Sampling at the bow: measuring ocean-atmosphere exchange

One of the main objectives in the NAAMES mission is to understand what gases and particles present in the surface ocean get into the atmosphere and influence clouds and climate. To help answer this question, our group measures gases present in both the ocean and atmosphere, as well as the rate at which the gases are exchanged- that is, how quickly they go into or go out of the ocean.

To do this, we need to observe the natural wind motions and gas concentrations with as small an influence from the ship as possible. The ship disturbs the natural wind field and can also be a source of gases and particles (especially from its exhaust stack). So we go up and out! We install the inlet on the forward mast, which minimizes these impacts from the ship itself. This is where we can get the air most representative of the North Atlantic environment while on board.

So before leaving the dock we lower the forward mast, climb on, and install long sampling inlet tubes. Then, before departing, we raise the mast and run the other end of the tubes back to a mass spectrometer which is running in a container van just aft of the mast. Then (assuming everything is working!) we continuously draw in air and measure two gases (dimethylsulfide and acetone). By simultaneously monitoring the 3D wind direction, we can find out how much of these two gases are entering the atmosphere from the ocean.

Written by Mike Lawler

Tags: NAAMES-III 2017