The Great Ocean Conveyor

I’ve just finished reading “The Great Ocean Conveyor: Discovering the Trigger for Abrupt Climate Change” by Professor Wally Broecker. Finding the odd 20 minutes here and there on trains is not the ideal environment to read a book like this, so a wet Sunday afternoon provided a good excuse to sit down and read it properly.

This isn’t a “global warming disaster” book on either side of the battle lines. In fact, as one reviewer describes it, it’s a new genre, the science detective thriller. Well actually, that might be taking it too far. There have many popular science books written in narrative form, often with plenty of human drama interwoven in. This is not that kind of book. Actually, it is right on the extreme between popular science and textbook or peer-reviewed journal, but none the worse for that.

Over 137 fairly dense pages, Broecker describes his original thesis for the global circulation system which drives heat exchange between the poles and the tropics, which he names the Great Ocean Conveyor. One part of this, the upper level North Atlantic limb is well known under the name of the Gulf Stream. He starts off with a preamble on the discovery and confirmation of the Milankovitch insolation cycles, and from this starting point looks at shorter term fluctuations in temperature and ice cover which are due to other factors than planetary mechanics.

Along the way, he describes the various proxy measurements of climate, starting with oxygen isotope concentrations in ocean sediments and ice cores, and techniques invented to provide reliable dating. The discussion of the sheer inventiveness of some of the methods used and the elegant ways in which they are developed to me is the core of this book.  In fact, if I have any criticism, it would be that some kind of overall treatment of the Great Conveyor itself seem to be missing. I would have liked to see a conclusion, and perhaps some better global illustration of what is known about it. The book focuses on the geochemistry, which is fine, but a little more ocean dynamics would have been nice.

The concluding chapter discuses the Anthropocene - defined as the geological period we’re now living in, starting from the point where human activity has a significant impact on atmospheric CO2 levels. One might expect this chapter to flourish a few dramatic, doom-laden scenarios as a dramatic sign off, and probably if it were a standard popular science book, the editor would have demanded this.  But actually, Broecker confesses that he’d rather avoid the mistake of crying wolf, and holds back from stating or implying that the conveyor-based mechanisms he has discovered for abrupt climate change necessarily apply the current context. However, he does emphasise that we are still far from having an answer to everything, and that the one constant is that the Earth’s climate system is full of surprises. We may well be able to deduce what happened in the past, but quite possibly we’ll only know if todays’s concerns about climate change hold up after the event.

A reader with no scientific background would probably have to skip some of the more technical discussion, which is a shame as I don’t doubt it these sections could be made more accessible. For myself, although I have had some exposure to glacier geochemistry, and can grasp the basics, there were still a few passages where my brain went blue-screen. In particular the discussion of NO4* as a proxy, which left me completely baffled - even more so as I haven’t been able to find any discussion of this anywhere else. There are a also a few key points which are presented as an elegant twist, a scientific sleight of hand, which would no doubt get a round of appreciative grunts, if not outright applause, in a scientific forum, but might be a little lost to a general readership. In shoer, and to some extent, this book does not quite seem to know who its audience is.  But that’s not a major issue. All in all, it’s an enthralling and mentally refreshing read, and I recommend it to anybody interested in what really lies behind the climate change story.