The weather deteriorated yesterday,
becoming more typical of this time of year. The wind increased to 40 knots and the increasing swell meant that the
camera sledge was moving up and down in the water column as it was
deployed. It was not possible to settle the sledge on the bottom
whilst getting a clear picture, so we were forced to abandon camera
work until the weather improved and focus on sediment sampling.
To give you a picture of what we have been up to, here is a quick run through of what is
involved in sediment sampling.
The ship’s captain, or officer in
charge of navigating the ship at the time, tells us when we are
at the correct location selected for sampling. We can track the ships
course using GPS and view it on a screen so we can see where the ship
is in relation to proposed sample locations.
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| Navigation screen |
Three ABs (able-bodied seamen) then
assist by winching the Day grab over the side of the vessel to the
seabed. It is possible to tell when the grab reaches the bottom, when
the winch wire goes slack. The ABs then call through to the survey
lab and a scientist takes a fix of the coordinates where the sample
was taken so it can be later plotted on maps. Before deployment, the
Day grab is set up with the jaws held open by a bar fitted between
hooks on the jaws. When the grab hits the seabed pressure is placed
on two plates at the base which push up the bar and release the jaws.
As the grab is winched back up the grab wires are pulled taut, closing the jaws of the grab so a sample is retained inside.
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| Grab sampler set for deployment |
When the grab is back on deck, the
scientists check the depth of the sample which must be at least 8cm
to ensure a sufficient proportion of the infaunal community is sampled. Infauna generally live
within the top 5cm of the seabed. If the depth is too shallow, or the
jaws of the grab have been held open by shells or stones, the grab
will be deployed again. If a good sample is retained,
scientists take a small core for particle size analysis which
gives information on the size of sediment present and a description
of the sediment type. For example, sandy mud or gravely sand, is noted
using a standard classification system. A photograph of the sample is
also taken as a record.
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| Depth measure and sediment corer |
The sample is then dropped into a crate and taken for processing for macrofaunal analysis. The sample
is first gently washed through a large 5mm sieve to remove the sediment
and large organisms such as sea potatoes, crabs and brittlestars. The
sediment and smaller fauna are washed through to a smaller sieve
below where fauna larger than 1mm in size are retained. All fauna are
then washed into a sample bottle using a funnel and water bottle and
then fixed in formalin. Care is taken to ensure no fauna are left
behind, and any small organisms caught in the sieve are painstakingly
removed using tweezers.
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| Scientist Dr Paul Whomersley washing sampled fauna from sieve to sample bottle |
Some interesting fauna retained in the
sieve last shift including several starfish which were tentatively identified as Astropecten irregularis. We even found a mutant individual with only four legs which we took to be good luck.
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| Retained macrofauna including a sea potato and a starfish, Astropecten irregularis |
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| Grab sample with seapen Pennatula phosphorea |
The Scientist in Charge set scientists
an imaginative challenge to keep them entertained during down-time.
Each shift was charged with creating their own coats of arms and
moto. A considerable amount of artistic flair and imagination went
into both entries, and the day shift was unanimously victorious with the highly
detailed design below (left).
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| Day shift's coat of arms |
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| Night shift's coat of arms |
The latin motto ‘Carpe Solum’ can
be translated (with some artistic license) as ‘grab the
earth/bottom’. The seagull and crab are reference to an amusing incident
on day shift when we caught a small crab in the grab. Just as we were
taking a photograph for records a sharp-eyed gull swept down intent
on an easy meal almost taking out an unsuspecting scientist in the
process.
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| Crab found in grab sample |
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| Hungry seagull making a quick getaway |
