How much oxygen is available to organisms in seawater? What are the temperatures? How many nutrients are dissolved in the water? Answers to these questions allow statements to be made about the state of a marine ecosystem. But it is not enough to collect them only once. Whether the environment is changing, whether there are shifts in the ecosystem, can only be detected if the same data are collected continuously over long periods of time. Marine researchers in Kiel recognized this 60 years ago.
At that time, Johannes Krey, Professor of Planktology at the Institut für Meereskunde in Kiel (IfM), initiated a time series that is still active today: Boknis Eck. It is thus one of the oldest continuous marine chemical and marine biological time series ever. Boknis Eck is ideal for studying a coastal ecosystem that is under the influence of pronounced changes in salinity. In addition, biogeochemical processes that respond to changes in dissolved oxygen can be monitored there.
The data from the time series station are in demand internationally because they reveal long-term environmental changes. They show, for example, that nutrient inputs to the Baltic Sea have decreased significantly since the 1990s. Nevertheless, phases of extreme oxygen depletion are becoming more frequent and longer - probably a consequence of rising water temperatures. Measurements at Boknis Eck, for example, show an increase in average water temperatures of 1.2 degrees Celsius since the beginning of the time series. The process of climate change is in full swing. It is therefore all the more important not to let the time series break in the future, so as not to be surprised by changes.
In addition to the monthly measurements, Boknis Eck was expanded in 2017 to include a permanent observatory. The Boknis Eck node system was developed as part of the COSYNA project (Coastal Observing System for Northern and Arctic Seas), which is coordinated at Helmholtz-Zentrum Geesthacht. The observatory on the seafloor contains sensors that record current speeds and directions, salinity, temperature, and concentrations of oxygen, carbon dioxide and methane. In August 2019, the platform and power supply node were unfortunately destroyed. They are scheduled to be reinstalled by mid-2023.