Abstract
A solution of the problem of determination of spatial variability of oceanographic fields with a fine structure resolution higher than it was possible previously using towed scanning probes was presented for the Baltic Sea. Another concurrently solved problem consists in obtaining data on the structure of waters in the bottom layer, which was difficult to implement by application of previous methods. Instead of scanning along inclined paths, a new measurement technique allows for a quasi-free probe drop with a constant sink rate and with reaching the bottom at each dive cycle along the route of the ship independent of the pitch of the ship and optimal for the applied probe. The new measurement technique is simpler and more efficient than the previous one. In addition, the problem of measuring velocity of both very weak and strong currents in a thin bottom layer, including stagnant zones, slopes, sills and underwater channels, was suggested to be solved using clusters consisting of a sufficiently large number of autonomous Tilt Current Meters (TCM) of original design. The innovation benefits are illustrated on the results of a monitoring campaign that was carried out in the southern Baltic Sea in 2016-2018. Among the new findings there are the highest ever recorded temperature, 14.3 °C, in the halocline of the Bornholm Basin measured after a baroclinic inflow event in early Autumn 2018, and an extraordinarily large current velocity of saltwater flow of more than 0.5 m/s, recorded by a TCM within a 1 m thick bottom layer at the eastern slope of the Hoburg Channel during a period when the northwesterly wind had intensified to severe gale.
Highlights
The Baltic Sea is under the influence of a large number of hazardous substances of technogenic nature, polluting its waters, bottom sediments, and biota
analyzing published materials based on the results of the general environmental monitoring
the authors concluded that the volume and completeness of the information received do not meet the requirements of the scientific community
Summary
The Baltic Sea is under the influence of a large number of hazardous substances of technogenic nature, polluting its waters, bottom sediments, and biota. Unexploded chemical weapons (CW) with chemical warfare agents (CWA), Innovative Measurements in Bottom Layer which were dangerous to leave on the coast and dumped into the sea in the post-war years, turned out to be outside the framework of general environmental monitoring (Sanderson et al, 2010; Bełdowski et al, 2018b) This problem, albeit belatedly, became the object of a special and still ongoing monitoring project (DAIMON Project, 2019). The CWAs that have survived to the present are highly stable in seawater; after the release, being sorbed by particles of fine suspendable silty mud, they can be relocated elsewhere and undergo chemical transformations along the way From all this it follows that the special monitoring cannot be reduced to observations at a limited number of regular monitoring stations. Taking into account the fact that the two largest CW dumpsites are located in the center of the Bornholm Basin and in the southern part of the Gotland Basin, i.e., on the path of inflow currents, it can be concluded that, as part of a special monitoring to assess the cumulative impact on dumped CW and to estimate the distribution area of polluted resuspended silt, it is necessary to carry out measurements along the entire path of spreading of primary and transformed inflow waters
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