The American National Ice Core Laboratory provides some information on how they store and keep ice cores. These include proxies for temperature, ocean volume, precipitation, chemistry and gas composition of the lower atmosphere, volcanic eruptions, solar variabilitysea-surface productivitydesert extent and forest fires. These locations make samples available for testing. Without precipitation how would or could you even guess at what a year would be. They spent two nights at each site, first collecting radar data and secondly collecting a 15 m shallow ice core.
Lower down the ages are reconstructed by modeling accumulation rate variations and ice flow.
Record-shattering 2.7-million-year-old ice core reveals start of the ice ages
Convince developing countries to wait until we have a solution free energy, etc. What happened at Lake Vida may have been the fate of other Antarctic lakes, during even colder times, and more tropical aquatic ecosystems during extreme global glaciations of the past, such as the 'snowball Earth' Million years ago. Ice from Greenland cores contains dust carried by wind; the dust appears most strongly in late winter, and appears as cloudy grey layers. Lemieux-Dudon B, et al. A second 10 cm diameter core was recovered in by the same drill rig to m. Retrieved 5 September