Fieldwork

What do we measure?CTD coming on board on RRS James Cook

The essential core data collected by the ship-based programme are temperature, salinity, nutrients, oxygen and water velocity at the 50 full-depth stations of the section.  These data are collected to the highest international standards, having skillfully applied calibrations and being fully documented.  Underway measurements are collected, including surface temperature and salinity, meteorological variables, bathymetry and shallow water velocity.  Many contemporary occupations of the section also include biological or biogeochemical measurements including chlorophyll, phytoplankton species, iron, carbon, trace metals and CFCs.

Floats and gliders cA glider at the surfacer after being deployedollect a great quantity of temperature and salinity over a wide region, but to a standard lower than ship-based observations, and typically only in the upper 2000m.

All data from the Extended Ellett Line programme are available from the British Oceanographic Data Centre.  The table of Individual Sections provides a link to the BODC page for each cruise, as well as a figure showing temperature, salinity and density sections.

 

The notorious North Atlantic weather

In the main lab of RRS Discovery during a roll of 18°Over the years the weather in the Rockall Trough has gained a fearsome reputation amongst the oceanographic community. Many of the planned expeditions to the region have been interrupted by big storms with high winds and high seas. To the scientists the bad weather results in a very interesting phenomenon; stirring of the ocean by the wind to depths rarely seen across the globe. It is this stirring action that releases heat from the ocean depths to the atmosphere above, keeping the UK climate relatively mild. David Ellett was among the first to recognise the importance to the UK of our local oceanic "radiator".

In February 2000, scientists on RRS Discovery encountered giant waves nearly 30m high in the Rockall Trough. Life on board became very difficult as the ship rolled as much as 30 degrees in the stormy seas (the photo shows a roll of nearly 20°). A study concluded that the monster waves were probably caused by resonant conditions, whereby a weather front moved at the same speed as the wave group for a long enough period for a fully developed sea to evolve (Holliday et al., 2006). The significant wave height of 18.5m (representing the height of the waves over 30 minutes) was the largest ever measured in the ocean, and the individual wave height of 29.1m was similar to those that have been observed under hurricanes. Waves of over 5m are common and frequently prevent work over the side of the ship.

graph showing wave records from 8th and 9th of February 2000

 

 

Cruise blogs

Read about life at sea on an Extended Ellett Line cruise:

http://www.sams.ac.uk/2013-ellett-line-expedition

http://ukosnap.wordpress.com/


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