Today my SO score topped 100k, peaked at around 100,050 and shortly afterwards dropped to 99,977. 

What could be causing this? I investigated further, and noticed this:

If I go via http://stackoverflow.com/ my reputation on the top bar shows 99,977.

If I go via http://meta.stackoverflow.com/ it is 100,062.

I think that the higher total is correct, as (cue the drum roll) I passed the 100k mark on SO today.

I tracked through my reputation history and it shows a large spike on Jan 14th of this year, which I recall, wasn't there on the day itself.