The Dow Jones Industrial Average closed above the key threshold of 16,000 for the first time Thursday, extending a rally that has seen the gauge add over 22 percent this year. At the closing bell, the Dow rose 108.91 (0.68 percent) to 16,009.73. The broad-based S&P 500 jumped 14.53 (0.82 percent) to 1,795.90, while the tech-rich Nasdaq Composite Index added 47.88 (1.22 percent) at 3,969.15.