Fig. 6: Geochemical approach to reconstructing ancient ocean salinity.
From: Fluid inclusions: tiny windows into global paleo-environments
Mixing correlations between a paleo-ocean and a crustal/hydrothermal endmember in fluid inclusions of a 3.49-Gyr-old Dresser formation, Warrawoona Group, Pilbara Craton at North Pole (Western Australia96), and b 2.5 Gyr-old chert samples from Hamersley Group (Western Australia97). a The strong linear correlation indicates two-component mixing. The red, blue, and green thick lines represent salinities of 0.5, 1, and 2 times the modern seawater composition, as expressed by Cl and K, for temperatures of 0 °C, 25 °C, 50 °C, and 75 °C. These ranges represent possible endmembers between present-day ocean bottom temperatures of 2 °C and those proposed for Archean oceans of up to 70 °C99. The correlation is not consistent with salinities twice the modern value116 or higher55,56,117. For a modern-like salinity, a temperature in the range of 20–40 °C is compatible with the data. b Only the main release steps (at 1400 or 1600 °C) from each sample are displayed here. They show Cl/36Ar values comparable to modern seawater salinity in the temperatures range 0–25 °C, but K/36Ar about two orders of magnitude higher than modern seawater, which the authors attribute to the presence of a K-rich phase97. Based on the low 40Ar/36Ar, seawater-like Cl/36Ar, and the ~2.4 Ga 40Ar–39Ar ages, the fluids are likely to be paleo-seawater containing dissolved atmospheric noble gases.
