Sampling the Deep Blue….
By Karen Wiltshire & Pauhla McGrane |
The Ocean out here, in this “corner” of the Atlantic at 21° 58 N 21°33 W, is of a clear deep blue at the surface.
For days now we have been sampling with a Rosette of Niskin Bottles with sensors of the CTD including temperature, salinity and fluorescence. We also have been deploying lots of different nets for zooplankton and phytoplankton. This is on stations which varied in depth from 100 metre to 4700 metre.
Putting it mildly: this taxes the scientific “personality”. It requires both speed and organization on the one hand and endless patience on the other. The organization is required before a station so that all equipment is ready to deploy. Speed is required when we arrive at a station, so that we get all the equipment is deployed smartly and then comes the” loooooong” part: watching the rosette with all our precious equipment descend out of sight, and disappear in to the deep. We watch endless wire being spooled off the winch spool and are delighted by the data sent back up the wire as our sensors measure each metre of water traversed.
We see the temperature getting cooler and cooler and then we reach what is known as the thermocline under which we have cool/cold water to the bottom until light no longer penetrates. Photosynthetic organisms position themselves in the upper layers in such a way that they receive enough light to photosynthesize and grow. At the same time they are often positioned on top of the thermocline above a layer known as the turbidity maximum where the decaying material collects forming a sort of floating “compost” with nutrients.
Below this we see different colder water- often of polar origin – layered under lighter warmer water.
We get excited on the way down by each change in profile- a shift in temperature and salinity giving us clues as to how water masses are positioned in our oceans. It is like looking at a blank piece of paper which is slowly revealed to be a picture filled with information.
On the way down we decide where we want to sample the water column- spacing our 24 water bottles to suit the questions the scientists have posed in advance. For example if we want to look at how organisms migrate up and down towards and way from the light at the surface we sample the water above the thermocline in great detail. And we trigger these samplers on the way back up to the surface having seen what the profile looked like on the way down. A profile to 4700 metre takes about 3 hours in total. We are on station for 6 hours before everything has been done- CTDs, Nets, light measurements.
The crew who drive the winch, and direct the deck work as well as the officer keeping the ship in position are even more patient than any scientist. They concentrate on each m of wire spooled off, making sure nothing goes awry.
Sitting in the winch room over the aft working deck on the Polarstern in collegial silence, punctuated with bursts of conversation, especially at night, regarding the data coming in out from the deep blue makes one contemplate the vastness and beauty of this life-giving planetary resource and awe is omnipresent.
There is nothing more rewarding in Ocean Observational Science than to sample and analyze from an excellent infrastructure, with wonderful crew, great teachers and highly motivated Scholars.
Greetings from the Polarstern
Karen Wiltshire, POGO/AWI
Pauhla McGrane, SMART- Chief Instructors NoSoAT Training cruise
