In carrying out the Ocean Change Expedition, scientific knowledge is required in addition to nautical and shipboard skills. In this blog, we need to delve a little deeper into the world of marine geochemistry to describe aspects of our measurements this year.

The oceans absorb not only much of the heat that is increasing as a result of climate change, but also the carbon dioxide that is released into the atmosphere. Even if this means they are still slowing climate change on land, they bear the brunt of its changes in the long term. The "evil little sister" of global warming is ocean acidification: CO2 dissolves in seawater to form carbonic acid, which reduces the pH value. This acidification negatively affects the life of mussels, corals etc.. The ocean can still counteract a certain buffer capacity by dissolved alkaline substances like carbonates, bicarbonates or hydroxides, which slows down the decrease of the pH-value. The measure of this buffering capacity is "alkalinity," the total content of alkaline buffering substances in seawater.

How does this buffering effect work? What is the effect of the natural mixing of different water masses, e.g. when water from the Atlantic flows into the North Sea? Could the introduction of suitable substances strengthen the alkalinity and thus the resistance of the sea to its acidification?
These and other questions are being researched by the German Marine Research Alliance as part of its "Marine Carbon Storage" mission in the "RETAKE" research network. Before alkalinity can be expanded in an ecologically compatible way by adding buffer minerals, the fluctuation range of alkalinity in natural systems is to be determined. This will be done, among other things, by studying the influx of water from the Atlantic into the North Sea. This will provide a good basis for the development of balancing and monitoring methods. An important element here is the characterization of water bodies of the shelf seas in order to trace their mixing pathways and the effects regarding alkalinity.

For this purpose, water samples were / are taken on the Dagmar Aaen in the North Sea and off the Scottish Atlantic coast, which are later analyzed for their alkalinity and other chemical constituents in the laboratory at the Helmholtz Center Hereon. The combination of alkalinity with dissolved trace elements (e.g., metal ions and naturally occurring radionuclides) provides a kind of fingerprint for a water mass that can be used to track mixing processes. In addition, to complete the understanding of the process, experiments are being conducted in mesocosms (large water tanks) for weathering of alkalinity-increasing minerals.
For sampling on the Dagmar Aaen, we use a water bailer, which is lowered into the water on a line after the ship is stopped. Flaps are attached to both ends of the tubular bailer, which are opened before use. The flaps are closed by a metal weight rushing down the line and hitting a mechanical trigger on the bailer. Once the bailer is back on board, a water sample is bottled for later laboratory analysis. It is very important to immediately note the time and position of the vessel at the time of sampling and to assign it to the particular sample: A sample whose exact origin cannot be reconstructed later is completely worthless.

These analysis data are supplemented by the oceanographic measurement data. Which were measured from the Dagmar Aaen at the water surface (using OceanPack) and in the water column (CTD probe).
In one of the next blogs we will go into more aspects of our ocean observations. Translated with www.DeepL.com/Translator (free version)