This is a really good thread.
My understanding (from my Intro to Physical Geology course) is that the dating of ice cores is achieved by counting layers which represent the change in seasons -- not unlike counting rings in a tree gives you the age of the tree. Has absolutely nothing to do with radiocarbon dating.
So, yes, that must have been tricky for Jehovah: no rain/precipitation until 4000 years ago; then lay down what looks exactly like 400K years of snowfall (including seasonal differences) in less than a year.
He just loves to test our faith!