As we reported yesterday, in the hours during and after the news of Michael Jackson’s cardiac arrest and ensuing death, tweets about the pop icon comprised 30 percent of total volume on Twitter, and that might be a conservative estimate.

Since then, we’ve learned a lot more about the story’s impact on the Web, and we now have some fascinating numbers and charts from Google, Yahoo, and others about how the Michael Jackson news impacted their services.

First, leading widget network Clearspring, which also owns content sharing service AddThis, reports that the Jackson story was actually most shared on Facebook and not Twitter. That’s not altogether surprising considering that Facebook’s userbase is still much larger, but the more real-time Twitter grabbed the early headlines. Clearspring’s chart shows the social media sites where users were sharing the news the most:

Finally, New Media Strategies notes that Jackson’s Wikipedia page logged 1.8 million visitors yesterday, compared to its daily average of just 20,000. It also saw a whopping 650 edits as users updated the entry furiously as news broke.

What to make of all these numbers? Simply that Jackson’s sudden and shocking death is one of the biggest news stories in recent memory, and will likely continue to dominate online chatter over the next few days.