Triple oxygen isotope and oxygen/argon ratio
measurements to enhance coastal and open ocean
production/respiration comparisons
Johanna
1,2
Gloël ,
C.
P.
2
1
G. Tilstone , J. Kaiser
1University
1
Robinson ,
of East Anglia, 2Plymouth Marine Laboratory
Motivation
Many methods to determine
productivity are error-prone,
small-scale (bottle incubations) or
depend on good calibrations
(satellite data).
Determine
Carbon
Cycle
Constrain
 Triple isotopes of oxygen and
O2/Ar ratios present the possibility
to measure continuously on a ship
with relatively small effort and
represent the conditions
integrated over approximately two
weeks.
Climate
Models
Enhance
Stratosphere
2.1
Non-mass-dependent
isotope effect
 Anomalous oxygen
O2, CO2
O2, CO2
Troposphere
Determine the gross and net community production at one
location in the English Channel and in the Atlantic Ocean
with the help of triple isotopes of oxygen (16O,
and O2/Ar ratios. Compare these results to productivity
measurements made with other methods.
Picture: K. Castro-Morales
Picture: K. Castro-Morales
Theory
Praxis
1. Oxygen and argon have similar solubility
parameters, but only O2 is produced biologically.
O2/Ar can therefore be used to determine the
biological contribution to O2 saturation and net
production can be calculated using wind speed
observations (Craig and Hayward, 1987).
Water is continuously
analysed on board
of a ship or discretely
in the lab with a
membrane inlet
mass spectrometer
(Kaiser et al., 2005).
NP≈ Fbio = kcsat ΔO2/Ar
1.
2.2
17O, 18O)
Picture: K. Castro-Morales
Method
O2, Ar
CO2 + H2O
Picture: K. Castro-Morales
2. A non-mass dependent isotope reaction in the
stratosphere leads to anomalous isotopic
composition of oxygen (Δ17O) , which is
introduced into the troposphere and the ocean.
Photosynthesis adds oxygen without this anomaly
to the ocean. The extent of this is a measure for
gross production (Luz and Barkan, 2000).
O2, Ar
Ocean
Ocean
Aim of study
 Are coastal and open oceans
net sources or sinks of CO2?
Photosynthesis
and
Respiration
1
Dennis ,
CH2O + O2
Mass-dependent isotope fractionation
during photosynthesis
 Adds oxygen without anomaly
GP= kcsat(Δ17O - Δ17Odiss )/(Δ17Ophoto - Δ17O )
Discrete water samples
are collected in
pre-evacuated bottles.
After the gases are
extracted from water,
they are analysed
with an isotope
ratio mass spectrometer.
Picture: A. Gonzalez-Posada
Δ17Odiss = 16x10-6; Δ17Ophoto = 249x10-6
Co-operations
Area of study
Analysis
The Western English Channel Observatory
(station L4) is located 10 nautical miles off the
coast from Plymouth in 50 m deep waters.
Sampling will take place once weekly for
one year and complement the extensive
characterisation of L4 that is already being
undertaken.
 Sampling and comparisons
2010, England to Falkland Islands
Picture: www.westernchannelobservatory.org.uk/
Data will also be collected in the
z
Atlantic oligotrophic gyres
on the
Atlantic Meridional Transect (AMT) in
2010 from England to the Falkland
Islands. This will be compared to
data from AMT16 and AMT17 in 2005
.
Continuous sampling at L4, compare
to results from other productivity
measurements
Funding
Work under themes 2 (Marine
Biogeochemical Cycles) and 10
(Sustained Observations)
Picture: www.bodc.ac.uk/projects/uk/amt
Literature
Kaiser et al. (2005) Marine productivity estimates from continuous O2/Ar ratio measurements by membrane inlet mass spectrometry. Geophysical Research Letters, 32, L19605.
Luz and Barkan (2000) Assessment of oceanic productivity with the triple-isotope composition of dissolved oxygen. Science, 288, 2028-2031.
Craig and Hayward (1987) Oxygen supersaturation in the ocean: biological versus physical contributions. Science, 235, 199-202.
Acknowledgements
J.G. thanks the National Environmental Research Council for Doctoral Training Grant
NE/R012608/1. J.K. thanks the Royal Society for a Wolfson Research Merit Award.