May 09 - CTDs
Date: 09 May 2004
Noon Position: lat 19 30.8 S, long 24 59.8 W (1045 nautical miles from
Rio de Janeiro)
Distance travelled since Immingham: 27704 nautical miles
Distance travelled since Stanley: 2580 nautical miles
Air temperature: 24.8°C
Sea temperature: 25.7°C
The JCR this Week.
Over the past week the ship has fallen into a working routine of science stations, meals, the evening film and sleep. However, a few events have marked special days. The first was the magnificent Lunar Eclipse on Tuesday night. Once again, being at sea is a real privilege, with an unobstructed view and complete absence of light pollution, we are surely in the best position to experience such an event. The huge, bright moon first turned red and then went almost completely dark, leaving only a sliver of itself visible with its brightness exaggerated by the dark. Slowly the moon re-emerged, giving me the odd sensation of seeing the shadow of our world pass across its face.
The stars were once again out to impress last night, with Venus appearing so bright that there was a band of light across the sea usually seen only with the brightest of moons. It took the Mate some time to convince me that a planet, several million miles away, could create so much light. Yesterday was also remarkable for being the first really warm day we have experienced. We arrived in the Tropics- north of 23.5 degrees, some time in the early hours of yesterday, and eventually shed the strong winds and big swell of the Southern Trades. The end result was a lovely day, calm and warm, and perfect for an afternoon on deck of backgammon, cool beers and even the odd water bomb. We'll be in the Tropics for a week or so, and will cross back into the northern hemisphere on Friday.
Science Bit In The Middle: AMT 14.
Science has fallen into a routine of 3 times daily CTDs, bongo nets and optics, an occasional additional dusk CTD and every third day a SAPS station. This is our routine, the whole ship being involved in some way or other, and the scientists trying their hardest to fit in adequate eating, sleeping and relaxation time (only the sleeping seems to be suffering so far).
The CTD is deployed. Click to enlarge.
So what is a CTD?
CTD stands for Conductivity, Temperature, Depth and is actually the name of a small instrument strapped to the huge frame, which we also (wrongly) refer to as the CTD. These parameters are measured continuously as the frame is deployed to depth and recovered, and provide background information which can be interpreted to provide a picture of what is happening in the water column at that place and time.
However, in addition to the CTD, there are 24 large water -collecting bottles attached to the frame. These can be fired by electronic wizardry from the ship's UIC room, and on command, they close, sealing within them a snapshot of the water column at that depth and time. When all of the bottles have been fired, usually at different depths, the frame is brought back on board and the scientists descend in a predetermined order to collect their samples.
| The morning CTD
Click to enlarge.
| A tired Dougal performs
Click to enlarge.
What they then do with their samples is varied and complex.
Tom measures the amount of a gas called dimethylsulphide (DMS) dissolved in the water. This compound is indirectly reduced by phytoplankton but is volatile and therefore evaporates into the atmosphere, where it is oxidised. In this form it attracts water and is a major influence in inducing cloud formation. Thus, incredibly, the tiny phytoplankton influence local atmospheric and climate changes. Tom measures the DMS using an apparatus called a gas chromatograph, which gives a highly sensitive reading of the amount of compound in his water samples.
Tom. Click to enlarge.
Niki uses entirely different methods to measure another dissolved gas, oxygen. This is both produced and utilised in the water and she measures it at different times of day, using the readings to work out whether there is overall gain or loss of oxygen, i.e. whether there are more phytoplankton producing it or zooplankton utilising it. The magic of her experiments is that she produces what looks like small clouds in her bottles.
Niki makes oxygen clouds in bottles. Click to enlarge.
Nick also measures a dissolved gas, nitrogen. He is studying the concept of nitrogen "fixing" by bacteria in the oceans. We know this happens in plants such as beans- nitrogen is fixed by bacteria living in nodules on the plants' roots. Nick's hypothesis is that this also happens in the oceans, and he is hunting the bacteria thought to be involved. His equipment is an array of complex-looking bottles and computers, which looks as if it should produce green smoke.
Nick, looking like a proper mad scientist. Click to enlarge.
Stuart also works on nitrogen- at the other end of the spectrum from Nick. He studies production rates of nitrogen by phytoplankton, using isotope-labelled nutrients.
Stuart in the lab. Click to enlarge.
Jenna's project is to measure the breakdown of dissolved organic products of phytoplankton. These are an important source of atmospheric carbon gasses including carbon dioxide. They also affect the optical properties of the water, influencing in turn the temperature and the amount of light absorbed and thus available for the phytoplankton. She is usually to be found filtering large volumes of tea as well as water.
A very studious Jenna. Click to enlarge.
The boys in red: the deck team
The science could not go ahead without the entire ship's crew: the cooks making 3 meals a day for 52, the engineers keeping the ship, the winches and the air-conditioning going, the stewards making our lives comfortable, serving our food and ensuring the place is clean and tidy. The deck department are the most visibly involved with the science. The officers of the watch are responsible for planning the route, and steering the ship along that route, working out when the sun will set and rise each day so the timing of the stations can be planned and keeping tabs on the amount of time we spend doing science, and the speed we need to go to ensure we will get home on time.
When we arrive at our science station, the watch-keeping officer slows and stops the ship, and engages the "Dynamic Positioning System". This keeps the ship in a stable position, either drifting with the currents or totally stationary, depending on factors such as the science, the wind speed and the strength of the current. Keeping the ship in position can be very difficult in some conditions, with the thruster motors working their hardest to combat the effects of wind and waves.
Once we are in a stable position, the work on deck starts, with the CTD deployed from the main gantry in the middle of the ship, the bongo nets from the small crane on the fore deck and the optical rig from the crane on the after deck.
Colin Lang, the Bosun, is the foreman of the deck crew. He not only organizes the ABs, but he also monitors operations on the aft deck and operates the crane which deploys the optical instruments.
The Bosun. Click to enlarge.
The Bosun's Mate, Dave Peck, is the 2nd in command of the deck crew, as well as being ship's carpenter and general Mr. Fix-it. He also drives the cranes and winches during cargo and science operations, and he is the man in control of the mid-ships gantry from which the CTD is lowered.
Dave Peck, in "winch control". Click to enlarge.
The ABs are the sailors, trained in rope and canvas work, painting, cargo operations, mast climbing and small boat driving. They are also the second pair of eyes when keeping look-out on the bridge. The ABs operate the smaller cranes and do the manhandling of deck equipment which enables the science operations. The ABs on this crew are Ian Raper, (Gorgeous) George Dale, Kevin Holmes, Mark (Tugs) Taylor and Martin Bowen.
Ian and George wait for the word to deploy the CTD. Click to enlarge
Kevin and Tugs also drive the cargo tender and work boat at times. Tugs has been with BAS for many years and is passing on his experience to Kev who, at 22, is the youngest member of the crew.
| Tugs assisting
with a buoy deployment.
Click to enlarge.
| Martin and Jon deploy the
Click to enlarge.
"Our" Kev. Click to enlarge.
A final thought ...
Many thanks are due to Young Nam Kim, scientist and nominated cruise photographer. His excellent photos humble the rest of us but provide me with some fantastic images for these diaries, such as the one below (click to enlarge):
Next week....... more CTDs (what else) and Neptune's Court.......