The geopolitics of deep oceans written by John Hannigan is a social scientific analysis of the ways in which we understand and construct the oceans of the world. With a background in environmental sociology and international politics as well as a life-long fascination with the deep oceans, the author draws together and comments on scientific research, media materials, the legacies of adventurers and explorers as well as popular culture – whose fictional representations ‘often swim in the currents of contemporary geopolitics’ (page 78) – in order to trace the historical development and real-world implications of the discourses of the deep. The outcome is an intriguing contribution to the contemporary discussion on the state and fate of the planet's deep oceans which is highly relevant also in the context of the Arctic, where the decrease in sea ice cover is opening if not the ocean at least the collective imagination to new kind of human activity and intervention.

In the book Hannigan identifies four competing (and overlapping) discourses – ‘interrelated set of storylines which interpret the world around us’ (page 5) – of the deep, each of them with their own historical contexts and basic assumptions regarding the roles, responsibilities and relationships of different actors and entities. While the discourses differ in the ways in which they perceive the ‘oceanic commons’ (page 12), they all ‘share a conception of the ocean as a previously empty or ‘smooth’ space that needed to organized, divided, classified and inscribed’ (page 17). What is interesting is that the author does not identify an economic discourse as an independent narrative in its own right: instead, the idea and potential of economic utilisation of the deep oceans is entangled with all the different discursive constellations within and through which we make sense of the sea.

The chapter Oceanic frontiers: Harvesting the commons portrays a discourse that ‘frames the deep as a ‘cornucopia’, a land of plenty whose fabulous mineral and biological wealth is just waiting to be harvested’ and whose commercial potential is ‘soon to be realized’ (page 20). However, this discourse is more than a storyline of economic potential and exploitation: its understanding of the ocean is intertwined with the excitement and adventure of scientific exploration and discovery. The following chapter, Governing the abyss: Sharing the commons introduces a legal and normative narrative that is most commonly referred to in contemporary policy discourse: the idea of oceans as a space that needs to be governed in order to regulate and redistribute ‘the resources that abound in the untamed frontier of the deep’ (page 75). The chapter traces the development of the United Nations Law of the Sea Convention through two opposing doctrines – mare clausum, ‘the right of individuals rulers and/or nations to assert unchallenged dominion over the sea’ (page 54) towards mare liberum, ‘the sea common to all’ (page 54).

Meanwhile, the chapter Sovereignty games: Claiming the oceans highlights a discourse that perceives the deep oceans not (only) as an economic Eldorado, but as ‘a territorial frontier that must be secured for political and military purposes’ (page 77). From this perspective, the oceans become primarily a matter of national security, political interests and military strategy that entangle to a zero-sum game of territorial claims and power politics. The last content chapter of the book is Saving the oceans: Protecting the commons. It depicts a discourse that understands the deep sea as the largest ecosystem on earth that has now come under threat as a consequence of human activities. Among others, climate change, ocean acidification, (plastic) marine pollution, biodiversity loss as well as seabed mining and other forms of economic exploitations are now threatening the survival of both individual species and whole oceans as habitats. However, the question remains why the deep sea needs to be protected and preserved: is it for the intrinsic value of the oceans and the species that inhabit them or is it to safeguard the essential functions that marine ecosystem services have in maintaining human life?

In the final part of the book, Hannigan concludes the argument by drafting an emergent discourse of the oceans as the ‘canary-in-the-mineshaft’ (page 136) of the changing climate; however, the author does not push this line of thought beyond some brief open-ended remarks. The book ends on a rather grim note on the risk of the world ‘being engulfed in a new geopolitics of the deep that revolves around an escalating competition for oceanic territory’ (page 141). To be honest, after such a comprehensive and conclusive analysis, a bit more detailed insights could have been expected from the conclusions of the book.

While the book as a whole is a wonderfully accessible, well-written, engaging and entertaining read for anyone with an interest in the ways in which we think about the world's oceans, why and with what kind of consequences, the title of the book and its cover might turn away some potential readers that would find its contents enjoyable. The word ‘geopolitics’ in the title combined with the US flag in the cover erroneously imply a traditional ‘realist IR’ focus of analysis, while in the context of this book ‘geopolitics’ refers to so much more – the irreducibly political nature of the ways in which we construct the (oceanic) spaces and places around us.