Research Plan Noble-gas and fluid transport processes in ... · Based on these approaches, we aim to consolidate and further expand the uses of noble gas geochemistry as a widely

Research Plan

Noble-gas and fluid transport processes in lakesediments

Main applicant: Prof. R. Kipfer

Keywords: Diffusion, pore fluids, gas, methane, proxy records, noble gas geochemistry

Contents1 Summary 1

2 Research Plan 22.1 Status quo—general . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22.2 Status quo—own research . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32.3 Detailed research plan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

2.3.1 Study sites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72.3.2 Work packages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92.3.3 Available methods, devices and support . . . . . . . . . . . . . . . . . 132.3.4 Personnel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

2.4 Time schedule . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142.5 Importance of this research project . . . . . . . . . . . . . . . . . . . . . . . . 15

1 SummaryIn the previous and the ongoing SNF projects, experimental techniques for the sampling andanalysis of dissolved noble gases in the pore water of lake sediments were developed (Bren-nwald et al. 2003, Tomonaga et al. 2009a). First applications of these methods indicate thatdissolved noble gases in sediment pore water are promising proxies for (palaeo)environmentalconditions in lakes and in the ocean, and for the transport of solutes in the sediment and their re-lease into the overlying water body and into the atmosphere (e.g. Brennwald 2004, Brennwaldet al. 2005, 2004, Chaduteau et al. 2007a,b, Holzner et al. 2008, Lan et al. 2009, Pitre and Pinti2010, Strassmann et al. 2005, Tomonaga et al. 2010a,b, 2009b).

From a conceptual point of view, the key conclusion of all these studies is that in somesediments the diffusivity of noble gases in the sediment pore water is similar to their moleculardiffusivity in bulk water. In other sediments, however, noble gases are quantitatively trappedin the sediment and diffusion is therefore strongly suppressed (e.g. Brennwald et al. 2005,2004, Pitre and Pinti 2010, Tomonaga et al. 2010a). This trapping results in a stratigraphicallycontrolled noble-gas record in the sediment, which allows a time scale to be associated withthe noble gas record in the pore water. However, the mechanisms resulting in this noble-gastrapping remain to be identified. A mechanistic understanding of the diffusion suppressionis required to establish the conceptual basis needed for future applications of noble gases asproxies for environmental conditions and transport of pore fluids.

The aims of the PhD research project proposed here are (i) to improve the mechanisticunderstanding of how and why noble gases are trapped in some sediments, but not in others(work packages A and B) and (ii) to apply the methods and concepts established in our previousprojects in a study targeted at specific geological and environmental questions in a Swiss lake(work package C):

A. Study of microscopic pore-space geometry in relation to diffusion suppression: We aim tostudy the microscopic pore-space geometry of different sediments to identify the mechanismsthat result in noble-gas trapping in the sediment.

B. Quantification of the effective diffusivities of noble-gas isotopes: We aim to measure theeffective noble-gas diffusivities in different sediments to quantify the extent of the diffusionsuppression.

C. Investigation of the dynamics and origin of CH4-rich fluids in the sediment of LakeLungern (Switzerland): the sediments of Lake Lungern contain large amounts of CH4-richfluids. We aim to use noble-gas isotopes as proxies for the transport and origin of these fluids,which may also be associated with the formation of distinct dome-like elevations (mounds) onthe generally flat lake floor.

Based on these approaches, we aim to consolidate and further expand the uses of noblegas geochemistry as a widely applicable tool to study the transport of fluids and solutes inunconsolidated sediments, and to extend the area of application of noble-gas geochemistry inthe environmental sciences.

Furthermore, knowledge of the transport properties of noble gases in relation to the charac-teristics of the sediment will allow targeted choices of the most suitable study sites for futureresearch projects. Also, this work will be of direct benefit to other research not covered by thecurrent project. For instance, interpretation of the noble-gas data that will be obtained from thedeep-drilling sediment cores of Lake Van (Turkey) within the framework of the ICDP-PaeloVanproject (Litt et al. 2009) will benefit directly from the improved knowledge on noble-gas trans-port mechanisms in lake sediments (see also Sect. 2.3.1 and Sect. 2.5).

1

2 Research Plan

2.1 Status quo—generalIn recent years, great interest in palaeoclimate reconstruction has developed. Various environ-mental archives, such as lake and ocean sediments, ice, groundwater and speleothems, havebeen utilised to explore climate evolution and past climatic conditions. In natural waters (lakes,oceans, groundwater), dissolved atmospheric noble gas concentrations reflect the environmen-tal conditions prevailing during gas exchange with the atmosphere or soil air. In contrast toother environmental proxies which only indirectly relate to environmental conditions, noblegas concentrations in water are a well-defined function of the water temperature and salinity aswell as the atmospheric pressure that prevailed during gas exchange with the atmosphere. No-ble gas concentrations are therefore direct and straightforward proxies for reconstructing theseenvironmental conditions (e.g Kipfer et al. 2002).

This principle, which is based a simple physical law (Henry’s law), has been widely ap-plied to successfully estimate palaeotemperatures and palaeoenvironmental conditions fromnoble gas concentrations in groundwater (see e.g. Ballentine et al. (2001), Beyerle et al. (1998,2003b), Marty et al. (2003), Stute et al. (1995, 1992), Weyhenmeyer et al. (2000), review byStute and Schlosser (2000)), and to study the water exchange and mixing conditions in lakes(see e.g. Hohmann et al. (1998), Igarashi et al. (1992), Peeters et al. (2000), Sano and Wakita(1987), Torgersen et al. (1977), Weiss et al. (1991), or review by Kipfer et al. (2002)).

In lakes and oceans, noble-gas concentrations correspond closely to atmospheric equilib-rium concentrations computed from the water temperature, salinity and atmospheric pressureprevailing during gas exchange at the water surface. The vertical distribution of dissolved noblegases in the water column is dominated by vertical transport due to macroscopic turbulent mo-tion (“eddy diffusion”). The atmospheric noble-gas concentrations measured at a given waterdepth therefore correspond closely to the atmospheric equilibrium concentrations calculatedfrom the water temperature and salinity at the same depth, as confirmed experimentally byPeeters et al. (2000) and Aeschbach-Hertig et al. (1999). Note that in large lakes and in theocean, bubbles entrapped in breaking waves may (partially) dissolve in the water, which canresult in small noble gas excesses (usually ≤5% for Ne, and even less for the heavier noblegases, see e.g. Craig and Weiss (1971), Peeters et al. (2000)).

During sedimentation, part of the open water just above the sediment surface is incorporatedinto the sediment pore space. The noble gas concentrations in this pore water are therefore carryinformation about the lake (or ocean) mixing conditions and deep-water exchange in the past(Brennwald et al. 2004, Strassmann et al. 2005).

Lakes generally react sensitively to changes in climatic forcing (e.g. Arnell et al. 1996,Fritz 1996). Sediment pore water was therefore proposed as a noble gas archive for palaeoen-vironmental reconstruction more than three decades ago (Barnes 1979). However, until ourrecent analytical developments, the lack of suitable experimental techniques has prevented thedevelopment of noble-gas geochemistry in this environment.

In addition to palaeoenvironment reconstruction, dissolved noble gases in sediment porewater are sensitive tracers for the transport of solutes in the pore water and their exchange withthe overlying water body. Especially the transient behaviour of radiogenic He isotopes (i.e. Heproduced by radioactive decay processes and other nuclear reactions) accumulating in the porewater allows the dynamics of the transport of solutes and fluids in the sediment to be studied.

However, apart from our pioneering work in these areas (see also Sect. 2.2), up to now onlyfew studies have been conducted to explore the behaviour of noble gases in lake sediment pore

2

water. These studies have concentrated mainly on the local flux of 4He through sediment at onesite in the Pacific Ocean (Barnes and Bieri 1976), and the injection of groundwater through thesediment of two small lakes (Stephenson et al. 1994). Recently, other research groups appliedour noble-gas analysis method to study denitrification in estuarine sediments (Pitre and Pinti2010) and to determine the origin and the rates of release of geogenic fluids from sediments(Chaduteau et al. 2007a,b, Lan et al. 2009).

2.2 Status quo—own researchOver the last few years our research group has developed concepts and methods to apply noblegas and transient tracer techniques (3H/3He, SF6, CFCs) to surface waters (e.g. Aeschbach-Hertig et al. 2007, Hofer et al. 2002, Hohmann et al. 1998, Holzner et al. 2008, Peeters et al.2003, 2000, Schubert et al. 2006a,b), in groundwater (e.g. Aeppli et al. 2008, Aeschbach-Hertiget al. 2000, Amaral et al. 2010, Cirpka et al. 2007, Holocher et al. 2002, Klump et al. 2006a,b,2007, Kreuzer et al. 2008, Peeters et al. 2002, Zhu and Kipfer 2010), and in other new envi-ronmental archives such as firn (Beyerle et al. 2003a, Huber et al. 2006), natural-gas hydrates(Winckler et al. 2002, 2001, 2000) and fluid inclusions in speleothems and other inclusion-bearing materials (Scheidegger et al. 2010, 2007, 2008). These tracer methods were success-fully used to infer palaeoclimate conditions from noble gas concentrations in groundwater, todetermine past hydraulic conditions and recharge dynamics in groundwater, to quantify thetransport and mixing dynamics both in lakes and in groundwater, to study the exchange of no-ble gases between different phases (water, gas, hydrates, etc.) and to study the fate of organicchemicals in groundwater. Based on its experience, our group was invited to give a compre-hensive review of the state-of-the-art use of noble gases and transient tracers in the aquaticenvironment (Kipfer et al. 2002).

Two PhD projects were conducted within previous SNF projects1 to explore the feasibil-ity and use of noble gas studies in the pore water of lake sediments. Within the first of thesePhD projects, the basic experimental methods for the sampling and analysis of dissolved noblegases in pore water were developed (Brennwald et al. 2003). For the first time, these methodsallowed the noble gas concentrations in sediment pore water to be used as tracers for palaeoen-vironmental conditions in lakes (Brennwald et al. 2005, 2004) and for the geochemical origin,transport and release of fluids (e.g. CH4 gas) from the sediment into the overlying water body(Brennwald et al. 2005, Holzner et al. 2008, Schubert et al. 2006a, Strassmann et al. 2005). Theachievements of our research based on the work of this first PhD project is documented in thefollowing peer-reviewed publications (main conclusions are given in italics):

• Brennwald et al. (2003) is the first publication of a reliable and robust method for theroutine sampling, quantitative extraction and analysis of dissolved noble gases from lakesediment samples. The concentrations and isotope ratios of the dissolved noble gases inthe pore water were found to correspond closely to those measured in the overlying lakewater.

• Brennwald et al. (2004) is the first published study where atmospheric noble gases insediment pore water were applied to determine palaeoenvironmental conditions. In this

12000-06819 “Edelgase als Indikatoren fur Umweltveranderungen in Seen”, 200020-105263 “Noble gases inlacustrine sediments as indicators of environmental change in lakes”, 200020-109465 “Noble gases as tracers fortransport of solutes and fluids in lake sediments”, 200020-121853 “Towards noble gas analysis in ocean sedimentsto characterise CH4 seepage”

3

study, the lake level and salinity of the large, terminal Lake Issyk-Kul (Kyrgyzstan) wasreconstructed during the Holocene.

• Strassmann et al. (2005) is the first published study where tritiogenic 3He and 3H insediment pore water were used to quantify the effective parameters that govern the trans-port and exchange of solutes in the open and connected pore space of unconsolidatedsediments. In addition, we showed that even without diffusion suppression, diffusionis outweighed by sediment burial for sediment cores longer than ∼10 m. Thus, even ifdiffusion does limit the usefulness of short sediment cores as noble-gas archives for en-vironmental conditions in lakes, long sediment cores will still contain noble-gas recordsthat are hardly affected by post-depositional diffusive exchange with the overlying waterbody. Sufficiently long sediment cores will therefore allow quantitative reconstruction oflong-term environmental changes in lakes and oceans (e.g. deep drilling cores, see alsoSect. 2.3.1 and Sect. 2.5).

• Brennwald et al. (2005) is the first published study where atmospheric noble gases insediment pore water were applied to study and reconstruct the biochemical production ofCH4 in the sediment and its release into the lake (and the atmosphere).

• Holzner et al. (2008) is the first published study where atmospheric and terrigenic noble-gas isotopes in sediment pore water were applied to study the injection and the geochem-ical origin of geogenic fluids into the deep water of the Black Sea and to determine CH4emissions from from high-intensity gas seeps in the vicinity of active mud volcanoes.

Within the second PhD project, the analytical methods were optimised towards an efficientand easily adoptable routine procedure which allows other researchers to quantitatively andreliably extract and analyse noble gases or other (volatile) trace gases dissolved in sedimentpore water (Tomonaga et al. 2009a). Also, the previous method relied on heating the sedimentsample for separation and degassing of the pore-water. In some sediments, this heating resultedin He contamination of the gas sample by radiogenic He released from the sediment grains,where it is produced by radioactive decay of U and Th isotopes. With the new method, thepore water is separated from the sediment matrix by centrifugation. Avoiding the heating stepprevents the release of He from the sediment grains and hence allows robust He analysis of thepore water. Furthermore, the new method is in principle suitable for quantitative analysis of“non-noble” gases dissolved in the pore water (e.g. CH4)

These experimental advances allowed us to quantify the fluxes and the geochemical originof terrigenic He isotopes injected into surface waters and to study the suppression of noble-gasdiffusion in different sediment types on an empirical basis:

• Noble-gas profiles in a sediment core taken in an estuary in the Stockholm Archipelagoshow pronounced concentration gradients that can only persist if the noble gases werequantitatively trapped in the sediment pore space (see Fig. 1 and Fig. 2 below, Tomonagaet al. 2010a). They are therefore hardly subject to diffusion in the pore water.

• In Lake Van, which is located in a region of high tectonic activity (Saroglu et al. 1992),the He flux in the sediment was determined at 24 sites. These analyses revealed thatthe He flux varies strongly within the lake basin from (1–50)·108 atoms/m2/s (Tomonagaet al. 2007a,b, 2010b), whereby the largest He fluxes are found on the steep borders ofthe central, deep part of the lake basin. In addition, the 3He/4He ratio of the excess He

4

is the same in all sediment cores and indicates that this He originates from a single sub-continental mantle source. This finding suggests that the He release from the underlyinglithosphere is limited to fault zones that are most likely related to volcanic activity in thepast and supports the hypothesis that the circular-shaped deep basin is formed by thecollapse of an ancient caldera.

• Off the coast of New Zealand, the geochemical origin of the CH4-rich fluids releasedfrom three gas seeps was identified using the isotopic He signature of the sediment porewater (samples taken during the Sonne expedition SO-191). Our 3He/4He data indicatethat at two of these seeps He of crustal origin is released (3He/4He≈ 5 ·10−7), whereasthe fluids released at the third seep show a 3He/4He ratio of 2.5·10−6. This 3He enrich-ment indicates that these fluids are related to a deeper source in the mantle (Tomonagaet al. 2009b).

From a conceptual point of view, the crucial finding of all our previous studies is that insome sediments the vertical diffusion of dissolved noble gases in the pore water shows an un-expectedly strong attenuation (e.g. in our studies in Lake Issyk-Kul, Soppensee, the StockholmArchipelago, and in some sediments of Lake Van). Also, other research groups (Pitre and Pinti2010) observed strong noble-gas concentration gradients in the pore water of the sedimentsof the St. Lawrence estuary (Quebec, Canada), which also indicate an unexpectedly strongattenuation of vertical diffusion in the pore space.

In sediments with strong suppression of diffusion, transport of noble gases by diffusionis outweighed by sediment burial on relatively small length scales of a few centimetres. Inthese sediments, the noble gas signature of the pore water is therefore trapped in the sedimentand hence reflects the noble gas concentrations in the overlying water at the time when thecogenetic sediment layers were deposited. In conclusion, these noble gas records can be usedto directly reconstruct the noble gas concentrations and the environmental conditions of theoverlying water body in the past (e.g. Brennwald et al. 2005, 2004).

However, in other sediments, e.g. in those of Lake Zug (Strassmann et al. 2005) and otherSwiss lakes, and in some sediments of Lake Van, we observed no noble-gas trapping. In thesesediments, noble-gas diffusion in the pore water is only slightly attenuated due to the porosityand tortuosity of the sediment matrix. Diffusion therefore smooths out the noble-gas concen-tration profiles. This smoothing may affect the usefulness of the noble-gas record as an archivefor palaeoenvironmental conditions in short sediment cores.

However, the mechanisms resulting in the trapping of the noble gases in the pore space arehardly understood on a mechanistic level. The suppression of diffusion is determined by theconnectivity and the geometry of the pore space, i.e. by the size, the shape and the geometricalalignment of the sediment grains. Our noble gas measurements in the layered sediments ofLake Issyk-Kul and Soppensee (Brennwald et al. 2005, 2004) as well as the noble-gas data ofPitre and Pinti (2010) from the sediments in the St. Lawrence estuary suggest that diffusionis strongly attenuated within these fine-grained sediments. Further, noble-gas profiles in asediment core taken in the Stockholm Archipelago (Tomonaga et al. 2010a) show pronouncedconcentration gradients that can only persist if the noble gases were quantitatively trapped inthe sediment pore space (Fig. 1, Fig. 2). The effective noble-gas diffusivities are several ordersof magnitude lower than their respective diffusivities in bulk water. The noble-gas profiles aretherefore hardly subject to diffusion in the pore water.

5

Ne (10-7 cm3STP/g)

Dep

th (m

)

Ar (10-3 cm3STP/g) Kr (10-7 cm3

STP/g) Xe (10-8 cm3STP/g)

X � 0.1 m

T � 100 a

0 4 8 0 1 2 0 2 4 60 2 4 6 8

0

0.1

0.2

0.3

0.4

0.5

Figure 1: Concentrations of Ne, Ar, Kr and Xe dissolved in the pore water of a sediment core taken in the Stock-holm Archipelago (circles: measured data, squares: atmospheric equilibrium concentrations, after Tomonaga et al.2010a). The uppermost 0.4 m of the sediment is varved (i.e. annually laminated), the layer below (grey shading)is a homogeneous mass-flow deposit. At the interface between the layered and the homogeneous sediment, thenoble-gas concentrations increase from the atmospheric equilibrium concentrations in the layered sediment to themuch higher concentrations found in the homogenous sediment. These higher concentrations indicate that themass movement originated near the air/water interface, where air bubbles were incorporated into the moving massand were subsequently dissolved in the pore water.The strong concentration gradients at the interface between the layered and homogeneous sediment have there-fore persisted within a characteristic depth range of X ≈ 0.1 m since the mass-movement event, which occurredT ≈ 100 years ago (as indicated by sediment dating using Cs and Pb). The effective noble-gas diffusion coef-ficients Deff can therefore be estimated using the relationship X ≈

√2DT as Deff ≈ 10−12 m2/s. This is about

about three orders of magnitude less than the molecular noble-gas diffusivities in bulk water (see also Fig. 2). Thevertical diffusion of noble gases is therefore strongly suppressed in the sediments of the Stockholm Archipelago.See Tomonaga et al. (2010a) for a more complete analysis of the diffusion suppression.

Undisturbed sediments (Deff,1)Deff = D0 / 50

Mass-flow deposit (Deff,2)

He (10-6 cm3STP/g)

1 20 2 3 4 51

Dep

th (m

)

0

0.1

0.2

0.3

0.4

0.5

Deff = D0 / 250

Deff = D0 / 1000

Initial conditions

Xe (10-8 cm3STP/g)

Figure 2: Left: He concentrations in the pore water of the sediment core taken in the Stockholm Archipelago,He concentration profile (after Tomonaga et al. 2010a, see also Fig. 1). The upward flux of terrigenic He isgiven by Fick’s Law ( jHe = −Deff∂He/∂ z, where z is depth). The in-situ production of terrigenic He by theradioactive decay of U and Th isotopes is negligible compared to the He produced in deeper strata. The He fluxcan therefore be considered constant throughout the sediment core, and to represent He released from deeperstrata (Torgersen and Clarke 1985). The larger He concentration gradient below 40 cm therefore indicates thatthe effective He diffusivity is strongly reduced in the mass-flow deposit as compared to the sediment above (i.e.Deff,2 ≈ 102×Deff,1).Right: Comparison of measured and modelled Xe concentrations (after Tomonaga et al. 2010a). The modelassumes a step-like initial concentration profile (dotted line) corresponding to the observed air excess in the mass-flow deposit (see text). The remaining curves correspond to Xe concentration profiles calculated for differentvalues of effective Xe diffusion rates. The comparison of the modelled and measured data implies that the effectiveXe diffusivity (Deff) in the sediment is at least two orders of magnitude smaller than the Xe diffusivity in bulk water(D0).

6

2.3 Detailed research planOur research (see Sect. 2.2) and the recent work by Chaduteau et al. (2007a,b), Lan et al.(2009) and Pitre and Pinti (2010) makes a strong case that dissolved noble gases in pore wa-ters of unconsolidated sediments (i) have a great potential to become a new and high-qualityenvironmental archive of great use in reconstructing the hydrological and biogeophysical dy-namics of lakes and oceans, and (ii) allow the transport of solutes through the sediments to beaddressed in a direct and quantitative way.

However, apart from these promising results, the fundamental questions on the mechanismscontrolling the transport and trapping of noble gases and other solutes remain open. Thesequestions need to be addressed to establish a robust scientific basis for the interpretation of thenoble-gas records in sediment pore waters in terms of the environmental conditions in lakesor the origin and transport of pore fluids in sediments. Within the framework of the projectproposed here, we therefore intend to develop a comprehensive mechanistic understanding ofthe trapping of noble gases in unconsolidated sediments.

To this end, we aim to explore the effects of the microscopic properties of the sediment porespace on the diffusion of noble gases (work packages A and B), which may also be of greatinterest for the transport of other dissolved species. Such deepened insight will significantlyconsolidate the mechanistic base of noble-gas applications, such as studying the dynamics andorigin of CH4-rich gases accumulating in the sediment of Lake Lungern (work package C).

The PhD project proposed here will focus on three study sites – the Stockholm Archipelagoand Lakes Lungern and Van (Sect. 2.3.1) – and will be structured around the following threework packages (see Sect. 2.3.2):

A. Study of microscopic pore-space geometry in relation to diffusion suppression (studysites: Stockholm Archipelago, Lake Van, Lake Lungern)

B. Quantification of the effective diffusivities of noble-gas isotopes (study sites: StockholmArchipelago, Lake Van, Lake Lungern)

C. Investigation of the dynamics and origin of CH4-rich fluids in the sediment of LakeLungern

We expect this PhD project to yield publications in peer-reviewed journals on the followingtopics:

• A mechanistic analysis of the trapping of noble gases in unconsolidated sediments inrelation to microscopic pore structure (combination of work packages A and B)• The experimental quantification of the diffusion coefficients of different noble gas iso-

topes (work package B)• An investigation of the origin and dynamics of CH4 in relation to mounds in Lake

Lungern (work package C)

2.3.1 Study sites

The Stockholm Archipelago (Sweden, Baltic Sea; work packages A and B) constitutesa geomorphological transition zone between a lake-rich land and the Baltic Sea. In the semi-enclosed bays of the Stockholm Archipelago, local conditions favour inflow and retention ofsettling particles, which leads to very high sedimentation rates of up to 5 cm/a (Meili et al.2000). The undisturbed sediment accumulation in these bays (especially in the deep regions)leads to the formation of varves with thicknesses of up to 5 cm (Meili et al. 2000, Persson and

7

Jonsson 2000). We demonstrated that vertical noble-gas diffusion is inhibited in these sedi-ments (see Fig. 1, Fig. 2 and Tomonaga et al. 2010a). Analysis of the texture and microstructureof these sediments is expected to yield insight in the mechanisms leading to the trapping of thedissolved noble gases.

Sediment samples from the Stockholm Archipelago will be available to us through ourcollaboration with regional partners (Prof. Markus Meili, University of Stockholm).

Lake Van (eastern Turkey; work packages A and B) is the world’s largest soda lake and,after the Caspian Sea and Lake Issyk-Kul, the third largest closed lake on Earth (Reimer et al.2008). Lake Van is located in a semi-arid region at ∼1650 m a.s.l., is ∼450 m deep and coversan area of∼3,600 km2 (Degens et al. 1984). Except in the fresher surface-water layer, the watersalinity exceeds 21 g/kg (Kipfer et al. 1994, Reimer et al. 2008). The sediments of Lake Van arevarved and have been shown to provide a high-resolution archive of palaeoclimate conditionsin Asia Minor (Landmann et al. 1996, Lemcke and Sturm 1997, Reimer et al. 2008, Wick et al.2003). Lake Van was chosen by ICDP2 (Litt et al. 2009) as a key site for deep continentaldrilling (ICDP/PaleoVan project) (i) to reconstruct climate evolution in the Van region and (ii)to study the origin and dynamics of geogenic fluids in a volcanic system.

Noble-gas analyses of 24 short sediment cores taken in the course of our previous SNFprojects and in collaboration with the ICDP pilot study on Lake Van were conducted to analyzethe lateral variability of the terrigenic He flux, and to determine the geochemical origin of theHe rich pore fluids (see 2.2 Tomonaga et al. 2010b). Within the PaleoVan project we willexpand these studies to the include the vertical dimension. Also, the sediments sampled by thedeep-drilling campaign at sediment depths of several hundred metres are expected to show amuch stronger degree of compaction and cementation than the sediments accessible by shortgravity cores. These unique samples, will therefore allow us for the first time to study thetransport mechanisms in such diagenetically ‘older’ sediments, which might be considered asanaloga for oceanic sedimens and their noble-gas geochemistry.

Sediment samples from Lake Van will be available to us through our direct involvement inthe ICDP/PaleoVan project.

Lake Lungern (central Switzerland; work packages A, B, C) is a small lake with an artifi-cially controlled water level (max. surface area ∼2 km2, max. depth 68 m) located in the SwissAlps (Canton of Obwalden). The sedimentary record of Lake Lungern, covering the time rangefrom the late Holocene to today, reflects a highly dynamic environment characterised by (i) sub-aquatic mass movements induced either by large lake level changes, seismic activity or deltainstabilities, and (ii) post-depositional deformation processes. This dynamic sedimentologicalregime might be related to migration or expulsion of gas from the sediment, and possibly toongoing tectonic activity along the Obwalden Valley strike-slip fault zone (Monecke 2004).

Lake Lungern is situated in an alpine shear zone and close to epicentres of historicallyreported major earthquakes. Seismic activity or rapid deposition of earthquake-triggered sedi-ment movements may have resulted in pore fluid overpressure, which triggered remobilisationof subsurface sediment. Further, a large natural gas reservoir was found near the village of Fin-sterwald, which is located in the mountain range 20 km to the north of the lake. Also, release ofgeogenic gas has been reported in the area around Lake Lungern (Bossard 1981), e.g. near thevillage of Giswil-Kleinteil. Noble-gas analyses of these natural gases indicate that they mainlyoriginate from a gas source in the crust (Etiope et al. 2010).

2International Continental Scientific Drilling Program. Note that Switzerland is full ICDP member since 2008.

8

CH4 gas seeps have been known to occur in the area around the lake during at least thelast 90 a. The gas released from a seep near the village of Giswil-Kleinteil shows a 3He/4Heratio of ∼ 10−7 (Etiope et al. 2010). Similar 3He/4He ratios were observed at gas seeps nearFinsterwald.

The generally flat lake floor of the central basin is characterised by the occurrence of severaldistinct dome-like elevations (‘mounds’) of up to 2.5 m height. However, based on availabledata it has so far not been possible to determine the age of these mounds and to identify theprocesses involved in their formation (Pfaffen 2007).

Seismic data indicate zones where gaseous fluids are present in the lake sediment. Onehypothesis is therefore that gas migration and release may contribute to the formation of themounds. Lake Lungern has a documented history of significant and abrupt artificial lake levelchanges (for instance an artificial 37 m lake-level drop in 1836 AD) that reduced the hydrostaticload on the sediment column. This may have induced gas expansion, sediment remobilisationin the subsurface and the formation of mounds (Pfaffen 2007). An alternative hypothesis pos-tulates that the mounds are formed due to mass movements triggered by earthquakes caused byseismic activity in the active fault zones (Pfaffen 2007).

Both hypotheses can be tested using the noble-gas signature of the sediment pore water,because the noble-gas isotope signature is characteristic for the geochemical origin of the fluidsin the mounds (see work package C).

2.3.2 Work packages

A. Study of microscopic pore-space geometry in relation to diffusion suppression: Thiswork package addresses the question of why the vertical diffusion of dissolved noble gases(and hence also of other solutes) is strongly attenuated in some sediments (Lake Issyk-Kul,Soppensee, Stockholm Archipelago, some sediments of Lake Van), but not in others (LakeZug, other Swiss lakes, some sediments of Lake Van). The suppression of diffusion is mostlikely related to the texture and (micro)structure of the sediment (i.e. the connectivity and thegeometry of the pore space, as well as the size, shape, and geometrical alignment of the sed-iment grains) and to diagenetic alterations due to biogeochemical processes such as calciteprecipitation or the formation of Fe/Mn hydroxides.

So far, we have developed two working hypotheses to explain mechanistically the strongreduction of diffusion in the pore water.

• The first hypothesis (Brennwald et al. 2004) is based on the fact that, due to the formationof minerals or the geometric realignment of the sediment grains during sedimentation,compaction and early diagenesis, the diameter of the channels connecting the sedimentpores can be as small as the free path length of the diffusing solutes (e.g. Horsemanet al. 1996). Then, as in firn (Beyerle et al. 2003a, Huber et al. 2006), the Renkin effectwill result in molecular diffusion being reduced by several orders of magnitudes (Renkin1954, Schwarzenbach et al. 2003).

• The second hypothesis postulates that a considerable fraction of the pore space consistsof ‘dead’ pores, i.e. pores that are not connected to the remaining pore space, whichis accessible for macroscopic diffusion in the pore water. Solutes are therefore trappedin the ‘dead’ pores and are therefore not subject to macroscopic transport by diffusionwithin the fully connected pore space.

Both hypotheses might be related to the diagenetic/geochemical processes in the sedi-ment, such as the precipitation of calcite. For instance, in the sediments of the Stockholm

9

Archipelago, the suppression of diffusion is strongest in the mass-flow deposits, which exhibitan excess of atmospheric gases and therefore seem to originate from the shallow-water zonebeneath the air/water interface (Fig. 1 and Fig. 2). Calcite concentrations in shallow water areoften near saturation levels. If this water is transported to deeper zones and is incorporated intothe mass-flow deposits, calcite may precipitate out in the mass-flow deposits due to changes inphysicochemical conditions or microbial activity. Calcite precipitation, or similar geochemicalprocesses causing an alteration of the microscopic structure of the sediments (e.g. the forma-tion of Fe/Mn hydroxides), will reduce the connectivity of the pore space, which may stronglyreduce the effective diffusivity of solutes in the pore water.

Most measurements of effective solute diffusivities in pore water of surface-water sedimentsrely on experimental methods that by principle only assess the fully connected part of the porespace. Also, ‘traditional’ transport models axiomatically exclude the occurrence of ‘dead’ pores(see e.g. Berner 1975, Imboden 1975, Strassmann et al. 2005), although the retention of solutesin ‘dead’ pores will result in a strong reduction of the overall diffusivity in the sediment. Toour knowledge, however, this axiomatic exclusion of ‘dead’ pores is often not based on solidexperimental evidence and may therefore be an inappropriate simplification of the models.

An additional speculative hypothesis brought forward by Pitre and Pinti (2010) is thatnoble-gases are adsorbed quantitatively onto the sediment matrix (e.g. on organic matter). Toour knowledge, quantitative sorption of noble gases on unconsolidated sediments has not beenobserved until now. However, if noble gases are indeed adsorbed quantitatively onto the sedi-ment matrix, only the fraction of the noble gases remaining dissolved in the pore water wouldbe subject to diffusion, whereas the adsorbed fraction would be retained on the sediment matrix.This would therefore result in a strong reduction in diffusive transport.

Although there is hardly any direct experimental evidence in favour of either of these hy-potheses, they offer a way to understand conceptually the strong reduction of diffusion that isobserved in some unconsolidated sediments. Our strategy to assess the above hypotheses willbe to characterise sediment texture, microstructure and noble-gas diffusion in different samplesof the sediments of the Stockholm Archipelago, Lake Van and Lake Lungern.

In collaboration with specialists in advanced 3D microscopy, we therefore intend to studythe pore-space geometry using high-resolution 3D imaging methods. Note that we have fullaccess to the microscopy centres at EMPA and ETH Zurich through the Eawag Particle Labo-ratory (Ralph Kagi). Some of the methods that will be used for these studies are, e.g.:

• 3D microscopy of cryo-stabilised sediment (e.g. Holzer et al. 2004, 2006, 2007). Wehave close contacts with Dr. Lorenz Holzer at EMPA Dubendorf, who has extensiveexperience in applying this technique to determine the 3D microstructure and pore-spacecharacteristics of various natural materials, including water-saturated clay.

• Microscopic pore-space analysis in resin-impregnated (Van den Berg et al. 2003) or cryo-stabilised sediment samples.

• X-ray or nuclear magnetic computed tomography (Kleinberg et al. 2003, Uchida et al.2000, Van Geet et al. 2000). We have contacts with Dr. Michael Hupfer at the IGB Berlin,who has already applied this technique to analyse pore geometries in lake sediments.

We aim to combine these complementary approaches with the diffusivity measurements ofwork package B to test the hypotheses on the diffusion suppression and to establish a robustand mechanistic understanding of the trapping of noble gases in the sediment.

10

B. Quantification of the effective diffusivities of noble-gas isotopes: The element-specificdiffusion coefficients of He, Ne, Kr and Xe in water are well known from the measurementscarried out by Jahne et al. (1987), who also measured the slight difference in the diffusivitiesof 3He and 4He. However, the diffusivity of Ar was not directly measured and was thereforeestimated from the measurements of the other noble gases using Graham’s Law (Di/D j =√

m j/mi, where Di, j are the diffusion coefficients of two species i and j and mi, j are theirrespective masses). Also, the diffusion coefficients were not measured for the different isotopesof Ne, Ar, Kr and Xe because, based on the 3He/4He experiments of Jahne et al., they wereassumed to follow Graham’s Law, too.

The extent of the suppression of noble-gas diffusion in sediment pore water can be con-strained using the observed isotope fractionation and the isotopic difference in the noble-gas diffusivities (i.e. Graham’s law, for details see Brennwald et al. 2005). However, recentmolecular-dynamics simulations (Bourg and Sposito 2008) questioned the validity of Graham’sLaw for noble-gas isotopes of the same element in water. In these simulations, the noble-gasisotopes were assumed to interact with the surrounding water molecules, which in turn domi-nate the effective mass of the diffusing noble-gas isotope. The relative difference of the effec-tive masses of two diffusing isotopes is therefore much less than would be expected from theirindividual isotope masses only. These computer simulations therefore suggest a lower isotopefractionation than would be expected from Graham’s Law. This lower fractionation would inturn affect the interpretation of the isotope fractionation observed in the sediment pore water interms of the suppression of noble-gas diffusion.

In order to establish a robust basis to interpret isotope fractionation in terms of diffusionsuppression, we aim to experimentally quantify the true isotope fractionation due to the diffu-sivity differences between different isotopes of the same element. We have planned a suitableexperimental set-up in collaboration with the authors of the molecular-dynamics simulationstudy, who will also be provide further scientific support in the assessment and interpretationof the experimental results.

The experiments will be carried out using a diffusion column analogous to that used byJahne et al. (1987). This set-up essentially consists of a column containing the diffusionmedium (e.g. water), which is exposed to an atmosphere of the gases in question on one sideand to an evacuated vessel on the other side. The diffusion medium is separated from thevacuum by a thin, gas-permeable membrane. If water is used as the diffusion medium, turbu-lent transport is prevented by immobilising the water by adding either gelatine or small glassspheres. The diffusivities are then quantified by analysing the accumulation rates of the gasesin the evacuated vessel. The rates of gas accumulation in the evacuated vessel, and hence thederived diffusion coefficients, are scaled by the tortuosity introduced by the gelatine or the glassspheres. However, the ratio of two diffusion coefficients (as in Graham’s Law) is not, becausethe toruosity is the same for all gases and isotopes diffusing through the water.

The gas diffusing out of the diffusion column will be analysed either by measuring aliquotsof the gas by static mass spectrometry or by continuous analysis by dynamic mass spectrom-etry. The static analysis yields a higher sensitivity than the dynamic analysis. Static analysistherefore allows the use of air as the test gas used in the experiment. While air only containstrace amounts of the noble-gas isotopes in question, its isotopic noble-gas composition is wellknown and therefore provides a well-defined reference of the unfractionated noble-gas isotopesbefore diffusion. On the other hand, dynamic analysis allows continuous measurement of thenoble-gas isotopes diffusing out the column. This analysis therefore directly yields noble-gasisotope fluxes as a function of time, which in turn also depends on the diffusion rates in the col-umn. Due to its lower sensitivity, however, the dynamic analysis will require a test gas that is

11

enriched with the noble-gas isotopes in question. The combination of static and dynamic anal-yses will therefore allow very accurate and precise quantification of the isotope fractionationdue to diffusion.

The same experimental set up-will be used to directly quantify effective diffusion rates indifferent sediments by placing sediment samples in the diffusion column. These experimentswill yield direct quantification of the suppression of diffusion in different sediments. Cor-relating observed diffusion rates with other properties of the sediment (e.g. occurrence of lay-ers/varves, organic matter content, grain size, porosity, microscopic geometry of the pore space,extent and type of geochemical or diagenetic alterations, etc.; as studied in work package A)will therefore provide independent insight into the mechanisms controlling the suppression ofnoble-gas diffusion in sediments.

C. Investigation of the dynamics and origin of CH4-rich fluids in the sediment of LakeLungern: We aim to study the dynamics and the geochemical origin of the gas present inthe sediments of Lake Lungern and the role of these gas occurrences in the formation of themounds.

Terrigenic fluids show a noble-gas isotope signature that differs strongly from that of air-saturated water. Terrigenic fluids are depleted in all noble gases except He (and sometimesAr), which are either of primordial origin (3He/4He≈ 10−5) or produced by radioactive decayprocesses (3He/4He ≈ 10−8). In contrast, sediment mass flows triggered by seismic activitywill be characterised by noble gases of atmospheric origin (3He/4He = 1.38 ·10−6), and may,as in the case of the Stockholm Archipelago, even show an air excess (Tomonaga et al. 2010a).The elemental and isotopic noble-gas signature of a fluid therefore allow identification of thegeochemical origin of different fluids.

Further, CH4 ebullition from sediments has been shown to cause a characteristic noble-gasdepletion in the pore water (Brennwald et al. 2005, Holzner et al. 2008). The depletion isstrongest for the lighter, more volatile gases. This depletion pattern is distinct from the concen-tration changes related to gas exchange with air. Degassing due to CH4 ebullition can thereforebe discerned straightforwardly from gas exchange with air (Brennwald et al. 2005, Holzneret al. 2008). The observed depletion pattern of the atmospheric noble gas concentrations can beinterpreted as a measure of the CH4 ebullition rate in the past (Brennwald et al. 2005), which al-lows reconstruction of the trophic state of the water body in the past. Atmospheric noble gasesin Lake Lungern are therefore expected to yield crucial information for past CH4 emission andits relationship to the migration and accumulation of deep crustal fluids.

In addition, our recent experimental improvements in the extraction and analysis of dis-solved gases from the sediment pore water will allow us to quantitatively analyse the concen-trations and isotopic signature of the dissolved CH4 in the sediment pore water. This approachovercomes the limitations of conventional CH4 analysis methods in sediment pore water, whichare prone to air contamination and degassing of the volatile CH4 from the pore-water sample.

In summary, dissolved noble gases in the pore water will allow us to study the dynamicsand origin of the pore fluids and the formation of the mounds. Based on our knowledge ofnoble-gas transport in the sediment of Lake Lungern (work packages A and B), we thereforeaim to analyse the concentrations and isotope ratios of the noble gases and CH4 dissolved in thepore water of the sediment. These analyses will yield a unique geochemical data set that willallow us to determine the geochemical origin and the dynamics of the CH4 and other terrigenicfluids in the sediment in the context of seismic activity, sediment mass flows, gas accumulation,and mound formation.

12

2.3.3 Available methods, devices and support

The Environmental Isotopes Group of the Dept. of Water Resources and Drinking Water atEawag/ETHZ has long and comprehensive experience in the analysis of noble gases, 3H/3He,ultra low-level 3H, SF6, CFCs, and in their application in the aquatic environment (Beyerleet al. 2000, Hofer and Imboden 1998, Hofer et al. 2002). New experimental methods havebeen developed to analyse noble gases in sediment pore water (Brennwald et al. 2003). Thelaboratory of the Environmental Isotopes Group possesses one of the few experimental facilitiesworld-wide that can analyse noble gases, ultra low-level 3H, SF6 and CFCs on a routine basis.

Our gas extraction methods were recently adopted successfully by other scientists (Chaduteauet al. 2007a,b, Lan et al. 2009, Pitre and Pinti 2010). However, to our knowledge, our researchgroup at Eawag/ETHZ is at the moment the only group world-wide which is capable of rou-tinely analysing concentrations of all noble gases (He, Ne, Ar, Kr, Xe) and their isotopic sig-nature in sediment pore waters with the high precision and accuracy required to reconstructpalaeoenvironmental conditions in lakes and oceans.

Sediment sampling equipment, small research vessels, standard analytical methods, andfurther scientific support and know-how are fully accessible to us via the Eawag/SURF sedi-mentology group.

3D analysis of sediment microstructure will be carried out in collaboration with Dr. LorenzHolzer (Dept. High Performance Ceramics at EMPA Dubendorf, Switzerland), who has agreedto fully support this work by providing access to his unique experimental methods and know-how.

The sampling campaign in the Stockholm Archipelago has been pre-arranged and will beconducted in collaboration with the Institute of Applied Environmental Research of StockholmUniversity.

Close collaboration with the Geology department of the Yunzuncu Yıl University in Van(Turkey) for the sampling campaign and the data analysis in Lake Van allows us to profit fromthe know-how, the equipment and the full logistic support of these research groups. During ourprevious work in Lake Van, we equipped the Yunzuncu Yıl University with a range of differentsampling equipment (cable winch, sediment corer, water samplers), which greatly reduces thelogistic effort required for field work in this remote area.

Most importantly, our research team is directly involved in the ICDP/PaleoVan deep drillingproject in Lake Van. We therefore have direct access to sediment samples for noble gas analysisin the pore water of deep drilling cores. We will also profit from the scientific exchange withinthe ICDP/PaleoVan project.

2.3.4 Personnel

The Environmental Isotopes Group at Eawag/ETHZ intends to offer a PhD the opportunity tofurther develop noble-gas geochemistry in sediments. This will allow the group to maintain itsscientific lead in this emerging field of environmental sciences.

13

2.4 Time scheduleJan. 2011 – Jun. 2011:

• Sediment sampling in the Stockholm Archipelago (work packages A and B)• Selection of sediment samples from Lake Van (work packages A and B)• Sediment sampling in Lake Lungern (work packages A, B and C)

Jul. 2011 – Dec. 2011:

• Microstructure analyses of sediment samples from the Stockholm Archipelago, Lake Vanand Lake Lungern (work package A)• Assessment of results from microstructure analyses (work package A; will be used to

guide the selection of samples to be analysed in work package B)• Building and testing the experimental set-up to quantify the diffusivities of noble-gas

isotopes (work package B)

Jan. 2012 – Jun. 2012:

• Experimental quantification of isotope fractionation due to molecular diffusion (workpackage B)• Experimental quantification of effective noble-gas diffusivities in sediments from the

Stockholm Archipelago, Lake Van and Lake Lungern (work package B)• Interpretation of results from microstructure-analysis and diffusion experiments (com-

bine results of work packages A and B)

Jul. 2012 – Dec. 2012:

• Analysis of dissolved noble gases and CH4 in the pore water of Lake Lungern (workpackage C)• Assessment of noble-gas and CH4 data from Lake Lungern (work package C)• Drafting of a publication on the mechanisms resulting in the noble-gas diffusion suppres-

sion (work packages A and B)

Jan. 2013 – Jun. 2013:

• Drafting of a publication on the extent of noble-gas isotope fractionation due to diffusionin water (work package B)• Drafting of a publication on pore-fluid dynamics and mound formation in Lake Lungern

(work package C)• Drafting PhD thesis

Jul. 2013 – Dec. 2013:

• Finalise manuscripts for publication (work packages A, B and C)• Finalise PhD thesis

14

2.5 Importance of this research projectOn the one hand, this project aims to fully establish the mechanistic understanding of the noble-gas trapping in unconsolidated sediments of lakes and oceans as a prerequisite for targetedselection of study sites and adequate interpretation of the noble-gas record in pore water oflacustrine and oceanic sediments.

On the other hand, the ground breaking work from the previous and ongoing SNF projectsclearly demonstrates that dissolved noble gases in sediment pore water provide valuable, ac-curate, and precise tools in palaeoclimate research and for studying fluid and solute dynamicsin unconsolidated sediments and the uppermost part of the crust. If sediment pore water cansuccessfully be established as a new type of noble gas archive for such applications in environ-mental research, this would pave the way for a whole new field in noble gas geochemistry inlakes and oceans.

To fully establish the mechanistic understanding of noble-gas geochemistry in sedimentpore waters and to further expand the uses of this new emerging area of terrestrial noble-gasgeochemistry we intend to consolidate the physical understanding of the trapping of noble gasesin sediments and to expand the applications of dissolved noble gases in sediment pore watersfor environmental studies in lakes:

• We propose to develop a complete understanding of the quality of dissolved noble gasesin sediment pore water as environmental proxies by advancing our knowledge of themechanisms involved in the transport of noble gases in the pore water. In some sedi-ments, the vertical diffusion of dissolved noble gases is attenuated to a level where itbecomes irrelevant for noble gas transport. In such sediments, the noble gas record istherefore linked to the sediment stratigraphy, which allows a time-scale to be associatedwith the noble-gas record and the information on environmental conditions containedtherein. While the available data suggest that the sediment texture controls the strong at-tenuation of vertical diffusion, the mechanisms responsible for noble-gas trapping remainunknown. To deepen our understanding of sediment pore water as a noble-gas archive forpast environmental conditions, we therefore need to identify the mechanisms responsiblefor the strong reduction of vertical diffusion (work packages A and B).

• We propose to study the dynamics and origin of the CH4-rich fluids in the sediment ofLake Lungern. The analysis of non-atmospheric noble-gas isotopes will yield informa-tion on the geochemical origin, accumulation and the dynamics of these fluids in thesediment. In addition, these analyses will be complemented by analyses of other spar-ingly soluble gases (e.g. CH4), utilising for the first time the same quantitative samplingand gas extraction methods as for noble gases. These analyses will yield a unique geo-chemical data set that is expected to allow the processes involved in the formation ofmounds in the otherwise flat lake bottom to be identified and constrained (work packageC).

The combination of these conceptual and application-oriented tasks is expected to furtheradvance the new and emerging field of noble-gas geochemistry in sediment pore waters to alevel that will allow other researchers to adopt our recently developed tools and methods forapplications in a wide range of scientific studies in lakes and oceans.

Last, but not least, our improved mechanistic understanding of noble-gas transport in sed-iments will be of paramount importance to the interpretation of the noble-gas concentrationsthat will be analysed in the a deep-drilling sediment core to be taken at Lake Van within the

15

framework of the ICDP/PaleoVan project (see also Sect. 2.3.1). On the one hand, a mechanisticunderstanding of the noble gas transport will provide a robust basis for the interpretation of theHe isotopes in terms of the origin and dynamics of geogenic pore fluids. On the other hand, thestratigraphically controlled archive of atmospheric noble-gas concentrations in the sedimentpore water is expected to provide fascinating quantitative information on climate change cov-ering the last ∼500 ka of the environmental history of a large lake and its catchment area in aclimatically sensitive region where the North Atlantic Oscillation and monsoonal atmosphericcirculation meet.

ReferencesAeppli, C., Berg, M., Hofstetter, T. B., Kipfer, R., and Schwarzenbach, R. (2008). Simultaneous quantification of

polar and non-polar volatile organic compounds in water samples by direct aqueous injection-gas chromatog-raphy/mass spectrometry. J. Chromatography A, 1181:116–124.

Aeschbach-Hertig, W., Holzner, C. P., Hofer, M., Simona, M., Barbieri, A., and Kipfer, R. (2007). A time seriesof environmental tracer data from deep meromictic Lake Lugano, Switzerland. Limnol. Oceanogr., 52(1):257–273.

Aeschbach-Hertig, W., Peeters, F., Beyerle, U., and Kipfer, R. (1999). Interpretation of dissolved atmosphericnoble gases in natural waters. Water Resour. Res., 35(9):2779–2792, doi:10.1029/1999WR900130.

Aeschbach-Hertig, W., Peeters, F., Beyerle, U., and Kipfer, R. (2000). Palaeotemperature reconstruction fromnoble gases in ground water taking into account equilibration with entrapped air. Nature, 405(6790):1040–1044, doi:10.1038/35016542.

Amaral, H., Berg, M., Brennwald, M. S., Hofer, M., and Kipfer, R. (2010). 13C/13C analysis of ultra-trace amountsof volatile organic contaminants in groundwater by vacuum extraction. Environ. Sci. Technol., 44:1023–1029,doi:10.1021/es901760q.

Arnell, N., Bates, B., Lang, H., Magnuson, J. J., and Mulholland, P. (1996). Hydrology and freshwater ecology.In Watson, R. T., Zinyowera, M. C., Moss, R. H., and Dokken, D. J., editors, Climate Change 1995 - Im-pacts, Adaptation and Migration of Climate Change: Scientific Technical Analyses. Contribution of WorkingGroup II to the Second Assessment Report of the Intergovernmental Panel on Climate Change, pages 325–363.Cambridge University Press, Cambridge.

Ballentine, C. J., Schoell, M., Coleman, D., and Cain, B. A. (2001). 300-myr-old magmatic CO2 in natural gasreservoirs of the west Texas Permian basin. Nature, 409(6818):327–331, doi:10.1038/35053046.

Barnes, R. O. (1979). Operation of the IPOD in situ pore water sampler. In Sibuet, J. and Ryan, W., editors,Initial reports of the Deep Sea Drilling Project, volume 47, part 2, pages 19–22. DSDP, Washington (U.S.Govt. Printing Office).

Barnes, R. O. and Bieri, R. H. (1976). Helium flux through marine sediments of the northern Pacific Ocean. EarthPlanet. Sci. Lett., 28(3):331–336, doi:10.1016/0012-821X(76)90194-1.

Berner, R. A. (1975). Diagenetic models of dissolved species in the interstitial waters of compacting sediments.Am. J. Sci., 275:88–96.

Beyerle, U., Aeschbach-Hertig, W., Imboden, D. M., Baur, H., Graf, T., and Kipfer, R. (2000). A mass spectromet-ric system for the analysis of noble gases and tritium from water samples. Environ. Sci. Technol., 34(10):2042–2050, doi:10.1021/es990840h.

Beyerle, U., Leuenberger, M., Schwander, J., and Kipfer, R. (2003a). Noble gas evidence for gas fractionation infirn. In Abstracts of the 13th Annual V.M. Goldschmidt Conference 2003, volume 67 of Geochim. Cosmochim.Acta, page A38, Kurashiki, Japan.

Beyerle, U., Purtschert, R., Aeschbach-Hertig, W., Imboden, D. M., Loosli, H. H., Wieler, R., and Kipfer,R. (1998). Climate and groundwater recharge during the last glaciation in an ice-covered region. Science,282:731–734, doi:10.1126/science.282.5389.731.

Beyerle, U., Ruedi, J., Leuenberger, M., Aeschbach-Hertig, W., Peeters, F., Kipfer, R., and Dodo, A. (2003b). Evi-dence for periods of wetter and cooler climate in the Sahel between 6 and 40 kyr BP derived from groundwater.Geophys. Res. Lett., 30(4), 1173, doi:10.1029/2002GL016310.

Bossard, P. (1981). Der Sauerstoff- und Methangehalt im Lungernsee. Diss. ETH, ETH Zurich.Bourg, I. C. and Sposito, G. (2008). Isotopic fractionation of noble gases by diffusion in liquid water:

Molecular dynamics simulations and hydrologic applications. Geochim. Cosmochim. Acta, 72:2237–2247,doi:10.1016/j.gca.2008.02.012.

16

Brennwald, M. S. (2004). The use of noble gases in lake sediment pore water as environmental tracers. Diss. ETHNr. 15629, ETH Zurich.

Brennwald, M. S., Hofer, M., Peeters, F., Aeschbach-Hertig, W., Strassmann, K., Kipfer, R., and Imboden, D. M.(2003). Analysis of dissolved noble gases in the pore water of lacustrine sediments. Limnol. Oceanogr. Meth-ods, 1:51–62.

Brennwald, M. S., Imboden, D. M., and Kipfer, R. (2005). Release of gas bubbles from lake sedi-ment traced by noble gas isotopes in the sediment pore water. Earth Planet. Sci. Lett., 235(1-2):31–44,doi:10.1016/j.epsl.2005.03.004.

Brennwald, M. S., Peeters, F., Imboden, D. M., Giralt, S., Hofer, M., Livingstone, D. M., Klump, S., Strassmann,K., and Kipfer, R. (2004). Atmospheric noble gases in lake sediment pore water as proxies for environmentalchange. Geophys. Res. Lett., 31(4), L04202, doi:10.1029/2003GL019153.

Chaduteau, C., Fourre, E., Jean-Baptiste, P., Dapoigny, A., Baumier, D., and Charlou, J. L. (2007a). A new methodfor quantitative analysis of helium isotopes in sediment pore-waters. Limmnol. Oceanogr. Meth., 5:425–432.

Chaduteau, C., Jean-Baptiste, P., Fourre, E., Charlou, J. L., and Donval, J. P. (2007b). Helium transport in sedimentpore fluids of the congo-angola margin. Geochem. Geophys. Geosyst., 10(1), doi:10.1029/2007GC001897.

Cirpka, O., Fienen, M. N., Hofer, M., Hoehn, E., Tessarini, A., Kipfer, R., and Kitanidis, P. K. (2007). Analysingbank infiltration by devonluting time series of electric conductivity. Ground Water, 45:318–328.

Craig, H. and Weiss, R. F. (1971). Dissolved gas saturation anomalies and excess helium in the ocean. EarthPlanet. Sci. Lett., 10(3):289–296, doi:10.1016/0012-821X(71)90033-1.

Saroglu, F., Emre, O., and Kuscu, I. (1992). Active Fault Map of Turkey. General Directorate of Mineral Researchand Exploration (MTA), Eskisehir Yolu, 06520, Ankara, Turkey.

Degens, E. T., Wong, H. K., and Kempe, S. (1984). A geological study of Lake Van, Eastern Turkey. GeologischeRundschau, 73(2):701–734.

Etiope, G., Zwahlen, C., Anselmetti, F., Kipfer, R., and Schubert, C. (submitted 2010). Origin and flux of a gasseep in the Northern Alps (Giswil, Switzerland). Geofluids.

Fritz, S. C. (1996). Paleolimnological records of climatic change in North America. Limnol. Oceanogr.,41(5):882–889.

Hofer, M. and Imboden, D. M. (1998). Simultaneous determination of CFC-11, CFC-12, N2 and Ar in water.Anal. Chem., 70(4):724–729.

Hofer, M., Peeters, F., Aeschbach-Hertig, W., Brennwald, M., Holocher, J., Livingstone, D. M., Romanovski, V.,and Kipfer, R. (2002). Rapid deep-water renewal in Lake Issyk-Kul (Kyrgyzstan) indicated by transient tracers.Limnol. Oceanogr., 47(4):1210–1216.

Hohmann, R., Hofer, M., Kipfer, R., Peeters, F., and Imboden, D. M. (1998). Distribution of helium and tritiumin Lake Baikal. J. Geophys. Res., 103(C6):12823–12838, doi:10.1029/97JC02218.

Holocher, J., Peeters, F., Aeschbach-Hertig, W., Hofer, M., Brennwald, M., Kinzelbach, W., and Kipfer, R. (2002).Experimental investigations on the formation of excess air in quasi-saturated porous media. Geochim. Cos-mochim. Acta, 66(23):4103–4117, doi:10.1016/S0016-7037(02)00992-4.

Holzer, L., Indutnyi, F., P, G., Munch, B., and Wegmann, M. (2004). 3D analysis of porous BaTiO3 ceramicsusing FIB nanotomography. J. Microscopy, 216:84–95.

Holzer, L., Munch, B., Wegmann, M., Flatt, R., and Gasser, P. (2006). FIB nanotomography of particulate systems– part I: particle shape and topology of interfaces. J. Am. Ceramic Soc.

Holzer, L., P, G., Kaech, A., M, W., Zingg, A., Wepf, R., and Munch, B. (2007). Cryo-FIB-nanotomography forquantitative analysis of particle structures in cement suspensions. J. Microscopy, 227:216–228.

Holzner, C. P., McGinnis, D. F., Schubert, C. J., Kipfer, R., and Imboden, D. M. (2008). Noble gas anomaliesrelated to high-intensity methane gas seeps in the Black Sea. Earth Planet. Sci. Lett., 265(3-4):396–409,doi:10.1016/j.epsl.2007.10.029.

Horseman, S., Higgo, J., Alexander, J., and Harrington, J. (1996). Water, gas and solute movement throughargillaceaous media. Technical Report CC-96/1, OECD Nuclear Energy Agency, France.

Huber, C., Beyerle, U., Leuenberger, M., Schwander, J., Kipfer, R., Spahni, R., Severinghaus, J. P., and Weiler, K.(2006). Evidence for molecular size dependent gas fractionation in firn air derived from noble gases, oxygen,and nitrogen measurements. Earth Planet. Sci. Lett., 243:61–73.

Igarashi, G., Ozima, M., Ishibashi, J., Gamo, T., Sakai, H., Nojiri, Y., and Kawai, T. (1992). Mantle heliumflux from the bottom of Lake mashu, Japan. Earth Planet. Sci. Lett., 108(1-3):11–18, doi:10.1016/0012-821X(92)90056-2.

Imboden, D. M. (1975). Interstitial transport of solutes in non-steady state accumulating and compacting sedi-ments. Earth Planet. Sci. Lett., 27(2):221–228, doi:10.1016/0012-821X(75)90033-3.

Jahne, B., Heinz, G., and Dietrich, W. (1987). Measurement of the diffusion coefficients of sparingly soluble gasesin water. J. Geophys. Res., 92(C10):10767–10776.

17

Kipfer, R., Aeschbach-Hertig, W., Baur, H., Hofer, M., Imboden, D. M., and Signer, P. (1994). Injection of mantletype helium into Lake Van (Turkey): The clue for quantifying deep water renewal. Earth Planet. Sci. Lett.,125(1-4):357–370, doi:10.1016/0012-821X(94)90226-7.

Kipfer, R., Aeschbach-Hertig, W., Peeters, F., and Stute, M. (2002). Noble gases in lakes and ground waters.In Porcelli, D., Ballentine, C., and Wieler, R., editors, Noble gases in geochemistry and cosmochemistry, vol-ume 47 of Rev. Mineral. Geochem., pages 615–700. Mineralogical Society of America, Geochemical Society.

Kleinberg, R. L., Flaum, C., Straley, C., Brewer, P. G., Malby, G. E., Peltzer, E. T., Friederich, G., and Yesinowski,J. P. (2003). Seafloor nuclear magnetic resonance assay of methane hydrate in sediment and rock. J. Geophys.Res.—Solid Earth, 108(B3).

Klump, S., Brennwald, M., and Kipfer, R. (2006a). Comment on “Noble gases and stable isotopes in a shallowaquifer in southern Michigan: Implications for noble gas paleotemperature reconstructions for cool climates”by C. M. Hall et al. Geophys. Res. Lett., 33:L24403.

Klump, S., Kipfer, R., Cirpka, O. A., Harvey, C. F., Brennwald, M. S., Ashfaque, K. N., Badruzzaman, A. B. M.,Hug, S. J., and Imboden, D. M. (2006b). Groundwater dynamics and arsenic mobilization in Bangladeshassessed using noble gases and tritium. Environ. Sci. Technol., 40(1):243–250, doi:10.1021/es051284w.

Klump, S., Tomonaga, Y., Kienzler, P., Kinzelbach, W., Baumann, T., Imboden, D., and Kipfer, R. (2007). Fieldexperiments yield new insights into gas exchange and excess air formation in natural porous media. Geochim.Cosmochim. Acta, 71:1385–1397.

Kreuzer, A. M., von Rohden, C., Friedrich, R., Chen, Z., Shi, J., Hajdas, I., Kipfer, R., and Aeschbach-Hertig, W.(2008). A record of temperature and monsoon intensity over the past 40 kyr from groundwater in the NorthChina Plain. Chem. Geol., doi:10.1016/j.chemgeo.2008.11.001.

Lan, T. F., Takahata, N., Kiyota, K., Tsutsumi, M., Kaneko, A., F, Y. T., and Sano, Y. (2009). Sampling andanalysis of dissolved noble gases in the porewater of marine sediments in northeastern Okinawa trough, Japan.In Proceedings of the DINGUE 2009 conference, Nancy, France.

Landmann, G., Reimer, A., Lemcke, G., and Kempe, S. (1996). Dating Late Glacial abrupt climate changesin the 14,570 yr long continuous varve record of Lake Van, Turkey. Palaeogeography, Palaeoclimatology,Palaeoecology, 122(1-4):107 – 118, doi:10.1016/0031-0182(95)00101-8.

Lemcke, G. and Sturm, M. (1997). δ18O and trace element measurements as proxy for the reconstruction ofclimate changes at Lake Van (Turkey): Preliminary results. In Dalfes, H. N., Kukla, G., and Weiss, H., editors,Third Millennium BC Climate Change and Old World Collapse, volume 49 of NATO ASI Series, pages 653–678. Springer, Heidelberg.

Litt, T., Krastel, S., Sturm, M., Kipfer, R., Orcen, S., Heumann, G., Franz, S. O., Ulgene, U. B., and Niessen,F. (2009). PALEOVAN, Inernational Continental Scientific Drilling Program (ICDP): site survey results andperspectives. Quaternary Sci. Rev., 28:1555–1567.

Marty, B., Dewonck, S., and France-Laord, C. (2003). Geochemical evidence for efficient aquifer isolation overgeological timeframes. Nature, 425(6953):53–58, doi:10.1038/nature01966.

Meili, M., Jonsson, P., and Carman, R. (2000). PCB levels in laminated coastal sediments of the Baltic Sea alonggradients of eutrophication revealed by stable isotopes (δ15N and δ13C). Ambio, 29(4-5):282–287.

Monecke, K. (2004). Earthquake-induced deformation structures in lake deposits – The Late Pleistocene toHolocene palaeoseismic record for Central Switzerland. Diss. ETH, ETH Zurich.

Peeters, F., Beyerle, U., Aeschbach-Hertig, W., Holocher, J., Brennwald, M. S., and Kipfer, R. (2002). Improv-ing noble gas based paleoclimate reconstruction and groundwater dating using 20Ne/22Ne ratios. Geochim.Cosmochim. Acta, 67(4):587–600, doi:10.1016/S0016-7037(02)00969-9.

Peeters, F., Finger, D., Hofer, M., Brennwald, M., Livingstone, D. M., and Kipfer, R. (2003). Deep-water renewalin Lake Issyk-Kul driven by differential cooling. Limnol. Oceanogr., 48(4):1419–1431.

Peeters, F., Kipfer, R., Achermann, D., Hofer, M., Aeschbach-Hertig, W., Beyerle, U., Imboden, D. M., Rozanski,K., and Frohlich, K. (2000). Analysis of deep-water exchange in the Caspian Sea based on environmentaltracers. Deep-Sea Res. I, 47(4):621–654, doi:10.1016/S0967-0637(99)00066-7.

Persson, J. and Jonsson, P. (2000). Historical development of laminated sediments – an approach to detect softsediment ecosystem changes in the Baltic Sea. Mar. Poll. Bull., 40(2):122–134.

Pfaffen, A. C. (2007). Seebodenuntersuchung des mittleren Lungernseebeckens. Master’s thesis, Swiss FederalInstitute of Technology Zurich (ETH), Switzerland.

Pitre, F. and Pinti, D. L. (2010). Noble gas enrichments in porewater of estuarine sediments andtheir effect on the estimation of net denitrification rates. Geochim. Cosmochim. Acta, 74:531–539,doi:10.1016/j.gca.2009.10.004.

Reimer, A., Landmann, G., and Kempe, S. (2008). Lake Van, Eastern Anatolia, hydrochemistry and history.Aquatic Geochemistry, online publication available at http://dx.doi.org/10.1007/s10498-008-9049-9.

Renkin, E. M. (1954). Filtration, diffusion, and molecular sieving through porous cellulose membranes. J. General

18

Physiol., 38:225–243.Sano, Y. and Wakita, H. (1987). Helium isotope evidence for magmatic gases in Lake Nyos, Cameroon. Geophys.

Res. Lett., 14(10):1039–1041.Scheidegger, Y., Baur, H., Brennwald, M. S., Fleitmann, D., Wieler, R., and Kipfer, R. (2010). Accurate analysis

of noble gas concentrations in small water samples and its application to fluid inclusions in stalagmites. Chem.Geol., doi:10.1016/j.chemgeo.2010.01.010.

Scheidegger, Y., Kipfer, R., Wieler, R., Badertscher, S., and Leuenberger, M. (2007). Noble gases in fluid in-clusions in speleothems. In Abstracts of the 17th Annual V.M. Goldschmidt Conference 2007, volume 71 ofGeochim. Cosmochim. Acta, page A886, Cologne, Germany.

Scheidegger, Y., Kluge, T., Kipfer, R., Aeschbach-Hertig, W., and Wieler, R. (2008). Paleotemperature recon-struction using noble gas concentrations in speleothem fluid inclusions. Pages News, 16(3).

Schubert, C. J., Durisch-Kaiser, E., Holzner, C. P., Klauser, L., Wehrli, B., Schmale, O., Greinert, J.,McGinnis, D. F., De Batist, M., and Kipfer, R. (2006a). Methanotrophic microbial communities asso-ciated with bubble plumes above gas seeps in the Black Sea. Geochem. Geophys. Geosyst., 7:Q04002,doi:10.1029/2005GC001049.

Schubert, C. J., Durisch-Kaiser, E., Klauser, L., Wehrli, B., Holzner, C. P., Kipfer, R., Schmale, O., Greinert,J., and Kuypers, M. (2006b). Recent studies on sources and sinks of methane in the Black Sea. In Neretin,L., Jørgensen, B., and Murray, J. W., editors, Past and Present Marine Water Column Anoxia, NATO ScienceSeries IV: Earth and Environmental Sciences. Kluwer Academic Publishers, Boston, Dordrecht.

Schwarzenbach, R. P., Gschwend, P. M., and Imboden, D. M. (2003). Environmental Organic Chemistry. JohnWiley and Sohns, New York, 2nd edition.

Stephenson, M., Schwartz, W. J., Melnyk, T. W., and Motycka, M. F. (1994). Measurement of advective wa-ter velocity in lake sediment using natural helium gradients. J. Hydrol., 154(1-4):63–84, doi:10.1016/0022-1694(94)90212-7.

Strassmann, K. M., Brennwald, M. S., Peeters, F., and Kipfer, R. (2005). Dissolved noble gases in porewa-ter of lacustrine sediments as palaeolimnological proxies. Geochim. Cosmochim. Acta, 69(7):1665–1674,doi:10.1016/j.gca.2004.07.037.

Stute, M., Forster, M., Frischkorn, H., Serejo, A., Clark, J. F., Schlosser, P., Broecker, W. S., and Bonani, G.(1995). Cooling of tropical Brazil (5 ◦C) during the Last Glacial Maximum. Science, 269:379–383.

Stute, M. and Schlosser, P. (2000). Atmospheric noble gases. In Cook, P. and Herczeg, A. L., editors, Environ-mental tracers in subsurface hydrology, pages 349–377. Kluwer Academic Publishers, Boston, Dordrecht.

Stute, M., Schlosser, P., Clark, J. F., and Broecker, W. S. (1992). Paleotemperatures in the Southwestern UnitedStates derived from noble gases in ground water. Science, 256:1000–1003.

Tomonaga, Y., Brennwald, and M. S., Kipfer, R. (2007a). Spatial variability in the release of terrigenic He fromthe sediments of Lake Van (Turkey). In 4th Mini Conference on Noble Gases in the Hydrosphere and in NaturalGas Reservoirs, Potsdam, Germany.

Tomonaga, Y., Brennwald, M. S., and Kipfer, R. (2007b). Spatial variability in the release of terrigenic He fromthe sediments of Lake Van (Turkey). In Abstracts of the 17th Annual V.M. Goldschmidt Conference 2007,volume 71 of Geochim. Cosmochim. Acta, Cologne, Germany.

Tomonaga, Y., Brennwald, M. S., and Kipfer, R. (submitted 2009a). An improved method for the analysis ofdissolved noble gases in the pore water of unconsolidated sediments. Limnol. Oceanogr. Methods.

Tomonaga, Y., Brennwald, M. S., and Kipfer, R. (submitted 2010a). Attenuation of noble-gas diffusion in lami-nated sediments of the Stockholm Archipelago. Earth Planet. Sci. Lett.

Tomonaga, Y., Brennwald, M. S., and Kipfer, R. (submitted 2010b). Spatial distribution of helium in the sedimentsof Lake Van (Turkey). Geochim. Cosmochim. Acta.

Tomonaga, Y., Haeckel, M., and Kipfer, R. (2009b). He characterisation near the active methane seepage off-shore the eastern edge of New Zealand. In Abstracts of the 19th Annual V.M. Goldschmidt Conference 2009,volume 73 of Geochim. Cosmochim. Acta, Davos, Switzerland.

Torgersen, T. and Clarke, W. B. (1985). Helium accumulation in groundwater, I: An evaluation of sources and thecontinental flux of crustal 4He in the Great Artesian Basin, Australia. Geochim. Cosmochim. Acta, 49(5):1211–1218, doi:10.1016/0016-7037(85)90011-0.

Torgersen, T., Top, Z., Clarke, W. B., Jenkins, W. J., and Broecker, W. (1977). A new method for physicallimnology—tritium-helium-3 ages—results for Lakes Erie, Huron and Ontario. Limnol. Oceanogr., 22(2):181–193.

Uchida, T., Dallimore, S., and Mikami, J. (2000). Occurrences of natural gas hydrates beneath the permafrostzone in Mackenzie Delta—visual and X-ray CT imagery. In Gas Hydrates: Challenges for the Future, volume912 of Annals of the New York Academy of Sciences, pages 1021–1033.

Van den Berg, E. H., Bense, V. F., and Schlager, W. (2003). Assessing textural variation in laminated sands using

19

digital image analysis of thin sections. J. Sedimentary Res., 73(1):133–143.Van Geet, M., Swennen, R., and Wevers, M. (2000). Quantitative analysis of reservoir rocks by microfocus X-ray

computerised tomography. Sedimentary Geology, 132(1-2):25–36.Weiss, R. F., Carmack, E. C., and Koropalov, V. M. (1991). Deep-water renewal and biological production in Lake

Baikal. Nature, 349(6311):665–669, doi:10.1038/349665a0.Weyhenmeyer, C. E., Burns, S. J., Waber, H. N., Aeschbach-Hertig, W., Kipfer, R., Loosli, H. H., and Matter, A.

(2000). Cool glacial temperatures and changes in moisture source recorded in Oman groundwaters. Science,287(5454):842–845, doi:10.1126/science.287.5454.842.

Wick, L., Lemcke, G., and Sturm, M. (2003). Evidence for Lateglacial and Holocene climatic change and hu-man impact in eastern Anatolia: high-resolution pollen, charcoal, isotopic and geochemical records from thelaminated sediments of Lake Van, Turkey. The Holocene, 13(5):665–675, doi:10.1191/0959683603hl653rp.

Winckler, G., Aeschbach-Hertig, W., Holocher, J., Kipfer, R., Levin, I., Poss, C., Rehder, G., Suess, E., andSchlosser, P. (2002). Noble gases and radiocarbon in natural gas hydrates. Geophys. Res. Lett., 29(10), 1735,doi:10.1029/2001GL014013.

Winckler, G., Aeschbach-Hertig, W., Kipfer, R., Botz, R., Rubel, A. P., Bayer, R., and Stoffers, P. (2001). Con-straints on origin and evolution of Red Sea brines from helium and argon isotopes. Earth Planet. Sci. Lett.,184(3-4):671–683, doi:10.1016/S0012-821X(00)00345-9.

Winckler, G., Kipfer, R., Aeschbach-Hertig, W., Botz, R., Schmidt, M., Schuler, S., and Bayer, R. (2000). Sub seafloor boiling of Red Sea brines: New indication from noble gas data. Geochim. Cosmochim. Acta, 64(9):1567–1575, doi:10.1016/S0016-7037(99)00441-X.

Zhu, C. and Kipfer, R. (2010). Noble gas signatures of high recharge pulses and migrating jet stream in the latePleistocene over Black Mesa, Arizona, USA. Geology, 38:83–86, doi:10.1130/G30369.1.

20