64PE365 - Day 1
06/03/2013 23:00
What is to say about a cruise day that only starts with embarking on 15.00 PM local time (14.00 UTC) and consists mostly of cruising to the first point of interest? Well a lot.
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| Stefani points out something to Anna. | This is what Stefani is pointing at: a set of sensors measuring light. |
We started out with a safety instruction and a tour of the ship. The movie, which showed us the safety protocol and regulations of the ship, was a horror movie not suitable for people under the age of 16. It scared the hell out of some of us at the moment when a door slammed into a hand (or was it a glove) and blood (or was it ketchup) splashed everywhere. The tour around the ship was an ordeal for some of us too, who wore nothing but a pair of socks (on their feet) and were forced to see the muster station on the front deck outside, where not all cleaning water had evaporated yet. Also the announcement of an unexpected safety drill tomorrow was not understood by everyone. The cruise leader wanted to shift the unexpected safety drill to today, so that it didn’t interfere with his meticulous cruise plan. However, this was unfortunately not possible. One of the scientists wanted to be informed about the exact time of the unexpected drill, the location was clear to her, though. The crew member, however, didn’t provide any information, besides that is sure wouldn’t be held during coffee time.
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Sven is setting up the bottles in the CTD frame sharp, which can then be ‘fired’ with one push on the button of the CTD-computer. |
So far, the fun part. Work had to be done too. A test station was planned at around 17.00 PM. The CTD-frame was lowered and on the way back up three bottles were closed at different depths. CTD stands for Conductivity, Temperature, Depth, which can be used to determine the salinity of the seawater, which mostly depends on the conductivity. But beside the CTD and the bottles, the frame is also equipped with and optical backscatter sensor (OBS) , a transmissiometer, a fluorometer and LISST (Laser in-situ ??). The OBS estimates the turbidity of the water by measuring the amount of light emitted from the device itself, that is reflected on the particles and received back by the device. The transmissiometer also estimates the turbidity, but in the exact opposite way as the OBS, namely it records the amount of light that passes through the water. The fluorometer measures how much plankton is in the water by recording the light emitted by the green particles in the water themselves. The LISST estimates the grain size distribution of particles by recording the scattering of a laser beam through a certain water volume. |
Besides this, also a Secchi disk was put over the side. This is a round white disk of a certain prescribed diameter, which is lowered by a rope, until it is no longer visible to the person who lowers it. Then it is hauled again and the depth at which the Secchi disk becomes visible again is noted. This is an ancient technique, which apparently gives very reliable estimates of the turbidity of the surface water.
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Stefani shows Anna and Thomas how to ‘operate’ a Secchi disk. |
Besides this, also a Secchi disk was put over the side. This is a round white disk of a certain prescribed diameter, which is lowered by a rope, until it is no longer visible to the person who lowers it. Then it is hauled again and the depth at which the Secchi disk becomes visible again is noted. This is an ancient technique, which apparently gives very reliable estimates of the turbidity of the surface water.
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The test went fine and after the test, students from Utrecht University, NIOZ-Yerseke and the rest of the colleagues were informed on how to do a proper filtration of seawater. This is done using a NIOZ-made filtration device which uses air pressure to push the water through a pre-weighted filter. The pore-size of the filter is about 7 micrometer, therefore all suspended material larger than this size remains on the filter, which is called suspended particulate matter or silt. And this is the stuff were ‘hunting’ for. All of the measurements described above will be performed numerous times in the coming days to estimate the amount of silt that is being transported across the North Sea from England to Denmark just northwest of the Netherlands in the so-called East Anglia Plume.
After opening the valve on the bottom of the bottle, the seawater captured at a certain depth runs out violently.