Her main areas of interest are marine biogeochemistry and ecological physiology of phytoplankton. Her research program seeks to understand variations in marine primary productivity and cycling of nutrient elements in the oceans. Dr. Varela’s long-term research goal is to link physiological studies on phytoplankton to larger marine phenomena, so as to better understand the effects of unicellular algae on earth's biogeochemical cycles, marine ecosystem structure and global climate change over geological times. Studies are conducted in the laboratory and on oceanographic cruises to coastal and open ocean waters in the equatorial and north Pacific Ocean, in the Arctic Ocean, and in the Antarctic.