At the stroke of midnight, I welcomed the new day by finishing oceanographic sampling work on the back deck of the Pacific Marlin. The night shift is a very quiet time around the ship but it’s also a very comfortable time for working outside. The night breeze is refreshing compared to the sweltering conditions during the day. There’s no horizon visible and the swaying night sky is beautiful yet disorienting. Our current location within the British Indian Ocean Territory is 1200m above a deep sea mount over 100 km from any of the Chagos atolls. We haven’t seen land for ~4 days.
Through the night we completed an east-west transect stopping every few miles to lower an instrument 300 m below the surface. On each decent, our microstructure profiler, or MSS, collects temperature, salinity, pressure, dissolved oxygen, chlorophyll fluorescence, and velocity shear data. Temperature, salinity and pressure are the three variables we need to calculate the density of the water. Just like oil floats above water, the ocean is organized with the lightest water at the surface and the densest water on bottom. How density changes with depth is called stratification which is important for how water mixes and adjusts to changes in flow direction or bottom features. The oxygen and chlorophyll measurements inform us about where plankton grow and decompose in the water column. Velocity shear probes detect motions in the water that are turbulent. Turbulence is a sign of water mixing which is very important for understanding the energetics of the ocean.
After the last MSS profile is completed, we radio to the bridge that the instrument is on board, rinse and dry the equipment, turn off the back deck lights and call it a night.
One tricky thing about night shift is making the specified meal times during the day. I often miss the 7am breakfast but thankfully cereal, yoghurt, and fruit are available 24/7. You can ask the kitchen staff to hold a plate of prepared food for you in advance. I’ve done this if I sleep through the 11:30am lunch or need to start work before the 5:30pm dinner. In general the prepared food has been very nice and a good mix of styles and ingredients. As on any cruise fresh veggies are limited after the first week.
As we are only a few days away from the end of the expedition, the science crew are busily writing up cruise reports. This entails writing up a description of our methods, measurements and preliminary results. At the end of the cruise, the chief scientist, Tom, will compile our individual reports and disseminate a final version to the cruise members and organizers.
At 5pm we arrive at our sampling location for the evening and once again start MSS profiles, taking turns from setting up the computer and lowering the instrument. We continue this for 4 hours, watching the sun set and the moon rise. One of the nice things about being at sea is having an unobstructed view of the moon and stars each night. Since there’s been no rain thus far on the cruise this has been especially true. It’s our last night shift of the cruise and because it was a short shift, I’m able to join the others who are relaxing in the bridge lounge watching a movie. In a few days we’ll be back in our respective homes telling our friends and family about the expedition. After a short while, we’ll be itching to go back to sea exploring these waters that few will ever see and a declining number of marine life inhabit.
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