My daily ship life, between CFCs and syringes

by Kelly McCabe

I am a graduate student participant on the cruise, and I primarily assist the chlorofluorocarbon (CFC) team—Jim Happell and David Cooper—with sampling the CTD and onboard sample processing (see picture below). Secondarily, I collect samples for land-based analyses of dissolved organic phosphorus (DOP) and nitrate stable isotopes. 

We are finishing up week five. Work has become routine. Little things boost morale. Confirmation of Taco-Tuesday elicited cheers. Smiley face stickers on my DOP bottles brought a smile to my face, despite losing sleep to sample a specific station. Singing and head bobbing resumed during CTD sampling, after the discovery of a few Spotify playlists that had yet to be deleted, even after exceeding the 30-day offline policy.

In the CFC lab, measuring CFC-12 and CFC-11 with the Gas Chromatograph
Date and time are measured by meals and shifts. In fact a majority of this week, the ship resided in time zone that did not exist on our electronic devices. The scenery though changing appears no different. Seawater is seawater is seawater. The unchanging nature of each day may test the sanity of the scientific crew, but it is an indicator that scientific operations are running smoothly. Exciting days are generally the result of damaged or broken equipment.

Twelve hours a day I help measure CFCs, a standard GO-SHIP measurement. CFCs, better known by their commercial name Freon, were common coolants for refrigerators. Upon discovering the ozone depletion qualities of CFCs in the atmosphere, the CFC-12 and CFC-11 compounds were phased out of the refrigeration industry. As inert gases, CFCs still persist in the atmosphere but their concentration is diminishing. The ocean sequesters CFCs and other gases in regions of water mass formation. Water masses can be identified and traced by their CFC concentration. Water mass CFC concentration is only affected by physical processes. This allows oceanographers to understand physical processes such as meridional overturning circulation, mixed layer air-sea dynamics, and eddy formation.

During my CFC shift, I can choose to “fill and/or empty” bottles as it is often bluntly phrased. Filling bottles refers to sampling the rosette. I carefully fill 300mL glass bottles with seawater from each of the 36 niskin bottles without trapping any air bubbles. Empting bottles refers to sample processing. I am the willing minion of Betty Boop, the programed computer voice, who informs me every twelve minutes that “the system is ready to receive inquiry,” indicating I may load a sample (picture above) and later instructs me “to push THAT BUTTON” to inject the sample. The gasses are stripped from the water and flow into the Gas Chromatograph (GC) (picture above). The GC produces a chromatagraph with peaks proportional to the concentration of CFCs present in the water sample. 

When I am not assisting the CFC team, I am often getting my daily hand and forearm workout, syringe filtering (picture below). DOP is operationally defined as any organic phosphorus molecule that passes through a 0.2um filter, thus all seawater taken for DOP analysis must be filtered. The DOP samples compliment GO-SHIP’s standard dissolved organic carbon and nitrogen measurements and will support my PhD thesis that aims to understand the role of DOP as a nutrient source supporting nitrogen and carbon fixation within the world’s oceans. It has been understood that most phytoplankton obtain their nutrients (carbon, nitrogen, and phosphorus) from inorganic forms, but in nutrient deplete regions, such as the south pacific subtropical gyre, research has shown that organic compounds can act as an additional source of phosporus and even nitrogen.

Syringe filtering for DOP
My daily routine may sound boring, but it is the reality of oceanographic data collection. It is the dedication of groups such as ODF and all those involved with the CLIVAR/GO-SHIP program that have led to the production of high resolution data sets that support oceanographic and climate based research around the world. These dedicated and enthusiastic people don’t spend months at sea doing routine measurements to perpetuate a hoax. They do it for science, in an attempt to understand the world as best as possible with the knowledge and technology available at the present time.


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