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08 October 2000 - Nearing Montevideo

RRS James Clark Ross: Diary entry, October 8th 2000

Noon Position : 30 degrees 06 ' South. 42 degrees 24 ' West
Distance travelled since Grimbsy: 6540 Nautical Miles
Air temperature @ noon: 17.7 degrees Celsius
Sea temperature @ noon: 18.7 degrees Celsius


NEARING MONTEVIDEO AND THE END OF THE AMT 11 CRUISE
After the fun and games of crossing the line, it's been back to the grindstone (not that it was ever left), as the science continues and all those end of cruise bits and pieces need sorting out. As we have headed further south, both sea and air temperatures have started to drop, and the wildlife, of which we've seen so little, has started to appear, mainly in the form of birds. We've had our first sighting of albatrosses this week, including a magnificent Wandering Albatross, I'm promised it was one, and it certainly resembled the example in the bird book. Below are a few examples of what we've been "spotting".

Grey Headed Albatross Southern Fulmar Great Shearwater
Grey Headed Albatross Southern Fulmar Great Shearwater

Unfortunately, so intent on watching the wandering albatross we missed getting a picture of it. I realise this may seem rather suspicious, but it is true.

Everyone has been hard at work, what with general maintenance and making sure all the science projects continue smoothly, there have also been the regular emergency drills during which the ship's staff and scientific personnel carry out safety training exercises. These are designed to maintain the equipment, and a high standard of competence in emergency response. Below are some photos during a recent fire drill.

Luke donning his gear helped by Doug Luke and Richard auditioning for Star Wars
Luke donning his gear helped by Doug Luke and Richard auditioning for Star Wars

There has also been a chance for people to hone up on their medical skills with the first aid at sea course. It has given us the opportunity to try out a few bits of new equipment, namely a new stretcher, which is shown in the photos with poor Margaret being the casualty. It was a great chance to see where it could and couldn't go, altough I think the patient came off a little worse for wear.

Margaret assuming the Coffin Position Lee and Simon practising Basic Life Support
Margaret assuming the "Coffin Position" Lee and Simon practising Basic Life Support

SCIENCE
The Science week gone by from the Principal Scientist

So this is the end of the final complete week of the Atlantic Meridional Transect (AMT) research cruise, and we are now thinking ahead to the arrival in Montevideo, demobilisation of all the equipment, and packing the container ready for it to be shipped back to the UK.

Since the very interesting area of the equatorial upwelling we have this week been sampling across the south Atlantic gyre, which can be succinctly described as an oceanic ‘desert’. Every sampling cast has seen a very deep mixed layer above the thermocline, and it is in this mixed layer that there is very little of anything. The number of plankton caught in the daily nets has diminished greatly to a very small number of the small size species. This contrasted to further north in the upwelling region where the ‘catch’ of the day was eagerly studied by us all to see the large numbers of very different species of large organisms that were being caught.

During this week the very deep thermocline, down to 180 metres at a couple stations in the central gyre, has seen some of the analysers tested to their limits of detection. In this ‘desert’ the water column is very stable and the concentrations of the nutrients like nitrate, nitrite, silicate, phosphate and ammonium are all below the detection limits of our conventional analysers, and this calls for specialist techniques. Normally the ‘work horse’ for nutrient analyses is an analyser called a segment flow autoanalyser, which  very simply adds chemicals to a stream of seawater, and produces a colour that is detected and recorded. This work is being done on this cruise by myself and Vas Kitidis.

It is one of the particular specialities at the Plymouth Marine Laboratory that we have the capabilities to analyse very low concentrations of nutrients, like nitrate, nitrite and ammonium using novel techniques like fluorescence, and also with new technologies like a liquid waveguide. With these machines we are able to analyse as low as 5-10 nanomolar, up to 50 times more sensitive than the conventional autoanalysers. Below there are pictures of the autoanalyser and the nanomolar ammonium analyser.

Nanomolar ammonium analyser Nutrient autoanalyser
Nanomolar ammonium analyser Nutrient autoanalyser

As the AMT cruises have now built up (this being AMT 11), a large data base of information has developed for things like the nutrients and also for other parameters like chlorophyll, fluorescence, particulate carbon and nitrogen, etc. Underway samples are taken and filtered roughly every four hours for the whole of the transect. Dave Suggett and Sandy Thomalla have been responsible for doing it all this trip, and Dave has penned a few words to describe the phytoplankton side:

Phytoplankton taxonomy and physiology
Phytoplankton contain pigments which are used to harvest the light that penetrates into the marine environment. Whilst different groups of phytoplankton contain specific suites of pigments, all contain the pigment chlorophyll a. Large volumes of water are collected each day from the CTD or at regular intervals from the underway seawater supply and filtered through very fine filters (0.2  um). A relationship exists between the chlorophyll a content and the amount each sample fluoresces. Therefore, we are able to measure the chlorophyll a biomass of each seawater sample on board using a calibrated fluorometer. Duplicate filters must be collected and returned to the laboratory for a technique known as HPLC (High Pressure Liquid Chromatography) to determine the remaining pigments. From these remaining pigments we can establish the alternate phytoplankton compositions throughout the cruise.

Dave retrieving the net


Dave retrieving the net

Net samples of phytoplankton are also taken at each CTD station. One is profiled throughout the upper 100 metres whilst a second drifts at the surface. These samples are preserved and later analysed directly under the microscope as a validation for any HPLC derivation of each phytoplankton community.

So, this is the last words from myself as the Principal Scientist, as we will be leaving this fine vessel in Montevideo and heading home again. This AMT has been an excellent cruise, and has dovetailed three science areas, with the Southampton Oceanography Centre ‘autoflux’ team with us as well as the swath bathymetry investigators.

All has gone very well, and thanks must go to Captain Burgan and his officers and crew for a most enjoyable cruise and for helping to make it so much easier to get the science done with few problems.

With good sense the Atlantic Meridional Transect project will continue, and contribute to extending the unique and long-term data base of information. Added to that there have been many very specific and exciting pieces of science that have been carried out on the cruises. Hopefully the rewarding and informative science will continue.

Its been a pleasure to be the Principal Scientist with the excellent science team we have here on RRS James Clark Ross, and I look forward to sailing together with them again in the future.

So, it's goodbye from me,
Malcolm Woodward, 8 October 2000. (AMT-11 - "The Science goes on")



Weekly diary entries