Research – Clay Carbon Ocean

Kiel Mesocosms 2024 – part 2

The star of this trip was the clay spraying apparatus which we had specially built for this purpose. Jeff Renk, who runs the electronics shop at Dartmouth, helped us to create a scaled-up version of the clay sprayer we used for our 1 L bottle experiments (see previous blog post: “Day 5: Spraying Clay” from last April). The small sprayer is built to fit snugly on top of the bottle neck, but now we needed a version that would fit over the rim of the mesocosms which are 2 m in diameter. In addition to being much larger and using 4 airbrush sprayers instead of one, it had to be built so that it could be easily folded or dismantled for international shipping and then reassembled in Kiel without Jeff.

Here you can see a picture of the clay sprayer 2.0 (and Vignesh) in action! The three bars holding it in place rest on top of the frame of the mesocosm, and the bar with the purple boxes spins around (operated by a control box that is not in the photo) so that the clay is sprayed in two concentric circles on the surface of the water. The purple boxes are simply 3D-printed houses that the airbrushes sit inside of – there are four airbrushes total, two “inner” and two “outer” that are evenly spaced from the center of the instrument. Each airbrush also has a detachable reservoir for the clay slurry, a 20 mL glass jar that screws onto the airbrush’s intake tube. These had to be removed, refilled, and reattached after each spraying. Pictured below is Dr. D Sharma holding up one of the jars (someone told us it looked like Bailey’s Irish Cream), and then a photo on a different day of Vignesh attaching it to the sprayer. In this second photo you can see the airbrushes more clearly as the plastic housing had been removed to attach the jars.

We experimented on three mesocosms in total – M3, M6, and M7, spraying clay only on M6 and M7 and keeping M3 as our control. Here is a link where you can see a video of the clay sprayer doing its thing: https://youtu.be/ck0VurB1zWc

One day was particularly windy, so as soon as we started spraying we noticed that a lot of the clay slurry was getting blown out of the mesocosm and not reaching the surface of the water. Here the mesocosm covers came in really handy, and we were able to fix this problem simply by closing the cover and then operating the clay sprayer as usual. (Not sure the picture is necessary to get the point across, but I look really cool.)

And don’t worry, we also had time to explore downtown Kiel!

Bonus fun fact: the metal bars of the clay sprayer are made of 8020 aluminum, which I learned while preparing the customs documents for shipping our supplies to Kiel. During this process I also learned that the name “8020 aluminum” has nothing to do with the actual composition of the metal but is just named for the Pareto Principle, which states 80% of outputs come from 20% of inputs for any given situation. Not that anyone asked my opinion, but I think they could have come up with something better if they weren’t going to choose a name based on its material properties.

Kiel Mesocosms 2024 – part 1

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.

Interactions between zooplankton and clay

Manasi is investigating whether clay minerals are ingested by zooplankton species such as copepods and are transported to deeper waters via fecal pellets. Copepods are the most abundant mesozooplankton taxa in the marine environment and represent a vital link in the marine food web between algae and higher predators such as fish, whales etc. Fecal pellets produced by copepods are an important nutrient source for deep water ecosystems and can rapidly transport organic matter to the ocean floor. Fecal pellet production rates of actively feeding copepods may exceed 10 pellets per hour.