Raman spectroscopic and statistical studies on natural clathrates from the Greenland Ice Core Project ice core, and neutron diffraction studies on synthetic nitrogen clathrates

Abstract

We present the results of Raman spectroscopic experiments on air clathrates in the GReenland Ice Core Project (GRIP) deep ice core, which differ markedly from previous measurements on the Dye 3 ice core. The N2/O2 ratio we observe is much closer to the atmospheric value. This has new implications for the interpretation of gas distributions in ice sheets. Raman spectroscopic scans to determine the N2/O2 ratios on different planes through a clathrate, in which the two axes of the scans are perpendicular to each other, give no indication of fractionation effects on the N2/O2 concentrations within a clathrate specimen. The frequency shift of the N2 and O2 peaks due to decomposition of a clathrate to an air bubble is shown qualitatively. From their peak integrals there is no indication of different retransformation rates to air bubbles between the oxygen and the nitrogen contents of clathrates. In air bubbles resulting from clathrate decomposition, the N2/O2 ratio shows similar values to those observed in clathrates and present atmospheric values. Statistical studies on the size, shape, and number concentration of clathrates are intended to give an estimate of the total amount of gas occluded in the clathrates. We present preliminary results obtained from 27 samples in a depth range between 1100 and 3000 m. The first neutron powder diffraction experiments reveal an overall degree of filling of 96.4% for a clathrate at a pressure of 449 bars and the existence of a type I phase at 1311 bars with an overall degree of filling of 107.5%.