Once again, I found myself playing with mud in the early morning. This time, our megacore (a big circular rig, with several coring tubes attached) arrived on deck at 6am, loaded with thick brown deep sea mud. The past 2 days have been focussing on coring, as we attempt to make up for lost time with the winch so our team of scientists have been up to their elbows in mud.
Andy has already explained what the biologists do with these cores to hunt out the tiny foraminifera and other critters that live in the upper 15cm of mud. Other tubes go to our geologists; who are more interested in the layers visible through the whole core and what these may tell us about the processes and sediment deposition in the top 40-50cm of the seafloor.
Piston cores are really useful, as they can show us a long way back through history at anything up to 21m in length. However, they are really big, heavy pieces of equipment and even with the stabilising piston, the upper sediment layers will often get disturbed and loose its structure (the ‘sediment-water’ interface). So the megacores, which are gentler, can show us the shallow sediment that the piston core misses.
The sediment on the seafloor builds up on average at 1cm per 1000 years, then a 40cm megacore will show us 4000 years of history. In canyon systems generally, the mud accumulates at different rates in different places. So having both core types can tell us a lot about how the mud (which eventually becomes sedimentary rock, like chalk and limestone on land) builds up and gets disturbed.
The recovered sediment record has been showing us that most recently (geologically speaking, so within the past 10,000 years!) there have been large sediment flows down the canyon every few thousand years. Before this time; when the UK and Europe were covered by retreating ice sheets, the sediment flows were smaller but occurred more frequently. In some cases flows are thought to have occurred every year as spring and summer melted the ice sheets further and provided a surge of water and sediment into the ocean.
Now with returned high winds and waves, we’re waiting on the weather to send ISIS on another mission to explore the seafloor…
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