The global budget of nitrous oxide is dominated by terrestrial and marine biological sources and atmospheric sinks. Details of the

budget remain unclear, including the cause of increasing atmospheric N_2O concentrations. Marine sources of N_2O include

denitrification and nitrification. Our understanding of the major microbial players in the nitrogen cycle has changed in recent years

(for example, the nitrifying Archaea), and the overall contributions of these organisms to N_2O production and their isotopic signatures

are poorly constrained [1]

Eiler, John

Kopf, Sebastian

Magyar, Paul

Orphan, Victoria

Caltech Authors - Main

Goldschmidt 2012 Conference Abstracts
Mineralogical Magazine | www.minersoc.org 2054
Measurement of nitrous oxide 
isotopologues and isotopomers by the 
MAT 253 Ultra 
PAUL MAGYAR1*, SEBASTIAN KOPF1, VICTORIA ORPHAN1 
AND JOHN EILER1  
1California Institute of Technology, Pasadena, CA, USA, 
pmagyar@caltech.edu (* presenting author) 
 
The global budget of nitrous oxide is dominated by terrestrial 
and marine biological sources and atmospheric sinks. Details of the 
budget remain unclear, including the cause of increasing 
atmospheric N2O concentrations. Marine sources of N2O include 
denitrification and nitrification. Our understanding of the major 
microbial players in the nitrogen cycle has changed in recent years 
(for example, the nitrifying Archaea), and the overall contributions 
of these organisms to N2O production and their isotopic signatures 
are poorly constrained [1].  
Here we examine the suitability of the MAT 253 Ultra, a new 
high resolution gas source mass spectrometer [2], for measurements 
of rare, previously unanalyzed isotopologues and isotopomers of 
N2O, including ‘clumped’ species and high-precision direct analysis 
of 17O-substituted species. Such measurements could provide 
additional constraints to the global cycle of N2O, and in particular 
offer a fresh opportunity for distinguishing among biosynthetic N2O 
sources. Preliminary experiments include examining N2O produced 
by pure cultures of denitrifying bacteria. 
In the instrument’s ‘medium resolution’ setting (16 μm entrance 
slit; resolving power ~16-18,000, M/∆M), [14N15N18O + 15N14N18O] 
is well resolved from 13C18O16O and the 15N18O fragment from 
17O18O. In zero-enrichment measurements, precision of 0.2‰ was 
achieved for mass 47 species and 0.4‰ for 15N18O; both equaled 
counting statistics limits for the integration times used (11 and 17 
minutes, respectively) and should be improved by increasing the 
source pressure, reducing resolution (e.g., using a 20 μm entrance 
slit) or increasing counting time. At mass 45, 14N217O is well 
resolved from [14N15N16O + 15N14N16O], with external precision of 
0.03‰ achieved after 11 minutes of integration (again, counting 
statistics limited and potentially improvable). 
By measuring both these species (as well as unsubstituted and 
singly substituted isotopologues), the position-specific clumping 
(i.e., clumping of 15N with 18O, and its dependence on site 
preference of 15N) can be examined. Such measurements will 
complement the information already available from N2O site 
preference measurements alone. Calculations suggest that site 
preference of 15N in thermodynamically equilibrated N2O will differ 
by ~1‰ between 16O and 18O isotopologues [3]. A larger range of 
signals could arise from photochemical and biological 
fractionations. Precise measurement of 17O will enable detection of 
even subtle contributions of atmospheric mass-independent 
fractionation, or study of variations in mass laws of biological and 
other fractionations. 
 
[1] Santoro et al. (2011) Science 333, 1282-1285. [2] Eiler et 
al. The MAT 253 Ultra — a novel high-resolution, multi-collector 
gas source mass spectrometer. Goldschmidt 2012. [3] Wang et al. 
(2004) Geochim. Cosmochim. Acta 68, 4779-4797.  
Oxygen isotopes from Chinese caves: 
records not of monsoon rainfall but 
circulation regime 
BARBARA A MAHER 1 * , ROY THOMPSON 2  
1University of Lancaster, Lancaster, UK, b.maher@lancaster.ac.uk 
(* presenting author)  
2University of Edinburgh, roy@ed.ac.uk 
 
Current interpretation of cave 18O records 
Oxygen isotope variations in Chinese stalagmites have 
been widely interpreted as a record of the amount of East Asian 
summer monsoonal rainfall. This interpretation infers decreasing 
monsoonal rainfall from the mid-Holocene and large, dipolar 
rainfall oscillations within glaciations.  However, the cave 18O 
variations conflict with independent palaeoclimate proxies (cave 
13C, loess/palaeosol magnetic properties, n-alkanes), which 
indicate no systematic decline in rainfall from the mid-Holocene, 
and no glacial rainfall maxima.  
 
Mass balance calculations show moisture source is key 
control 
Using mass balance calculations, we demonstrate that the cave 
18O variations cannot be accounted for by summer rainfall changes, 
nor rainfall seasonality nor winter cooling, but instead reflect 
changes in moisture source. A possible driver of the 18O variations 
in Chinese stalagmites is precessional forcing of inter-hemispheric 
temperature gradients, in a mechanism similar to that of the modern 
day Indian Ocean dipole.  Through such forcing, Indian monsoon-
sourced 18O may have dominated at times of high boreal summer 
insolation, local Pacific-sourced moisture at low insolation.  
Suppression of summer monsoonal rainfall during glacial stages may 
reflect diminished sea and land surface temperatures and the 
radiative impacts of increased regional dust fluxes. 
 


English

Measurement of nitrous oxide isotopologues and isotopomers by the MAT 253 Ultra

Goldschmidt 2012 Conference Abstracts
Mineralogical Magazine | www.minersoc.org 2054
Measurement of nitrous oxide 
isotopologues and isotopomers by the 
MAT 253 Ultra 
PAUL MAGYAR1*, SEBASTIAN KOPF1, VICTORIA ORPHAN1 
AND JOHN EILER1  
1California Institute of Technology, Pasadena, CA, USA, 
pmagyar@caltech.edu (* presenting author) 
 
The global budget of nitrous oxide is dominated by terrestrial 
and marine biological sources and atmospheric sinks. Details of the 
budget remain unclear, including the cause of increasing 
atmospheric N2O concentrations. Marine sources of N2O include 
denitrification and nitrification. Our understanding of the major 
microbial players in the nitrogen cycle has changed in recent years 
(for example, the nitrifying Archaea), and the overall contributions 
of these organisms to N2O production and their isotopic signatures 
are poorly constrained [1].  
Here we examine the suitability of the MAT 253 Ultra, a new 
high resolution gas source mass spectrometer [2], for measurements 
of rare, previously unanalyzed isotopologues and isotopomers of 
N2O, including ‘clumped’ species and high-precision direct analysis 
of 17O-substituted species. Such measurements could provide 
additional constraints to the global cycle of N2O, and in particular 
offer a fresh opportunity for distinguishing among biosynthetic N2O 
sources. Preliminary experiments include examining N2O produced 
by pure cultures of denitrifying bacteria. 
In the instrument’s ‘medium resolution’ setting (16 μm entrance 
slit; resolving power ~16-18,000, M/∆M), [14N15N18O + 15N14N18O] 
is well resolved from 13C18O16O and the 15N18O fragment from 
17O18O. In zero-enrichment measurements, precision of 0.2‰ was 
achieved for mass 47 species and 0.4‰ for 15N18O; both equaled 
counting statistics limits for the integration times used (11 and 17 
minutes, respectively) and should be improved by increasing the 
source pressure, reducing resolution (e.g., using a 20 μm entrance 
slit) or increasing counting time. At mass 45, 14N217O is well 
resolved from [14N15N16O + 15N14N16O], with external precision of 
0.03‰ achieved after 11 minutes of integration (again, counting 
statistics limited and potentially improvable). 
By measuring both these species (as well as unsubstituted and 
singly substituted isotopologues), the position-specific clumping 
(i.e., clumping of 15N with 18O, and its dependence on site 
preference of 15N) can be examined. Such measurements will 
complement the information already available from N2O site 
preference measurements alone. Calculations suggest that site 
preference of 15N in thermodynamically equilibrated N2O will differ 
by ~1‰ between 16O and 18O isotopologues [3]. A larger range of 
signals could arise from photochemical and biological 
fractionations. Precise measurement of 17O will enable detection of 
even subtle contributions of atmospheric mass-independent 
fractionation, or study of variations in mass laws of biological and 
other fractionations. 
 
[1] Santoro et al. (2011) Science 333, 1282-1285. [2] Eiler et 
al. The MAT 253 Ultra — a novel high-resolution, multi-collector 
gas source mass spectrometer. Goldschmidt 2012. [3] Wang et al. 
(2004) Geochim. Cosmochim. Acta 68, 4779-4797.  
Oxygen isotopes from Chinese caves: 
records not of monsoon rainfall but 
circulation regime 
BARBARA A MAHER 1 * , ROY THOMPSON 2  
1University of Lancaster, Lancaster, UK, b.maher@lancaster.ac.uk 
(* presenting author)  
2University of Edinburgh, roy@ed.ac.uk 
 
Current interpretation of cave ?18O records 
Oxygen isotope variations in Chinese stalagmites have 
been widely interpreted as a record of the amount of East Asian 
summer monsoonal rainfall. This interpretation infers decreasing 
monsoonal rainfall from the mid-Holocene and large, dipolar 
rainfall oscillations within glaciations.  However, the cave ?18O 
variations conflict with independent palaeoclimate proxies (cave 
?13C, loess/palaeosol magnetic properties, n-alkanes), which 
indicate no systematic decline in rainfall from the mid-Holocene, 
and no glacial rainfall maxima.  
 
Mass balance calculations show moisture source is key 
control 
Using mass balance calculations, we demonstrate that the cave 
?18O variations cannot be accounted for by summer rainfall changes, 
nor rainfall seasonality nor winter cooling, but instead reflect 
changes in moisture source. A possible driver of the ?18O variations 
in Chinese stalagmites is precessional forcing of inter-hemispheric 
temperature gradients, in a mechanism similar to that of the modern 
day Indian Ocean dipole.  Through such forcing, Indian monsoon-
sourced ?18O may have dominated at times of high boreal summer 
insolation, local Pacific-sourced moisture at low insolation.  
Suppression of summer monsoonal rainfall during glacial stages may 
reflect diminished sea and land surface temperatures and the 
radiative impacts of increased regional dust fluxes. 
 


http://authors.library.caltech.edu/39808/1/Eiler_2012p2054.pdf

Measurement of nitrous oxide isotopologues and isotopomers by the MAT 253 Ultra

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