Abstract
Marine Geochemistry describes the chemical cycles occurring in the largest, most dynamic element of the Earth system, cycles which have the capacity to shape our climate both now and in the future. Twenty years ago, we took the view that the ocean was largely unchanging; if you went to a station in the open ocean and found a different set of properties to those which had previously been measured at that site, you would be surprised. Now our assumption is that the oceans are slowly evolving as they take up around 25% of the carbon released into the atmosphere by man’s activities, in the process becoming more acidic and trapping 93% of the heat retained in the planetary system. Understanding how this ocean uptake works and predicting how it will evolve are among the largest challenges that exist in environmental science and demand a step change in the ability of the researchers entering the field to synthesise information from a range of sources and disciplines. This book will help them achieve the level of understanding needed for this crucial task.
Roy-Barman and Jeandel have used all their experience to pull together a vast array of theoretical material and observational data into a coherent whole which allows the dedicated reader to gain an appreciation of the role of the whole ocean system in the Earth system. This has been no small task; recent years have seen the pioneering observational campaigns of GEOSECS, JGOFS and WOCE complemented by the massively ambitious GEOTRACES campaign which aspires to do for trace element and isotope ocean chemistry what those earlier campaigns did for our understanding of macronutrient and carbon cycles and ocean circulation. Now that the field phase of GEOTRACES is over, it is time to begin deciphering and understanding what this enormous body of material tells us about the puzzles left behind by previous programmes and how the oceans function now, have evolved over time and will change in the future.
Achieving a thorough understanding of how ocean chemistry works and what it means for us into the future demands that information from a wide range of ocean sub-disciplines, including marine chemistry, biological oceanography and ocean circulation studies, be brought together. For this reason, the book begins with detailed treatments of the fundamental building blocks of the field: ocean circulation treated from a theoretical and mathematical perspective, basic concepts of ocean chemistry, numerical modelling, isotopes and radioactive decay. The meat of the book really arrives about halfway through the 11 chapters when these basic concepts are brought together in a series of synthetic chapters dealing with ocean productivity, gas exchange, particle flux, large-scale circulation and how the oceans have changed over time.
This is a logical division which recognises the dominant role that biological processes play in shaping the chemistry of the oceans via photosynthesis and its subsequent effect on transferring carbon across the air–sea interface and across isopycnals in the interiors as particles sink. I was particularly impressed with the way that the penultimate chapter brings together these various aspects and how it links to the final chapter where the vast array of isotope and trace element–based proxies for circulation are discussed. If I have one criticism of the structure, it is that the interaction of the crust with the oceans could have usefully had a chapter of its own, but this is a minor quibble set against the breadth of the material presented.
Each chapter contains a series of worked problems, with the final part of the chapter containing examination-style questions linked to comprehensive answers at the end of the book. These are well grounded in the recent literature (often classic papers) and provide good examples of the sorts of calculations real chemical oceanographers do in their professional life. To take a random example, the chapter on advection–diffusion models contains questions on diagnosing gas diffusion from SF6 enrichment of a lake on a remote island in the Southern ocean, the way in which nitrogen is supplied to the surface waters of the subtropical gyre (a classic and still unresolved problem), ocean margin exchange, mixing in the deep and southern oceans from the DIMES experiment and horizontal dispersion of chlorophyll from the SOIREE experiment. Used as a teaching aid, these sets of problems will introduce the prospective student not only to some elegant and important calculations but also to the pieces of work which have revolutionised our study of the ocean and its role in climate.
Two particularly interesting and satisfying aspects of this book are the occasional anecdote around ocean science or example drawn from real-world human behaviour. I never knew, for example, that the first scuba apparatus was designed in 1864 and tested under a bridge in central France or that ancient humans believed that ocean salt came from a sunken merchant vessel. Similarly, I will never be able to look at a beach full of people with adults on shore and children in the sea, or a line of cinemagoers, without recalling the geochemical processes that their behaviour is likened to – I will leave you to guess which processes they are!
Overall, I really enjoyed reading this book. It is a fantastic introductory text to a crucial area of Earth science suitable for the undergraduate or graduate student alike – but it is so much more than that. It is also a great companion for seasoned researchers who want to acquaint themselves with the latest theoretical breakthroughs in the field or to gain a good overview of a new area of ocean science. I can imagine this being a well-thumbed book over the remainder of my career, at home, in the laboratory, in the classroom, and above all at sea. I would suggest that all oceanographers pack a copy in their sea chest for their next expedition.