Fluid Inclusions of speleothems I Stable isotopes & noble gas temperatures

Transcription

1 IUP - Institut für Umweltphysik Fluid Inclusions of speleothems I Stable isotopes & noble gas temperatures Prof. Dr. Werner Aeschbach-Hertig Heidelberg Center for the Environment (HCE) Institute of Environmental Physics (IUP) Heidelberg University

2 Contents Fluid Inclusions I Stable Isotopes and Noble Gases Fluid inclusions in speleothems Fluid inclusions as paleowater archive: Link to groundwater Stable isotopes in fluid inclusions Noble gases in fluid inclusions 2

3 Literature Review on isotopes in (fluid inclusions of) speleothems McDermott, F., Schwarcz, H., Rowe, P.J., Isotopes in speleothems. In: Leng, M.J. (Ed.), Isotopes in Palaeoenvironmental Research. Springer, Dordrecht, p Recent reviews on noble gas temperatures Aeschbach-Hertig, W., Solomon, D. K., Noble gas thermometry in groundwater hydrology. In: Burnard, P. (Ed.), The Noble Gases as Geochemical Tracers. Springer Verlag, p Brennwald, M. S., Vogel, N. Scheidegger, Y., Noble Gases as Environmental Tracers in Sediment Porewaters and Stalagmite Fluid Inclusions. In: Burnard, P. (Ed.), The Noble Gases as Geochemical Tracers. Springer Verlag, p

4 Fluid Inclusions in Speleothems 4

5 Some Pictures of Fluid Inclusions 20 µm 20 µm Dennis et al. (2001), GCA 65:

6 Some Pictures of Fluid Inclusions van Breukelen et al., Earth Planet. Sci. Lett. 275,

7 Some Pictures of Fluid Inclusions Scheidegger et al., Chem. Geol. 288,

8 Some Pictures of Fluid Inclusions Genty et al., Chem. Geol. 184,

9 Empirical Findings on Fluid Inclusions Abundance Size - Water/Calcite ratio of 0.01 to 0.5 % by weight (typical 1 or 1 mg/g) - Non-uniform distribution (layered, high abundance: milky) - Typically 1 to 100 µm (but up to mm in rare cases) Shape - Often elongated or thorn shape, oriented parallel to C axis Content - Water or air or both (air bubbles in water-filled inclusion) - Air to water volume ratio about 1, but highly variable from < 0.1 to > 10 9

10 Fluid Inclusions as Paleowater Archive: Link to Groundwater 10

11 Subsurface Water Archives meteoric water modification in soil drip water speleothem fluid inclusions recharge water groundwater Picture from Wackerbarth 2012, modified from Spötl et al. (2007) and Fairchild et al. (2006) 11

12 Groundwater as an Archive Temperature Proxy Temp Proxies: Stable isotopes Noble gases Time Distance, Age ( 14 C) Dispersion leads to smoothing of climate signals low time resolution 12

13 Stable Isotopes in Palaeogroundwaters From: Clark and Fritz, Environmental Isotopes in Hydrogeology 13

14 Stable Isotopes in Palaeogroundwaters From Clark & Fritz,

15 Noble Gases: Conservative Tracers noble inert conservative rare tracers ideal physical tracers Sources of noble gases in water Atmosphere (Ne, Ar, Kr, Xe) Temperature Nuclear processes (He, Rn) Age 15

16 The Noble Gas Thermometer P x i T, S C i Air Water Dissolved noble gas concentrations in equilibrium with air: C ( ) i, eq =bi T, Spi heavy NG light NG Bunsen Solubility b [cm 3 STP cm -3 atm -1 ] Slope ~ 4 % / C Xe Kr Ar Ne He Temperature [ C] 16

17 Noble Gas Components tritiogenic Concentration relative to equilibrium radiogenic excess air equilibrium Solubility Xe Kr Ar He Ne Temperature temperature 0 3 He 4 He Ne Ar Kr Xe 17

18 Noble Gas Components tritiogenic radiogenic excess air equilibrium p n n b - n p 3 H 3 He p Concentration relative to equilibrium U, Th a time X + a ( 4 He) 0 3 He 4 He Ne Ar Kr Xe 18

19 Noble Gas Components tritiogenic radiogenic excess air equilibrium Concentration relative to equilibrium ??? 0 3 He 4 He Ne Ar Kr Xe 19

20 Excess Air from Inclusion of Air Bubbles Classical model: Complete dissolution of entrapped air bubbles composition of excess air = composition of atmospheric air 12% 10% 8% 6% 4% 2% ASW + air water + air + air entrapment air entrapment a Ac i A = V V complete dissolution compl. dissolution a w 0% He Ne Ar Kr Xe Excess pattern c = Hc UA: Unfractionated Air a eq i i i 20

21 Inverse Determination of Parameters Problem: Determine T and A from Data: Model: meas C i (i = Ne, Ar, Kr, Xe) 2 free parameters, 4 constraints: overdetermined Inversion: Find values of T and A, which minimise the weighted deviation between model and data: 2 c = i ( meas mod C - ) i Ci s 2 i 2 Aeschbach-Hertig et al., Water Resour. Res., 35:

22 Example: Serra Grande & Cabeças, Brazil Cooling of tropical Brazil (5 C) during the Last Glacial Maximum. Stute et al., Science 269:

23 Example: Glatt Valley, Switzerland ~ 0.5 / C DT Holocene LGM 5 C Recharge gap in LGM Beyerle et al., Science 282,

24 PALAEAUX: d 18 O-NGT Relation in Europe ~ 0 / C 0.35 / C Continental Coastal Loosli et al., Geol. Soc. Special Publ., Vol. 189, pp

25 China: d 18 O Temperature Relation modern weak monsoon Amount Temperature ~ 30 kyr strong monsoon ~ 7-10 kyr strong monsoon Kreuzer et al.,2009. Chem. Geol. 259:

26 Stable isotopes in fluid inclusions 26

27 Stable Isotopes: From Rain to Carbonate Similar to groundwater, but higher resolution and better dating d 2 H, d 18 O of drip water Additional information in H 2 O CO 3 fractionation From Wackerbarth 2012 d 18 O of carbonate 27

28 The Carbonate-Isotope-Thermometer Precipitation of carbonates from water in isotopic equilibrium induces a T- dependent fractionation: ε eq (T) = 18 O CO3-18 O H2O This thermometer is accessible with calcite plus fluid inclusions! Problems: Precipitation in equilibrium? Which e(t) curve is correct? Low t-resolution of inclusions Possible O-isotope exchange 28

29 First Fluid Inclusion Studies Schwarcz and Harmon, 1976, GCA 40, Goal: Paleotemperature through water-calcite-fractionation Assumptions: - Equilibrium conditions can be ascertained by a Hendy-Test - 18 O of fluid inclusion water exchanges with calcite - d 2 H is not altered and used to reconstruct d 18 O via GMWL Harmon, Schwarcz, and O'Neil, EPSL 42, Goal: Reconstruction of isotopic composition of precipitation Result: d 2 H of glacial water depleted relative to modern precip. Similar results were later obtained for Europe by Rozanski and Dulinski, In: Isotope Techniques in Water Resources Development. pp , IAEA, Vienna. 29

30 Methods for Water Extraction Crushing by Squeezing a Tube Harmon et al., 1979 Not very efficient crushing mechanism (coarse grains, low yield) Needs very large samples (up to 20 g) bad age resolution Possible bias due to incomplete transfer of water (adsorption) 30

31 Methods for Water Extraction Thermal decrepitation Heating of sample to between about 700 and 900 C. Vennemann & O Neil, 1993, Chem. Geol. 103, Better yield, smaller samples, but offset in d 2 H of extracted water from original water: D ex between -22 (Yonge, 1982, PhD thesis) to -30 (Matthews et al., 2000, Chem. Geol. 166, ). Production of CO 2 at high temperatures, definitely leads to oxygen isotope exchange not applicable for 18 O. 31

32 Methods for Water Extraction Crushing and mild heating in vacuum cell Heating to 150 C avoids adsorption of water on calcite surfaces, which otherwise leads to water loss and isotope fractionation. Produces reliable d 2 H-values. Used e.g. by Fleitmann et al., 2003 (Quat. Res. 60, ) to reconstruct changing sources of drip water (precipitation) in Oman. Dennis et al., 2001, GCA 65,

33 Methods for Water Extraction Crusher linked to continuous flow IRMS Dublyanski and Spötl, 2009, Rapid Commun. Mass Spectrom. 23, Also see Vonhof et al., 2006, Rapid Commun. Mass Spectrom. 20,

34 First FI-Paleotemperature Record Vancouver Island: Absolute temperature from d 2 H w - d 18 O c Zhang et al., Geochim. Cosmochim. Acta 72:

35 Methods for Water Extraction Optimisation of thermal decrepitation Verheyden et al., Chem. Geol. 247, No offset in d 2 H for heating up to 550 C. Jimenez de Cisneros et al., Geol. Acta 9, Optimal conditions: Pre-crushing and heating to C. Logan, Abstracts / Quat. Internat , 286. Sample size of 20 mg with heating to 350 C and continuous flow. Crushing combined with cavity ring-down spectroscopy Affolter et al., Geophys. Res. Abstr.15, EGU

36 Noble gases in fluid inclusions 36

37 Noble gases in caves Introduction Expectation: Drip water in solubility equilibrium with cave air NGT measures cave T, which is close to mean annual air T Adapted from J. Fohlmeister Bunsen Solubility b [cm 3 STP cm -3 atm -1 ] Xe Kr Ar Ne He Temperature [ C] 37

38 Noble gases in caves Introduction Reality: Air-filled inclusions Water inclusions contain T-information in dissolved noble gas concentrations Air inclusions add air-derived noble gases and mask the information Analogous to excess air in groundwater, but much higher air contribution Scheidegger et al., 2010, Chemical Geology Air-Excess Parameter: A = V air /V water water filled inclusion air-filled inclusion 20µm Groundwater: Typically A < 0.01 Speleothems: Typically A ~ 1 Maximum tolerable value of A is ~ 0.1 Thick section of stalagmite H12 38

39 Air/Water Ratio A in Speleothems Oman (H12) Kluge et al. 2008, EPSL 269: Cuba 39 39

40 Stalagmites from Bunker Cave, Germany BU-1 BU-Uwe Niggemann et al., 2003 QSR

41 NG Temperatures from Bunker Cave First speleothem NGTs Pollen data BU-1 BU-U Kluge et al. 2008, EPSL 269: Davis et al., QSR 22, 2003 Temperature difference is ok Absolute temperature too low? (Modern MAAT ~ 9.5 C) Due to water adsorption during crushing: Resolved by heating crusher to 150 C 41 41

42 Methods for Noble Gas Extraction Mechanical crushing in vacuo to extract gases and water gases MS water 42 42

43 Reduction of the Air/Water Ratio Stepwise crushing (or heating): Opens air inclusions first Separation of air and water during extraction is needed. Air inclusions tend to sit at grain boundaries (B1). 43 Scheidegger et al. 2008, PAGES News 16/3:

44 Pre-Crushing and Sieving Brennwald et al., 2013, In: The Noble Gases as Geochemical Tracers, p

45 Crushing and Sieving under Vacuum Vogel et al., in press. Geochem., Geophys., Geosystems, DOI /ggge

46 Crushing and Sieving under Vacuum Vogel et al., in press. Geochem., Geophys., Geosystems, DOI /ggge

47 Crushing and Sieving under Vacuum Vogel et al., in press. Geochem., Geophys., Geosystems, DOI /ggge

48 Excess Neon From the Lattice (?) Some stalagmites have more Ne than expected Ne cannot be used R = (X/Ar) sample /(X/Ar) air Possible reason for Ne excess: Lattice-trapped He and Ne Scheidegger et al., 2010, Chem. Geol. 272,

49 Ne Excess under Stepwise Crushing Example: H12 (Hoti Cave, Oman) Neon excess visible from the first extraction step on! 49

50 Test with Air-Equilibrated Water (AEW) µaew µl-size samples of airequilibrated water Temperature known expected equilibrium concentration known Sander et al., in preparation 50

51 Summary Stable isotopes of meteoric water and atmospheric noble gases are established climate proxies in groundwater Fluid inclusions in speleothems are a promising new archive for both proxies, with many benefits Extraction and analysis are challenging, but much progress is being made Reliable absolute temperatures from the NG thermometer plus drip water isotopes should help to understand d 18 O c 51 51

52 Error Analysis for T Depending on A groundwater speleothems analyt. error s The goal DT < 1 C requires A < 0.3, s < 1 % or A < 0.1, s < 2 % 52 52