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

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.

Name dc:type.qualificationname

other

Level dc:type.qualificationlevel

masters

Grantor dc:publisher.institution

University of East Anglia

Year dc:date.issued

2015

Author dc:creator

• Van Der Meer, Anne

Language dc:language

en