By Jenny Gales and other more reluctant bloggers….
The BGS team (Davie, Keith, Mike, Alan, Joe and Jenny) have been busy collecting sediment cores using the BGS remotely operated vibrocorer, with 39 successful cores recovered so far, 14 of which were in the last 24 hours.
The BGS vibrocorer weighs in at 5000kg, in the super-heavyweight class, and can be deployed to a water depth of 2000m. The system consists of a 6 m hollow tube of steel, called a barrel, which is driven into the seafloor by a 1 tonne vibrating pot at the top of the barrel. The whole thing is held in a vertical upright position by a three legged metal frame that keeps it from tipping over on the seabed we hope… Our team, all six of us operate a round-the-clock 24 hour operation, in two shifts of three people, (day-watch Davie, Keith and Alan) and (night-watch Mike, Jenny and Joe) given we occasionally need sleep and time off to read and drink tea.
Each deployment of the beast starts with the vibrocorer lying horizontal on the back deck of the ship. First, a hard plastic core liner is put into the barrel. Next, a metal core catcher is added to the end of the plastic liner, to stop sediment falling back out when the core is raised back onto the ship. Finally, a core cutter is attached to the end of the barrel, which cuts through the seafloor. The vibrocorer is then raised up into a vertical position by a BGS winch system and the ship’s A-frame. It’s then lowered over the back deck to the seafloor at about 30 meters per minute. When the vibrocorer lands on the seabed, the corer is started from a purpose built container on the back deck which is fitted with a control and acquisition system. The barrel is driven into the seafloor by the weight filled vibrating pot and collects a core of sediment as it goes down. This usually takes between 15 minutes to 1 hour depending on how hard the sediment is or how persistently nagging the science team are. The materials in the south Celtic Sea have been a little challenging, with coarse sands and other materials proving tough to penetrate. Also the much sought after glacial muds have been tricky to find! Once the coring is finished, the vibrocore is easily (for the most part) extracted from the sea bed and raised back onto the deck of the ship and the now sediment filled barrel is removed. The sediment-filled core liner is taken out of the barrel and is carefully labelled and cut into 1 m sections. The sediment core is now ready to pass on to an expectant science party craving muds……