Spatial distribution and flux of terrigenic He dissolved in the sediment pore water of Lake Van (Turkey)
Introduction
The flux of He from the upper mantle into the oceans was estimated by Craig et al. (1975) from surpluses (with respect to the expected atmospheric equilibrium concentrations) determined on the East Pacific Rise (see also Farley et al., 1995, Bianchi et al., 2010, Lan et al., 2010). However, until now only very few direct measurements have been available to assess He release from the continents, which in theory are responsible for most of the terrestrial He release (Mamyrin and Tolstikhin, 1984, Ballentine et al., 2002).
Various studies during the past few decades have tried to quantify continental He emission based on noble-gas and He concentrations (i) in ground waters (Andrews et al., 1985, Torgersen and Clarke, 1985, Martel et al., 1989, Stute et al., 1992, Marty et al., 1993, Pinti and Marty, 1995, Tolstikhin et al., 1996, Pinti et al., 1997, Castro et al., 1998a, Castro et al., 1998b, Castro et al., 2005, Ma et al., 2005); (ii) in crater lakes (Sano et al., 1990, Collier, 1991, Igarashi et al., 1992, Kipfer et al., 1994, Aeschbach-Hertig et al., 1996b, Aeschbach-Hertig et al., 1999, Aeschbach-Hertig et al., 2002) and other lakes (Aeschbach-Hertig et al., 1996a, Hohmann et al., 1998, Peeters et al., 2000, Kipfer et al., 2002); and (iii) in gas wells (Sano et al., 1986). A major constraint in calculating the He fluxes is given by the average renewal rates of lake bottom water and groundwater, and by the residence time of gas in gas wells. These turn out to be notoriously difficult to determine. Moreover, spatial and temporal heterogeneity in the He emission severely limits its determination. As a result, data-based studies involving the direct determination of He emission on a local scale remain scarce.
Although the earth’s global He budget is understood conceptually, a mechanistic understanding of local-scale continental He emission is still lacking. Various observations indicate that He emission is focused on particular geological structures within the crust, and is related to tectonic activity in extension zones, fault zones, calderas, and volcanoes (Mamyrin and Tolstikhin, 1984, Oxburgh et al., 1986, Oxburgh and O’Nions, 1987, Ballentine et al., 2002, Kennedy et al., 1997, Kennedy and van Soest, 2007). These observations show that the release of He from the continents into the atmosphere is highly variable in space and time. However, the fast mixing processes that occur both in air and in water commonly prevent the atmosphere and hydrosphere from recording and tracking the specific points of terrestrial He release.
Pore waters of lacustrine sediments represent an ideal geochemical environment for assessing local He emission, thus, in principle, allowing fluid transport in the uppermost part of the continental crust to be studied. The transport of He within the sediment column can be described by advection and molecular diffusion, where He migrates through the connected pore space of the sediment (Berner, 1975, Imboden, 1975, Strassmann et al., 2005). As a porous medium, lacustrine sediments suppress the strong horizontal and vertical transport (e.g., by turbulent diffusion) which dominates in the overlying bulk water (Lerman et al., 1995, Schwarzenbach et al., 2003). In contrast to the bulk water, pore water in lacustrine sediments are therefore in principle able to record and store the spatial signals of the local He emission. From this conceptual point of view, pore waters in lake sediments are very suitable for analyzing the variability of the He flux on spatial scales smaller than the diameter of the lake being studied.
In this work we present and concentration data measured in the pore water of the sediments of Lake Van (Turkey) between 2004 and 2007.
The lake is known to accumulate terrigenic He from a depleted mantle source (Kipfer et al., 1994, Kaden et al., 2010). The release of He into Lake Van seems to be under the control of certain geological and tectonic features, such as fault lines and volcanic activity (Degens et al., 1984, Şarogˇlu et al., 1992).
In order to quantify the terrestrial He emission, we determined the solute transport within the sediments (e.g., the effective diffusivity in the pore space) by analyzing the vertical distribution of in the sediment column (see Strassmann et al., 2005). Based on the vertical concentration gradients of He within the sediment column and the calculated effective diffusivity, local He fluxes were estimated at the geographical positions of the cores within the lake basin.
For the first time, direct measurements of fluxes of terrigenic He covering a region in area are reported. These measurements allow the mapping of local He emission within a lake environment, which we discuss within the context of the surrounding geology and the available seismic profiles. This provides insight into the fluid transport within the sediment pore space and into the formation of the lake basin. The He fluxes determined also provide further evidence for the heterogeneity of He emission from the solid earth.
Section snippets
Study site
Lake Van, the largest soda lake on earth, is located in a tectonically active region of eastern Anatolia (Turkey) at ∼1650 m a.s.l. (Fig. 1). This region is situated in the vicinity of the triple junction of the Eurasian, Afro-Arabian and Persian plates. Many faults, probably also extending from the shores into the lake basin, are described in the Fault Map of Turkey (Şarogˇlu et al., 1992) and reproduced in Fig. 1. The geology of the northern part of the basin is dominated by volcanic rocks
Methods
The sampling and noble-gas analysis methods employed are described in detail by Brennwald et al. (2003). The cores were taken with an Uwitec gravity corer (http://www.uwitec.at). After recovery on board, each core was squeezed and the bulk sediment was transferred into small copper tubes. Each tube was sealed air-tight on both ends with two special clamps to avoid air contamination in the sample.
Noble-gas concentration determinations and isotopic analyses were carried out in the Noble Gas
He concentration profiles
The dissolved He concentrations determined in the pore-water of all cores (see Table 1 for the details related to the sampling stations) are listed in Table 2 and plotted in Fig. 2. From the 140 samples collected, six were affected by major experimental problems (air contamination or partial extrusion of the sample during gas extraction). The data relating to these samples are not reported.
Eight samples from two cores taken in the Erciş basin (cores and ) appear to be strongly degassed, as
Conclusions and outlook
The observed maximum terrestrial He flux of correlates well with the seismic features (e.g., Litt et al., 2009) along which terrigenic fluids may preferentially migrate in the sediments of Lake Van. Even at such “hot-spots”, however, the flux is from seven to sixteen times lower than the expected continental flux (O’Nions and Oxburgh, 1983). The flux estimates from the He data collected in the water column ( and , Section 4.4) indicate
Acknowledgments.
We would like to thank Prof. Dr. Bernard Marty, Dr. Igor N. Tolstikhin, and two anonymous reviewers for their valuable comments on the manuscript. We thank Aysegül Feray Meydan, Ismet Meydan, Münip Kanan, Mete Orhan, Mehmet Sahin, Dr. Mustafa Karabiyikoğlu, Prof. Dr. Sefer örçen and the staff of Yüzüncü Yıl University in Van for their invaluable support during the Lake Van expeditions over the last few years. Thanks are also due to Frank Peeters, Heike Kaden and Andrea Huber of the University
References (69)
- et al.
Accumulation of mantle gases in a permanently stratified volcanic lake (Lac Pavin, France)
Geochim. Cosmochim. Acta.
(1999) - et al.
Quantification of gas fluxes from the subcontinental mantle: The example of Laacher See, a maar lake in Germany
Geochim. Cosmochim. Acta
(1996) - et al.
A radiochemical, hydrochemical and dissolved gas study of groundwaters in the Molasse basin of Upper Austria
Earth Planet. Sci. Lett.
(1985) - et al.
Infiltration of river water to a shallow aquifer investigated with , noble gases and CFCs
J. Hydrol.
(1999) - et al.
Low helium flux from the mantle inferred from simulations of oceanic helium isotope data
Earth Planet. Sci. Lett.
(2010) - et al.
2-D numerical simulations of groundwater flow, heat transfer and transport implications for the He terrestrial budget and the mantle heliumheat imbalance
Earth Planet. Sci. Lett.
(2005) - et al.
Excess in deep water on the East Pacific Rise
Earth Planet. Sci. Lett.
(1975) - et al.
Mantle helium flux from the bottom of Lake Mashu, Japan
Earth Planet. Sci. Lett.
(1992) Interstitial transport of solutes in non-steady state accumulating and compacting sediments
Earth Planet. Sci. Lett.
(1975)- et al.
Injection of mantle type helium into Lake Van (Turkey): the clue for quantifying deep water renewal
Earth Planet. Sci. Lett.
(1994)
Evaluating Earth degassing in subduction zones by measuring helium fluxes from the ocean floor
Earth Planet. Sci. Lett.
Dating late glacial abrupt climate changes in the 14,570 year long continuous varve record of Lake Van, Turkey
Palaeogeogr. Palaeocl.
PALEOVAN, International Continental Scientific Drilling Program (ICDP): site survey results and perspectives
Quaternary Sci. Rev.
Analysis of deep-water exchange in the Caspian Sea based on environmental tracers
Deep-Sea Res. I
Noble gases in crude oils from the Paris Basin, France: implications for the origin of fluids and constraints on oil–water–gas interactions
Geochim. Cosmochim. Acta
Helium and carbon fluxes in Lake Nyos, Cameroon: constraint on next gas burst
Earth Planet. Sci. Lett.
Water transport through Lake Kinneret sediments traced by tritium
Earth Planet. Sci. Lett.
Dissolved noble gases in porewater of lacustrine sediments as palaeolimnological proxies
Geochim. Cosmochim. Acta
Helium and argon isotopes in rocks, minerals, and related groundwaters: a case study in northern Switzerland
Geochim. Cosmochim. Acta
Helium accumulation in groundwater, I: an evaluation of sources and the continental flux of crustal in the Great Artesian Basin, Australia
Geochim. Cosmochim. Acta
Preparation and calibration of the 1978 National Bureau of Standards tritiated-water standards
Int. J. Appl. Radiat. Isot.
Mantle helium in Lake Van and Lake Nemrut, Eastern Turkey
Terra Abstracts
The physical structure and dynamics of a deep, meromictic crater lake (Lac Pavin, France)
Hydrobiologia
Density-driven exchange between the basins of Lake Lucerne (Switzerland) traced with the 3H–3He method
Limnol. Oceanogr.
Performance and blank components of a mass spectrometric system for routine measurement of helium isotopes and tritium by the ingrowth method. Sitzungsberichte der Heidelberger Akademie der Wissenschaften Mathemathisch-naturwissenschaftliche Klasse 5
Diagenetic models of dissolved species in the interstitial waters of compacting sediments
Am. J. Sci.
A mass spectrometric system for the analysis of noble gases and tritium from water samples
Environ. Sci. Technol.
Analysis of dissolved noble gases in the pore water of lacustrine sediments
Limnol. Oceanogr. Methods
Atmospheric noble gases in lake sediment pore water as proxies for environmental change
Geophys. Res. Lett.
Noble gases as natural tracers of water circulation in the Paris Basin, 2. Calibration of a groundwater flow model using noble gas isotope data
Water Resour. Res.
Noble gases as natural tracers of water circulation in the Paris Basin, 1. Measurements and discussion of their origin and mechanisms of vertical transport in the basin
Water Resour. Res.
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