By Cecile Mantovani and Denis Balibouse CHAMONIX, France (Reuters) – Standing on a snowy mountainside about 2,500 metres above sea level, Eric Marechal holds up a crimson test-tube. Inside is an algae sample known as “snow blood,” a phenomenon that accelerates Alpine thaw and that scientists worry is spreading. “These algae are green. But when it’s in the snow, it accumulates a little pigment like sunscreen to protect itself,” said Marechal, research director at Grenoble’s Scientific Research National Center, who was collecting laboratory samples on Le Brevent mountain with teammates. Around h…