Alison Criscitiello removes the inner barrel of drill containing an ice core from the West Antarctic Ice Sheet. Snow accumulates on the ice sheet in layers, so drilling deeper reveals older ice crystals. The MIT/WHOI Joint Program graduate student will measure the concentration of a chemical compound in the ice called methanesulfuric acid, or MSA, in samples from the cores to reconstruct how sea ice coverage has changed over hundreds of years. (Photo by Sarah Das, Woods Hole Oceanographic Institution)