Monday, 23 July 2012

Day 18 - Size Matters

We are collecting samples of the seafloor sediment for their particle size distributions to be analysed. This information tells us about the basic seafloor environment that animals live in and on. We already know that they live at high pressures, low temperatures and without light, but what is the bottom like?

The seafloor has hills and flat areas that are surveyed with bathymetry, and we can add the particle size of the sediments to that information. Due to the interactions of particles with ocean currents, the particles on higher areas can be coarser (i.e. sandy), than areas in valleys or flatter areas, where there can be higher proportion of very small clay particles. Core samples are sliced into several depths, and will be analysed at NOC. We shine a laser into the samples, and measure the light diffraction to find the size of the particles, since particles of different sizes bend the light at different angles. We can then determine the proportion of particles of each size.
The megacorer collects sediment in its tubes

Much of the sediment at the Porcupine Abyssal Plain is very soft and light brown in colour. We were very interested to see stones that have fallen from melting icebergs. These stones have travelled far from the continent, and provide a hard surface for some fauna to grow on. Clinker dropped from steam-powered ships provides other hard surfaces.

Sediment contains organic matter that falls from the surface ocean, which is consumed by deposit feeders such as sea cucumbers. Soft sediment with small particles is important for feeding and for fauna that bury themselves into the sediment. Looking at particle size differences at different locations around the plain can give us important information about spatial differences in faunal communities in the deep, potentially explaining why we might find differences in one area when compared with another.

Jen Durden and Steve Lawler