Coordinator Boknis Eck
Prof. Dr. Hermann Bange, GEOMAR
Düsternbrooker Weg 20 | D-24105 Kiel
Tel. +49 431 600 4204
hbange(at)geomar.de
www.bokniseck.de
Trip on RV LITTORINA to Boknis Eck to take water samples for the time series and further research projects. Photo: Ilka Thomsen/GEOMAR
Water sampling at Boknis Eck. A CTD rosette provides a vertical profile of water temperature and salinity, bringing water to the surface from various depths. Photo: Ilka Thomsen/GEOMAR
Junior scientists on board the LITTORINA prepare the CTD roseette for another sampling at the Boknis Eck measuring point. Photo: Ilka Thomsen/GEOMAR
The first measurements at Boknis Eck took place on April 30, 1957, and continued until 1975 with the research vessels Hermann Wattenberg and Alkor (I). Photos: GEOMAR archive
Since 1975, sampling at Boknis Eck has been carried out mainly by the Kiel research cutter LITTORINA. Photo: Bernd Brockmann
For the time series, the Kiel researchers selected a position that is ideal for the western Baltic Sea. It is located at the exit of the Eckernförde Bay, where no rivers flow into the Baltic Sea. Map of the Kiel Bight from Babenerd & Gerlach (1987)
At the same time, Boknis Eck is located far enough out of the bay to be exposed to the influences of typical inflow events through the Great and Little Belt, resulting in high salinity variability. Map: Esri
The Boknis Eck Time Series Station
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 Boknis Eck Data
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.
The Boknis Eck Node
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.
