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Chasing salt

Observing upper ocean turbulence

Gripping the desk as waves rock the ship back and forth, it is occasionally hard to sit upright at sea, let alone walk about the ship. I have strapped my chair to my desk with a bungee cord to keep me from sliding across the lab. A few minutes ago a large wave washed across the stern of the ship and sent salt water into the lab. Some of our equipment got wet, but nothing too bad.

The days are long and the work is challenging, but watching the sunrise across a clear blue sky with nothing in sight makes all of this worth it. As an observational physical oceanographer, going to sea is part of life, and a part that I love tremendously. Leaving port, working far away from land, and knowing that everything you need is on the ship with you provides a feeling of joy and sense of fulfillment surpassed by little else I do in life.

I am currently on the R/V Endeavor, operated by the University of Rhode Island, for the second of three U.S. cruises, which are part of the Salinity Processes in the Upper Ocean Regional Study, or SPURS. The first SPURS cruise was on the R/V Knorr, operated by the Woods Hole Oceanographic Institution (WHOI), and took place in September and October 2012. That cruise was 34 days long, starting in Woods Hole, MA and ending in the Azores. The second cruise is 31 days, starting and ending in Narragansett, RI. On both cruises we steamed nearly eight days to the salinity maximum of the North Atlantic to find the saltiest ocean water in the world.

The project, funded by the National Science Foundation and NASA, hopes to answer questions specifically about salinity in the upper ocean, in conjunction with the Aquarius-SAC/D satellite that infers sea surface salinity from space. The data we collect provides in situ salinity observations to compare with the satellite observations. In a world with a changing climate, precipitation patterns are expected to change, causing wetter areas to become more wet and drier areas to become more dry. Understanding upper ocean salinity processes will unlock secrets of how changing climate may impact the water cycle, both over the ocean, where the majority of it occurs, as well as over land. Changes over the ocean will impact the entire cycle, including the water we drink on a daily basis.

Although my research does not directly look at the salinity process, it does focus on the physical processes that affect salinity in the upper ocean. As a physical oceanography student in the MIT-WHOI Joint Program for Oceanography, my research focuses on the stably stratified upper ocean. Just as oil floats on water, when the sun heats the upper ocean, a fairly thin stable layer floats atop the ocean. Depending on weather conditions such as low wind speeds and high incoming solar radiation, the upper ocean can warm and cool several degrees on a daily basis. At the surface of the ocean, heat and moisture are transferred between the atmosphere and ocean. Understanding the details of the physics in the upper ocean is fundamental to understanding how the sea and air interact.

In order to observe the upper ocean at very small scales, on the order of centimeters to meters, we are using special instruments that make measurements over 500 times each second. One type, called a Vertical Microstructure Profiler (VMP), is tethered with a wire and released over the stern of the ship. The VMP allows us to record a time series of measurements in one place by continuously releasing the instrument and bringing it back to the surface. The second type we use is a small package attached to autonomous Slocum gliders. The gliders use buoyancy to maneuver around the ocean for up to a few weeks at a time. This data is used to tell us how the ocean mixes, and more specifically what processes cause the mixing.

Although being at sea can be quite a bit of work, it is nice to take time to reflect on the beauty of nature when time allows. My favorite days at sea are when the wind is calm enough to create seas so flat that the clouds reflect in the ocean. Although I must admit, it is not just because it creates a beautiful sight, but also because on those days the ocean warms the most, creating a stable boundary layer.

Alec Bogdanoff G is a physical oceanography graduate student in the Department of Earth, Atmospheric, and Planetary Sciences.

1 Comment
Anonymous about 10 years ago

Does the Slocum package differ from the towed VMP or does it also measure in the same way but at greater depth?