book reviews

### Oceanography books

reviewed by T. Nelson

book review

### Descriptive Physical Oceanography: An Introduction, 6e Talley, Pickard, Emery, and Swift Elsevier, 2011, 555 pages

Reviewed by T. Nelson

Last month I realized I needed to know more about the dihydrogen oxidey part of the world, so I got a copy of Descriptive Physical Oceanography, 6th edition by Lynne D. Talley, George L. Pickard, William J. Emery, and James H. Swift of Scripps Institution of Oceanography—a decidedly salty crew indeed.

It turns out that the famous applied oceanography book Moby Dick (which I'm only now getting around to reading) also has some useful information:

In a full grown sperm whale something less than 2000 square feet—the pressure of the water is immense. We all know what an astonishing atmospheric weight we ourselves stand up under; even here, above-ground, in the air; how vast, then, the burden of a whale, bearing on his back a column of two hundred fathoms of ocean! It must at least equal the weight of fifty atmospheres. One whaleman has estimated it at the weight of twenty line-of-battle ships, with all their guns, and stores, and men on board.

Melville's calculations were remarkably close. I calculate that at 200 fathoms (1200 feet), the ocean pressure at the latitude where Ahab sights it, is 548.946 pounds per square inch (only 37.34 atmospheres; Melville was a bit off) or 425.43 tons per square meter. Assuming the sperm whale has a square cross-section, it would have a surface area of about 163.84 square meters (1763.6 sq. ft) and it would be subject to 69,702.97 tons of pressure. An average battleship in 1850 weighed about 3000 tons, so the whale would experience a total pressure of 23.23 19th-century battleships.

In fact, the whale would have more pressure on it than the WWII battleship Bismarck, which only weighed 58,704 short tons.

Unlike Moby Dick, this book has many color-coded maps of sea surface temperatures, color charts of potential temperature, salinity, density, and oxygen content, current velocities, and infrared satellite images. It looks like it was anticipated that the color images would be available only online: the illustrations amidst the text are all grayscale and quite uninterpretable, but the publisher, perhaps realizing this, stuck the color ones in the back, as if taking pity upon the poor broadband-deprived students at the last minute.

The first eight chapters give you a good understanding of waves and current, and it gives a reasonable (but somewhat superficial) description of the physical properties of seawater. You will learn, for example, that the Mediter­ranean Sea is saltier than the Atlantic, so the water that flows out immediately sinks to the bottom despite its warmer temperature.

What goes down must come up, and there is a thorough cataloging of different currents. The distinction between tides and waves is pretty fuzzy; some waves have their period measured in months or even years. Waves don't just occur on the surface: low frequency waves occur at interfaces of two different densities, and there are many different kinds of currents, mostly caused by the wind, temperature and salinity differentials interacting with the Coriolis effect.

There is very little discussion of ocean chemistry, only a few pages on sound propagation, and no discussion of animal or vegetable life. Chapters 9 to 13 are a cataloging of the currents in the Atlantic, Pacific, Indian, Arctic, and Southern oceans.

Typical paragraph:

The geostrophic shear of the ACC [Antarctic Circumpolar Current] is large, as reflected in the downward slope of the isopycnals toward the north across the current. Surface currents decrease from about 50 cm/sec at the sea surface to 4–10 cm/sec at the bottom (direct current observations in the Pacific by Donohue et al., 2001). The ACC fronts, which are identified using potential temperature and salinity (not shown) are evident in the ocean bottom embedded within the general slope of the ACC isopycnals.

This sort of thing has a tendency to induce seasick­ness, if not scurvy, after a while if you're not used to it, but it's very professionally written. The writing is at a level suitable for undergraduates and there are 31 pages of references for those wanting a higher level discussion.

It covers important topics like geostrophic shear, isopycnals, molecular and eddy diffusivity, and topics like the North and South Subsurface Countercurrents, but says nothing about whales. So you will have to read both books.

feb 04, 2017; edited feb 07, 2017