Sampling for biogeochemistry of the surface ocean

Several of our posts mentioned the GoFlo bottles that we use to sample the ocean water. Those sampling bottles are specifically designed for trace metal research. We will explain their functioning in a follow-up post. Today, I wanted to show you some impressions of the sampling using so-called Niskin bottles. These bottles are assembled around a carousel. 24 Niskin bottles fit on one carousel. Once all 24 bottles are hooked onto the carousel and secured, the whole carousel is lowered into the ocean through a door on the starboard side of the ship. In this case, the carousel is lowered down to 500m water depth, as we only probe the upper ocean  layer. Several sensors are attached onto the carousel too. One of the most important ones monitors changes in water conductivity (i.e. salinity), temperature, and pressure (i.e. water depth). This sensor is the reason why we often call the carousel-bottle assemblage a CTD (Conductivity, Temperature, Depth). Other frequently used sensors are measuring oxygen content and fluorescence, for instance, that give some insights into the biology and chemistry of the water with depth.

Once the CTD-carousel has reached 500m, we bring it up again, slowly, as each bottle is now going to be closed at a different depth. For instance, the first bottle is triggered (closed) at 500m water depth, the next one at 300, next one at 250m etc. Each bottle therefore collects water from a different depth. Once the CTD-carousel is back at surface, it is safely secured inside and the side door closes again. The bottles are now ready for the eager scientists to subsample the water from the depths that are of interest for each project. All involved teams in this case are from the universities Stellenbosch, UCT and CPUT. They all sample for various parameters around the interactions between biological organisms (algae and bacteria) and the ocean chemistry, i.e. how the organisms are affected by the enviromental conditions and how the environmental conditions (e.g. nutrient abundance) is affected by the organisms.




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