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On Tuesday, the Dow Jones industrial average, already down 9 percent in 2008 on glum economic news, plummeted nearly 600 points (5 percent) before rallying after the announcement of an emergency three-quarter-point interest-rate cut by the Federal Reserve, the biggest such reduction in 24 years.

Does 'on glum economic news' mean 'according to glum economic news' ?

Or does it mean that the down of Dow Jones industrial average 'resulted from glum economic news'?

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AhnOn Tuesday, the Dow Jones industrial average, already down 9 percent in 2008 on glum economic news, plummeted nearly 600 points (5 percent) before rallying after the announcement of an emergency three-quarter-point interest-rate cut by the Federal Reserve, the biggest such reduction in 24 years.

Does 'on glum economic news' mean 'according to glum economic news' ?

Or does it mean that the down of Dow Jones industrial average 'resulted from glum economic news'?

That's probably what it means. The sentence, however, is poorly written, so don't be surprised that you have trouble understanding it.
Comments  
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I am pretty sure that it means the later. The glum economic news reduced investors' confidence, and that lead to a drop in the Dow Jones IA.
Thanks for the answers.
I looked up 'on' in a dictionary, and I found that one of the definitions that 'on' has is 'used to show the basis or reason for sth'.
So can I guess that 'on' in 'on glum economic news' in this sentence fits this definition?