by Mark Stinchcombe
For an Oceanographer, the twilight zone conjures up images of the dark and murky depths of the ocean, just under the sunlit surface waters with many marine ‘monsters’ living there. Fish with large eyes, mouth and teeth ready to eat anything they happen to come up against, squid of varying, sometimes terrifying, proportions, and bright red crustaceans trying to hide in the dark from all of the above.
On this cruise, however, the twilight zone can also be used to describe the time where you’ll find that most elusive of creature, the oceanographer on the night shift. Between the hours of 18:00 and 06:00 (or between dinner and breakfast) these members of the scientific party emerge, like zooplankton from the deep, to sample as much water as they can under the safety of darkness, then retiring to their cabins again before their light sensitive eyes are hurt by the sunlight that is emerging over the horizon.
The reality for us night shifters is not as bleak as all that. I am Mark Stinchcombe and I work within the Nutrients Group. As has been mentioned previously, the work we are doing on this cruise happens around the clock, and therefore the deck department (as Colin has already talked about in his post) and the science party also work around the clock. There are four groups who have member on the night shift, the physics, nutrients, carbon and CFC groups all have people working on shifts to cover every hour of the day. In the nutrients group this was decided by the drawing of lots, and as usually happens in these scenarios I draw the short straw, literally.
The nutrients group consists of Sinhue Torres (our leader, and on the 06:00 to 18:00, coincidence…??), Hannah Donald (PhD student on the 12:00 to 00:00) and Carolyn Graves (PhD student on the 00:00 to 12:00) and of course me (18:00 to 06:00). We are in charge of making inorganic and organic nutrient measurements, as well as dissolved oxygen measurements, from the water samples collected using the CTD rosette. The nutrients are analysed on an instrument called a Segmented Flow Autoanalyser, or ‘The Beast’ as we have affectionately named it. This has been analysing the water samples for silicate, phosphate, nitrate, nitrite, ammonia and total dissolved nitrogen. Nutrients play a very important role in the growth of phytoplankton, single-celled algae in the surface waters. If you think of your garden at home, if you want the best out of your tomato plants you need to add nutrients, in the form of fertilisers or compost, to the soil. The same is true at sea, although the nutrients at sea are mixed into the surface waters by vertical mixing of the water column during the winter, or close to land by run-off, and other processes. By analysing the water for these we can see how much is available for use, how much has already been used and whether these have changed with time by comparing against previous cruises to the same area.
The dissolved oxygen measurements are analysed using a method known as titration, where the volume of a chemical needed to complete a reaction is measured. In this case it is a specific method, called a Winkler titration. These are analysed to calibrate a sensor which is one of many on the underside of the CTD frame. Dissolved oxygen is a very good tracer of water masses, along with temperature and salinity. Different water masses will have different oxygen, temperature and salinity signatures and so can be identified and tracked along our cruise track, as Penny has already shown.
At midnight it is meal time. Paddy, the 2nd cook, is also on the night shift, so we usually all meet up for a chat around midnight over breakfast/lunch/dinner (depending on what part of the day it is for you). With some people coming off shift and some people coming on, it’s a busy period and is a good chance to get the latest news from the other groups or to talk to your own group about what’s been happening and what is likely to come up over the next part of the day.
By 06:00, when my shift has come to the end, I pass over to Sinhue. I give him all the information from the night before about what we’ve done and where we’re up to in terms of our analysis. I then wave goodbye to the other groups as I walk through the labs, away from the sunshine that I’m sure is getting brighter every day and is a hint that I should once again make a journey to the darkness of my cabin. Black-out blinds are a must for those of us sleeping during the day and give us the security of darkness. After reading a few pages of my book it’s time to go back to sleep, another night’s hard work is over.
Images: “the Beast” and oxygen titration equipment in the Main Lab, and the night shift sampling the CTD (Stefan, Mark, Carolyn, Gary, Claudia). Photos by Mark Stinchcombe.