Innovative Closely Spaced Profiling and Current Velocity Measurements in the Southern Baltic Sea in 2016–2018 With Special Reference to the Bottom Layer

A solution to the problem of determination of spatial variability of oceanographic fields, which contained a fine structure resolution higher than what was possible previously using towed scanning probes, was presented for the Baltic Sea. Another concurrently solved problem consisted in obtaining data on the structure of waters in the bottom layer, which was difficult to implement by way of 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 which reaches 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 the 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 by the results of a monitoring campaign that was carried out in the southern Baltic Sea in 2016–2018. Among the new findings is 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 a severe gale

Ventilation of the Baltic Sea deep water: A brief review of present knowledge from observations and models

The ventilation of the Baltic Sea deep wateris driven by either gale-forced barotropic or baroclinic salt water inflows.During the past two decades, the frequency of large barotropic inflows(mainly in winter) has decreased and the frequency of medium-intensity baroclinic inflows(observed in summer) has increased. As a result of entrainment of ambient oxygen-rich water,summer inflows are also important for the deep water ventilation.Recent process studies of salt water plumes suggest that the entrainmentrates are generally smaller than those predicted by earlier entrainment models.In addition to the entrance area, the Słupsk Sill andthe Słupsk Furrow are important locations for the transformation of water masses. Passing the Słupsk Furrow, both gravity-driven dense bottom flows and sub-surface cyclonic eddies,which are eroded laterally by thermohaline intrusions,ventilate the deep water of the eastern Gotland Basin.A recent study of the energy transfer from barotropic to baroclinicwave motion using a two-dimensional shallow water model suggests thatabout 30% of the energy needed below the halocline for deep water mixingis explained by the breaking of internal waves.In the deep water decade-long stagnation periods with decreasingoxygen and increasing hydrogen sulphide concentrations might be caused by anomalously largefreshwater inflows and anomalously high mean zonal wind speeds. In differentstudies the typical response time scale of average salinity was estimated tobe between approximately 20 and 30 years.The review summarizes recent research resultsand ends with a list of open questions and recommendations

NESTOR: A status report

NESTOR is an underwater neutrino astrophysics laboratory to be located in the international waters of the southwest of Greece. The first phase of this experiment is the construction and deployment of one hexagonal tower consisting of 168 optical modules, with effective are of 20000m2 for E ⩾ TeV neutrinos. Over the past few years detailed studies of the site have been carried out while many tests have been performed. The current status of the preparation of the experiment and the future plans will be presented