Studying the motion in the ocean
An oceanography research trip to Admiralty Inlet is fueled by a sea of caffeine
The ship’s engine roared to life at 2:30 a.m. and jolted me out of semi-consciousness. My head throbbed — in my dreams I hadn’t stopped cycling through the next day’s research plan, albeit in a strange, nightmarish way. I opened the curtain of my berth and took in my surroundings: the sounds of snoring shipmates — at least someone was getting extra sleep — the sight of my field notebook perched on top of the laptop with which I had spent my weekend synchronizing instruments, and the smell of coffee, coffee, coffee. Nightmare forgotten, reality filled me with eager anticipation.
I am a graduate student in the MIT Joint Program with Woods Hole Oceanographic Institution, and an aspiring coastal physical oceanographer. I am excited about waves, fieldwork, and understanding the effect of coastal physics on water quality and current patterns. This summer, I had the opportunity to act as co-chief scientist during a two-day research cruise in Puget Sound, WA, through a coastal fluid dynamics course at the University of Washington Friday Harbor Laboratory.
Coastal physical oceanography research includes the study of fluid dynamical, meteorological, and other physical forces affecting the transport, mixing, and dispersion of mass, momentum, energy, sediments, marine organisms, and pollutants. My mission in Admiralty Inlet, the main shipping channel of Puget Sound, was to investigate how the estuary manages to remain so tenaciously stratified in layers of density, despite intense turbulent mixing due to strong tidal currents. This persistent stratification could contribute to issues in the estuary, such as oxygen depletion, called hypoxia, which can lead to a devastating decrease in biodiversity in the region through fish kills and other events.
Once we had studied up on Admiralty Inlet, we consulted the moon and the sun for guidance on our fieldwork plans. Either we coastal oceanography researchers are all secretly astrologers or tides affect almost everything we study — you decide. Especially strong tidal currents were expected during our two days of ship time, due to the summer solstice. I was interested in measuring vertical profiles of density along the length of the inlet channel. This meant casting a conductivity (a measure of salinity), temperature, and depth (CTD) sensor over the side of the ship on a long wire to a maximum depth of about 100 meters. In 3-meter-per-second tidal currents, having a long wire hanging over the side of a 58-foot ship is not the most stable setup. Sure, I wanted to see how the stratification changed as the salty ocean water flooded into the fresher waters of Puget Sound. However, keeping the crew safe is more important, so density profile measurements were confined to times around slack tide, when the currents were weakest.
I still marvel that no one yelled mutiny and tossed me overboard after I announced a 3:30 a.m. departure to catch the first slack tide of the day at 4:30 a.m. They were either a very gracious bunch, or just a little bit crazy about oceanographic fieldwork, too. Or perhaps we were all resigned to the job because the ship carried coffee. Lots of coffee. As I had prepared for the cruise, programing instruments, changing batteries, and deciphering the tangle of wires by the ship’s head, someone had made sure the ship was supplied with plenty of coffee. Thanks, someone.
Between slack tides, we swiveled a 2-meter-long pole with a current profiler into the water and steered the ship back and forth across the inlet, measuring vertical profiles of velocity. My teammate used this information to examine energy fluxes, as Admiralty Inlet is considered an ideal site for tidal-powered renewable energy. We also practiced essential oceanographers’ skills on deck, such as jumping rope on a moving platform, grilling delicious shish kebabs without burning up the ship, identifying surface expressions of cool physics on the water, solving differential equations, and spotting porpoises, seabirds and distant fireworks.
Apollo 8 astronaut William Anders once said, “We came all this way to explore the moon, and the most important thing is that we discovered the Earth.” In the sweet moment when I touched solid earth once again after a 22-hour workday at sea, I couldn’t have agreed more. During the past several months of sharing these experiences and describing the science I learned at Admiralty Inlet to friends and family, one of the most rewarding aspects of my work has been helping others discover the Earth, too.