Not really related, but Interesting paper on DNA degradation rates in fossils. They do discuss optimal temp for storage at -5c.
"In an attempt to document a correlation between sample age and DNA preservation, we use a quantitative real-time PCR (qPCR) design to measure relative copy numbers of mitochondrial DNA (mtDNA) fragments from bones of the extinct New Zealand moa "
http://rspb.royalsocietypublishing.org/content/279/1748/4724
This is great, by using small interlocking magnetic fields, you can keep the water in a higher vibrational state, allowing a "super-cooling" without getting crystallization and cell rupture
Subzero 12-hour Nonfreezing Cryopreservation of Porcine Heart in a Variable Magnetic Field
"invented a special refrigerator, termed as the Cells Alive System (CAS; ABI Co. Ltd., Chiba, Japan). Through the application of a combination of multiple weak energy sources, this refrigerator generates a special variable magnetic field that causes water molecules to oscillate, thus inhibiting crystallization during ice formation18 (Figure 1). Because the entire material is frozen without the movement of water molecules, cells can be maintained intact and free of membranous damage. This refrigerator has the ability to achieve a nonfreezing state even below the solidifying point."
http://mobile.journals.lww.com/transplantationdirect/_layouts/15/oaks.journals.mobile/articleviewer.aspx?year=2015&issue=10000&article=00005#ath