I knew Priscu and worked with some of his grad students at Montana State.
Here's one of their papers on the Lake Whillans project.
One of the more relevant findings is that many of the most abundant organisms (by genetic analysis of small subunit ribosomal RNA genes) were closely related to chemolithoautotrophic organisms. Basically, organisms that can obtain energy by oxidizing inorganic compounds. They found that there was sufficient chemolithoautotrophic carbon incorporation to support the heterotrophic demands of the ecosystem. They also found an abundance of organisms related to nitrifiers (organisms that oxidize ammonia into nitrite and nitrate), along with sufficient ammonia, suggesting that nitrification is a primary pathway of new organic carbon production in the ecosystem.
Christner, Brent C., et al. "A microbial ecosystem beneath the West Antarctic ice sheet." Nature 512.7514 (2014): 310-313.