Ninety Per Mil Enrichment of Neon In Firn Air At South Pole
Abstract
Firn air was sampled in 2001 from the South Pole with the objective of reconstructing the composition of the atmosphere over the past century. As reported previously, a layer near the bottom of the Firn from 114 m to 122 m appears not to mix with the atmosphere and is called the "lock-in zone" or the "non-diffusive zone". Our noble gas measurements of Firn air show that the neon-22 to argon-36 ratio is progressively enriched with depth in the lock-in zone, reaching maximum values in the deepest sample of +90.7 per mil (uncertainty of 0.3 per mil) with respect to atmosphere. This value includes a correction for gravitational enrichment using the argon 40/argon-36 ratio. Molecular oxygen is also progressively enriched in the lock-in zone, with neon changing 33 times more than oxygen (corrected for atmospheric change due to fossil fuel burning). We propose that the neon enrichment is due either to 1) size-dependent fractionation of air expelled from the closing bubbles, or 2) diffusion of neon through the ice in response to the overpressure in the newly formed bubbles, in either case with accumulation of excess neon in the remaining open Firn layers.
- Publication:
-
EGS General Assembly Conference Abstracts
- Pub Date:
- 2002
- Bibcode:
- 2002EGSGA..27..510S