The Water Column

by Lorraine Brasseur Thu, 24 Jul 2008 11:02 PM PDT

The water column.  I’ve spent a good third of my life contemplating the water column and the enigmatic goings on within it.  But what sort of column is the water column?  Corinthian? Doric?  Greek, certainly.  I live in a veritable sea of acronyms and jargon, immersed in them so thoroughly that sometimes I forget that others don’t know what I’m talking about when I start waxing philosophic over the data from the CTD or the XBT or the TowCam and why these measurements of the surface mixed layer or the benthic boundary layer of that elusive column we chase across the ocean are so important.

From Wikipedia (what would we do without Wikipedia?) we find out that “A water column is a conceptual column of water from surface to bottom sediments. This concept is used chiefly for environmental studies evaluating the stratification or mixing (e.g. by wind induced currents) of the thermal or chemically stratified layers in a lake, stream or ocean.” Clear as bottom sediment, isn’t it? This conceptual column came about because most of the methods that we historically used to study the ocean were things that we could lower from our research vessels to the sea floor and retrieve again, getting a single profile or column of information from a single location in the vastness of the ocean.  It seems almost miraculous that from these scattered single columns of data that we can deduce anything true about the whole three dimensional ocean, yet with additional information and insight, we can. The water currents can be estimated from as few as two profiles of temperature and salinity; the likelihood of small marine plants being able to sustain themselves can be inferred from temperature, salinity, and the amount of light that can filter down through the water; and many other deductions can be made by the detectives of the sea from the few clues that we have from each column of water that we sample.

Our tools for finding clues in these conceptual columns include all the acronyms above and more.  One of my favorites is the CTD.  The CTD stands for Conductivity, Temperature and Depth.  The oceans are salty and the saltier the ocean, the more electricity it conducts, giving us a relatively quick and easy way to deduce salinity.  An XBT – Expendable BathyThermograph is another way of finding the temperature profile from a ship, this time without having to stop the ship and pull the instrument back.  The TowCam is a Towed Camera system that can photograph the goings on of the animals, plants and physical structure of the water column and especially the very bottom of it, the sea floor itself.  On the way down, the TowCam uses its own CTD and also has bottles to collect samples of water that can be used by scientists to study chemicals in the water, mud suspended in the water, or microbes living in the water among other things. 

For me, this conceptual column is so much more than a concept, it is at once familiar and mysterious, it keeps me up at night, sometimes on a research vessel where our sampling goes on both in the daytime and at night (science never sleeps) and sometimes back in my office as I struggle to understand more of the processes that govern the very real and complex conceptual column of water that I will never quit following.