Smelly and saturated with seawater, the marsh muck sucks at the waders of UC Santa Cruz graduate student Aliya Khan as she walks along a channel in Elkhorn Slough. She places a tube into the water, which will collect samples that will help uncover the salt marsh’s ability to serve as a carbon dioxide vacuum and vault. Khan’s research is taking place at an important time. … Salt marshes, which have historically been drained and turned into farms or land ripe for real estate development, are emerging as a powerful tool in the fight against global warming.