Tunnicliffe decided then to become a marine biologist and dedicate her time to learning the name and origin of all the creatures that created those shells.

During a post-doctoral fellowship at the Institute of Ocean Sciences, Tunnicliffe instead became the first woman on the West Coast to lead deep-sea research expeditions from Vancouver Island.

She only meant to stay in British Columbia for two years, but by 1983 Tunnicliffe helped to discover hydrothermal vent systems off the coast, explored previously unknown sections of the deep sea, and was part of the discovery of over 80 new marine species.

[7] Her research on hydrothermal systems helped establish Canada's first Marine Protected Area: the Endeavour Hot Vents MPA.

She was also a leader of the Deep-Ocean Stewardship Initiative Minerals Working Group, which provides interdisciplinary guidance regarding sustainable deep-sea mining.

Her main work in the network is discovering ways to conserve the Canadian marine ecosystems in an ocean environment that is changing rapidly.