The Twilight Zone
About 15 years ago, the 'Twilight Zone' or more correctly the 'Mesopelagic layer' (100-1000m depth) was one of academic curiosity, a place with strange-looking animals which made their living in a region of decreasing light and increasing pressure. This ecosystem was thought to be of little relevance from a commercial perspective and the environment in which it lived to have limited global significance.
The naturalist William Beebe ventured there for the first time in the 1930s encased in a tiny bathysphere (pictured right) making live radio broadcasts describing the wonderful and extraordinary life forms he could see out of a tiny porthole. His mission as an explorer was to venture into unknown territory, satisfy curiosity and communicate his experiences to the public.
It was not until very recently that we started to appreciate that this vast environment has a role in earth system function. It is no longer simply a region of novelty in which we find marvellous creatures but is thought to have a crucial role in modifying the global carbon cycle and the heat balance. Some of the current sets of data are completely incompatible with each other which demands new approaches and sharp minds to improve our understanding. An example of this is the fact that the fauna living there seem to need much more organic supply (food) than is thought to be available from the overlying part of the water column where such material is produced. One or both of these factors are completely wrong and we are now using some of the smartest technology and techniques to address these issues.
In particular we are looking at the rate at which material arrives at different depth horizons using the PELAGRA trap and from the decrease in flux with increasing depth, we can determine the rate at which the organic matter is consumed by the twilight zone fauna. In addition, we collect the sinking particles using the 'Marine Snow Catcher' which is a 100 litre water bottle designed to collect fragile large particles so they can be examined microscopically and chemically.
The crucial physical aspect of this part of the water column is that the water and material within the upper part of it are mixed up to the surface in the winter such that any carbon dioxide generated there as a result of respiration of the fauna is exposed to the atmosphere. If the material sinks below the depth of this winter mixing, it, and the CO2 produced from it can be isolated from the atmosphere for hundreds of years in the very deep-ocean water masses.
There is much to be learned about this environment which has such a significant role in the regulation of our global climate.
