The Sensex at the Bombay Stock Exchange on Tuesday surged 170 points, to 16,526 in opening trade, on fresh buying by investors. But the Sensex later surrendered all those gains, and stood 11 points, or 0.1 percent in the red, at 16,345, amid volatile trade, a short while ago.Key stock indices in Japan, China, South Korea, and Hong Kong traded mixed, on Tuesday.However, the US markets had closed 1.2 per cent higher overnight, after the US Institute of Supply Management said its manufacturing index climbed to 58.4 per cent in January, the best number since 2004, and well ahead of the 50 per cent that indicates growth.