 9 456.38 13.3 0 11 15 13.3 8 17 13 11 8 14 27 13 9 16 4 13 14 25 13 15 17 16 16 23 18 18 19 23 20 26 δ − − − − − − − − − − − − − − − − − − − − − 17 δ D δ 434.3 437.9 436.3 432.8 441.5 434.0 435.8 444.7 446.9 442.0 441.2 445.1 442.7 436.5 435.2 428.6 425.0 432.1 435.5 440.4 437.8 − − − − − − − − − − − − − − − − − − − − − 2 − 6930 6929 ) (mm we) 3 − 0.5 0.311 − 58RAE RAE 60 excess ect of inversion winds on topographic detail and mass balance on inland ice ff (m) (gcm MD00 (m) (cm) density lation Glaciological, radio-echo-sounding and geodetic data used in this study. Pointname Distance Altitude Stake from height a.s.l.MD00 Snow (cm) Mean 0 3424.25 Snow 300 Isotope content build-up 58 RAE 292 snow 4 accumu- Depths of internal reflection horizons (m) 0.358 14 MD01MD02MD03MD04 88 192MD05 3424.92 291 3425.75MD06 151 393 3426.37 172MD07 493 3427.09 170MD08 152 163 3427.86 195 592MD09 170 175.5 690 3428.35 4.5MD10 190 797 3428.51 169 0MD11 165 894 3428.73 171.5 2.5MD12 5.25 167 992 3428.65 193.5MD13 154 0.330 1066 3428.61 187.5 1MD14 177 8.75 3428.44 1168 0.338 169.5 0.367MD15 170 0.355 8.25 179 1289 3428.18MD16 150 8.75 1394 3427.64 162 15 0.345MD17 9.75 146 1493 3427.53 190.5 0.335 0.346MD18 148 1593 3427.53 204 16.5 158 20 0.345MD19 0 8 1698 3427.76 196 7 16.25 0.370MD20 188 3428.17 171 1796 32 0.363 178 157 1901 3428.73 8 28 3 0.344 165 1983 3429.6 188 9 31 140 0.330 3430.17 3 34 209 178 184.5 8.5 57 0.360 5 172 201 55 0.337 6.25 4 21 0.385 0.435 28 0.348 0.335 28 0.420 11 32 18 19 13 face mass balance on Amundsenisen Plateau,studies, Antarctica, Ann. derived Glaciol., from 39, ice-penetrating 265–270, radar 2004. 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Res., 104,over 31067–31076, the 1999. past 250Abstr., years 16, based 285, 2014. on the “105 km” ice coresheets, geochemical J. Glaciol., data, 14, Geophys. 85–90, Res. 1975. Antarctic ice sheet exceed losses,2015. J. Glaciol., 61, 1019–1036, doi:10.3189/2015JoG15J071, Swithinbank, C.: Antarctica, US Geol. Survey Prof. Rap. 1386-B, USThiery, Geological Survey, W., Wash- Gorodetskaya, I. V., Bintanja, R., Van Lipzig, N. P. M., Van den Broeke, M. R., Van der Veen, C. J., Mosley-Thompson, E., Gow, A., and Mark, B. G.: Accumulation at South Whillans, I. M.: E Severinghaus, J. P., Albert, M. R., Courville, Z. R., Fahnestock, M. A., Kawamura, K., Town, M. S., Warren, S. G., Walden, V. P., and Waddington, E. D.: E Vladimirova, D. O. and Ekaykin, A. A.: Climatic variability in Davis Sea sector (East Antarctica) Zwally, H. J., Li, J., Robbins, J. W., Saba, J. L., Yi, D., and Brenner, A. C.: Mass gains of the Table 1. Rotschky, G., Eisen, O., Wilhelms, F., Nixdorf, U., and Oerter, H.:Scambos, Spatial T. distribution of A., sur- Frezzotti, M., Haran, T. V., Bohlander, J.,Schoenemann, Lenaerts, S. W., Schauer, J. A. J., T. and Steig, M., E. J.: Van Measurement of den SLAP2 and GISP 5 15 10 20 25 30 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 6932 6931 Vicinities of Vostok Station and the location of the study area. The mega-dunes are GPR registration recorded along the MD00 profile. Figure 2. Figure 1. highlighted by hatching. Black line isglaciological the profile route is of shown GPR inadapted and the geodetic insert from profiles. (MD00-MD20). Popov The and White location line Masolov of is (2007). the the Vostok lake shoreline Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | , σ (b) 1 ± , dxs (a) D δ Surface (20 cm) snow density, in- Mean snow build-up in 2013–2014, (d) (e) 6933 6934 The elevation of the ice sheet surface and of 7 internal (g) D the points show the individual samples and the red line is the av- Surface slope calculated over 20 m intervals of the ice sheet surface. δ (f) . For (c) Isotopic content of the surface (1.5 m) layer of the snow thickness, The results of the glaciological, GPR and geodetic survey in the Vostok mega-dune is the error of the average of 5 individual values). σ axis is reversed. (a–c) ) of 2-year average accumulation value as deduced from Vostok stake network. Note that Y σ 1 ± area. Figure 3. erage of the 58 andis 59 RAE reversed. samples. For For dxs 17O-excess only we the showed average is the shown. 5-point Note running that the means dxs with axis the error bars ( and 17O-excess where dividual values (points) and 3-pointindividual running values mean (points) (line). and 3-point( running mean. Dashed lines show the confidence interval the Negative values mean that(from the south-west local to slope north-east). is the opposite of the general slope in this region reflection horizons (IRH) above seavey. level The defined by gray the shading geodetic depictsmeasured. measurements The and the GPR dashed snow sur- lines layerThe connect (1.5 values m) the to in the fold right which hingesis are the used the spread snow estimated to from ages isotopic calculate south-west of content theindividual (left each values IRH was part dune shown relative drift of to in the velocity. January Fig. 2015. figure) 3 The to can profile the be north-east found in (right Table part), 1. see Fig. 1. The Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | A combination of Depth-age function (b) (c) – erosion zone, leeward slope of the The values of snow accumulation rate (a) (a) purple from Fig. 5a). + 6936 6935 Simulated vertical profile of snow isotopic composi- (d) – deposition zone, the hollow between dunes. (b) Simulated isotope profile in MD00 point. Photo of the snow surface in points MD02 tion calculated using thewith data the from real Fig. vertical 5bMD00, and profile in depth-age of blue. function snow (Fig. isotopic 5c), composition in measured red, in compared the core drilled in point Figure 5. (blue) and isotopic composition (red)sure them that as could long be asFig. observed the 3a in dune point and travel MD00 e, acrosstopic if and this one composition data point. would To on in calculate mea- the the thisclimatic dune Vostok we and region drift used dune-related velocity. taken the isotopic Purple data from variabilityfor – from (red Ekaykin the climatic et snow variability al. thickness of (2014). in the point snow MD00. iso- Figure 4. dune – and MD13