Probably increased press coverage and the Pirateat40 scam/scams coming to an end
As the fictitious nature of the ponzi deposits are exposed, the "m2" money supply of bitcoins is reduced (people who think they are holding bitcoins, are in fact not holding anything), and there is a rush to buy more as many of the disenfranchised investors/marks are still hoping the value of bitcoin itself will appreciate against the dollar.