Merrill Profit Falls, Global Markets Down  NEW YORK (Reuters) - Merrill Lynch   Co. &lt;A HREF="http://www.investor.reuters.com/FullQuote.aspx?ticker=MER.N target=/stocks/quickinfo/fullquote"&gt;MER.N&lt;/A&gt; on Tuesday  said third-quarter profit fell 8 percent, hurt by reduced  trading in debt and equity markets.