Late Pleistocene - Holocene climate variations over central Europe reconstructed from groundwater data

Transcription

1 Late Pleistocene - Holocene climate variations over central Europe reconstructed from groundwater data J.A. Corcho Alvarado Institute of Radiation Physics, Univ. Hospital and Univ. of Lausanne, Switzerland R. Purtschert, M. Leuenberger Climate and Environmental Physics, Univ. of Bern,.Switzerland R. Kipfer Dep. of Water Resources and Drinking Water, EAWAG, Switzerland Institute of Geochemistry and Petrology, ETH Zurich, Switzerland University of Bern

2 Outline 1. Reconstruction of past climate conditions from groundwater data: a short introduction 2. Groundwater ages in investigated aquifers of the Bohemian Cretaceous Basin 3. Reconstruction of past climate conditions 4. Conclusions

3 Climate Recharge conditions Groundwater as a climate proxy Precipitation (P) P Soil Humidity (Recharge rate) Re Soil Temperature Re Groundwater Groundwater

4 Solubility Noble gases (He, Ne, Ar, Kr, Xe) 1. Reconstruct recharge temperatures: NGT-noble gas recharge temperature Temperature Quasisaturated zone W E L L Water table fluctuations Recharge-Precipit. Humidity Input of meltwater Aquifer 2. Reconstruct humidity conditions: ΔNe- Excess air Inverse modeling of the observed noble gas concentrations is used to interpret the data in terms of recharge temperature and excess air.

5 Stable isotopes ( 2 H and 18 O ) as paleoclimate proxies Reconstruct paleotemperature (T effect) Reconstruct paleoprecipitation (amount effect) Stute and Schlosser, Atmospheric noble gases, in Environmental tracers in subsurface hydrogeology, Cook and Herczeg (ed). Kluwer Academic Publishers

6 Low resolution paleotemperature record Recharge area Discharge area Aquifer

7 EUROPE: last glacial maximum Scandinavian ice sheet Bohemian Cretaceus Basin a) A large number of small glaciers developed in the Krkonose Mountains b) The basin was covered by discontinuos permafrost Alpine ice field A key region for understanding late Pleistocene climate and glacial development Ice age Earth at glacial maximum. Based on: "Ice age terrestrial carbon changes revisited" by Thomas J. Crowley (Global Biogeochemical Cycles, Vol. 9, 1995, pp

8 Cenomanian and Turonian sands aquifers, Czech Republic Flow direction N Uranium mining Liberec S VP7502 VP7506 Duba syncline VP7523 VP7500 Turnov VP7512 VP7524 Zivonin syncline VP7515 Mlada Boleslav VP7517 Vltava river VP7520 VP7519 Karany B 1. Noble gases: He, Ne, Ar, Kr, Xe 2. Stable isotopes: 2 H, 18 O, 13 C 3. GW dating tracers: 3 H/ 3 He, 85 Kr, 39 Ar, C 4. Hydrochemistry, etc. Prague Important faults Wells in the Cenomanian sandstone Wells in the Turonian sandstone

9 C activity vs distance from recharge C age vs distance from recharge C in DIC (pmc) Input of mantle CO 2 Mixture C age (yrs.) An average ground water flow velocity within the aquifer of 2.3 m/y is estimated Distance from recharge (km) Piston-Flow Model Distance from recharge (km) Initial C ages were corrected with the 39 Ar ages Spreadsheet, NETPATH and PHREEQC calculations were performed to account for chemical reactions and isotope exchange.

10 [ 4 He] (cm 3 STP/g water) Concentration of 4 He vs C age 1.5x x10-5 Vertical flux of helium from deeper formations [ 4 He] = 4.8E-10 * (Age) + 1.6E-7 R = 0.99 Piston-Flow Model 5.0x10-6 Aquifer accum. rate (calculated) 2E-11 cm 3 STPHe/cm 3 water/yr C age (yr) The C model ages are further confirmed by the linear correlation with the concentrations of radiogenic 4 He.

11 Age distribution along the flow direction Flow velocity: 2.3 m/yr Last ice age

12 δ 18 O ( ) δ 2 H ( ) LGM Low resolution stable isotope ( 18 O and 2 H) records Oxygen-18 Deuterium Depleted δ 18 O and δ 2 H during the LGM confirm low air temperatures Depletion consistent with isotope shift in the ocean surface during the LGM C age (yrs) -83 Stute and Schlosser, 2001.

13 ΔT~ 7 0 C ΔT~ 5 0 C NGT ( o C) LGM Low resolution noble gas temperature (NGT) record Late Holocene (Modern) Pre-industrial Holocene 1. Low NGT of just above the freezing point during the LGM 2. Glacial/interglacial warming of 5 to 7 o C 2 0 LGM NGT = 0.8 o C C age (yrs) The closed-system equilibration (CE) model was used to describe the NGT and excess air component (Aeschbach-Hertig et al., 2000).

14 Glacial/interglacial shifts in Europe, groundwater Ice covered/permafrost region -> No Infiltration during LGM, etc. Coastal areas: large variations of air Temp. Bath et al., 1979; Rudolph et al., 1984; Stute and Deák, 1989; Beyerle et al., 1998; Huneau et al., 2002; Zuber et al., 2000; Vaikmäe, 2001; Zuber et al., 2004; Blaser et al., 2010; Varsanyi et al., 2011

15 LGM ΔNe (%) Excess air in groundwater (expressed as ΔNe) High excess air in GW during the LGM a) meltwater input? - Pure meltwater: ΔNe > 500 % - Stable isotopes: not highly depleted - Recharge of large amounts of another water component Typical in groundwater: % C age (yrs) b) Increased water table fluctuations and hydraulic loading due to frequent intense rain events? c) Abrupt change in recharge dynamics? - progression and retreat of ice covers and permafrost During the LGM: a) The climate was dry, with air temperatures near freezing point b) A large number of small glaciers developed in the Krkonose Mountains (Recharge area) c) The Bohemian basin was covered by discontinuos permafrost

16 Deuterium excess ( ) Glacial Deuterium excess in groundwater d excess ( ) Temporal decrease of deuterium excess from pre-industrial Holocene to present days Decrease of deuterium excess linked to an increase of air temperatures Present days d-excess= 8.6 in precipitation Modern 6 MA - Cracow, Poland CA + TA - Czech Republic C activity (pmc) MA Oligocene Mazonian basin (Poland) (Zuber et al., 2000) d = (NGT) R² = NGT ( o C) Froehlich et al., 2002

17 Conclusions 1. The low resolution NGT-record indicated a glacial cooling of at least 5 7 C for the Bohemian Cretaceous Basin region, consistent with other studies in Europe. 2. A high excess air (ΔNe) in groundwater at the end of the Pleistocene is possibly related to changes in the recharge dynamics of groundwater by the progression and retreat of ice covers and permafrost 3. A temporal decrease of deuterium excess in groundwater from preindustrial Holocene to present days is linked to an increase of the air temperatures

18 Thank you for your attention!!!