Re-examination of the recent history of meromictic Waldsea ...
Lake Kivu A Multi-Methodological Approach Tackeling ... · Lake Kivu is an meromictic East African...
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Lake Kivu – A Multi-Methodological Approach Tackeling Questions on Age, Dynamics and Gas Concentrations Maximilian Schmidt 1,2 ,David Wachs 2 , Zhongyi Feng 1 , Arne Kersting 2 , Lisa Ringena 1 , Julian Robertz 1 , Fabian Bärenbold 4,5 , Bertram Böhrer 6 , Werner Aeschbach 2,3 , Markus K. Oberthaler 1 1: Kirchhoff Institut für Physik, Heidelberg 2: Institut für Umweltphysik, Heidelberg 3: Heidelberg Center for the Environment 4: EAWAG Kastanienbaum/Luzern 5: Eidgenössische Technische Hochschule, Zürich 6: Umweltforschungszentrum, Magdeburg References: 1) Ebser et al., 39Ar dating with small samples provides new key constraints on ocean ventilation. Nature Communications (2018)9:5046 2) Feng et al., Dating glacier ice of the last millennium by quantum technology, PNAS April 30, 2019 116 (18) 3) Schmid et al., Weak mixing in Lake Kivu: New Insights indicate increasing risk of uncontrolled gas eruption,Geochem. Geophys. Geosyst., 6, Q07009 4) Bärenbold et al., Updated dissolved gas concentrations in Lake Kivu from an intercomparison project, in review 2019 Limnology and Oceanography Lake Kivu Residence Times ArTTA relies on the quantum optical method of laser cooling commonly used in atomic physics. Due to an isotopic shift and nuclear spin effects the resonance frequency of 39 Ar is shifted about 0,001 nm in respect to other Ar isotopes. The necessity of the consecutive scattering of > 10 6 resonant photons for laser cooling and trapping leads to the distinguishability from 39Ar against its huge background by utilising single atom detection. The detection rate of 39 Ar atoms and comparison to artificial reference samples then leads to the relative 39 Ar content and thus the tracer age. Setup of our current ArTTA machine. A liquid nitrogen cooled plasma discharge source provides meta stable 39Ar necessary for optical cooling. A Collimator and a 2D magneto optical trap (MOT) collimate and narrow the atom beam, an increasing B- field Zeeman-slower slows the atoms down, before they are trapped and detected in a 3D MOT. Our most resent campaigns you can find here [1] and here [2] Lake Kivu is an meromictic East African Rift Lake between Rwanda and the Democratic Republic of Congo with a maximum depth of 485m and a mixed layer of 60 – 80 m. Lower layers are very stable and deep layers contain extremely high amounts of methane and carbon dioxide. The large storage of methane is aimed to be used as an energy ressource but potential limnic eruptions may be a fatal threat to residents [3]. 39Ar dating with ArTTA offers the possibility to date the different layers and might give valuable input to flow model calculations. In spring 2018 and in summer 2019 we were able to gather gas and water samples from lake Kivu and present now the first 39Ar dating of lake water using ArTTA. googlemaps This project is in cooperation with M. Schmid and F. Bärenbold from EAWAG Aquatic Research Institute, Luzern Argon Trap Trace Analysis – ArTTA 39 Ar is a cosmogenic radioisotope with a halflife of 269 years. Its chemical inertness and quasi constant input function makes it a very powerful dating tracer covering ages in between 50 and 1000 years corresponding to timescales important in hydrological systems. 39 Ar has long been restricted to groundwater studies due to its long lifetime ( 1/2 = 269 ) and its extremly low abundance of 39 Ar/Ar = 8 ∙ 10 −16 requiring sample sizes about 1000 L for low level counting. ArTTA makes the transition from decay counting towards direct atom counting and thus reducing required sample sizes down to 0,5 ml STP pure Argon, which corresponds to about 1L of water or 5 – 10 kg of glacier ice. Lake Kivu on the border between Rwanda and DRC. The red cross indicates the sampling location. Source: Schmid et al. 2005 [3] 357±40 years 94±31 years 0±40 years Single Atom detection by APD and CCD-Camera Lake Kivu Sample Preparation and Handling For the preparation of the water and gas samples from lake Kivu we use a slightly adapted preparation line to isolate Argon: The principle of the preparation lies in the chemical inertness of argon, passing the gas through two hot and cold titanium-sponge getters, where all reactive gases are bound and the noble gases remain. In addition to this standard procedure we need to handle high amounts of CO 2 , CH 4 and H 2 S. For this purpose we are reacting H 2 S with pure copper, binding it via the production of coppersulfite, we guide the gas through hot CuO to react CH 4 to CO 2 and H 2 O and trap CO 2 in cold traps resublimating it to dry ice. Consequent treatment of the remaining gas mixture leads to Argon purities around 99%, perfectly suitable for ArTTA. Our typical standard sample sizes range from 0,5 – 20 L of water or 5 – 10 kg of ice achieving argon volumes of typically 0,5 – 10 ml STP Investigating a quick (and dirty?) Method to Measure Partial Dissolved Gas Pressures Modified Pro Oceanus Mini TDGP Probe with Sea & Sun CTD Probe CH 4 CO 2 Our measurement device is a modified total dissolved gas sensor by Pro Oceanus. It has been modified to be capable of measuring the very high total dissolved gas pressures in Lake Kivu, which are lying far beyond normally occurring values. During a measurement the dissolved gases (here mainly CO 2 and CH 4 ) are diffusing through a semi-permeable membrane, through a metal sinter mesh into a total pressure gauge, which is independent in gas composition. = 1 ∗ 1∓ − − 0 1 + 2 ∗ 1∓ − − 0 2 This project is in cooperation with B. Böhrer from Umweltforschungszentrum UFZ Magdeburg Typical data from a pressure measurement run. The probe is submerged into the lake and halts at specific depths in order to wait for the pressure to equilibrate. This equilibration time now is the key to our approach. Assuming different migration times for different gas species one can expect for the measured total pressure to develop over time like a sum of bounded exponential growth functions, one for each gas species weighted by thei respective partial pressure and their specific migration time constants. Our first results of investigating this method to measure the partial pressure of gases using only a total dissolved gases pressure probe are showing us, that this method can offer the possibility for a very easy measurement routine for an otherwise absolutely non trivial problem. The very high gas pressures occuring in this lake are causing immense problems e.g. for gathering samples and finding appropriate equipment and thus are demanding highly educated scientist and strong economical possibilities. Regarding Lake Kivu‘s location on the border between Rwanda and the Democratic Republic of Kongo one sees the need for a cheap and easy to use alternative for the governments programs monitoring the lake‘s gases for economic and risk management purposes. If we might be able to refine this method improving reliability and accuracy it could bear the possibility to give these countries a quick and easy - and hopefully not so dirty anymore - tool. Resulting partial pressures in comparison to data by F. Bärenbold and B. Böhrer [4] gathered by approved methodologies. One can observe, that our obtained partial pressures are in good correspondence although showing some fluctuations especially in the range of low pressures. The data shown are reduced to the steps, where the pressure develops like in the described model. Obvious casualties (e.g. as marked with red circles) can‘t be explained by now, showing the need of further investigations. Natural Water or Gas Sample N 2 O 2 H 2 CO 2 CH 4 H 2 S Ar Cool Trap at -120°C -H 2 O - CO 2 Cool Trap at -120°C -H 2 O - CO 2 Copper Wool -H 2 S Hot CuO Furnace at 800 – 1000 °C CH 4 +CuO -> CO 2 + H2O Hot Ti Furnace at 800 °C -O 2 , N 2 , reactive Gases Cold Ti at Room Temperature -H 2 Cool act. Charcoal Trap at -196°C to trap Ar
Transcript of Lake Kivu A Multi-Methodological Approach Tackeling ... · Lake Kivu is an meromictic East African...
Lake Kivu – A Multi-Methodological ApproachTackeling Questions on Age, Dynamics and Gas Concentrations
Maximilian Schmidt1,2,David Wachs2, Zhongyi Feng1, Arne Kersting2, Lisa Ringena1, Julian Robertz1,Fabian Bärenbold4,5, Bertram Böhrer6, Werner Aeschbach2,3, Markus K. Oberthaler1
1: Kirchhoff Institut für Physik, Heidelberg 2: Institut für Umweltphysik, Heidelberg 3: Heidelberg Center for the Environment4: EAWAG Kastanienbaum/Luzern 5: Eidgenössische Technische Hochschule, Zürich 6: Umweltforschungszentrum, Magdeburg
References:1) Ebser et al., 39Ar dating with small samples provides new key constraints on ocean ventilation. Nature
Communications (2018)9:50462) Feng et al., Dating glacier ice of the last millennium by quantum technology, PNAS April 30, 2019 116 (18)3) Schmid et al., Weak mixing in Lake Kivu: New Insights indicate increasing risk of uncontrolled gas
eruption,Geochem. Geophys. Geosyst., 6, Q070094) Bärenbold et al., Updated dissolved gas concentrations in Lake Kivu from an intercomparison project, in review
2019 Limnology and Oceanography
Lake Kivu Residence Times
ArTTA relies on the quantum optical method of laser cooling commonly used in atomic physics. Due to an isotopic shift and nuclear spin effects the resonance frequency of 39Ar is shifted about 0,001 nm in respect to other Ar isotopes. The necessity of the consecutive scattering of > 106 resonant photons for laser cooling and trapping leads to the distinguishability from 39Ar against its huge background by utilising single atom detection. The detection rate of 39Ar atoms and comparison to artificial reference samples then leads to the relative 39Ar content and thus the tracer age.
Setup of our current ArTTA machine. A liquid nitrogen cooled plasma discharge source provides meta stable 39Ar necessary for optical cooling. A Collimator and a 2D magneto optical trap (MOT) collimate and narrow the atom beam, an increasing B-field Zeeman-slower slows the atoms down, before they are trapped and detected in a 3D MOT.Our most resent campaigns you can find here [1] and here [2]
Lake Kivu is an meromictic East African Rift Lake between Rwanda and the Democratic Republic of Congo with a maximum depth of 485m and a mixed layer of 60 – 80 m. Lower layers are very stable and deep layers contain extremely high amounts of methane and carbon dioxide. The large storage of methane is aimed to be used as an energy ressource but potential limnic eruptions may be a fatal threat to residents [3].39Ar dating with ArTTA offers the possibility to date the different layers and might give valuable input to flow model calculations.In spring 2018 and in summer 2019 we were able to gather gas and water samples from lake Kivu and present now the first 39Ar dating of lake water using ArTTA.
googlemaps
This project is in cooperation with M. Schmid and F. Bärenbold from EAWAG Aquatic Research Institute, Luzern
Argon Trap Trace Analysis – ArTTA39Ar is a cosmogenic radioisotope with a halflife of 269 years. Its chemical inertness and quasi constant input function makes it a very powerful dating tracer covering ages in between 50 and 1000 years corresponding to timescales important in hydrological systems. 39Ar has long been restricted to groundwater studies due to its long lifetime (𝜏1/2 = 269 𝑦) and its extremly low abundance
of 39Ar/Ar = 8 ∙ 10−16 requiring sample sizes about 1000 L for low level counting. ArTTA makes the transition from decay counting towards direct atom counting and thus reducing required sample sizes down to 0,5 mlSTP pure Argon, which corresponds to about 1L of water or 5 – 10 kg of glacier ice.
Lake Kivu on the border between Rwanda and DRC. The red cross indicates the sampling location.
Source: Schmid et al. 2005 [3]
357±40 years
94 ±31 years
0±40 years
Single Atom detection by APD and CCD-Camera
Lake Kivu Sample Preparation and Handling
For the preparation of the water and gas samples from lake Kivu we use a slightly adapted preparation line to isolate Argon: The principle of the preparation lies in the chemical inertness of argon, passing the gas through two hot and cold titanium-sponge getters, where all reactive gases are bound and the noble gases remain. In addition to this standard procedure we need to handle high amounts of CO2, CH4 and H2S. For this purpose we are reacting H2S with pure copper, binding it via the production of coppersulfite, we guide the gas through hot CuO to react CH4 to CO2 and H2O and trap CO2 in cold traps resublimating it to dry ice. Consequent treatment of the remaining gas mixture leads to Argon purities around 99%, perfectly suitable for ArTTA. Our typical standard sample sizes range from 0,5 – 20 L of water or 5 – 10 kg of ice achieving argon volumes of typically 0,5 – 10 mlSTP
Investigating a quick (and dirty?) Method to Measure PartialDissolved Gas Pressures
Modified Pro Oceanus Mini TDGP Probe with Sea & Sun CTD Probe
CH4
CO2
Our measurement device is a modified total dissolved gas sensor by Pro Oceanus. It has been modified to be capable of measuring the very high total dissolved gas pressures in Lake Kivu, which are lying far beyond normally occurring values. During a measurement the dissolved gases (here mainly CO2 and CH4) are diffusing through a semi-permeable membrane, through a metal sinter mesh into a total pressure gauge, which is independent in gas composition.
𝑃 = 𝑃1 ∗ 1 ∓ 𝑒−𝑡 −𝑡0𝜏1
+ 𝑃2 ∗ 1 ∓ 𝑒−𝑡 −𝑡0𝜏2
This project is in cooperation with B. Böhrer from Umweltforschungszentrum UFZ Magdeburg
Typical data from a pressure measurement run. The probe is submerged into the lake and halts at specific depths in order to wait for the pressure to equilibrate. This equilibration time now is the key to our approach. Assuming different migration times for different gas species one can expect for the measured total pressure to develop over time like a sum of bounded exponential growth functions, one for each gas species weighted by thei respective partial pressure and their specific migration time constants.
Our first results of investigating this method to measure the partial pressure of gases using only a total dissolved gases pressure probe are showing us, that this method can offer the possibility for a very easy measurement routine for an otherwise absolutely non trivial problem. The very high gas pressures occuring in this lake are causing immense problems e.g. for gathering samples and finding appropriate equipment and thus are demanding highly educated scientist and strong economical possibilities. Regarding Lake Kivu‘s location on the border between Rwanda and the Democratic Republic of Kongo one sees the need for a cheap and easy to use alternative for the governments programs monitoring the lake‘s gases for economic and risk management purposes. If we might be able to refine this method improving reliability and accuracy it could bear the possibility to give these countries a quick and easy - and hopefully not so dirty anymore - tool.
Resulting partial pressures in comparison to data by F. Bärenbold and B. Böhrer [4] gathered by approved methodologies. One can observe, that our obtained partial pressures are in good correspondence although showing some fluctuations especially in the range of low pressures. The data shown are reduced to the steps, where the pressure develops like in the described model. Obvious casualties (e.g. as marked with red circles) can‘t be explained by now, showing the need of further investigations.
Natural Wateror Gas SampleN2 O2 H2 CO2
CH4 H2S Ar
Cool Trapat -120°C- H2O- CO2
Cool Trapat -120°C- H2O- CO2
Copper Wool- H2S
Hot CuO Furnaceat 800 – 1000 °CCH4 +CuO -> CO2 + H2O
Hot Ti Furnaceat 800 °C- O2, N2, reactive Gases
Cold Tiat Room Temperature- H2
Cool act. Charcoal Trapat -196°Cto trap Ar
