# Theoretical and Experimental Analysis for Cleaning Ice Cores from EtisolTM 140 Drill Liquid
## 3 Experimental Testing
### Longlasting Preservation  
The conservation of ice cores is fundamental for preserving their precious information for future studies. Ice cores are stored in refrigerated rooms. In some storage facilities the cores are placed on shelves in cardboard \"tubes\", in others on shelves in cardboard boxes and in others inside insulated crates on shelves. From previous analysis, the only driver for ice sublimation is the different partial pressure of water vapor at the ice surface and in the ambient air. If RH is 100%, then a temperature difference between the ice and the air is needed to drive sublimation. The air in a freezer/cold-room is close to saturated (RH 100%) because when the door is opened, warm moist air is introduced. The excess moisture condenses in the freezer units and most of it is subsequently physically removed through drainpipes by the de-frost cycle of the freezer. However, some of the vapor is re-introduced into the freezer air during de-frosting because the units are heated. So, when de-frost is over and freezing resumes, that air becomes supersaturated and the surplus vapor condensates again in the freezer units. RH of close to 100% is quickly restored. In reality, the air in the freezer is slightly under-saturated, because for the cooling units to work, they are typically \(-35\,^{\circ}\)C in a \(-30\,^{\circ}\)C cold room. So why do we see sublimation of ice cores in cold storage, particularly when they are forgotten on worktables? The answer is the transient temperature check of the de-frost cycle. Depending on the freezer and season (moist summer air or dry winter air) defrosting is required at rates from twice a day to several times a week. The cooling is stopped and the air is heated up to melt the ice in the evaporators. This creates a temperature difference between ice and air, and the ice core warms up while some condensation frost is formed on the surface. When cooling resumes, the core is now warmer than the air, so there will be sublimation. However, the ice that is sublimating is not the same as was condensed. Observations are in agreement with what is predicted by a diffusion approach [6] with stronger sublimation at the sharp edges which become rounded. If the exposed ice core is stored inside a plastic bag, the net transport of vapor through the bag is zero. However, we still observe that the edges of the core become rounded and we see a significant amount of frost forming on the inside of the bag, indicating a net transport of ice from the core to the inside surface of the plastic. Over time, this process significantly decays the quality of ice cores. That is why ice cores should never be exposed to defrost cycles (or any changes in temperature) by storing them in, e.g., cardboard boxes or tubes. EPICA and BEOI have chosen to store all cores inside the same insulated boxes that are used for shipping ice cores  
Figure 4: Amount of drilling liquid in the ice cores as a function of time. from the field to the freezer and around the world. Because of the heavy insulation, the cores are not experiencing the defrost cycles and the temperature is almost constant. Just recently, in the Copenhagen storage, we observed perfect conservation of ice cores 40 years after drilling. The samples were in mint condition with sharp edges and no frost on the inside of the plastic, providing a strong and clear experimental confirmation that the only driver of sublimation in a cold room is temperature oscillations. Of course, if the cores are stored in a snow cave (very stable temperature), the snow walls will ensure RH of 100%, so no sublimation will occur as soon as the ice cores reach the same temperature as the cave. When people enter the cave, they bring in some outside summer air and they also emit water vapor through breathing. This will condensate as frost on both ice cores and walls.