Air clathrate hydrates in the EDML ice core, Antarctica

Abstract

In the deeper part of polar ice sheets, air hydrates trap most of the ancient air molecules, which are essential for understanding past climate. We use digital image analysis to create a high-resolution record of air hydrate number, size, and shape from ice thick-section microphotographs of the EPICA Dronning Maud Land (EDML) ice core, Antarctica, over a depth range from 1255–2771 m. We confirm that the air hydrate number and size correlate with paleoclimate and that the correlation disappears in the deeper parts of the ice core, which was previously shown for the Vostok and Dome Fuji ice cores in Antarctica and the GRIP ice core in Greenland. We also observe that the air hydrates grow with depth. Furthermore, we identify two peculiarities: a distinctive change in air hydrate aspect ratio (AR) and orientation at about 2030 m and a region of increased air hydrate clustering from 2392–2545 m depth. Remarkably, they coincide with regions of distinctive changes in ice microstructure as a response to changes in local ice dynamics; therefore, we discuss the influence of ice deformation on the air hydrate ensemble.