Sullivan graduated from William Howard Taft High School in the Woodland Hills district of Los Angeles, California, in 1969. She took both French and German in high school, and resolved to have a career in the foreign service. She chose to enter the University of California, Santa Cruz (UCSC), on account of its excellent Russian language program. The university required that humanities students take three science classes and vice versa. She chose to take courses in marine biology, topology and oceanography. She enjoyed these, and altered her course to take in more science subjects. She was an exchange student at the University of Bergen in Norway for the 1971–1972 school year and the two summers around it, and decided to change her major to oceanography. She was awarded a Bachelor of Science degree in Earth Sciences from UCSC in 1973, and a Doctor of Philosophy in geology from Dalhousie University and the Bedford Institute of Oceanography in Nova Scotia, Canada, in 1978, writing her doctoral thesis on The structure and evolution of the Newfoundland Basin under the supervision of Michael John Keen. While at Dalhousie, she participated in several oceanographic expeditions that studied the floors of the Atlantic and Pacific oceans.
