Shades of Mud

By Kaycee Handley, Macquarie University

When I was a child, my parents never let me play with mud because it was too messy. So naturally I choose a career that is centred around playing with mud, whether it be looking at it, feeling it between your fingers, or even tasting a small amount to see if you can feel any grains between your teeth (this helps us to see decide how big the grains are).  So I get to satisfy a childhood wish while I work at understanding what environment laid down these sediments in the first place.

After two days on site, we have collected Kasten cores at three different locations, and two Smith-Macintyre grabs at another location. Both of these methods allow us to collect sediment off the seafloor, but look at two very different things. The Smith-Macintyre grab works like a mouse trap which is held open until the device hits the bottom of the ocean, where a trigger plate on its base will go off, closing the mouth and capturing a ‘snapshot’ of the top 20 cm of the modern seafloor.

The Smith-Macintyre grab sampler is deployed over the rail from RV Investigator at sunset as part of CAPSTAN's hands-on training in marine science
The Smith-Macintyre grab sampler being deployed. Photo Credit: April Abbott

Once the grab was back on the ship, we trialled a new method of sampling the top of the seabed. We first pushed a sampling jar with a small hole in its bottom into the top of the sample, and then used a finger to seal the hole. This held the sediment in the jar while we pulled the sample out of the mud, preserving the top layer of the seabed. Fortunately, this worked relatively well as three out of four of the samples were recovered successfully, while the fourth sample failed to capture any sediment, most likely due to a small burrow in the mud, which interfered with the suction.

CAPSTAN student Kaycee collects a sample from the Smith Macintyre grab using a small sampling jar through the top of the grab sampler as part on hands-on marine science training on RV Investigator
Collecting a sample from the Smith-Macintyre grab. Photo Credit: April Abbott

The Kasten core differs from the Smith-Macintyre grab as it looks at a 3 m long vertical section of the sea bed. This allows us to sample a slice of time (a boxy slice, as the core is square). And within these cores, the sediment at the top of the core is the youngest as it is was deposited more recently than the sediment 3 m below the seabed.

Before we begin sampling each Kasten core, an archive core must be created. To do this, the core is first gently cleaned in order to remove the top layer of sediment. We do this because as the core is pressing into the seabed, sediments around the outer edge of the core ‘stick’ to the edge and the layering can be displaced.

CAPSTAN student Bella uses a metal scraper to clean off the kasten core before sampling commences.  The scraper is used to remove the sediment smeared on the edges as the core penetrates the sea floor.
Fellow CAPSTAN participant Bella cleans the Kasten Core. Photo Credit: April Abbott

Once that is completed, and the layering is exposed we place 1m long drainpipe halves along the centre of the core and gently press them into the sediment. A cheese wire is then used to separate the drainpipe core from the total core and flipped, exposing a perfect copy of the Kasten core. We then seal the top and bottom with an improvised duct tape plug, wipe down the outside to remove as much mud as possible, and wrap each archive in two layers of cling wrap to stop oxidation changing the colour of the core. The wrapped drainpipes are then stored in a large refrigerator.

CAPSTAN student Kaycee adds an archive half to the collection of archive cores and sample containers in the refrigerator in the sediment lab component of the at-sea marine training on board RV Investigator
Placing an archive core into the refrigerator. Photo Credit: April Abbott

We then collected various samples from the Kasten core that we can analyse over the next week. With the core looking bruised and battered after a few hours of heavy sampling, we must sadly say goodbye to our core and clean out the remaining mud to make room for the next core, because as soon as one sediment core is finished another one is ready to take its place, and then the cycle continues…

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