Photographer Mark Cosslett

Pushing to depths considered impassable in the labyrinth of caves in the Pang Mapha district of northern Thailand was a feat Photographer Mark Cosslett was uniquely prepared to tackle for "The CO₂ Chronicles" (read excerpt). Recipient of a Shipton/Tilman grant for new exploration, Cosslett returned to the region for the third time to test a new oxygen breathing device to go deeper than ever thought possible.

For two weeks, the expedition group, which included writer Tim Cahill, professional outdoor athlete Will Gadd, caving safety expert Maria Cashin, and New York University Professor Richard Borowsky, pushed the CO₂-laced caves while accomplishing a laundry list of goals, from studying a highly evolved species of blind river fish to dropping to unexplored depths in the caves' bat-covered, spider-spawning bowels.

"We were hoping to find some archaeological or biological finds—we assisted Richard Borowsky in his biological research and located some coffins that were probably undiscovered," says Cosslett, who recently competed in a solo 24-hour mountain biking race. "But the primary goal was to open up caves worldwide that are blocked by carbon dioxide all over the equatorial region."

But while the technical aspects are intriguing, Cosslett finds the human aspect of photography highly rewarding. "The most satisfying shots are the ones that require some dedication and gaining the trust of your subject—especially when you don't speak the language," says Cosslett. "You can't rush it, but it makes all the difference in the photograph."

Portrait courtesy of Mark Cosslett