This thesis explores how oceans in 21st century SF (science fiction, speculative fabulation) engage with posthumanist modes of knowing in three works of contemporary speculative fiction that address real and speculative damage to our planet's oceans: Nnedi Okorafor’s Lagoon (2014), Rita Indiana’s Tentacle (2018) and Alexis Pauline Gumbs’ M Archive: After the End of the World (2018). I contend with Elizabeth DeLoughrey’s identification of a new oceanic imaginary, in which she argues that the oceans are becoming identified through their intra-active agency. These explorations are informed by the critical intersections of the blue humanities, ecocriticism and new materialism by Donna Haraway, Stacy Alaimo and Astrida Neimanis, whose work facilitates an understanding of human-oceanic material interdependencies, and the deep naturecultural effects of human histories of colonialism and hetero-patriarchy on our environments.

I argue that SF, as a mode of imagining which estranges and calls into question the onto-epistemological boundaries of the human, is able to story the diverse more-than-human agencies that make up the materiality of the ocean. In critically analysing the oceanic imaginaries of three works of contemporary SF, I argue the texts are engaged in oceanic practices of dislocating and deterrestrialising. In doing so, they open us to posthuman and nonhuman ways of knowing and being in the Anthropocene.