Isotopic Argon in the Ocean
Argon (Ar), as the most abundant gas in the Earth’s atmosphere, has a natural atmospheric-oceanic gas exchange process. Inert noble gases, such as Ar, are known to be proxies to measure mean global ocean temperatures. As the ocean cools, more gas can be dissolved, ultimately lowering the atmospheric concentration of noble gases in the atmosphere.[1]. Using samples from polar ice cores, paleoclimate scientists can estimate past mean oceanic temperatures by looking at the concentration of Ar trapped in small air bubbles within the ice.
There are three stable Ar isotopes: argon-40 (40Ar), argon-38 (38Ar), and argon-36 (36Ar). Each isotope has constant atmospheric ratios for up to 100,000 years. The presence of these isotopes in ice cores are thermally dependent, with the heavier isotope (40Ar) being more abundant during times of colder ocean temperatures [2]. However, gravitational enrichment due to isotopic mass can affect what isotopes will be present in the different sections of the ice core. Because of the greater mass of 40Ar, gravity pulls the isotope to the bottom of the ice column where the bubble close-off happens [3].
Oftentimes, Ar is paired with other inert gases, such as nitrogen (N2), as tracers because there is an assumption that noble gases and N2 exist in a closed system of exchange between the atmosphere and the ocean. Their ability to be inert allows for temperature dependent solubility between the two systems.[1] A study done by Rites, Stocker, & Severinghaus conclude that atmospheric noble gas concentrations are a great way to measure past global mean ocean temperature- especially when examining periods of glaciation and deglaciation.[1]
References[edit]
- ↑ 1.0 1.1 1.2 Ritz, S., Stocker, T., & Severinghaus, J. (2011). Noble gases as proxies of mean ocean temperature: sensitivity studies using a climate model of reduced complexity. Quaternary Science Reviews, 30, 3728-3741.
- ↑ Severinghaus, J., Grachev, A., Luz, B., & Caillon, N. (2003). A method for precise measurement of argon 40/36 and krypton/argon ratios in trapped air in polar ice with applications to past firn thickness and abrupt climate change in Greenland and at Siple Dome, Antarctica. "Geochemica et Cosmochimicia Acta", 67(3), 325-343.
- ↑ Haeberli, M., Baggenstos, D., Schmitt, J., Grimmer, M., Michel, A., Kellerhals, T., & Fischer, H. (2020). Snapshots of mean ocean temperature over the last 700,000 yr using noble gases in the EPICA Dome C ice core. "Climate of the Past Discussions", 1-38.
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