Supporting Information Novel use of cavity ring-down spectroscopy to ...
Supporting Information Novel use of cavity ring-down spectroscopy to investigate aquatic carbon cycling from microbial to ecosystem scales Damien T Maher1, Isaac R Santos1, Jasper R F W Leuven2 Joanne M. Oakes1, Dirk V Erler1, Matheus C Carvalho and Bradley D Eyre1
1
Centre for Coastal Biogeochemistry, School of Environment, Science and Engineering, Southern
Cross University, Lismore, NSW, 2480, Australia 2
Faculty of Geosciences, Utrecht University, Utrecht, The Netherlands
* Corresponding author: Email: [email protected] Phone: +61 2 66203577 Fax: +61 2 66212669
The supporting information contains 7 pages, 2 Figures and 1 Table
S1
Experimental Section Instrumentation A commercially available CRDS (G2201-I Picarro Inc, Santa Clara, CA. USA) was used to determine quasi-continuous concentrations of dissolved 12CO2, 13CO2, 12CH4 and 13CH4 in a number of experimental setups. Gas is pumped through the instrument using a vacuum diaphragm pump at a flow rate of ~ 30 sccm. The gas flows through a pressure (0.1947 ± 0.0002 atm) and temperature (40 ± 0.005°C) controlled high finesse cavity, which contains three highly reflective mirrors. Light is emitted from a laser source at a specific wavelength and once the light within the cavity reaches a threshold value (measured with a photodetector), the laser is switched off. Light is circulated around the cavity reflected by the mirrors, giving an effective pathlength of ~ 20 km. Light within the cavity leaks through the mirrors and is absorbed by the target molecules, and concentration of the target gases is determined by the decay time (ring-down). To check for instrument accuracy and drift, four calibration gases (two for CO2 and two for CH4) were run prior to, during, and following each of the experiments. CO2 standards had a concentration of 306 ppm (δ13C-CO2 = -14.4‰) and 2017ppm (δ13C-CO2 = -17.1‰) with the δ13C values referenced to IRMS δ13C-CO2 which is calibrated against NIST certified standards. CH4 standards had a concentration of 3 ppm (δ13C-CH4 = -45.9‰) and 200 ppm (δ13C-CH4 = -40.1‰). The δ13C-CH4 values of the standards were obtained by running the standards through a factory calibrated CRDS, and they were later referenced against certified standards obtained from Isometric Instruments (Tiso 1, δ13C-CH4 = -38.3 ± 0.2‰ and Liso1, δ13C-CH4 = -66.5 ± 0.2‰). Accuracy of CO2 concentrations was better than 1 ppm and δ13CCO2 accuracy for a 5 min average was better than 0.5‰. CH4 concentration accuracy was
S2
better than 80 ppb. δ13C-CH4 accuracy for a 5 min averaging interval was better than 0.6‰ for both Tiso1 and Liso1 standards. Experimental Design To extract the dissolved CO2 and CH4 we used 2 different gas equilibration devices (GED). The first was a shower-head equilibrator and the second a Liqui-Cel membrane contactor (see 1
for a further description of these systems). A second shower-head equilibrator with the
headspace open to the atmosphere was connected to the vent of the first to ensure no pressure differential between the atmosphere and the equilibrator. The gas stream from each GED was dried through a Drierite column, passed through the CRDS and returned to the GED (i.e. a closed air loop). The shower head equilibrator was used for the survey (experiment 1) and open water time series (experiment 2) (Figure S1A), while the Liqui-Cel membrane contactor was used for the chamber experiment (experiment 3) where a closed water and air loop was necessary (Figure S1B). The showerhead was chosen over the Liqui-Cel GED for the survey and time series experiments to minimize any potential blockage or microbially mediated CO2 production within the GED1. A laboratory experiment showed no differences in concentrations or δ13C values measured using the two GED systems. The pulse chase experiment measured CO2 concentrations in a headspace of air within a sealed core via a closed gas loop flowing through the CRDS (experiment 4) (Figure S1C).
Calculation of δ13C-DIC from δ13C-CO2 To compare the δ13C-CO2 values from the CRDS to in situ δ13C-DIC measured by IRMS, we used the fractionation factors reported by 2 ε(DIC-CO2 (g)) ‰ = 10.53 -0.107x T + 0.014 x fCO3 x T S3
where T is the temperature (°C) and fCO3 is the carbonate fraction (CO3-2/DIC). The carbonate fraction was calculated from salinity, temperature, pCO2 and pH using CO2SYS3. Results There was excellent agreement between CO2 concentrations measured with CRDS and NDIR (Figure S2) and δ13C-DIC-Calculated by CRDS and measured with IRMS (Table S1). Table S1 δ13C-DIC calculated and δ13C-DIC Measured in the survey and time series experiments Experiment Survey Survey Survey Survey Survey Survey Survey Survey Survey Survey Survey Survey Survey Survey Survey Survey Survey Survey Survey Survey Survey Survey Survey Survey Survey Survey Survey Survey Time Series Time Series
δ13C-DIC-Calculated (CRDS) 0.1611 0.7084 0.5149 -0.5189 -2.3106 -6.0508 -10.2707 -1.0295 -1.6941 -4.2951 -7.9654 -10.9887 -12.2250 -10.4315 0.3891 0.6064 -1.2964 -3.4805 -6.0255 -10.2368 -11.5798 -2.2965 -3.1756 -5.1963 -6.6013 -10.7930 -11.9565 -10.4321 -10.7930 -11.9565
δ13C-DIC-Measured (IRMS) 0.8500 0.7690 -0.1180 -1.1050 -2.4960 -3.0910 -8.0650 -0.7190 -1.9610 -3.7540 -8.0930 -10.3880 -10.6840 -8.2760 0.3610 -0.7930 -1.2760 -3.1470 -5.8780 -9.7120 -11.1490 -1.1340 -1.9490 -3.8940 -7.8650 -10.3620 -11.4990 -9.4300 -10.3620 -11.4990 S4
Time Series Time Series Time Series Time Series Time Series Time Series Time Series Time Series Time Series Time Series Time Series Time Series Time Series Time Series Time Series Time Series Time Series Time Series Time Series Time Series Time Series Time Series Time Series Time Series Time Series Time Series Time Series
-0.4394 -0.3558 -0.7257 -1.4568 -2.3216 -2.0749 -1.3515 -0.1321 0.6539 0.2109 0.2403 0.3261 3.8967e-3 -0.5157 -1.6793 -4.5521 -10.1000 -9.6000 -3.7044 -3.1180 0.9581 1.2090 0.2903 0.2181 -0.2574 -0.8722 -0.8722
0.5730 0.4150 -0.2750 -0.8530 -2.1550 -2.0060 -1.3820 -0.5170 0.4590 0.4140 0.3070 0.1360 -0.2080 -0.5240 -1.4730 -3.3320 -10.6590 -10.2230 -4.2330 -4.3480 -0.9200 -0.1360 -0.2840 -0.3670 -0.6820 -1.6670 -1.6670
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Figure S1 Experimental setup for; A. the survey and time series, B. chamber, and C. pulse-chase experiment.
S6
Figure S2 Linear regression of CRDS calculated δ13C-C-DIC versus IRMS measured δ13C-C-DIC References 1.
Santos, I. R.; Maher, D. T.; Eyre, B. D., Coupling automated radon and carbon
dioxide measurements in coastal waters. Environ. Sci. Technol. 2012, 46, 76857691:10.1021/es301961b. 2.
Zhang, J.; Quay, P. D.; Wilbur, D. O., Carbon isotope fractionation during gas-water
exchange and dissolution of CO2. Geochim. Cosmochim. Acta 1995, 59, 107-114 3.
Lewis, E.; Wallace, D. W. R. Program developed for CO2 system calculations.;
ORNL/CDIAC-105; Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, US Department of Energy.: Oak Ridge, Tennessee, 1998.
S7
1
Centre for Coastal Biogeochemistry, School of Environment, Science and Engineering, Southern
Cross University, Lismore, NSW, 2480, Australia 2
Faculty of Geosciences, Utrecht University, Utrecht, The Netherlands
* Corresponding author: Email: [email protected] Phone: +61 2 66203577 Fax: +61 2 66212669
The supporting information contains 7 pages, 2 Figures and 1 Table
S1
Experimental Section Instrumentation A commercially available CRDS (G2201-I Picarro Inc, Santa Clara, CA. USA) was used to determine quasi-continuous concentrations of dissolved 12CO2, 13CO2, 12CH4 and 13CH4 in a number of experimental setups. Gas is pumped through the instrument using a vacuum diaphragm pump at a flow rate of ~ 30 sccm. The gas flows through a pressure (0.1947 ± 0.0002 atm) and temperature (40 ± 0.005°C) controlled high finesse cavity, which contains three highly reflective mirrors. Light is emitted from a laser source at a specific wavelength and once the light within the cavity reaches a threshold value (measured with a photodetector), the laser is switched off. Light is circulated around the cavity reflected by the mirrors, giving an effective pathlength of ~ 20 km. Light within the cavity leaks through the mirrors and is absorbed by the target molecules, and concentration of the target gases is determined by the decay time (ring-down). To check for instrument accuracy and drift, four calibration gases (two for CO2 and two for CH4) were run prior to, during, and following each of the experiments. CO2 standards had a concentration of 306 ppm (δ13C-CO2 = -14.4‰) and 2017ppm (δ13C-CO2 = -17.1‰) with the δ13C values referenced to IRMS δ13C-CO2 which is calibrated against NIST certified standards. CH4 standards had a concentration of 3 ppm (δ13C-CH4 = -45.9‰) and 200 ppm (δ13C-CH4 = -40.1‰). The δ13C-CH4 values of the standards were obtained by running the standards through a factory calibrated CRDS, and they were later referenced against certified standards obtained from Isometric Instruments (Tiso 1, δ13C-CH4 = -38.3 ± 0.2‰ and Liso1, δ13C-CH4 = -66.5 ± 0.2‰). Accuracy of CO2 concentrations was better than 1 ppm and δ13CCO2 accuracy for a 5 min average was better than 0.5‰. CH4 concentration accuracy was
S2
better than 80 ppb. δ13C-CH4 accuracy for a 5 min averaging interval was better than 0.6‰ for both Tiso1 and Liso1 standards. Experimental Design To extract the dissolved CO2 and CH4 we used 2 different gas equilibration devices (GED). The first was a shower-head equilibrator and the second a Liqui-Cel membrane contactor (see 1
for a further description of these systems). A second shower-head equilibrator with the
headspace open to the atmosphere was connected to the vent of the first to ensure no pressure differential between the atmosphere and the equilibrator. The gas stream from each GED was dried through a Drierite column, passed through the CRDS and returned to the GED (i.e. a closed air loop). The shower head equilibrator was used for the survey (experiment 1) and open water time series (experiment 2) (Figure S1A), while the Liqui-Cel membrane contactor was used for the chamber experiment (experiment 3) where a closed water and air loop was necessary (Figure S1B). The showerhead was chosen over the Liqui-Cel GED for the survey and time series experiments to minimize any potential blockage or microbially mediated CO2 production within the GED1. A laboratory experiment showed no differences in concentrations or δ13C values measured using the two GED systems. The pulse chase experiment measured CO2 concentrations in a headspace of air within a sealed core via a closed gas loop flowing through the CRDS (experiment 4) (Figure S1C).
Calculation of δ13C-DIC from δ13C-CO2 To compare the δ13C-CO2 values from the CRDS to in situ δ13C-DIC measured by IRMS, we used the fractionation factors reported by 2 ε(DIC-CO2 (g)) ‰ = 10.53 -0.107x T + 0.014 x fCO3 x T S3
where T is the temperature (°C) and fCO3 is the carbonate fraction (CO3-2/DIC). The carbonate fraction was calculated from salinity, temperature, pCO2 and pH using CO2SYS3. Results There was excellent agreement between CO2 concentrations measured with CRDS and NDIR (Figure S2) and δ13C-DIC-Calculated by CRDS and measured with IRMS (Table S1). Table S1 δ13C-DIC calculated and δ13C-DIC Measured in the survey and time series experiments Experiment Survey Survey Survey Survey Survey Survey Survey Survey Survey Survey Survey Survey Survey Survey Survey Survey Survey Survey Survey Survey Survey Survey Survey Survey Survey Survey Survey Survey Time Series Time Series
δ13C-DIC-Calculated (CRDS) 0.1611 0.7084 0.5149 -0.5189 -2.3106 -6.0508 -10.2707 -1.0295 -1.6941 -4.2951 -7.9654 -10.9887 -12.2250 -10.4315 0.3891 0.6064 -1.2964 -3.4805 -6.0255 -10.2368 -11.5798 -2.2965 -3.1756 -5.1963 -6.6013 -10.7930 -11.9565 -10.4321 -10.7930 -11.9565
δ13C-DIC-Measured (IRMS) 0.8500 0.7690 -0.1180 -1.1050 -2.4960 -3.0910 -8.0650 -0.7190 -1.9610 -3.7540 -8.0930 -10.3880 -10.6840 -8.2760 0.3610 -0.7930 -1.2760 -3.1470 -5.8780 -9.7120 -11.1490 -1.1340 -1.9490 -3.8940 -7.8650 -10.3620 -11.4990 -9.4300 -10.3620 -11.4990 S4
Time Series Time Series Time Series Time Series Time Series Time Series Time Series Time Series Time Series Time Series Time Series Time Series Time Series Time Series Time Series Time Series Time Series Time Series Time Series Time Series Time Series Time Series Time Series Time Series Time Series Time Series Time Series
-0.4394 -0.3558 -0.7257 -1.4568 -2.3216 -2.0749 -1.3515 -0.1321 0.6539 0.2109 0.2403 0.3261 3.8967e-3 -0.5157 -1.6793 -4.5521 -10.1000 -9.6000 -3.7044 -3.1180 0.9581 1.2090 0.2903 0.2181 -0.2574 -0.8722 -0.8722
0.5730 0.4150 -0.2750 -0.8530 -2.1550 -2.0060 -1.3820 -0.5170 0.4590 0.4140 0.3070 0.1360 -0.2080 -0.5240 -1.4730 -3.3320 -10.6590 -10.2230 -4.2330 -4.3480 -0.9200 -0.1360 -0.2840 -0.3670 -0.6820 -1.6670 -1.6670
S5
Figure S1 Experimental setup for; A. the survey and time series, B. chamber, and C. pulse-chase experiment.
S6
Figure S2 Linear regression of CRDS calculated δ13C-C-DIC versus IRMS measured δ13C-C-DIC References 1.
Santos, I. R.; Maher, D. T.; Eyre, B. D., Coupling automated radon and carbon
dioxide measurements in coastal waters. Environ. Sci. Technol. 2012, 46, 76857691:10.1021/es301961b. 2.
Zhang, J.; Quay, P. D.; Wilbur, D. O., Carbon isotope fractionation during gas-water
exchange and dissolution of CO2. Geochim. Cosmochim. Acta 1995, 59, 107-114 3.
Lewis, E.; Wallace, D. W. R. Program developed for CO2 system calculations.;
ORNL/CDIAC-105; Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, US Department of Energy.: Oak Ridge, Tennessee, 1998.
S7
