Unfortunately, we can't directly measure OH (it has a 1-second lifetime) and we have very little knowledge about how it has changed in the past. 14CO, however, is stable in the atmosphere, has a known source (cosmic rays), and is almost entirely destroyed by OH. So, by measuring 14CO and modeling its production we can attribute observed 14CO differences from expectations as changes in oxidation by OH.
How do we get 14CO samples before atmospheric measurements? Luckily, firn--the porous upper 100 meters or so of polar ice sheets (a 15-cm section of which is pictured in the header photo)--has been trapping samples of the atmosphere for millennia. We plan to measure 14CO trapped in Antarctic ice cores to reveal the history of atmospheric oxidation over the past 150 years.
14CO in ice has the added complication that some 14C is produced "in-situ" as the ice sits near the surface of the ice sheet, due to bombardment from secondary cosmic rays. To get around this, we have proposed to travel to a location with one of the highest snowfall rates in Antarctica: the "DE-08" site on Law Dome in Australian Antarctic territory. The high snowfall quickly shields ice from in-situ production, thus minimizing this undesired 14C component. For more on 14C production in ice, see Petrenko et al., 2016.
To get enough carbon for accelerator mass spectrometer measurement, we need about 300 kilograms of ice. We have designed and built a stainless-steel chamber with a hot water bath to melt and extract old air from the bubbles trapped inside the ice. This will travel with us to Antarctica, allowing us to extract gas samples in the field and ship them home.
Drilling the world's fattest (9.5"ø) 100,000 year-old ice cores.— Peter Neff (@peter_neff) February 26, 2018
Taylor #Glacier, #Antarctica □□.
Set up tripod
Make sure hole is straight
Drill baby, drill (@US_IceDrilling)
Pull out ice cuttings
Deliver 100 lb ice core to waiting #scientist
[□@heidiroop & me] pic.twitter.com/C3n59CorMs