title: Nonequilibrium air clathrate hydrates in Antarctic ice: a paleopiezomdter for polar ice caps.
abstract: "Craigite," the mixed-air clathrate hydrate found in polar ice caps below the depth of air-bubble stability, is a clathrate mixed crystal of approximate composition (N2O2).6H2O. Recent observations on the Byrd Station Antarctic core show that the air hydrate is present at a depth of 727 m, well above the predicted depth for the onset of hydrate stability. We propose that the air hydrate occurs some 100 m above the equilibrium phase boundary at Byrd Station because of "piezometry"--i.e., that the anomalous depth of hydrate occurrence is a relic of a previous greater equilibrium depth along the flow trajectory, followed by vertical advection of ice through the local phase-boundary depth. Flowline trajectories in the ice based on numerical models show that the required vertical displacement does indeed occur just upstream of Byrd Station. Air-hydrate piezometry can thus be used as a general parameter to study the details of ice flow in polar ice caps and the metastable persistence of the clathrate phase in regions of upwelling blue ice.
authors.affiliation: Isotope Laboratory, Scripps Institution of Oceanography, University of California at San Diego, La Jolla, CA 92093, USA.
authors.forename: H
authors.initials: H
authors.lastname: Craig
authors.forename: H
authors.initials: H
authors.lastname: Shoji
authors.forename: C C
authors.initials: CC
authors.lastname: Langway