Czerski, Helen. 2023. The Blue Machine: How the Ocean Works. Norton & Co., New York, NY. ISBN 978-1-324-00671-8 (Hardcover). 446p. ~US$30.00

Arguably, no one since Rachel Carson has so eloquently captured the grandeur of life in the sea around us (Carson 1950), and no one since Wallace Broecker has so elegantly traced the ocean's mysterious physical–chemical inner workings (Broecker 1998). In her new book, The Blue Machine: How the Ocean Works, ocean physicist Helen Czerski of University College London seamlessly bridges these areas of the chemistry of life and the physics of the ocean, ranging from microscopic to global scales. In doing so, she has illustrated how the dynamic and living ocean symphony operates, with the ocean engine serving as the principal beating heart of our planet.

Powered by the sun, Earth's ocean functions as a gigantic engine driving enormous flows of matter and energy with consequences for every living creature on our ocean planet—from climate to biodiversity to the very state of our civilization. The Blue Machine makes its debut at a time when there are worrying trends of record-breaking oceanic warming, freshening of polar waters, acidification, deoxygenation, overfishing, and pollution that could tip the currently stable ocean ecosystem into an alternate unfavorable state (Watts, 2024; van Westen et al. 2024). In this text, plain language is used to explain how the ocean engine works (e.g., by converting sunlight into movement and life) and how the ocean is inextricably linked to all of life on Earth (e.g., by serving as the cradle of life and as its thermostat), and how the ocean acts as the largest buffer in the Earth system dampening anthropogenic climate change. In exploring these areas, Czerski aims to impart an understanding to readers that will motivate us to protect the only Blue Machine there is.

The book starts off with an Introduction in which the author describes partaking in ceremonial canoeing between the islands of Hawaii along the lines of ancient mariners who voyaged the Pacific. Later, introducing the concept of water movement, she pauses to narrate how dead water (internal waves) in the Ambracian Gulf two millennia ago may have hindered Mark Anthony's navy from mounting a surprise pre-dawn attack on Octavian's forces that likely led to the fall of the Roman Republic. Other historical asides from the 1800s include a detailed description of the transition from sailship to steamship and its modern-day consequences, and of saving the River Thames from the untreated sewage of London that has lessons for managing riverine and coastal health today. In addition, there are numerous personal stories, such as going on a ship-board expedition during a raging 2013 autumn storm in the North Atlantic to obtain field measurements of air–sea gas exchanges as bubbles furiously broke at the surface.

The body of the book is organized into three parts, each of which has subsections and subtopics. Part 1, What is the Blue Machine? is divided into the Nature of the Sea (how temperature, salinity, and wetness of water play out on a rotating planet), the Shape of Seawater (how the shape-shifting ocean fills varied basins), and the Anatomy of the Ocean (how the ocean's water masses circulate). This is then followed by Part 2, Travelling the Blue Machine, which covers Messengers (physical–chemical and biological tracers that define underwater climate), Passengers (plankton hitchhiking ocean currents), and Voyagers (swimmers like turtles, eels, tuna, penguins, and whales that travel thousands of miles to feed and breed). And finally, Part 3 focuses on The Blue Machine and Us, which includes a chapter on the Future (knowing the ocean engine as an essential life support system). Each of the book's three parts, in turn, contains numerous cool and intriguing subtopics where matters are discussed in detail. Going from the beginning of the book to the very end, a selection of these subtopics include: Stacked Water (mixed versus stratified water column), Coping with Salt (a loggerhead turtle sheds liters of tears each hour to rid itself of excess salt), Color of Water (why water appears the way it does), Ocean Banquet (rich fisheries fueled by nutrients brought up by upwelling waters), Leaky Surface (vertical flux of carbon or Biological Pump), Towers of Plankton Microbes (how trillions of Earth's smallest critters manage its largest ecosystem), Tales from a Whale's Ear (what stress hormones tell about whale welfare), Floating Fertilizer (how whale poo fertilizes Antarctic surface waters), Deep Ocean Breaths (how ocean circulation picks up and spits out gasses or Biophysical Pump), A Penguin's Commute (how life cycles hinge on predictable food availability in space and time), and Oceans and Us (reconciling current knowledge of the changing ocean and how the fate of oceans and humans are tied to wise management—with which globally distributed ocean observatories can help, https://ioos.noaa.gov/).

Throughout, the text is characterized by lucid descriptions of complex subjects. The book is further enriched by numerous personal stories that connect to each of the themes explored, useful footnotes that enlighten the reader with key facts and concepts, and convenient chapter-by-chapter literature references to the topics covered. These strengths more than compensate for some weaknesses we found in the text. Primarily, while there are maps of prevailing winds and surface currents in the book, there is no map of the Great Ocean Conveyor or Global Ocean Thermohaline Circulation in the ocean's interior. Moreover, there is not a detailed description of this vital and largest ocean mixing phenomena central to the operation of the ocean engine—although it refers to it often (e.g., pp. 61–62, 196–207, 318). Finally, the text could have been supplemented with supportive images or sketches of the many curious organisms discussed, linking biological structure to ocean function with which readers will not be familiar (e.g., Janthina janthina, a floating snail that only lives at the surface clinging to bubbles it generates).

In summary, The Blue Machine is a rich and almost poetic tapestry interweaving history, culture, personal experiences, biogeochemical and physical inventories, and fluxes related to how our dynamic Ocean engine really works. Reading through this treatise, we appreciated how the author got us to first appreciate the magnificent ocean engine that operates our planet before ending with a discussion of the many threats that it now faces. Indeed, as the quote in the last chapter of the book by NASA astronaut Lacy Veach suggests, we can only protect what we understand. Czerski has enabled us to see the full physical, chemical, and biological beauty and complexity of the ocean and appreciate its everyday role in the well-being of people and the planet—understanding that can help develop the urgent global-level cooperation required to restore and protect our one and only watery home.