You can maybe get some understanding from the data gathered by Hacker News Karma Tracker. This can only be done starting in February 2013, though, since it only includes accounts that have made comments since mid-January.

3326: http://hn-karma-tracker.herokuapp.com/month/february-2013

2013: http://hn-karma-tracker.herokuapp.com/month/march-2013

1115: http://hn-karma-tracker.herokuapp.com/month/april-2013

1557: http://hn-karma-tracker.herokuapp.com/month/may-2013

2717: http://hn-karma-tracker.herokuapp.com/month/june-2013

973+: http://hn-karma-tracker.herokuapp.com/month/july-2013

Perhaps it is a change-in-season thing? (biggest months above are February and June, although July looks like it will also be high.)