Laboratory for Stable Isotopes (Sediments and Water)

GFZ - German Research Centre for Geosciences

last updated: July 19, 2023

About the Laboratory

Laboratory for Stable Isotopes (Sediments and Water)

GFZ - German Research Centre for Geosciences

@ Section 4.3 Climate Dynamics and Landscape Evolution

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Networks: Geo.X

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Description

In our laboratory, the stable isotopes of the light elements carbon (C), nitrogen (N), oxygen (O) and hydrogen (H) in continental geoarchives such as lake sediments and speleothems as well as in precipitation and surface water are measured. Stable isotopes are non-radioactive nuclides of an element with the same number of protons and different numbers of neutrons and thus different atomic masses. This results in different physical properties that can lead to a shift in the isotope ratios in a substance (in our case water, organic matter or carbonate). These isotope ratios leave fingerprints of past environmental conditions and can indicate changes in precipitation, temperatures, vegetation or organic productivity in our archives.
Shifts in isotope ratios during natural processes are often very small. These changes can be measured very accurately using isotope ratio mass spectrometers (IRMS) or cavity ring down spectroscopy (CRDS).

Instruments

Instrument used for measuring carbon, hydrogen, nitrogen, sulfur or oxygen content in organic and other types of materials. Group: Instrument_Details Entry_ID: CHNS/O ELEMENTAL ANALYZERS Group: Instrument_Identification Instrument_Category: In Situ/Laboratory Instruments Instrument_Class: Chemical Meters/Analyzers Short_Name: CHNS/O ELEMENTAL ANALYZERS End_Group Online_Resource: http://las.perkinelmer.com/content/RelatedMaterials/Brochures/BRO_2400SeriesIICHNSOelementalAnalyzer.pdf Creation_Date: 2009-10-15 End_Group (Source: Global Change Master Directory (GCMD). 2023. GCMD Keywords, Version 16.3 [...] )
EA - Elemental Analyzer
Measurement and study of the relative abundances of the different isotopes of an element in a material using a mass spectrometer. (Source: IUPAC; https://doi.org/10.1351/PAC-REC-06-04-06) (Source: Global Change Master Directory (GCMD). 2023. GCMD Keywords, Version 16.3 [...] )
IRMS - Isotope Ratio Mass Spectrometer
Isotopic Ratio Mass Spectrometer
Nearly every small gas-phase molecule (e.g., CO2, H2O, H2S, NH3) has a unique near-infrared absorption spectrum. At sub-atmospheric pressure, this consists of a series of narrow, well-resolved, sharp lines, each at a characteristic wavelength. Because these lines are well-spaced and their wavelength is well-known, the concentration of any species can be determined by measuring the strength of this absorption, i.e. the height of a specific absorption peak. But, in conventional infrared spectrometers, trace gases provide far too little absorption to measure, typically limiting sensitivity to the parts per million at best. CRDS - Cavity Ring-Down Spectroscopy - avoids this sensitivity limitation by using an effective pathlength of many kilometers. It enables gases to be monitored in seconds or less at the parts per billion level, and some gases at the parts per trillion level. In CRDS, the beam from a single-frequency laser diode enters a cavity defined by two or more high reflectivity mirrors. Picarro analyzers use a three-mirror cavity, as in the figure below, to support a continuous traveling light wave. This provides superior signal to noise compared to a two-mirror cavity that supports a standing wave. When the laser is on, the cavity quickly fills with circulating laser light. A fast photodetector senses the small amount of light leaking through one of the mirrors to produce a signal that is directly proportional to the intensity in the cavity. When the photodetector signal reaches a threshold level (in a few tens of microseconds), the continuous wave (CW) laser is abruptly turned off. The light already within the cavity continues to bounce between the mirrors (about 100,000 times), but because the mirrors have slightly less than 100% reflectivity (99.999%), the light intensity inside the cavity steadily leaks out and decays to zero in an exponential fashion. This decay, or "ring down", is measured in real-time by the photodetector, and the amount of time it takes for the ring down to happen is determined solely by the reflectivity of the mirrors (for an empty cavity). Consider that for a Picarro cavity of only 25 cm in length, the effective pathlength within the cavity can be over 20 kilometers. Now, if a gas species that absorbs the laser light is introduced into the cavity, a second loss mechanism within the cavity (absorption) is now introduced. This accelerates the ring down time compared to a cavity without any additional absorption due to a targeted gas species. Picarro instruments automatically and continuously calculate and compare the ring down time of the cavity with and without absorption due to the target gas species. This produces precise, quantitative measurements that account for any intra-cavity loss that may be changing over time, and it allows the discrimination of loss due to absorption from losses due to the cavity mirrors. Furthermore, the final concentration data is particularly robust because it is derived from the difference between these ring down times and is therefore independent of laser intensity fluctuations or absolute laser power. This scheme of comparing the ring down time of the cavity without any absorbing gas, with the ring down time when a target gas is absorbing light is accomplished not by removing the gas from the cavity, but rather by using a laser whose wavelength can be tuned. By tuning the laser to different wavelengths where the gas absorbs light, and then to wavelengths where the gas does not absorb light, the "cavity only" ring down time can be compared to the ring down time when a target gas is contributing to the optical loss within the cavity. In fact, the laser is tuned to several locations across the target gas's spectral absorption line (and ring down measurements are conducted at all these points) and a mathematical fit to the shape of that absorption line is what is actually used to calculate the gas concentration. (Source: Global Change Master Directory (GCMD). 2023. GCMD Keywords, Version 16.3 [...] )
CRDS - Cavity Ring Down Spectrometer
CRLAS

Analytical Methods

Instrument used for measuring carbon, hydrogen, nitrogen, sulfur or oxygen content in organic and other types of materials. Group: Instrument_Details Entry_ID: CHNS/O ELEMENTAL ANALYZERS Group: Instrument_Identification Instrument_Category: In Situ/Laboratory Instruments Instrument_Class: Chemical Meters/Analyzers Short_Name: CHNS/O ELEMENTAL ANALYZERS End_Group Online_Resource: http://las.perkinelmer.com/content/RelatedMaterials/Brochures/BRO_2400SeriesIICHNSOelementalAnalyzer.pdf Creation_Date: 2009-10-15 End_Group (Source: Global Change Master Directory (GCMD). 2023. GCMD Keywords, Version 16.3 [...] )
EA - Elemental Analysis
Total Organic Carbon (TOC) analysis is a well-defined and commonly used methodology that measures the carbon content of dissolved and particulate organic matter present in water. Many water utilities monitor TOC to determine raw water quality or to evaluate the effectiveness of processes designed to remove organic carbon. Some wastewater utilities also employ TOC analysis to monitor the efficiency of the treatment process. In addition to these uses for TOC monitoring, measuring changes in TOC concentrations can be an effective "surrogate" for detecting contamination from organic compounds (e.g. petrochemicals, solvents, pesticides). Thus, while TOC analysis does not give specific information about the nature of the threat, identifying changes in TOC can be a good indicator of potential threats to a system. Additional information available at "http://www.epa.gov/safewater/security/guide/ chemicalsensortotalorganiccarbonanalyzer.html" [Summary provided by the EPA]
Total Organic Carbon (TOC) analysis is a well-defined and commonly used methodology that measures the carbon content of dissolved and particulate organic matter present in water. Many water utilities monitor TOC to determine raw water quality or to evaluate the effectiveness of processes designed to remove organic carbon. Some wastewater utilities also employ TOC analysis to monitor the efficiency of the treatment process. In addition to these uses for TOC monitoring, measuring changes in TOC concentrations can be an effective "surrogate" for detecting contamination from organic compounds (e.g. petrochemicals, solvents, pesticides). Thus, while TOC analysis does not give specific information about the nature of the threat, identifying changes in TOC can be a good indicator of potential threats to a system. Additional information available at "http://www.epa.gov/safewater/security/guide/ chemicalsensortotalorganiccarbonanalyzer.html" [Summary provided by the EPA] (Source: NASA; UUID: 58ac7544-7271-4957-a70a-ea7c1a1ae094) (Source: Global Change Master Directory (GCMD). 2023. GCMD Keywords, Version 16.3 [...] )
TOC - Total Organic Carbon Analysis
Total Organic Carbon
Measurement and study of the relative abundances of the different isotopes of an element in a material using a mass spectrometer. (Source: IUPAC; https://doi.org/10.1351/PAC-REC-06-04-06) (Source: Global Change Master Directory (GCMD). 2023. GCMD Keywords, Version 16.3 [...] )
IRMS - Isotope Ratio Mass Spectrometry
Stable Isotope Mass Spectrometry
Nearly every small gas-phase molecule (e.g., CO2, H2O, H2S, NH3) has a unique near-infrared absorption spectrum. At sub-atmospheric pressure, this consists of a series of narrow, well-resolved, sharp lines, each at a characteristic wavelength. Because these lines are well-spaced and their wavelength is well-known, the concentration of any species can be determined by measuring the strength of this absorption, i.e. the height of a specific absorption peak. But, in conventional infrared spectrometers, trace gases provide far too little absorption to measure, typically limiting sensitivity to the parts per million at best. CRDS - Cavity Ring-Down Spectroscopy - avoids this sensitivity limitation by using an effective pathlength of many kilometers. It enables gases to be monitored in seconds or less at the parts per billion level, and some gases at the parts per trillion level. In CRDS, the beam from a single-frequency laser diode enters a cavity defined by two or more high reflectivity mirrors. Picarro analyzers use a three-mirror cavity, as in the figure below, to support a continuous traveling light wave. This provides superior signal to noise compared to a two-mirror cavity that supports a standing wave. When the laser is on, the cavity quickly fills with circulating laser light. A fast photodetector senses the small amount of light leaking through one of the mirrors to produce a signal that is directly proportional to the intensity in the cavity. When the photodetector signal reaches a threshold level (in a few tens of microseconds), the continuous wave (CW) laser is abruptly turned off. The light already within the cavity continues to bounce between the mirrors (about 100,000 times), but because the mirrors have slightly less than 100% reflectivity (99.999%), the light intensity inside the cavity steadily leaks out and decays to zero in an exponential fashion. This decay, or "ring down", is measured in real-time by the photodetector, and the amount of time it takes for the ring down to happen is determined solely by the reflectivity of the mirrors (for an empty cavity). Consider that for a Picarro cavity of only 25 cm in length, the effective pathlength within the cavity can be over 20 kilometers. Now, if a gas species that absorbs the laser light is introduced into the cavity, a second loss mechanism within the cavity (absorption) is now introduced. This accelerates the ring down time compared to a cavity without any additional absorption due to a targeted gas species. Picarro instruments automatically and continuously calculate and compare the ring down time of the cavity with and without absorption due to the target gas species. This produces precise, quantitative measurements that account for any intra-cavity loss that may be changing over time, and it allows the discrimination of loss due to absorption from losses due to the cavity mirrors. Furthermore, the final concentration data is particularly robust because it is derived from the difference between these ring down times and is therefore independent of laser intensity fluctuations or absolute laser power. This scheme of comparing the ring down time of the cavity without any absorbing gas, with the ring down time when a target gas is absorbing light is accomplished not by removing the gas from the cavity, but rather by using a laser whose wavelength can be tuned. By tuning the laser to different wavelengths where the gas absorbs light, and then to wavelengths where the gas does not absorb light, the "cavity only" ring down time can be compared to the ring down time when a target gas is contributing to the optical loss within the cavity. In fact, the laser is tuned to several locations across the target gas's spectral absorption line (and ring down measurements are conducted at all these points) and a mathematical fit to the shape of that absorption line is what is actually used to calculate the gas concentration. (Source: Global Change Master Directory (GCMD). 2023. GCMD Keywords, Version 16.3 [...] )
CRDS - Cavity Ring Down Spectroscopy
CRLAS, Cavity Ring-down Laser Absorption Spectroscopy

Laboratory Keywords

In addition to the instruments and analytical methods listed above, these keywords help to describe the work done in the laboratory. This may include the type of samples, standard materials, specific preparative or analytical methods and specific instrument characteristics.

Total Carbon (TC)
Total Nitrogen (TN)
δD
δ¹³C
δ¹⁵N
δ¹⁸O

Disciplines

Geoscience > Geochemistry > Geochemistry
Geochemistry
Geoscience > Geology > Geology
Geology
Geoscience > Geology > Sedimentology
Sedimentology
Geoscience > Paleogeosciences > Paleoclimate
Paleoclimate

Links

Key Publications: