Minipropsal CASCADE

December 2015

Sinikka Lennartz is back from her miniproposal on carbonyl sulfide cycling in aphotic depth (CASCADE) and reports about her research.


Shedding light on the “dark production” of carbonyl sulfide, a climate relevant sulfur gas

Miniproposal CASCADE: Carbonyl Sulfide Cycling in aphotic depths

Carbonyl sulfide is the most abundant sulfur gas in the atmosphere. It strongly influences Earth’s albedo and can additionally be used as a tracer for terrestrial net primary production – under the condition that all sources and sinks to the atmosphere are well understood. The ocean is believed to be the major source of this gas to the atmosphere, but the magnitude, distribution, and processes underlying the oceanic contribution are currently debated. While the marine photoproduction of carbonyl sulfide is well understood,  a light-independent, so called “dark production” has been assumed – but not much is known about it. This was the starting point of my Miniproposal.
To understand light-independent production, I wanted to take samples from the place that is most suitable for this: deep under the water surface, where it is dark. This is not easily done, however, when the measurement system needs a continuous water flow of several liters per minute. Niskin bottles from the CTD cannot be used, as they are discrete. The CASCADE grant was used to build a submersible pumping system that is operated from the ship’s deck and, thus, provides the possibility to measure continuous depth profiles. I was therefore able to obtain the first depth profiles of the gas in the Peruvian upwelling area, and considering concurrent depth profiles of a variety of oceanic parameters will investigate the main factors determining dark production.
The Miniproposal gave me the extremely valuable experience of carrying out a project from the idea to its implementation. I learned a lot by designing the set-up, thinking together with technicians from the TLZ about possible ways to implement it and finally coordinating the deployment on the ship. The four shipboard deployments were technically and scientifically successful and other working groups showed interest in deploying the system on future oceanographic campaigns.