Dating antarctic ice cores
During this time, ice cores are stored below -10 °C to prevent cracking due to expansion at higher temperatures.
At drilling sites, a relaxation area is often built within existing ice at a depth which allows ice core storage at temperatures below -20 °C.
In ice from the Vostok core (Antarctica), the outer portion of the cores have up to 3 and 2 orders of magnitude higher bacterial density and dissolved organic carbon than the inner portion of the cores, respectively, as a result of drilling and handling. When brought to the surface, there is a drastic change in pressure. It has been found that allowing ice cores to rest for some time (sometimes for a year) makes them become much less brittle.
Due to the internal pressure and varying composition, particularly bubbles, sometimes cores are very brittle and can break or shatter during handling. Decompression causes significant volume expansion (called relaxation) due to microcracking and the exsolving of clathrate hydrate (enclathratized) gases.
Stable oxygen and hydrogen isotopic ratios are normally reported relative to the SMOW standard ("Standard Mean Ocean Water" (Craig, 1961b)) or the virtually equivalent VSMOW (Vienna-SMOW) standard.
Carbon stable isotope ratios are reported relative to the PDB (for Pee Dee Belemnite) or the equivalent VPDB (Vienna PDB) standard.
These differences are reflected in the core processing facilities.It has been observed that the internal structure of ice undergoes distinct changes during relaxation.