Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Mg Mg: 26 26 δ δ 0.10 ‰) Climate ± , 3 , and 0.15 ‰) and of the Past 5 ± 4.20 Discussions ¨ otl − 0.73 ‰; SPA 59: 4.17 ± − Mg: , C. Sp 26 1 3.00 δ Mg) isotope data as con- − erent sources of magne- ff 26 δ , D. F. C. Riechelmann , A. Geske 2 1 0.07 ‰ and HK3: ± 1836 1835 4.26 0.07 ‰; BU 4 mean − ± ¨ oder-Ritzrau 4.01 − , J. A. Wassenburg 4 , A. Schr Mg: 1 26 δ ected by glacial versus interglacial climate change with outside ff Mg values (GDA: 26 ecting soil zone activity and weathering balance. Several data points , D. Buhl 1 δ ff 1 , H. B. Vonhof 1 0.04 ‰) but only minor variations in Mg-isotope composition, which is in con- 0.43 ‰) are a ¨ atsstraße 150, 44801 Bochum, Germany ± ± 3.96 3.70 This discussion paper is/has been under review for the journal Climate of the Past (CP). Please refer to the corresponding final paper in CP if available. Heidelberg Academy of Sciences, ImJohannes Neuenheimer Gutenberg-University Feld Mainz, 229, Institute 69120 of Heidelberg, Geography, Germany Faculty of Earth and Life Sciences, Vrije Universiteit Amsterdam,Leopold-Franzens-University De Innsbruck, Boelelaan Institute 1085, for Geology and Palaeontology, Innrain 52, Ruhr-University Bochum, Institute for Geology, Mineralogy and Geophysics, 2 3 Johann-Joachim-Becher-Weg 21, 55099 Mainz,4 Germany 1081 HV Amsterdam,5 The Netherlands 6020 Innsbruck, Austria Received: 30 April 2012 – Accepted: 3Correspondence May to: 2012 S. – Riechelmann Published: ([email protected]) 22 May 2012 Published by Copernicus Publications on behalf of the European Geosciences Union. 1 Universit tations of the magnesium isotope proxy applied in continental climate research. An A. Immenhauser cert with the ratherGermany stable (AH-1 equatorial mean climaterecord changes at in this outside air site.The temperature Holocene as alpine stalagmites driving Pleistocene factor from rather− flowstones than rainfall from amount. Austriaair temperature (SPA a 52: in the Austrian andvalues two due to data sampling points in detrital inThe layers the (Mg-bearing data clay German and minerals) speleothems of their the are interpretation speleothems. shifted shown to here higher highlight the potential but also the limi- time of water inthe the lowest soil mean and karstthe zone. data are Pleistocene well stalagmites explainedHolocene from in stalagmites terms Morocco from of Peru show show changes the in− highest aridity mean over value time. (NC-A and The NC-B Pleistocene to the semi-arid to arid (Morocco),(Peru) the and warm-temperate the (Germany), cold-humid the (Austria)isotope equatorial-humid climate signature zones. Changes with infrom the time these calcite are speleothems. magnesium placed Similarber to against of other carbon proxies, environmental, the and equilibriumfractionation non-trivial oxygen and interaction in non-equilibrium isotope of continental processes a records sium settings. governs num- isotopes the These such includebiogenic as the activity, rain di shifts water in or silicate versus snow carbonate as weathering well ratios as and soil residence and hostrock, soil zone Here we explore the potentialtinental of time-series climate magnesium proxies ( six in Pleistocene speleothem and Holocene calcite stalagmitesand archives. from two For caves flowstones in this from Germany, a Morocco purpose, and cave a Peru in total Austria were of investigated. These caves represent D. K. Richter Abstract The magnesium isotope record ofcarbonate cave archives S. Riechelmann Clim. Past Discuss., 8, 1835–1883, 2012 www.clim-past-discuss.net/8/1835/2012/ doi:10.5194/cpd-8-1835-2012 © Author(s) 2012. CC Attribution 3.0 License. 5 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | ¨ ¨ otl otl ect ff erent ff ¨ otl et al., 2005; Asrat et al., 2008; cult to constrain. In this respect, validation ffi 1838 1837 erent caves (Williams et al., 2004; Mangini et al., ff Mg time-series data sets from Pleistocene/Holocene 26 δ Mg isotope data from six stalagmites and two flowstones. Mg) data. Previous work dealing with Mg isotope fraction- 26 26 δ δ ect proxy data remain di ff ¨ Mg ratios from rain, snow, riverine, soil and drip water as well as hostrock eron et al., 2011; Reynard et al., 2011) may provide valuable information 26 δ Mg fractionation between land surface and cave carbonate deposition, to (2) apply ¨ uhlinghaus et al., 2007; DePaolo, 2011; Dreybrodt and Scholz, 2011) work, several Here we report on the potential and limitations of Mg isotope time series proxy Despite significant advances in field studies (Sp More recently, it has been proposed that multi-proxy studies including novel ap- 26 2 Case settings This study makes use of These include two stalagmiteslagmites from Germany from (Atta Morocco Cavemites (Grotte and from Bunker d’Aoufous Peru (Cueva Cave), and del two TigreCave). Grotte Perdido) sta- and The Prison two reader flowstones de from is Austriacave referred Chien), (Spannagel parameters to and two Fig. speleothems stalag- investigated. 1 and Table 1 for detailed information regarding continents. The goalsδ of thisthese study findings are to all to available speleothems and (1) flowstones. review parameters known to a and cave carbonates andGaly, 2004; soil de Villiers and et caveBrenot al., silicate et 2005; al., Tipper data et 2008; (Galyet al., Immenhauser al., et 2006b, 2012b). et 2008, al., Nevertheless, 2010; al., with 2002;et Buhl 2010; the et al. Young Pokrovsky exception al., and (2007), et of 2007; a the al.,data critical preliminary is 2011; work lacking. application Riechelmann shown of in the Buhl above-cited work todata speleothem interpretation time series from eight speleothems collected in six caves on three di and complement more traditional proxy data.proxies Amongst are these Mg more recently isotope established ( ation in Earth surfaceand environments field includes and investigations laboratoryclude from precipitation carbonate experiments. archives Data available in the literature in- 2010; Da proaches such as fluidisotope inclusions, noble systems gases, (Kluge clumped et isotopes al., and non-traditional 2008; Scheidegger et al., 2008; Immenhauser et al., Verheyden et al.,and 2008; Fairchild, Riechelmann 2001; et(M Collister al., and 2011), Mattey, includingparameters 2008; that experimental a Polag (Huang etof proxy al., data from 2010) individual coeval andVollweiler stalagmites et within al., numerical a 2006) given and cave between (Dorale di 2005; et Fohlmeister al., et 1998; al., 2012) is a key issue. and Borsato, 2010), as well(Tooth and as Fairchild, equilibrium 2003; Miorandi and et disequilibrium al.,speleothem 2010; conditions precipitation Sherwin in in and the the Baldini, cave 2011) aquifer et (White, and during 2004; al., Tremaine 2012a). et al., 2011; Riechelmann 1 Introduction Carbon and oxygen isotopeused ratios as proxy well data aset from trace al., elemental speleothem 2002; abundances archives are LachnietScholz (e.g. widely et et Genty al., al., 2004; and 2009;chemistry Cruz Rudzka include Massault, et ambient et 1999; environmental al., al.,et Sp al., parameters 2007; 2011). 2005; (Baker Fairchild Baldini The and et and factors al., Genty, McMillian, 2008), that 1998; carbonate 2007; control Sp mineralogy (Frisia speleothem et al., geo- 2000, 2002; Frisia a hitherto rather poorly understoodresearch. but extremely Limitations important are component most inneeded obvious cave for archive in analysis. the Future research low shouldpects resolution including focus and on quantitative and high experimental well and sample calibrated conceptual amount leaching as- and precipitation experiments. obvious potential lies in its sensitivity for even subtle changes in soil-zone parameters, 5 5 25 15 20 10 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | ± ± Mg 26 4.18 2.58 δ − − Mg values 26 Mg: δ 26 δ Mg value at 7.9 ka 26 δ ¨ amper et al. (2005), Buhl 0.01‰ and Mg is less variable. Stalag- ± 26 δ Mg values range from 0.07‰ (Figs. 2 and 3a, Tables 2 26 1.34 ) was prepared. The samples were δ 3 ± Mg. The sample was taken because − Mg show again a more depleted value 26 26 δ Mg: 4.01 δ Mg signatures. Stalagmite AH-1 from Ger- − 25 26 δ δ 1840 1839 89, = n Mg-enriched values and a higher overall variability is Mg. Stalagmites AH-1 (Germany) and GDA (Morocco) 26 26 ∆ Mg value becomes slightly depleted whilst subsequently the 26 δ Mg value is found at 8.7 ka BP.An enriched Mg values is observed and between 9.0 to 6.0 ka BP and 4.2 26 26 0.03‰ with a mean of δ δ ± ¨ otl et al. (2007), van Breukelen et al. (2008), van Breukelen (2009), (65% : 31%). Subsequently, the solution was evaporated and again re- Mg ratio is present. At 1.2 ka BP, 3.86 2 26 − O δ 2 Mg between bulk (with intact fluid inclusions) and grounded samples (without 26 :H 3 ∆ Mg, whilst stalagmites NC-A and NC-B (Peru) reveal the lowest degree of variability The results from the fluid inclusion test runs are presented in Table 4 and Fig. 4. Moroccan stalagmites GDA and HK3 and stalagmite BU 4 from Germany yielded The stalagmite AH-1 (Atta Cave) provided material that was tested for the impact of 26 to their aliquots containing fluid inclusions (Fig. 4). Error bars of all these samples, found. At 3.2 ka BP,the value is again moredecrease enriched again at and 2.5 ka thendepleted BP. increase Between between 2.5 1.6 and and 1.6whilst ka 1.5 the ka BP most BP. recent At data 1.5 ka point, dated BP at the 0.7 least kaThe BP is less depleted. fluid inclusions) is not exceeding theare second decimal. systematically Nevertheless, grounded lower samples by 0.01 to 0.08 ‰ in their Mg-isotope composition relative BP and less depleteda values between trend 6.0 to andto lower 0.7 ka 0.7 ka BP. Between BP, a 6.0found. and weak The lowest 4.2 trend ka to BP, BP coincides with a detritus layer. Between 4.2 to 3.5 ka BP, a trend to higher values is δ and therefore the smallest show intermediate amplitudes (Fig. 2). 4.1 Stalagmite AH-1, Atta Cave, Germany Holocene to recent0.05‰ (1997 to AD) stalagmiteand 3). AH-1 Stalagmite AH-1 yielded overall more depleted values between 9.0 and 6.0 ka are least depleted in termsmany of and their mean the Peruvian stalagmites NC-Avalues and (Fig. NC-B yielded 2). intermediate Thetheir mean Mg-isotope flowstones composition. SPA 52 Inmite and contrast, HK3 (Morocco) SPA stalagmite 59 and stalagmite show BU the 4 highest (Germany) variations show in the highest amplitudes in the most depleted mean values, whilst flowstones SPA 52 and SPA 59 from Austria 4 Speleothem geochemistry: results Carbon and oxygen isotope time seriesand data 5–10 as well are as publishedet U-Th age in al. data Niggemann (2007), shown in et Sp Wassenburg Figs. al. 3 et (2003), al. Holzk (2012)flowstone and Mg Fohlmeister isotope et datageochemical al. are characteristics (2012). shown are summarized Time in for series Tables each 2 stalagmite speleothem and analyzed. and 3 and Fig. 2. Below, the main it contains numerous fluidtracted and inclusions. half of Calcite each samples samplesubsequently grounded from analysed in for this acetone their to stalagmite magnesium removesamples the isotope were were fluid signature. analysed ex- inclusions Aliquots too and and of results non-treated compared. columns (BioRad ion exchangedryness resin and AG50 a W-X12, 500 200 ppbanalyzed Mg-solution to with (in 400 3.5 a mesh), % Thermo HNO evaporatedsolution. Fisher to Scientific The Neptune external MC-ICP-MSsolution using precision Cambridge DSM3 was 1 standard repeatedly determined ( 0.03‰). by For measuring details of the the mono-elemental analytical procedure refer tofluid Immenhauser inclusions et in al. the (2010). calcite fabric on the bulk Powder subsamples from longitudinally cutin stalagmites and 6 M flowstones were HCl. dissolved HNO The solution was drieddissolved in and 1.25 M re-dissolved HCl. with The Mg-bearing 250 µl fraction was of extracted by a using 1 ion-exchange : 1 mixture of 3 Magnesium isotope analysis 5 5 25 15 20 10 20 25 15 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Mg Mg- 26 26 δ 0.07‰ δ ± 0.04‰ to ± Mg value is 4.34 26 − δ 0.05‰; Figs. 2 4.06 ± − 0.07‰ (Figs. 2 and ± 4.17 Mg-depleted. The last Mg values range from Mg values range from − 26 26 26 δ δ 4.26 − 0.04‰ (Figs. 2 and 6a, Tables Mg values show ranges from ± 26 δ 0.73‰) and from 3.96 Mg values range from Mg value at 7.0 cm dfb (Fig. 9a). Be- 0.10‰ (Figs. 2 and 5a, Tables 2 and − ± 26 26 ± Mg values. Between 1.8 and 1.1 ka BP, 0.06‰ (mean: δ δ Mg ratios are slightly less depleted. increase towards the overlying aragonite Mg-enriched value is recorded reaching 26 ± 26 26 3.00 δ δ 4.20 − 1842 1841 − calcite 3.89 − Mg values are again observed between 7.0 and Mg 26 26 δ Mg value coincide with a hiatus marked by coralloid δ 0.43‰; Figs. 2, 9a and 10a, Tables 2 and 3), respec- 26 Mg-enriched. These shifts, however, barely exceed the δ ± 26 0.05‰ with a mean value of 0.04‰ (mean 0.03‰ with a mean of 3.70 Mg and therefore, the potential impact of fluid inclusions on 0.02‰ and ± ± ± − Mg values show more depleted values in the lower third of the 26 ± Mg value for SPA 52 is located at 0.7 cm distance from base 26 ∆ 0.115Ma, Table 1) stalagmite GDA 26 Mg is again depleted at 2.3 cm dft. 4.17 δ 1.42 ± δ 3.88 − 26 − 4.29 − δ − 0.05‰ with a mean value of Mg is not considered of significance here. ± 26 0.05‰ to 0.05‰ (mean: 0.02‰ to 0.04‰ to δ ± ± ± ± 3.91 Mg values are invariant with one higher value at 1.1 ka BP. The lowest measured − 3.63 2.47 4.39 4.03 26 (dfb) in a detrital layertween followed 7.0 by and a 9.1 depleted cm dfb the values slightly increase again. At 10.3 cm dfb the interval (Fig. 8a). 4.6 Flowstones SPA 52 and SPA 59,The Spannagel Pleistocene Cave, Austria flowstones− SPA 52 and− SPA 59 tively. The highest et al. (2012). The transitionsBP are located (Wassenburg between et two al., ageanalysed points 2012). as – Samples 27.48 the and from Mgvalues 23.53 ka the content between low-Mg of aragonite aragoniteand layers is 8a, Tables were too 2 and not low.intervals, 3). The Overall, whilst calcite isotope layer ratios yields remain invariant in the central portions of the calcite 3.1 cm dft, whilst 4.5 Stalagmite HK3, Grotte Prison deThe Chien, Morocco Pleistocene toand Holocene calcitic stalagmite layers HK3 reflectingclimate consists alternatingly conditions. of more Data arid several from (aragonite) samples primaryand and across from aragonitic two less calcite transitions arid from to (calcite) aragonite aragonite to are calcite used and were described in detail in Wassenburg the stalagmite GDA stalagmite; i.e. between 13.6At and 9.7 8.9 cm cm distance dft, fromplateau i.e. the the values top middle between (dft) part, of 8.9more the a and enriched stalagmite. more 7.7 at cm 6.3 dft. dft The and magnesium a isotope second value plateau is phase again is reached between 6.3 and the University of Berne, Switzerland), therefore error bars are large. From the base of − 7a, Tables 2 and 3). Age dating was performed by the U-Pb method (measured at with fluctuations mostly withinslightly the enriched analytical at error. 2.8point Speleothem ka at NC-A BP 0.06 ka and BP aterror is bars 1.9 ka of again NC-B. BP the value is 4.4 Stalagmite GDA, Grotte d’Aoufous, Morocco Pleistocene (2.134 4.3 Stalagmites NC-A and NC-B, CuevaUpper del Tigre Pleistocene Perdido, to Peru recent− stalagmites NC-A and2 and NC-B 3). Magnesium isotope values in speleothem NC-B (13.1 to 3.6 ka) are invariant to 3). Between 8.2 and 7.8 kaaround BP, a 7.6 ka trend towards BP. More lower values6.0 depleted ka is found BP. The that least is inversedlayer depleted at and detrital material dated 5.5between ka 3.9 BP. Subsequent to speleothem calcite 1.8 ka precipitated δ BP with decreasing value was dated 0.4 ka BP. Subsequently, however, exceed the calcite 4.2 Stalagmite BU 4, Bunker Cave,Holocene Germany to recent (2007 AD) stalagmite BU 4 5 5 25 15 20 10 20 15 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 2.2 1‰; − − Mg values Mg isotope C from 4 to 26 ◦ Mg depleted Mg-enriched Mg-enriched 5.3 to 26 δ − δ 26 26 26 Mg-depleted be- ecting the Mg and is located 26 ff 26 δ C (Galy et al., 2002). ◦ C; Richter et al., 2011), Mg values of SPA 59 are ◦ 26 Mg ratio of dolostone ( 2.47‰; Fig. 10a). Samples ecting Mg isotope fraction- δ ff − 26 δ Mg: 26 δ C between 4 and 18 Mg dependency of 0.011 ‰ per 1844 1843 ◦ 26 ect the Mg-isotope composition of the soil water δ ff Mg fractionation during calcite precipitation is a minor factor 0.1‰; Immenhauser et al., 2010). Biological Mg fractionation 26 + δ Mg is higher at 41.1 mm dfb (Fig. 10a). This sample was taken at Mg-enriched and diagenetically stabilized low Mg-calcite limestones Mg-enriched with increasing distance to the marine aerosol source 26 26 26 δ 1.1 to − Mg signature of all involved Mg sources – rain water, soil cover (silicates) 26 Mg-isotope fractionation in continental karst systems δ Mg-depleted; (iv) the residence time of soil and karst water in the aquifer above 26 26 δ 1.1‰; Li et al., 2012) is in general higher than that of limestone ( C (Li et al., 2012) and 0.02 ‰/AMU/ Mg values are again higher (at 14.4 cm dfb) and are again lower at 16.7 cm dfb ◦ − In contrast, even when considering the maximum range of Pleistocene to recent Rain water is Between 25.4 to 33.6 mm distance from base (dfb) the 26 minerals) weathering is relatively increasing during warmer and drier climate conditions to Li et al., 2012),composition whilst ( silicate rocksby and plants clay and minerals soilin microorganisms have a variable the degrees most dependingmetabolisms on the (Tipper amount et of al.,and Mg 2010; wetter involved conditions Riechelmann and soil et activity plant is al.,growth and increased induces 2012b). (Harper a microbial stronger et Clearly, biological al., under fractionation. 2005)in Grass, warmer and for comparison enhanced example, with is plant its rain water source (Tipper et al., 2010). Silicate (Mg-bearing clay 45 and may reveal temperature-related fractionationcompared patterns, to rain i.e. (Tipper snow et is set al., is 2010; perhaps too Riechelmann limited et to al., draw 2012b) solid conclusions. but The the existing data silicate (Mg-bearing clay minerals)with clays and being carbonate weatheringbeing ratio inthe the cave soil and (v) zone, carbonate precipitation rates in the caveair environment. temperature changetemperature-related in caves inwith Germany experimental (ca. data 9 suggesting a to 10 and Riechelmann et al. (2012b).eters Considering are the of published significance work, for the thedata: interpretation following (i) param- of speleothem time-series and hostrock (limestone ortrolled dolostone); mainly (ii) by the water biogenic availability and activity air of temperature; the (iii) soil the zone balance con- between the et al. (2007), Brenot et al. (2008), Immenhauser et al. (2010), Pokrovsky et al. (2011) ation in Earthand surface Galy systems (2004), have de been Villiers described et in al. Galy (2005), et Tipper al. et (2002), al. Young (2006b, 2008, 2010), Buhl many; (iii) equatorial-humid climatewinters in and Peru cold and summers) (iv)lowing in factors alpine Austria directly (Kottek climate relate et (humid, toaccording al., climate, snow-rich to 2006). the climate discussion Given zones. of that Mg-isotope most data of is the organized 5.1 fol- Environmental, equilibrium and non-equilibrium factors a Environmental, equilibrium and non-equilibrium factors a 5 Interpretation and discussion The study sites aretemperate and grouped semi-arid into (dry thein and following Morocco; hot (ii) present-day summers) warm climate to temperate regions (warm arid (i) summers) (desert and warm and humid hot climate arid) in climate Western Ger- low before the a hiatus with detrital materialfore at the the highest top. value At is 56.4taken reached mm at at dfb 47.5 60.3 the mm and value dfb is 60.3are ( mm again dfb depleted contain 65.7 detrital mmincrease dfb material. occurs and Afterwards, show the between a 80.5dfb decreasing and (Fig. trend 94.2 10a). to mm 80.5 dfb mm dfb. followed A by slight a decrease to 110.9 mm is slightly depleted. Thein sample a at calcite 13.2 layer cmδ containing dfb slight is amounts higher of(Fig. in 9a). detritus. These its After two a sample hiatus points coincide of with ca. detrital 53 layers. ka the 5 5 25 15 20 10 25 20 15 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Mg val- 26 δ Mg-enriched 26 Mg values in the 26 δ Mg value. Following 26 Mg data from Morocco δ 26 δ . Therefore, the direct applicability of 1 − for AH-1, BU 4, NC-A, NC-B, SPA 52 and 1 − 1846 1845 Mg values (Riechelmann et al., 2012b). Where 26 δ ect the soil and aquifer water ff ) that exceed those of most natural speleothems (range of 1 /0.1 to 1140 µmyr − 1 − 0.36‰) is observed and documented in Fig. 8a. Carbon, oxygen Mg-depleted aquifer water is longer and hence leading to a bigger = Mg values. Under most hydrogeochemical conditions, the limestone 26 Mg-depleted water. For shorter water residence times it is the opposite 26 Mg δ 26 26 ∆ ecting weathering rates in carbonate-silicate settings are complex, spatially Mg on water isotope ratios will be subdued (Galy et al., 2002) due to the ff 26 Mg is found at rates exceeding 200 µmolh We used the stalagmite HK3 Mg-isotope data to test the above-described impact The Moroccan stalagmite HK3, characterized by alternating aragonitic and calcitic Longer water residence times in the karst aquifer lead to lower Mg enriched clays are leached, and (ii) prior calcite precipitation, which takes place 26 and magnesium isotopes show aever, highly it similar should trend be in noticed the that calcite near layer the (Fig. calcite-to-aragonite 8). transition How- the possibility of of increasing aridityessence, and rainfall soil amount water predictablysition decreases residence (27.48 towards time to the 23.53 on ka calcite-to-aragoniterates in BP), tran- the the whilst aquifer Mg-isotope should soil increase. signature.clay-derived water Under Mg increased residence In input a time of shift isotopically and towards moreexpected. higher silicate positive, Indeed, values weathering near this the shift calcite-to-aragonitearagonite transition in ( is isotope ratios in the calcite layer near the transition to surface), leading to a higher Mg-contentdolomite of (Table 1) the fluid. results The in factprior an that calcite enriched the precipitation Mg-content hostrock also contains of increasestion the the drip state. pH These water, of too. factors the In giveWassenburg fluid addition, et rise and al., to lowers 2012). aragonite the precipitation fluid (Frisia satura- and Borsato, 2010; intervals, documents the aboveMg relationships in aragonite (Fig. (Okrusch 8).intervals. and Based Due on Matthes, high-resolution to 2005), carbon the and samplingtal oxygen low abundances, was isotope Wassenburg data restricted abundance et as to of al. wellaragonite as the (2012) precipitation elemen- was documented calcite favoured whilst that calcite during layersing typify more more less arid arid arid phases, conditions. periods, Dur- two mainthe factors increased trigger residence aragonite26 time precipitation. of These include water (i) in the soilin as the well karst as aquifer zone in (i.e. the the karst precipitation system, of where calcite prior to reaching the stalagmite their high Mg-content anddolostones higher or dolomite-rich limestonesderived form the cave hostrock,Mg-rich the hostrock impact mineralogy. of silicate- als (Appelo and Postma,Mg-bearing 2005). clay minerals Nevertheless, will even be a recorded slightly in soil-zone increased and solubility karst of aquifer waters due to diverse and debated inet the al., literature 2011). (Tipper Nevertheless, etwell as rain al., biogenic 2006a; water soil Li abundanceet activity et and al., are al., residence 2010). considered 2010; time Related significantstone Pokrovsky in (Tipper to weathering et the these balance al., factors, soilthe 2006a, changes a as 2010; above in Li discussion, the a soilduces higher clay relative mineral increase to inand host the dolostone lime- weathering solubility in of soil soil water clay and minerals aquifer in- waters exceeds that of clay miner- the precipitation experiment datatems shown is in at Immenhauser present et unclear. al. (2010) to5.2 natural sys- Warm-(semi-)arid climate: speleothem time series Factors a (Riechelmann et al., 2012b).hauser Based et al., on 2010), laboratory lowerues precipitation carbonate and precipitation experiments vice rates (Immen- lead versa.more to This, decreasing saturated however, refers than to those commonly experimentalrates found fluids (50 in that to cave are environments 6300.0008 considerably µmolh and to to 9.94 precipitation µmolh SPA 59). A statisticallyδ significant impact of experimental precipitation rate on calcite more humid and cooler conditions (Buhl et al., 2007;drip Immenhauser waters, et because al., the 2010). mixing timewater between and younger, newly older infiltrating portion of the compared to carbonate weathering, which is always dominant but particularly so under 5 5 25 15 20 10 25 20 10 15 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | erent fractionation ff Mg data from Peru 26 δ 0.115Ma) and speleothem Mg values of the GDA show ± O ratios, respectively (Fig. 6). 26 18 δ 0.08‰; Fig. 2; Buhl et al., 2007), δ ± erent for aragonite and calcite (Ro- ff Sr under more arid conditions due to ˜ 3.63 na et al. (2003) and Feddi et al. (2011), C and 86 − 13 Sr/ δ Mg record of the two Moroccan speleothems 1848 1847 87 Mg values for the Moroccan stalagmite GDA 26 O values (Fig. 7). Problems arise because sta- 26 δ O values (Figs. 7 and 8) represent less arid and 18 δ ¨ aßer, 1999); and was probably in the order of 940– δ 18 ers significantly from that of the Moroccan case ex- Mg and δ ff 26 δ C and C, Sr and Mg elemental data and Sr isotopes (Buhl et al., ˜ na et al. (2003) found changes in the dust amount, inter- C and 13 13 δ 13 (Table 1; Str δ δ 1 − O, Mg of Grotte d’Aoufous ( 18 Mg, 26 δ data that decrease during the Holocene due to a gradual increase of 26 δ δ at the beginning of the Holocene (15–30 % increase of rainfall amount 1 calcite − O 0.07‰; Fig. 2; Immenhauser et al., 2010) values of the caves in Germany dis- 18 ± Sr ratios – i.e. more radiogenic δ 86 3.72 In contrast to the Moroccan case examples, the Peruvian stalagmites NC-A and NC- In essence, the concepts as explained above provide a comparably robust and inter- The hostrock The Mg-isotope record of the calcitic stalagmite GDA from Grotte d’Aoufous is Sr/ − B lack a correlationApplying between the concepts laid out above, the limited changes in the (short) soil water during the Holocene; van Breukelenhumid et climate. al., 2008), Average a annual value temperaturesthrough that the seem indicates Holocene to an (van overall have Breukelen very in remained et the rather al., constant 2008). Thisrainfall overall amount pattern (van is Breukelen documented etwere al., short 2008). It due seems to likely,no that the changes water high in residence and the times Mg-isotope constantly values high should rainfall be amount expected. at this site. Therefore, 5.3 Equatorial-humid climate: speleothem time series The Holocene climate inamples. Peru The di present-day rainfall amountis in around 1344 the mmyr vicinity of1140 mmyr the Cueva del Tigre Perdido 87 longer siliceous rock/water interactiontowards (Buhl lower et al.,perhaps 2007) lower – temperatures itdesert whilst is climate higher proposed (Fig. isotope that 11).tope ratios shifts The data point above from to considerations warm-(semi-)ariddriven more suggest settings changes that arid are in speleothem the useful and carbonate-silicate Mg and hot weathering iso- sensitive balance. proxies for climate climate in Germany. Hence,could be lower expected. nally consistent interpretation forshown the here. Combined with evidence from Sr and Mg abundances and calcite the northern rim of the Sahara were expectedly longer than those in the warm-humid cussed below. Aquifer water residence time under the arid conditions that characterize component of thearid eccentricity. and According less to ariddocumented these conditions evidence authors, occur for during temperature changes changesThese the between in general Gelasian. patterns more the Similarly, are Gelasian Feddi arguably fromfore et showing also pollen al. changes recorded analyses. between (2011) in more stalagmite aridin GDA, and the which warm Mg-isotope and is composition. less there- arid and warm conditions a Turonian marine( limestone, is slightly higher than that of the Devonian hostrock 2007). Climate reconstructions fromhowever, Larrasoa support the interpretation ofGelasian stalagmite (1.806–2.588 GDA Ma), from i.e. Buhl thestalagmite et time GDA, al. interval (2007). Larrasoa For thatpreted the coincides as with changes in the the U-Pb amount age of of rainfall that coincides with changes of the 400-kyr equally well understood in the contextwere of thought aridity changes. to The reflect Mg-isotopeaccordance data changes (Fig. with between 7a) more or2007). less Similar arid to conditions, thea which Moroccan similar were stalagmite pattern in HK3, aslagmite the the GDA is considerablygrowth in older the (U-Pb Grotte age d’Aoufous of ceased 2.134 several times in the Pleistocene (Buhl et al., fractionation of carbon andmanek oxygen et isotopes al., 1992; is Kim di andfactors O’Neil, also 1997), apply it may for be Mg.calcite-to-aragonite possible that Therefore, transition di changes may in the alsofactor. Mg-isotope be composition induced near the by a change of the fractionation a mixing of predominantly calcite with small amounts of aragonite is found. Since the 5 5 25 15 20 10 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | ± Mg Mg 26 26 δ δ erences ff Mg relative to 26 δ Mg-enriched values 26 Mg relative to the cal- 26 ) but the same drip char- 1 δ − Mg data from Germany 26 δ barely exceeding the analytical Mg values would be expected rather calcite 26 0.001mlmin δ ± Mg Mg value of AH-1 drip water are expected 26 Mg-enriched values are found as opposed 26 δ erences in their drip rate (AH-1: 0.019 26 Mg time series data from Atta and Bunker 1850 1849 δ ff 26 δ Mg sampling points and the invariant Mg-isotope 26 δ Mg values of stalagmite AH-1 from samples that were 0.10‰; Fig. 2 and Table 3) compared to speleothem AH-1 26 ± δ Mg of the fluid contained in these inclusions shifts the bulk cal- 4.20 26 − δ erences in drip water chemistry might also be the reason for the ff 0.07‰; Fig. 2; Immenhauser et al., 2010) and soil properties, we sug- ± ; Niggemann, 2000; BU 4: 0.002 1 − 3.72 Mg value ( 0.07‰, Fig. 2 and Table 3). This because the aquifer water in Bunker Cave − 26 ± δ Mg: erences in mean Mg-isotope composition of 0.19 ‰ between these two caves. Drip 4.01 The portion of stalagmite AH-1 representing the time interval between 9.0 to 6.0 ka In AH-1, carbon and oxygen isotope values (Fig. 3b) are enriched in the dark, dense Nevertheless, di The interpretation of speleothem Both drip sites show only slight di 26 ff − δ all wetter (Niggemann et al., 2003) and 6 ka BP andvalues Present correspond with is the typified darkcorrespond and by with compact the a crystal white white fabric and and porous and crystal porous fabric. crystalfabric (9.0 fabric. to Lower 6.0 ka BP),conditions a (Niggemann fact that et was al., interpretedclimate as 2003). in evidence As for essence overall argued drier shiftstopically climate in less the Riechelmann depleted silicate (silicate) et values. versus al. Higher than carbonate lower (2012b), values weathering as drier observed. ratio Between towards 6.0 and iso- the present day, the climate was over- for the drip water of BUlimestone 4. (Li Given et that al., dolomite is 2012),and generally found. higher elevated mean in BP is characterized by a dark and compact crystal fabric. Calcite precipitated between has a longer reaction time with the isotopically depleteddi hostrock in the karst zone. water samples taken aboveNiggemann, AH-1 2000) relative is to considerably drip water enrichedHigher samples Mg in taken above concentrations Mg BU in 4 (Mg/Ca the (Mg/Caalong ratio: ratio: aquifer fissures 0.06). may 0.67; be in due thepossibly to percolating dolomitisation hostrock along of (Krebs, the these 1978). limestone dolomitized Water fissures. feeding This the seems not drip to site be of the AH-1 case is bly suggests that the waterresidence feeding time the compared AH-1 to drip thatis of site supported the (Atta by BU Cave) field 4 has evidencemean drip a given site shorter that (Bunker speleothem water Cave). BU This( 4 assumption is characterized by a lower drip rate of the AH-1 drip site is ten times faster than that of the BU 4 drip site proba- 0.001mlmin acteristic (seepage flow) using the terminology of Baker et al. (1997). The fact, that the et al., 2012) – is influencedthis by fluid the (Riechelmann same et factors as al., the 2012b). calcite that has precipitatedCaves from is challenging. Given the very( comparable climate setting, hostrock composition gest that the same setbetween of the factors two drive sites Mg include fractionation drip in characteristics these as two well caves. Di as drip water chemistry. same sample that have nottime been is treated the in same this for manner.concluded, The the that trend crushed the in samples Mg-isotopes and with cite the Mg-isotope bulk composition samples by (Fig. 0.01 4).the to From fluid 0.08 this representing ‰ it towards the is higher dripcite values. (Galy water This et chemistry is al., – because 2002; enriched Young and in Galy, 2004; Immenhauser et al., 2010; Riechelmann of the low temporalsignatures, resolution it of is here proposed thatcase the setting Peruvian that stalagmites is represent an less end-member than suitable for Mg5.4 isotope proxy data. Warm-humid climate: speleothem time series Figure 4 documentscrushed all prior to analysis and that are isotopically depleted relative to aliquots of the the Late Pleistocene toMg-bearing Late montmorillonite Holocene – (Sanchez the andratios soil Buol, in is 1974) mainly stalagmite – composedspeleothem NC-B of resulted recorded (Fig. kaolinite in subtle and 6a). invariant error changes In that in contrast, are the not Late reflected Holocene in to the recent C NC-A or O isotope ratios. Considering the limitations residence and a rather constant carbonate versus silicate weathering ratio throughout 5 5 25 15 20 10 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 2 C 13 δ Mg values. 26 δ Mg are calibrated, 26 Mg values coincided δ Mg is noted (Fig. 3a), 26 δ 26 δ Mg values took place when 26 δ C is influenced by vegetation cover 13 δ O data of BU 4 indicate a trend to drier 18 δ O data of BU 4 recorded changes in both Mg values both show a decreasing trend 18 1852 1851 26 δ δ C and Mg values (Fig. 5), perhaps explained by an overall O record with that of the Atta Cave stalagmite AH- 13 26 δ 18 O record of stalagmite AH-1, Mangini et al. (2007) δ δ 18 Mg. If these considerations hold true, the general trend C and δ 26 C signal decreases, which is due to a denser vegetation 13 δ towards higher values may bear witness of an overall in- 13 Mg values may be due to enhanced dissolution of carbon- Mg ratios shift to higher values at this level (Fig. 5a) but the δ 26 26 δ δ AH-1 C values and vice versa (Fohlmeister et al., 2012). 13 Mg O and higher δ 26 18 δ δ O data (Fig. 5). As a consequence, it seems that temperature is again the Mg is mainly outside air temperature controlled. Between 9 to 6 ka BP car- 18 δ C values decrease but to a lesser degree (Fig. 3b). The direct comparison 26 C and δ 13 13 δ δ Mg-depleted values as expected for dominant carbonate weathering under wet- C and 26 BU 4 magnesium-isotope ratios between 1.6 and 0.7 ka BP anti-correlate with BU 4 From 5.5 to 1.8 ka BP, Between 8.2 and 6.0 ka BP, the The stalagmite BU 4 consists of a columnar fabric with the exception of a thin interval Following Fohlmeister et al. (2012), Using oxygen isotope data of AH-1 (Niggemann, 2000; Niggemann et al., 2003) as The following lines of evidence (Riechelmann et al., 2012b) suggest that under an 13 lower of the Bunker Cave stalagmites 1 reveals similar patternsevidence that (Fohlmeister stalagmites et in al.,signals. both 2012). caves recorded This essentially observation the is same environmental considered δ factor dominating soil processes and linked1.1 to this, to weathering 0.7 ratios ka, (Fig. the 11). Between Medieval Warm Period (Fohlmeister et al., 2012) is characterized by of the loessTherefore, (at decreasing present aate loess between loam) 5.5 may to 1.8BP have ka lead BP. for The speleothem processes to might AH-1. decreasing whilst also Here, apply a between 5.7 decreasing and trend 4.2 ka in the and cooler climate with lesscrease soil (Fig. respiration 5a). (Fig. Following our 5b),carbonate previous whilst weathering set the of with Mg-isotope arguments, temperature values this overruling(Fig. de- points rainfall 11). to amount a as shift the towards driving factor (Fig. 5). Soil respiration expectedlyof increased a during denser this vegetation time coveris due (Fohlmeister increased to et and the al., development leads 2012).to to Hence, the the higher increased production dissolution amount of rates of CO of carbonic the acid in low-Mg the calcite karst hostrock system. due Also the decalcification et al., 2012). Betweenvalues. 9 After to 7 ka 7 ka BPcover BP the and soil thus respiration higher wasrate soil lower lead respiration leading to (Fohlmeister higher to et higher al., 2012). Periods of lower drip and vice versa (Fig. 5b). Theabove first the order cave signal of while the second order signal is influenced by drip rate (Fohlmeister dated as 7.6 ka BP thatof is interest characterized to by dendritic note crystals that relation (Riechelmann, between 2010). crystallography and It Mg is isotopecrystal ratios is fabrics still are underexplored. Columnar formedforms under preferentially under stable conditions precipitation farBorsato, from conditions, 2010). equilibrium while (Frisia dendritic et al., fabric 2000; Frisia and temperature and rainfall amount – at higher values the climate was cooler and drier a tentative benchmark againstthe which following the pattern smaller emerges:mean variations Shifts rainfall in amounts towards decreased higher with whilst overall shifts more towards humid lower climate (Figs. 3 and 11). is favoured (Harper etminerals al., such 2005). as Related montmorillonite,general chlorite to shift and this, in illite the in weatheringcreased the influx of soil of Mg-bearing clay-derived zone clay isin increased. AH-1 The bonate weathering increased relativeto to colder clay temperatures. Between mineral 6 weathering katemperature BP favoured in silicate to the Present, weathering soil a in renewed the zone increase soil due in zone outside (Figs. air 3a and 11). to ter conditions. Based onproposed an the overall climatic warming for the last 6 kaoverall BP. humid climate and increasing mean air temperature microbial soil-zone activity 5 5 25 15 20 10 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | C. ◦ ¨ ¨ amper amper ´ a et al., ¨ amper et al., erences from ff C values imply 13 δ 3‰; Holzk C; Galy et al., 2002), the + ◦ ¨ otl and Mangini, 2007). In O (Figs. 9 and 10). Higher ¨ otl et al., 2007; Holzk ¨ otl et al., 2007; Holzk 18 2 to Mg data from Austria δ + 26 δ C of 13 Mg and δ 26 δ ¨ Mg ratios (Fig. 5; Fohlmeister et al., 2012) otl et al., 2007; Sp 1854 1853 26 δ ¨ otl et al., 2002). Mg records in a setting characterized by comparably 26 δ ´ a, 2006). It seems thus likely that clay mineral-derived, C values thus reflect a genuine vegetation signal during 13 δ ¨ otl et al., 2007). Hence, changes in rainfall amount that in turn O and lower Mg records obtained (Fig. 11). In principle, all of these factors 18 26 δ δ C and 13 C (Negendank, 2004). Given the low dependency of Mg isotope fractiona- Mg values in BU 4 coincide with a hiatus at 5.5 ka BP containing detrital ma- ◦ δ 26 δ ect soil activity can be excluded as main factor controlling Mg-isotope fractionation, Both flowstones show similar patterns in Flowstones yield numerous detrital layers, which were sampled (red triangles in Carbon isotope ratios of both studied flowstones (Figs. 9b and 10b) are influenced by High The Little Ice Age, dated between 0.7 to 0.2 ka, is characterized by a shift to higher ff Figs. 9 and 10). As found in the case of BU 4 and AH-1, Mg-bearing clay minerals During interglacials the availabilityduring glacial of periods (Sp water (rain,a snow and icebecause melt) speleothems is can higher notavailability form than as a without controlling water factor,subtle availability. temperature Having changes remains ruled in the main silicate out parameterapplies versus water controlling carbonate for weathering the ratios Holocenemonths (Fig. with of 11). snow warm This cover summer probably per months year; Sp and cold winter months (7 to 8 et al., 2005). Decreasing periods, when carbon iset al., anti-correlated 2005). with oxygen (Sp values during warm conditions may thus imply more silicate weathering and vice versa. the present-day setting, sparsethickness alpine does meadows not cover a exceedmeaning soil 20 not cm. above covered Portions the by of soil cave or the and vegetation. soil hostrock above thethe composition cave of are the bare, marine2005) marble hostrock and ( the input ofare soil-derived high organic during C warm inmore and the biological low drip activity during water. in Oxygen cold the isotope soil climate values zone conditions. and Low vice versa (Sp Speleothem deposition in the high-elevationinterglacial Spannagel conditions. Cave is Cold-climate biasedand precipitation, towards attributed warm however, to has the presence alsofication) of and been sulphides a in observed warm-based the ice hostrock cover (providing (Sp acidity for karsti- 5.5 Cold-humid climate: speleothem time series sium (Figs. 3a and 5a).full In complexity essence, of the speleothem twosubtle cave records climate from changes Germany over exemplify time.suggested the Based that on weathering the patterns argumentskarst in brought zone, the forward driven soil here, by zone it meandriving above is the factors outside in caves air the as temperature wellare and as present rainfall in at amount, all the are times the but main temperature seems to overrule rainfall amount in general. terial (Fig. 5a) as doesBesides one quartz, sample feldspar taken from anderals stalagmite mica, that AH-1 detrital are at in 7.9 layers ka1998; part contain BP Komadel dissolved high (Fig. and in 3a). amounts Madejov 6Misotopically of HCl heavy clay especially magnesium min- during is heating analysed (Madejov in parallel with the calcite-derived magne- Western Germany between Little Iceof Age 2 and to Medieval 2.5 Warmtion Period are on temperature on during the calcite order observed precipitation (0.02 isotope ‰/AMU/ shifts wouldEvidence require for cave a temperature temperatureture changes shift is in thus in excess of ruled thisprecipitation. 10 out order as of a magnitude main is factor lacking driving and Mg tempera- isotope fractionation during calcite Mann et al., 2009). values in indicating overall drier andgendank, cooler 2004; climate Mann (Esper et et al., al., 2009). 2002; Published mean Soon air et temperature al., di 2003; Ne- wetter and warmer climate (Esper et al., 2002; Soon et al., 2003; Negendank, 2004; 5 5 25 15 20 10 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Mg. 26 Mg on δ 0.15‰; 26 ± δ Mg values of Mg. 3.48 26 − 26 δ δ erences in soil and ff Mg. 26 Mg data in speleothems δ 26 0.04‰; Table 2) and sam- δ Mg SPA 52: ± 26 Mg-enriched. Given that these δ Mg variations. 26 1.42 26 − δ 3.88‰). This may indicate that the − Mg ratios, mean values should be cal- Mg: 26 26 δ Mg: δ 26 ers from the Moroccan stalagmites 1856 1855 ff δ 0.24‰ (Fig. 2) and therefore closer to the mean 0.12‰). ± ± Mg records from caves in Germany are complex. This 0.05‰; Table 2) are taken from thick detrital layers with 3.23 26 ± 3.88 − δ − 2.47 − Mg: Mg ratio is Mg in a manner that di 26 Mg records seems not feasible at present. Therefore, comparisons be- 26 Mg SPA 59: δ 26 26 δ δ 26 δ δ cult at present. The sampling of speleothem calcite containing detrital material Mg in natural samples observed. ffi 26 Mg analysis is large and – combined with the time-consuming and expensive an- δ Finally, an improved understanding of the factors that control Mg leaching from soil One of the obvious strengths of the Mg isotope proxy is its sensitivity for subtle pro- The interpretation of the Flowstone SPA 52 is characterized by considerably elevated mean In conclusion, the Spannagel flowstones represent a cold, alpine endmember setting 3.48‰ relative to flowstone SPA 59 ( 26 on zone clay minerals and clay containedtablished in leaching hostrock experiments carbonates under is controlled required.the laboratory Carefully way es- conditions forward. might represent are di should be avoided duethe to contamination calcite problems. precipitation The ratemenhauser dependency et is of al., the known 2010), but fromtation awaits laboratory rates further that work precipitation are using more experiments water similar compositions (Im- to and those precipi- found in nature, since there was no influence of soil zone processesin can the be application achieved. ofmain. Nevertheless, Mg-isotopes Due despite as to significant a theδ advances continental low Mg climate content proxy, unsolved ofalytical issues many work re- speleothems, – the inhibitO sample high-resolution isotopes. size speleothem Specifically, required aragonite Mg for tion speleothems isotope of are their records low similartween in to high-resolution C, Mg C O and so or elemental that data records an with interpreta- carbonate-silicate weathering patterns driving the cesses in the soil zonereservoir (weathering ratios; water Buhl residence et time al., (Riechelmannevidence 2007) et and and other al., di isotope 2012b). systems Combined such with as elemental Sr, C, and O, an improved understanding In the cold, alpine end member, outside air temperature seems the dominant driver of is because severalspeleothem of the factors, namely temperature and rainfall amount, control Data shown here suggest thattrols a the limited, Mg albeit complicated isotopeof bundle composition climatic of of zones. parameters speleothems. Obviously, con- cavesnounced Here, changes situated we in in mean show climate air data temperatureacterized domains or by from characterized rainwater more availability a pronounced by are shifts series expectedly pro- (Fig. char- set 11). A from prominent example Morocco. is found Conversely,climate in speleothem the parameters data records such as characterized the by Peruvian data, rather show constant no variability in characterized by mainly temperature-driven– weathering changes where in present the –activity thin and above soil increased the cover silicate cave weathering leading (Fig. to 11). enriched Warmer5.6 periods favour Potential, more problems soil-zone and future work new mean − drip water feeding SPA 59 experiencedthe an hostrock overall longer residenceisotopic time. composition Furthermore, of SPA 52with relative a to short SPA 59, hostrock a water feature residence that time. is in good agreement towards higher values. Sampleple SPA SPA 52 59 f b ( ( a high clay mineraldata content points and are are not thereforeculated representing highly without the samples calcite containing detritus (new mean were also partly dissolved during sample preparation and shift the Mg-isotope ratios 5 5 15 20 10 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Mg 26 ects of δ ff ect the subtle ff . hostrock ects of mean air temperature ff Mg Mg ratios in order to obtain a co- 26 26 δ δ with fluid Mg stalagmite signatures, semi-quantitative 1858 1857 Mg 26 Mg values to environmental and kinetic factors Mg values. δ 26 26 δ 26 δ Mg records. δ 26 δ Mg in a predictable manner. Caves situated in invariant 26 cult to interpret. This is because factors interfere in a more δ ffi Mg values from warm-temperate climate zones such as Western We thank our colleagues in the non-traditional isotope laboratory at 26 δ Mg values are found where hostrock values are low and long residence 26 δ ects drip water ff The results shown here summarizeMg the isotope present proxy level research. of An knowledge improved understanding in of speleothem the complex processes Comparing hostrock andestimates mean of aquifer waterlagmite residence time can betime obtained. resulted in Depleted equilibration mean of sta- involved requires well calibrated experimental workitation including experiments. leaching and precip- and weathering ratios outsideratios of and the hence speleothem cave is temperature controlling weathering The sensitivity of speleothem strongly depends on the overall climate setting. Pronounced variations in mean air climate domains, such ascharacterized tropical by Peru invariant during the Pleistocene toStalagmite Holocene, are Germany are more di complex manner. These factorsand include rainfall mean amount. air Thesebalance temperature factors outside between drive the silicate soil-zone cave and and activity O carbonate data and must weathering be a usedherent rates. in interpretation combination Here, and with multi-proxy to separateand C the rainfall amount relative on e soil zone activity. Layers of detrital material inproblems. Particularly, speleothems Mg-bearing must clay be minerals shift avoidedratios. bulk due values to to contamination higher In high-latitude and alpineglacial and climate interglacial air settings temperature, exposed the main to driving pronounced factor of changes soil-zone activity in temperature and rainfall amount withMorocco, time, result such in as changes in the the caseturn silicate in versus a the carbonate weathering Pleistocene ratio of that in 1998. content of stalagmite drip1997. waters in Lower Cave, Bristol, Hydrol. Process., 11, 1541–1555, Mechara caves, Southeastern Ethiopia:Int. implications J. for Speleol., speleothem 37, 207–220, palaeoclimate 2008. studies, changing surface land use and increased cave tourism, J. Environ. Manage., 53, 165–175, A. A. Balkema Publishers, Amsterdam, 649 pp., 2005. 6. 5. 2. 3. 4. 1. Baker, A., Barnes, W. L., and Smart, P. 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Therecovery Speleogroup in Letmathe Atta is and thanked Bunker forin Cave. supporting Morocco Uranium-lead sample age was dating performed of atcollaborative the the research Grotte University initiative d’Aoufous of DAPHNE stalagmite II, Berne, founded Switzerland. by This the is DFG. a contribution to the The analysis of Mgsenting as five well climate zones as leads C to and the O following conclusions: isotope ratios from eight speleothems repre- 6 Conclusions 5 5 25 20 15 10 20 25 15 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Mg 26 ´ etaux δ ´ eg ` emes v , 2012. C time series of 13 , 2008. δ ´ ecosyt , 2011. , 2005. C and 14 ` ene des into calcite under karst-analogue + , 2005. 2 flux in a grassland ecosystem, Global ´ eistoc 2 , 2008. ¨ otl, C., Riechelmann, D. F. 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A.: The mag- Str Str 5 5 20 15 10 30 25 20 15 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | E 0 E 0 247 59 ◦ 40 − ◦ ◦ N/10 0 N/11 0 212/54 25 5 ¨ aßer (1998) − ◦ ◦ Calcitic, Jurassic mar- ble Snow. Fully humid with cool summers Spannagel Cave, Alps, Austria ) indicates data ◦ W 47 0 00 ◦ N/4 27.48 92 0 − 13 ¨ aßer (1999) Str ◦ Brecciated,Jurassic Upper with limestone dolomite subordinate and hot summers Grotte Prison de Chien, MiddleMorocco Atlas, Mg’ 25 W 34 0 ∆ 14 ◦ σ 115 4.24 2 N/2 0 ± ± 37 ¨ aßer (1999) Str ◦ Massive, Upper Cre- taceous limestone Arid. Desert, hot arid Warm temperate. Dry Grotte d’Aoufous, Anti-Atlas, Morocco Mg 26 W 31 W – – 47 0 0 σ δ 2 58 18 ◦ ◦ ± Mg’ data were calculated using the equations S/76 S/78 0 0 25 ¨ aßer (1999) Str 0.009–4.3/3.2–14 2134 02 54 ◦ ◦ ∆ 1961–1990 1961–1990 1961–1990 1961–1990 Massive,limestone Triassic Equatorial. Fullymid hu- withwarm temperatures constantly Cueva del Tigredido, Per- Foothills ofAndes, Peru the 6 Str ∼ Moyobamba, Peru Bechar, Algeria Taza, Morocco Zugspitze, Germany 1868 1867 Mg 25 δ (‰ DSM3) (‰ DSM3) E 6 E/ E 0 0 0 www. / 40 29 45 ◦ ◦ ◦ N/7 N/7 0 0 22 25 23’ N/7 ◦ ◦ ◦ 2010 Massive, Middle De- vonian limestone Warm temperate. Fully humid with warm summers Bunker Cave, Rhen- ish SlateGermany Mountains, www.dwd.de meteomedia.de Germany 51 E 51 E 51 Speleothem Sample AH-1AH-1AH-1AH-1 09AH-1 08AH-1 07AH-1 06AH-1 05 –2.17AH-1 04 –2.13AH-1 03 –2.14AH-1 02 –2.09 0.02AH-1 01 –2.11 0.01AH-1 1 –2.12 0.02AH-1 –4.18 2 –2.14 0.01AH-1 –4.07 0.05 3 –2.12 0.02AH-1 –4.13 0.05 4 –2.10 0.02AH-1 –4.02 0.07 0.01 5 0.02 –0.01 AH-1 –4.08 –2.11 0.04 6 0.01AH-1 –4.14 –2.05 0.06 0.02 7 0.01AH-1 –4.11 –2.08 0.04 0.00 8AH-1 –4.11 –2.07 0.02 0.04 0.01 9AH-1 –4.06 –2.07 0.02 0.07 0.04 10AH-1 –2.07 0.02 0.05 0.01 11 –4.06AH-1 –2.08 0.03 0.02 12 –3.95 0.05AH-1 –2.07 0.01 0.02 13 –4.00 0.03AH-1 –2.08 0.02 14 –3.99 –2.08 0.03 0.01 AH-1 0.02 14wh –4.01 –2.09 0.05 0.01 AH-1 0.02 14 –3.97 mean –2.08 0.02 0.01 AH-1 0.03 15 –4.00 –2.10 0.04 0.01 0.03AH-1 16 –3.99 –2.10 –2.09 –2.10 0.02 0.02 0.03AH-1 17 –4.03 0.05 0.01 0.02AH-1 –4.04 18 0.03 0.01 0.02AH-1 –4.02 0.06 18wh 0.04 –2.07 0.02 0.01 0.04AH-1 –4.02 0.04 18 mean –2.07 0.02 AH-1 –4.04 0.03 0.02 19 –2.04AH-1 –4.05 –4.02 –4.07 0.02 0.00 19wh –2.08 –2.05 –2.10 0.03AH-1 0.09 0.03 0.09 0.02 19 mean 0.02AH-1 0.01 20 0.02AH-1 –3.98 0.01 0.01 0.02 21 –2.03 –2.04 0.04 –2.02 0.02 0.01AH-1 –3.95 0.05 22AH-1 –3.93 0.02 23AH-1 –3.99 –3.96 –4.02 0.03 0.01 24 0.03 –2.04 0.03 0.03 –0.01 AH-1 0.05 0.05 0.04 25 –2.06AH-1 0.01 25wh –2.06 –0.01 –3.91 –3.93 –3.89 0.00 0.02 25 mean –2.06 0.03 0.08 0.03 0.08 26 –2.08 0.02 27 –1.99 –1.99 –2.00 0.02 –3.93 0.01 0.01 0.00 0.02 –3.97 0.04 0.03 –3.98 0.06 0.02 –2.06 0.02 0.02 –3.98 0.03 0.01 –2.05 –3.97 0.05 0.01 –3.87 –3.86 –3.87 0.05 0.01 0.02 0.05 0.03 0.05 0.02 0.04 –0.01 –3.98 0.03 0.02 0.02 –3.94 0.05 0.07 0.02 0.01 0 0 55 50 ◦ ◦ N/7 N/7 0 0 7 2 ◦ ◦ vonian limestone Fully humid with warm summers Atta Cave,Slate Mountains, Rhenish Ger- many www.meteomedia.de C) 9.1 9.9 22.6 20.9 17.6 –4.8 ◦ C) 9.4* 10.8 (monitoring data) – – 13.9 (monitoring data) 1.2 to 2.2 ◦ Magnesium-isotope values of all speleothem samples. Repeated analyses are marked Locality, hostrock composition, climate setting, weather stations and speleothems used ¨ otl et al. (2002). Monitoring data for Bunker Cave represent the period 2006 to 2010 and Altitude of weatherstation (m a.s.l.)Time period used 309Data from 2003–2010 100/200 2006–2007/2008– 833 773 519 2962 Altitude of cave entrance (mHostrock a.s.l.) 265 184 Massive, Middle De- 1000 1000 360 2531 Climate after Kottek et al. (2006) Warm temperate. Cave air temperature ( Mean annual temperature ( Speleothem, labelSpeleothem, year of samplingSpeleothem, age (ka) 1997 AH-1 0.015–9 2007 0.005–8.6 BU 4 2003 NC-A/NC-B 2005 GDA 2009 HK3 2000 SPA 52/SPA 59 Coordinates 51 Annual precipitation (mm)Weatherstation 1172 Olpe, Germany 971 (monitoring data) Hagen-Fley/Hemer, 1344 82 801 2004 Coordinates of weatherstation 51 “wh” and mean values are indicated “mean”. Table 2. of Young and Galysamples (2004) (July in to August order 2007),samples to BU (January document 4: to 23 the February samples2011) accuracy and 2008), (February of SPA to GDA: 52/SPA analytical 59: March 18 8/12 results. 2011), samples, samples, NC-A/NC-B: AH-1: October June 3/6 2009 36 2006), to HK3: January 6 2010). samples (June Table 1. in this paper. Asterisk (*) indicates data by Niggemann et al. (2003) and circle ( monitoring data for Grotte Prison de Chien represent the period 2009 to 2011. by Sp Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Mg’ 25 ∆ Mg’ 25 σ ∆ 2 ± σ 2 ± Mg 26 Mg 26 σ δ 2 ± σ δ 2 ± Mg 25 1870 1869 δ Mg (‰ DSM3) (‰ DSM3) 25 δ (‰ DSM3) (‰ DSM3) Speleothem Sample HK3HK3HK3HK3 CA24HK3 CA37HK3 CA41SPA 52 –2.02 CA45SPA 52 –2.20 CA63SPA 52 –2.23 CA74 aSPA 52 –2.22 0.03 bSPA 52 –2.23 0.03 cSPA 52 –2.16 0.01 g –3.89SPA 52 0.04 d –4.21SPA 0.06 52 –1.48 0.02 h –4.29SPA 0.07 59 –1.35 0.02 e –4.27SPA 0.02 0.01 59 –1.61 –0.01 f –4.26SPA 0.09 59 0.02 –1.8 a –4.13SPA 0.04 0.00 59 –1.72 0.03 aaSPA 0.03 0.00 59 –1.86 0.02 –2.84 abSPA 0.00 59 –1.89 –2.62 –0.01 0.02 0.06 acSPA 59 0.03 –0.73 –3.11 0.06 adSPA 59 –2.10 0.09 –1.96 0.00 0.02 ae –3.47SPA 59 0.05 –3.33 –2.05 0.02 bSPA 59 0.04 0.02 –3.58 0.02 –2.07 0.01 cSPA 59 0.02 –3.63 –1.96 0.14 0.04 dSPA 59 0.01 –1.93 0.05 0.02 0.03 –1.42 da –4.06 0.01 0.05 e 0.04 –3.80 –1.29 0.04 0.00 0.03 f –3.97 –2.06 0.07 0.05 0.01 –3.99 –1.86 0.02 –1.79 0.02 –3.80 0.03 0.02 0.09 –3.70 –1.99 0.04 0.02 0.02 0.03 0.07 0.01 –1.96 –2.47 0.02 0.02 –3.97 0.05 0.01 0.00 –3.59 0.07 –3.43 0.04 0.06 0.00 0.03 –3.83 0.01 0.03 0.01 –3.78 0.00 0.06 0.01 0.01 Speleothem Sample BU 4BU 4BU 4BU 4 0BU 4 1BU 4 2BU 4 3BU 4 4BU 4 5BU 4 6BU 4 7BU 4 8 –2.09BU 4 9 –2.14BU 4 10 –2.23BU 4 11 –2.14 0.02BU 4 12 –2.24 0.02BU 4 13 –2.18 0.02BU 4 –4.02 13A –2.01 0.02BU 4 –4.12 0.02 14 –2.13 0.03BU 4 –4.29 0.03 14A –2.17 0.02BU 4 –4.13 0.06 0.01 15 –2.19 0.02BU 4 –4.29 –2.24 0.02 0.01 15A 0.02BU 4 –4.21 –2.19 0.04 0.00 16 0.02NC-A –3.91 –2.22 0.03 0.01 16A 0.03NC-A –4.12 –2.19 0.05 0.00 0.02 17 –2.16NC-A –4.18 0.03 0.01 0.02 17ANC-B –4.22 –2.20 0.03 0–0.5 0.03 0.01 cm –4.32 –2.17NC-B 0.06 10–10.5 0.02 0.02 cm –4.21 0.01 0.02NC-B –2.24 20–20.5 0.01 cm –4.26 –2.12 0.02NC-B 0.5 0.01 0.01 -01 cm –4.21 0.02 0.03 0.01 NC-B –4.18 –2.19 5–5.5 cm –2.26 0.06 0.01 NC-B 0.02 11.5–12 0.01 cm –2.00 –2.08 –4.24 0.02 0.00 NC-B –4.17 –2.21 18.5–19 cm –2.03 –2.21 0.02 0.01 NC-B 0.05 18.5–19 0.02 0.02 cm wh –4.31 0.06GDA –4.08 18.5–19 –2.05 cm mean 0.03 0.02 0.01 0.01 GDA 0.02 25.5–26 0.01 0.02 cm –2.05 –2.08 –4.22 0.01 0.01GDA –4.34 28.5–29 cm –2.04 –2.04 –2.03 0.02 0.00 GDA –3.88 –4.03 0.07 0.00 0.02 pos –4.26 3/4GDA –3.92 –4.27 0.03 0.04 pos 0.02 0.02 5 0.01 0.01 GDA 0.01 0.01 0.00 pos 0.03 –2.07 0.02 –3.96 0.03 10GDA 0.02 0.02 pos –2.05 17 0.01 0.05GDA –3.97 –3.99 0.02 0.02 pos 22aGDA –3.95 –3.94 –3.96 0.03 0.01 pos 0.02 25GDA 0.01 0.06 0.03 0.06 pos –2.22 0.02 30GDA 0.02 0.00 pos 37GDA –4.00 0.02 0.01 –2.24 0.03 pos 45 –2.28GDA –3.96 0.04 pos 0.03 14/15 –2.27GDA 0.03 –2.19 pos 20GDA 0.01 0.02 pos 40 –2.21 0.02GDA –4.28 0.02 pos 33a –2.17 0.02GDA 0.04 0.02 pos –4.33 33b –2.20GDA –4.38 pos –2.26 33e –2.25 0.04 0.02 0.02 –4.39 0.05 pos –4.23 33d 0.01 0.02 pos 33f –2.23 0.01 0.02 0.03 –4.26 0.01 pos 0.02 33c –2.16 0.02 –4.17 –2.19 0.04 0.01 0.01 –4.23 –2.18 0.05 0.03 –4.35 –4.31 –2.17 0.06 0.01 0.02 0.05 –2.18 0.08 0.01 0.01 –4.26 0.01 0.01 –2.19 –4.18 0.01 0.04 0.00 –2.18 0.02 –4.22 0.03 0.03 –4.20 0.01 –0.01 0.01 –4.19 0.03 0.02 0.02 –4.21 0.03 0.02 0.03 0.01 –4.22 –4.19 0.01 0.02 0.01 0.04 0.01 0.01 Continued. Continued. Table 2. Table 2. Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 0.43 0.04 0.05 ± ± ± 3.70 4.06 2.47 erence be- − − − ff Mg 26 ∆ 0.73 0.05 0.04 Mg (di ± ± ± 26 σ ∆ 3.00 3.63 1.42 2 − − − ± 0.15 0.02 0.06 ± ± ± Mg 3.89 4.17 4.29 26 − − − Mg between these samples. 0.07 0.02 0.05 26 ± ± ± σ δ ∆ 2 ± 4.26 4.39 4.17 − − − 1872 1871 0.04 0.04 0.03 Mg ± ± ± 26 total without δ sample fluids 3.96 4.03 3.88 (‰ DSM3) (‰ DSM3) − − − 0.10 0.07 0.05 ± ± ± 4.20 4.34 3.91 − − − 0.05 0.03 0.07 ± ± ± 4.01 4.18 3.86 − − − Speleothem Sample AH-1AH-1AH-1AH-1AH-1 05AH-1 2AH-1 4AH-1 –4.08 6AH-1 17 –3.95 0.06 23 –3.99 24 0.03 –3.97 –4.10 –3.93 26 0.05 –3.98 27 –3.97 0.04 0.02 0.03 –3.97 –4.00 0.05 –3.98 0.03 0.05 –4.03 –4.00 0.05 –3.94 0.05 0.02 –4.03 0.05 0.01 0.01 0.06 –3.98 0.07 0.06 0.02 –4.01 0.08 0.05 –3.98 0.05 0.04 0.02 0.02 0.03 0.03 Mean Mg-isotope ratios, minimum and maximum values and Magnesium isotope composition of several samples of the stalagmite AH-1 measured Mg 0.32 0.44 0.14 0.22 0.40 2.21 1.59 Mg AH-1 BU 4 NC-A/NC-B GDA HK3 SPA 52 SPA 59 26 26 δ (‰ DSM3) Mean min max ∆ Table 4. with and without fluid inclusions and the calculated Table 3. tween maximum andused minimum for value) statistics varies of between 6 speleothems and discussed 36. here. Number of samples Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | ) indicates data from Buhl et al. (2007). ◦ 1874 1873 Map with the locations of studied caves. Atta and Bunker Cave (Germany) are repre- Overview of Mg-isotope data of the studied speleothems and hostrock. Mean value is Fig. 2. indicated by thin vertical line,data width from of Immenhauser horizontal et bars al. indicate (2010) data range. and Asterisk circle (*) ( indicates Fig. 1. sented by a single green dot. Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Carbon (dark (b) 1876 1875 set. ff Mg-isotope data plotted against age in ka BP using the StalAge model of Scholz (a) mann (2011). Red triangle indicates sample taken in a detritus layer. Magnesium, carbon and oxygen isotope data of the stalagmite AH-1 from Atta Cave, ff Magnesium isotope composition of aliquots of samples from stalagmite AH-1. Dark blue Fig. 4. indicates crushed samples insamples. Note order systematic to o remove fluid inclusions whilst light blue indicates bulk Fig. 3. Germany. and Ho blue) and oxygen (magenta) isotopeet data al., plotted 2003). Portions against ofblue, age those the in characterized speleothem ka by characterized BP a by (data white a from porous dark Niggemann facies compact are facies shown are in shown yellow. in Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | (a) (b) mann (2011). ff 1878 1877 Mg-isotope data (NC-A: light green squares; NC-B: green triangles) (a) Carbon (dark blue) and oxygen (magenta) isotope data plotted against age in ka BP Magnesium, carbon and oxygen isotope data of the stalagmite BU 4 from Bunker Cave, Magnesium, carbon and oxygen isotope data of stalagmites NC-A and NC-B from Cueva (b) plotted against age in ka BP using the StalAge model of Scholz and Ho del Tigre Perdido, Peru. Fig. 6. Carbon (NC-A: dark blue; NC-B:isotope light data blue) plotted and against oxygen age (NC-A:2009). in magenta; ka NC-B: BP light (data from magenta) van Breukelen et al., 2008; van Breukelen, (data from Fohlmeister et(MWP) al., and 2012). of Samples the taken Little Ice at Age the (LIA) time are of indicated the with Medieval black arrows. Warm Period Fig. 5. Germany. Black line marksMg-isotope hiatus data characterized plotted against by age alayer. in coralloid ka layer BP. Red and triangle detrital indicates sample material. taken in a detritus Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Carbon (b) Mg-isotope data are plotted against distance (a) 1880 1879 Mg-isotope data plotted against depth of the transect (top at 0 mm). Carbon (dark blue) and oxygen (magenta) isotope data plotted against distance from (a) Magnesium, carbon and oxygen isotope data of the stalagmite GDA from Grotte (b) Magnesium, carbon and oxygen data of the stalagmite HK3 from Grotte Prison de Chien, Fig. 8. Morocco. (dark blue) and oxygenet (magenta) al., isotope 2012). data Colour plotted code against refers to depth aragonite (data or from calcite Wassenburg intervals. d’Aoufous, Morocco. Black lines mark hiati. Fig. 7. from top in cm. Open triangles2007). indicate multiple samples along atop single in growth cm layer (Buhl (data et from al., Buhl et al., 2007). Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | ¨ amper et al., ¨ amper et al., 2005). ¨ otl et al., 2007). Red triangles ¨ otl et al., 2007). Marine isotope Carbon (dark blue) and oxygen (b) Mg-isotope data (green) and age data (a) Mg-isotope data (green) and age data (orange) (a) Carbon (dark blue) and oxygen (magenta) isotope 1882 1881 (b) ¨ otl et al. (2007). ¨ otl et al. (2007). Magnesium, age, carbon and oxygen isotope data of flowstone SPA 59 from Span- Magnesium, age, carbon and oxygen isotope data of flowstone SPA 52 from Spannagel 2005). Marine isotope stages after Sp Red triangles indicate(magenta) samples isotope taken data plotted in against distance detritus from base layers. in mm (data from Holzk Fig. 10. nagel Cave, Austria. Thick black lines indicate hiati. (orange) plotted against distance from base in mm (age data from Holzk indicate samples taken in detritus layers. stages (MIS) after Sp Fig. 9. Cave, Austria. Thick black lines indicate hiati. plotted against distance from base indata cm plotted (age against data distance from from base Sp in cm (data from Sp Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | ecting Mg-isotope ratios of speleothems ff 1883 erent climate zones. ff Conceptual model summarizing factors a Fig. 11. from four di