What a day for Amazon: According to this New York Times report by David Streitfeld, the company’s “market cap shriveled in one day by about $16 billion.”A Bloomberg report by Danielle Kucera estimates Jeff Bezos’s personal stock holdings in the company may have plummeted by “as much as $4.67 billion in value” on Tuesday.

What’s going on? While sales at the company remain huge, increasing 44 percent this quarter to $10.88 billion, net income fell 73 percent to $63 million, or 14 cents a share, down from $231 million, or 51 cents a share for the same period last year. The Bloomberg story points to a few key areas of loss — perhaps most notably in an area where you might think Amazon would excel: shipping.

Analyst Colin Gillis calls attention to a serious “rise in customers using Amazon’s Prime program, which offers unlimited two-day shipping for $79 a year. The company’s shipping fees generated $360 million in the third quarter, dwarfed by $918 million in shipping expenses.”

There’s also the fact that company’s newest product, Kindle Fire, which Bezos touts as driving sales throughout the third quarter, simply doesn’t make the company money in the short run: a second analyst cited in the Bloomberg report puts Amazon’s operating margin on the device at just “1 percent or 2 percent.”

And it’s been a bad quarter in other ways, as Streitfeld notes in his Times‘ report:

First came the lengthy fight with the state of California over whether Amazon would collect sales tax. Even more damaging was a long article in The Morning Call of Allentown, Pa. It revealed that workers in Amazon’s local warehouse were collapsing from heat stress as they struggled to ship [books]… It was a striking snapshot of the underbelly of the Internet economy: Amazon arranged with the local ambulance service to have vehicles stationed outside the warehouse on peak heat days. As workers fell down on the job, they were whisked away to the hospital, the newspaper said.

While Amazon stock may quickly rebound, the company’s short-term future doesn’t look all that bright: Amazon says a fourth quarter loss, perhaps as much as $200 million, is a real possibility.