RAMAN-SPECTROSCOPIC AND STATISTICAL STUDIES ON NATURAL CLATHRATES FROM THE GREENLAND ICE CORE PROJECT ICE CORE, AND NEUTRON-DIFFRACTION STUDIES ON SYNTHETIC NITROGEN CLATHRATES

We present the results of Raman spectroscopic experiments on air clath rates in the GReenland Ice Core Project (GRIP) deep ice core, which di ffer markedly from previous measurements on the Dye 3 ice core. The N- 2/O-2 ratio we observe is much closer to the atmospheric value. This h as new implications for the interpretation of gas distributions in ice sheets. Raman spectroscopic scans to determine the N-2/O-2 ratios on different planes through a clathrate, in which the two axes of the sca ns are perpendicular to each other, give no indication of fractionatio n effects on the N-2/O-2 concentrations within a clathrate specimen. T he frequency shift of the N-2 and O-2 peaks due to decomposition of a clathrate to an air bubble is shown qualitatively. From their peak int egrals there is no indication of different retransformation rates to a ir bubbles between the oxygen and the nitrogen contents of clathrates. In air bubbles resulting from clathrate decomposition, the N-2/O-2 ra tio shows similar values to those observed in clathrates and present a tmospheric values. Statistical studies on the size, shape, and number concentration of clathrates are intended to give an estimate of the to tal amount of gas occluded in the clathrates. We present preliminary r esults 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 degre e of filling of 107.5%.