The Rosette: Chemical Oceanography Workhorse.

The job of studying the deep ocean is daunting.  Deep water here in the North Pacific is old... having last been in contact with the atmosphere hundreds of years ago when it sunk in the North Atlantic or off the coast of Antarctica.  It has accumulated chemicals and carbon from sinking particles that have been processed by bacteria along its path.  How do you understand the chemical properties and potential for reactions of water at 4000 meters beneath the sea surface?  Well, simply put, you bring it to the surface and into your laboratory on the ship.  The instrument package we use for this is called a Rosette.

Rosette being lowered in the ocean

It consists of 24 Nisken bottles that hold 10 liters each.  They are cocked open on deck, descend to depth as a cylinder open on both ends, with the tops and bottoms cocked and connected to "rubber bands." These slam the cylinder shut when fired from the ship trapping water from whatever depth you choose.  It takes about 2.5 hours just to lower the package to 4000 meters, more time to retrieve and we have done this about 25 times so far over the past week.  The cable that lowers the rosette has an electrical connection at its core that both feeds  information on depth, salinity, and temperature (from a CTD sensor on the bottom of the rosette) up to the ships controls, but also will send an electrical signal to the rosette to sequentially "fire" each bottle when it is at the depth selected to capture a deep water feature.  The coordination between the wench operator, the CTD technician, and scientists is complex and many things can go wrong (bottles don't close, bottle leak, etc.) but usually this results in 240 liters of water collected from between 0 and 4000 meters being set on the deck where scientists carefully remove the water through a small nipple on the bottom.

The Control Screen for Rosette/CTD operations

The bottles are sealed until the nipple is opened so contamination is limited and extremely small concentrations can be measured.  Other groups on the ship are collecting water to measure oxygen, dissolved and particulate organic carbon, nitrogen, phosphorous, silica, bacterial abundance, organic microgels, bacterial DNA, molecular distributions, and other things.

Jade filters water from Rosey

We are collecting water for photochemical experiments on the ship (...more on that later) and measuring/mapping the optical properties of the water from the surface to the bottom.  The optical properties are important to photochemistry since these reactions are dependent on absorbing the energy from sunlight.  They also track deep water masses originating from different places and traveling to different destinations.  Since we can't see the very slow motion of deep water, chemical and optical tracers let us understand how the water moves at great depth.

Ooops! Just arrived at the next station....
Latitude 057 26.951 North, Longitude 141 08.988 West, 3457 meters to the bottom.  Gotta go get Rosey on her way.  Water back up on deck in 3.5 hours if all goes well.  Wish us luck!

- Bill