Constraining air-sea equilibrium and biological end-members for marine gross productivity estimates using oxygen triple isotopes

Van Der Meer, Anne (2015) Constraining air-sea equilibrium and biological end-members for marine gross productivity estimates using oxygen triple isotopes. Masters thesis, University of East Anglia.

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The measurement of biological production rates is essential for our understanding how
marine ecosystems are sustained and how much CO2 is taken up through aquatic
photosynthesis. Traditional techniques to measure marine production are laborious and
subject to systematic errors. A new biogeochemical approach based on triple oxygen
isotope measurements in dissolved oxygen (O2) has been developed over the last few
years, which allows the derivation of gross productivity integrated over the depth of the
mixed layer and the time-scale of O2 gas exchange (Luz & Barkan 2000). This approach
exploits the relative 17O/16O and 18O/16O isotope ratio differences of dissolved O2
compared to atmospheric O2 to work out the rate of biological production. Two
parameters are key for this calculation: the isotopic composition of dissolved O2 in
equilibrium with air and the isotopic composition of photosynthetic oxygen. Recently, a
controversy has emerged in the literature over these parameters (Kaiser, 2011) and the
main goal of this research was to provide additional data to help resolve this
controversy. In order to obtain more information on the isotopic composition of marine
biological oxygen, gas from the headspace of airtight bottles with Picochlorum sp. and
Emiliania huxleyi cultures was sampled every 48 hours during eight days, after which
the triple oxygen isotopic composition was determined. Results indicate the 17O excess
obtained for both species is in the range of estimations by Kaiser and Abe (2012) based
on different triple oxygen isotope measurements of VSMOW vs. air and the speciesspecific
photosynthetic fractionation reported by Eisenstadt et al. (2010). The obtained
17O excess for E. huxleyi was higher (249±11 ppm) than for Picochlorum (180±13 ppm),
which seems consistent with results of Eisenstadt et al. (2010). In addition, the triple
isotopic composition of dissolved oxygen at air saturation was determined for different
temperature (0, 22 and 39 °C) and salinity conditions. While 22 °C tests yielded a Δ17O
of ~15-20 ppm, ~10 ppm lower values were obtained for tests at either zero or 39 °C.

Item Type: Thesis (Masters)
Faculty \ School: Faculty of Science > School of Environmental Sciences
Depositing User: Users 2259 not found.
Date Deposited: 29 Jan 2016 13:04
Last Modified: 04 May 2023 01:38

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