He is an expert in the general circulation of the oceans and the role of the ocean in the climate system.

Roemmich teaches courses on large-scale ocean circulation and oceans and climate. He advises graduate students in the Climate, Ocean, and Atmosphere Program (COAP), and postdoctoral researchers.

Roemmich is a leader in the Argo Program, a long-term systematic observing system of the physical state of the global ocean. Argo achieved a milestone of 3,000 free-drifting profiling floats in 2007 and has sustained over 3,000 floats for more than a decade since then. Using technology developed at Scripps, Argo floats drift about a mile below the ocean surface for a period of 10 days. The floats then rise to the sea surface, collecting a profile of temperature and salinity that is immediately transmitted via satellite to an Argo Data Center. The floats return to their assigned depth and continue making measurements for a lifetime of over five years, surfacing every 10 days to report their data. All Argo data are publicly available on the Internet and are used by researchers around the world.