Conservation comment: Mystery of ocean heat sink

Oceans may be slowing down warming of land and the atmosphere.

By Ian Sutherland

IN AN interview on December 11 last year, Donald Trump's answer to a question about man-made global warming ("Nobody really knows") is not as bad as it sounds. However, this does puts him at odds with those scientists working on the atmosphere at the changes that can now be measured there.

Those who study climatology know the atmosphere is warming and roughly by how much. The sea is another matter, and there Mr Trump has his point. Climatologists also strongly suspect that the oceans are warming. The amount of heat already in storage is also unknown. This is a most important measurement.

Most suspect the greater heat capacity of seawater explains the warming slow-down of recent years. However, without decent data it is hard to be sure to what extent this is happening in the oceans, and, just as importantly, for how long they can act as a significant "heat sink", damping the rise in land and atmospheric global temperatures.

However, things are looking up. Scientists at the Goddard Space Flight Centre in Maryland recently described a project based on the ocean's magnetic field. They discovered that small magnetic changes in the sea can be observed and measured by satellites, and appear to be induced by many small movements in seawater. These movements are both electively conductive (a fancy way of saying magnetic) and constant. Such a moving conductor can measure any magnetic field that passes through it. Salt water's conductivity increases with temperature.

Earth's magnetic field is generated within the planet and penetrates the whole ocean system from top to bottom. This means that if you know where and how ocean waters are moving, the changes in the magnetic field can be tracked by satellite. This will tell you the heat content.

Drs Tyler and Sabaka realised there was a regular, twice-daily magnetic change, which has been extensively studied. This is the result of the twice-daily tidal movements generated by the moon. They built a model and crunched as much data as they could find.

Sadly, even with the currently available magnetic and temperature data, they found that using the effect of the moon alone was not enough. They needed more data. This will be generated by including more measurements of, for instance, solar tides and other water movements, and more satellites. Three recently launched European satellites, nicknamed "Swarm" are already gathering this information.

The magnitude of these changes depends on the water temperatures occurring all the way down to the ocean floor, giving for the first time "a window into the oceans" and easy access to valuable data.

Until now, measurements of things in the deep sea almost always involved placing instruments there by either lowering them from a ship or by putting them on board a submarine device. The most useful recent data gathered has been the addition of several thousand "Argo" probes, floating robots roaming the oceans, capable of diving to 2000 metres. This still leaves ocean temperatures severely under-sampled, but help is on the way to answering these highly important questions.

� Ian Sutherland is a retired pathologist who has lived and worked in many, predominantly warm, countries and has always had an interest in conservation and environmental matters.