On a sunny Sunday afternoon, we hauled the Piston Corer on deck, and began disassembling the heavy steel pipe, in order to split the tube of mud inside. Once we removed the core catcher (a metallic device, which acts like a valve to allow mud to travel up the tube under pressure, but stops it sliding back out again), from the end of the core, everyone took a step back - this core STANK!
The smell of hydrogen sulphide (smells like rotten eggs) is caused by large quantities of organic matter, getting buried (by more sediment) before it is completely broken down. The core was darker and smellier (which indicates more organic matter) towards the bottom (where the older sediment is).
Water from land (terrestrial river discharge) generally tends to contain more organic matter than the deep ocean. We think that at the end of the last glacial period, the ice sheets blocked most routes for rivers to flow out of northwest Europe and the UK. The English Channel then became a major route, and brought all this organic matter out into the canyons. This also explains why the eastern canyons are smellier than the western ones, as the eastern canyons are closer to the channel.
As the ice-sheets retreated, alternative routes opened up, and less terrestrial sediment now finds its way to these canyons, which means the little organic matter which is deposited now, can be consumed by the creatures that live on the seafloor (like sea cucumbers), so our core is sandier, lighter and less smelly in the more recent (in the past 10,000 years) layers.
< Previous diary entry
| Next diary entry >