Triple Oxygen Isotopic Compositions of Ocean Water from the Mariana Trench

Abstract

High-precision triple oxygen isotope data on 40 water samples (5–10 923 m in depth) collected at the Challenger Deep of the Mariana Trench are reported in this study. The analyses at Laboratoire des Sciences du Climat et l’Environnement yield mean isotope values δ18O = −0.084 ± 0.224‰, δ17O = −0.061 ± 0.117‰, and 17O-excess = −17 ± 5 per meg, with standard deviations reported at 1σ. The range of δ18O (from −0.480 to 0.544‰) falls within records of the Global Seawater Oxygen-18 Database at the Mariana Trench. The average 17O-excess value at the Mariana Trench is more negative than the average 17O-excess value of −5 ± 4 (1σ) per meg in the only prior data set including deep ocean samples. The slope (λ) of the three-isotope plot of Mariana Trench water is 0.521 ± 0.003 (1σ), lower than λ of 0.528 ± 0.001 (1σ) for ocean water in the prior study. The new data set matches the prediction of the ocean isotope mass balance model, suggesting that it may represent a more appropriate ocean endmember for triple oxygen isotope thermometry. The 17O-excess of ocean water with respect to Vienna Standard Mean Ocean Water (VSMOW) is recognized to be a necessary correction in quantifying gross oxygen productivity of euphotic regions and relative humidity of moisture source regions.