Major averages ended mixed in a volatile session Tuesday. The Dow Jones industrial average gained 0.4%, the S&P 500 added 0.3% and the Nasdaq eased 0.1%. Preliminary data showed Nasdaq volume coming in lower than Monday. NYSE volume rose a bit. Stocks turned sharply lower about a half hour into the session. The Nasdaq fell 1% on reports a U.S. cargo vessel was seized by Iran. The seized ship turned out to be a Marshall Islands flagged vessel.