The fate of humanity is increasingly recognised to be connected to the fate of the ocean: rising sea levels, 'Ocean Decades', deep sea mining, and new 'blue' disciplines all speak to a rising interest in further understanding and exploiting the sea. But what places do the ocean and the marine sciences have in the various disciplines represented at ISHPSSB? What does it mean for a discipline to be 'marine'? Why do marine sciences exist in the first place, and why have some humanities disciplines been slow to engage with the marine environment and the sciences that study it? In this talk, we discuss these issues, drawing together considerations around the nature of the ocean with reflections on the nature of the disciplines that do, or might, study it.