US stocks posted moderate gains Tuesday, lifted by a positive start to the corporate earnings season and Chinese trade data that spurred speculation that Beijing would loosen monetary policy. After a triple-digit opening surge, the Dow Jones Industrial Average was up 68.80 points (0.56 percent) to 12,461.49 in closing trade. The tech-rich Nasdaq Composite added 25.94 points (0.97 percent) to 2,702.50, and the broader S&P 500 advanced 11.27 points (0.88 percent) to 1,291.97. Wall Street welcomed Alcoa\'s unofficial kickoff of corporate earnings season Monday after the markets closed. Alcoa shares were up 1.1 percent on Tuesday. \"Traders are celebrating the aluminum giant\'s stronger-than-expected top-line results, as well as its forecast for growing global demand,\" said Andrea Kramer at Schaeffer\'s Investment Research.