The Memorability of Polar Ice Grain Size on Temperature and Its Implications for Reconstructing Paleoclimate Conditions

Abstract

The physical basis of grain size in polar ice crystals as a climate proxy has remained largely elusive. Here, this work investigates the influence of temperature, specifically between –30 and –3 °C, on grain evolution in firn samples from Summit, Greenland, simulating conditions encountered during the transport and storage of ice core samples. Utilizing 2-D optical micrographs, 3-D X-ray micro-computed tomography, and grain development models, the research reveals negligible variation in ice crystal grain size. Notably, the ability of these grains to return to their original size at a specific temperature, despite subsequent temperature changes, is referred to as the memorability of grain size on temperature (MoGSoT). This phenomenon can be attributed to the reduction in grain size caused by temperature gradient metamorphisms and the screw-step growth observed under isothermal conditions. In addition, sinusoidal signals incorporating six composite frequencies were developed to model temperature variations related to grain size, elucidating periodic climate cycles spanning multi-decadal, multi-centennial, and ten-millennial periods. Beyond establishing MoGSoT, which highlights the fundamental physics of polar ice grain size and its role in paleoclimate reconstruction, this work also emphasizes the intricate interactions between external factors, e.g., astronomical, orbital, solar, and planetary influences, and the internal dynamics of the climate system, including ocean-atmosphere oscillations, thereby offering new perspectives on the origins of climate change, whether anthropogenic or natural.

Keywords: paleoclimate, grain size, temperature, climate proxy, firn, ice