C051-07
Inversion Studies of Molecular Hydrogen in Megadunes Firn Air

Monday, 14 December 2020: 16:24
Virtual
John Patterson1, Murat Aydin1, Jeffrey P Severinghaus2, Gabrielle Petron3,4, Andrew M Crotwell3,4 and Eric S Saltzman1, (1)University of California Irvine, Irvine, CA, United States, (2)Scripps Institution of Oceanography, La Jolla, CA, United States, (3)Cooperative Institute for Research in Environmental Sciences, Boulder, CO, United States, (4)National Oceanic and Atmospheric Administration, Global Monitoring Division, Earth System Research Laboratory, Boulder, CO, United States
Recorded Presentation
Abstract:

Molecular hydrogen (H2) is one of the most abundant reactive trace gases in Earth’s atmosphere. Previous work using South Pole firn air indicates that atmospheric H2 levels increased by roughly 30% over the 20th century, likely due to anthropogenic emissions of H2 precursors (Patterson et al., 2020). In this study, we extend the atmospheric history of H2 into the 19th century by inverting firn air measurements from Megadunes, Antarctica

Megadunes is a low accumulation site located in the interior of Eastern Antarctica near Vostok Station. The oldest firn air ever sampled was recovered from the Megadunes site (Severinghaus et al., 2010). Megadunes firn air was sampled in 2004 and subsequently analyzed for H2 at NOAA/GMD. Sample depths ranged from the surface to 69 m. H2 levels in the deepest samples were 340 ppb. H2 levels increase linearly to 540 ppb, near modern levels, at 64 m. Above 64 m, H2 levels were approximately constant near modern levels. An atmospheric history was obtained by inverting the UCI_2 firn air model (Patterson et al., 2020). The parameterization of pore close-off fractionation of H2 in the model is updated using newly available laboratory measurements for the permeability of H2 in ice.

The study shows that H2 levels over Antarctica increased from 290-410 ppb from 1880-1950. After 1950, the growth rate increased, and H2 levels reached 545 ppb around 2000. The atmospheric history obtained from Megadunes is in good agreement with the South Pole results for the period of overlap (1910-2000).

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