It’s been an exciting spring for the Sharma lab! In late March three of us (Diksha, Vignesh, and myself) set out for Kiel, Germany to participate in a mesocosm experiment we had been preparing for since fall. Kindly hosted by the Riebesell group at GEOMAR, we were able to carry out the same types of clay spraying experiments we have been doing at sea and in lab on a much larger scale. While past experiments took place in 1 L plastic bottles, these mesocosms hold thousands of liters of seawater. In the photo below you can see some of the mesocosms (there were 12 in total), which are set up along a dock right outside the old GEOMAR building on the west side of the fjord.
Each mesocosm consists of a large plastic bag attached to a metal frame – the frames are reused for many experiments but the bags are replaced after each campaign. The bags taper to a small opening at the bottom where there are sediment traps to collect particles that settle out of the water column – in the above photo the little piece of tubing that comes out from under the yellow platform and ties onto the rope is part of the sediment trap sampling apparatus.
The mesocosms also have umbrella-like covers that stay closed most of the time but can be easily propped open when researchers need to access the water for sampling, spraying clay, etc. They help protect the mesocosms from things like precipitation (which Kiel has no shortage of, at least this time of year) that may affect the ongoing experimentation. They do not, however, prevent researchers from dropping personal or lab items into the mesocosms while leaning over the rim to sample.
The Riebesell group started their experiment at the beginning of February – here you can read more about the ocean alkalinity work they are doing https://www.geomar.de/en/news/article/the-ocean-as-ally-in-climate-protection-how-does-ocean-alkalinity-enhancement-affect-marine-life. This is a different approach to marine carbon dioxide removal (CDR) than the one we are investigating, and also seeks to tackle ocean acidification.
Their sampling finished in late March right as we arrived, so we were able to observe and learn their sampling techniques before starting our work with the clay sprayer. On one of our first days in Kiel they were cleaning the mesocosms, which entails scrubbing down the sides with a long-handled brush so that anything stuck to the walls (e.g., bacterial growth or abiotic particles) falls into the sediment traps at the bottom. Pictured below is Dr. D Sharma cleaning mesocosm #8.
