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Updated: Jul 11, 2026

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The Benthic Exchange of O2, N2 and Dissolved Nutrients Using Small Core Incubations
Published on: August 3, 2016
Atmospheric oxygen: isotopic composition and solubility fractionation
Summary
Atmospheric oxygen shows an oxygen-18 enrichment of 23.5 per mil compared to ocean water. Dissolved oxygen in seawater is further enriched by 0.85 per mil at 0°C, with a temperature-dependent solubility.
Area of Science:
- Geochemistry
- Oceanography
- Atmospheric Science
Background:
- Atmospheric oxygen exhibits a significant enrichment in the stable isotope oxygen-18 (¹⁸O) relative to standard mean ocean water (SMOW).
- Oxygen isotopes in natural waters are influenced by physical processes like evaporation and precipitation, as well as gas exchange between the atmosphere and oceans.
Purpose of the Study:
- To quantify the enrichment of oxygen-18 in atmospheric oxygen relative to ocean water.
- To determine the isotopic fractionation of oxygen dissolved in seawater at 0°C.
- To establish the temperature dependence of oxygen-18 enrichment in dissolved seawater.
Main Methods:
- Comparison of oxygen-18/oxygen-16 ratios in atmospheric oxygen samples with Standard Mean Ocean Water (SMOW).
- Measurement of oxygen-18/oxygen-16 ratios in seawater samples equilibrated with atmospheric oxygen at controlled temperatures.
- Mathematical modeling to determine the temperature dependence of isotopic solubility enrichment.
Main Results:
- Atmospheric oxygen is enriched by 23.5 ± 0.3 per mil (‰) in ¹⁸O relative to SMOW.
- Oxygen dissolved in seawater is further enriched by 0.85 per mil (‰) at 0°C.
- The temperature dependence of this solubility enrichment is described by the equation: ε (‰) = 0.85 - 0.010 * t (°C).
Conclusions:
- The study confirms a substantial ¹⁸O enrichment in atmospheric oxygen.
- The solubility of oxygen in seawater introduces an additional temperature-dependent ¹⁸O enrichment.
- These findings contribute to understanding the global oxygen isotope budget and its sensitivity to temperature.
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