Search

This report is based on preliminary data. Ventspils (Latvia). 01-02 March 2015 and 07-09 March 2015 Purpose of the cruise The original scientific goal of this cruise, conducted in the framework of the WGL/Pakt project ILWAO-II, was the investigation of the role of internal waves for basin-scale vertical mixing in the deep basins of the Baltic Sea. In agreement with IOW’s board, however, it was decided to devote a substantial part of the cruise time to the observation of one of the rare major saline inflow events that reached the central Baltic Sea exactly at the time of this cruise. In addition to the physical measurements, microbiological and chemical investigations were conducted, focusing on the role of methane-oxidizing bacteria in pelagic redoxclines.

04.-20. September 2012; Dates and names of ports of call Visby (Sweden) from 13 to 15 September 2012; This interdisciplinary cruise aimed at exploring the effects of lateral intrusions and turbulent mixing on the microbiology and biogeochemistry of the redoxcline in the deep basins of the Baltic Sea.

This paper focuses on the impact of an oscillating low-speed current on the structure and dynamics of the bottom-boundary layer (BBL) in a small stratified basin. A set of high-resolution current profile measurements in combination with temperature-microstructure measurements were collected during a complete cycle of the internal oscillation ('seiching') in the BBL of Lake Alpnach, Switzerland. It was found that even a relatively long seiching period of 24 hours significantly changed the form of the near-bottom current profiles as well as the dynamics of the turbulent dissipation rate compared to the steady-state law-of-the-wall. A logarithmic fit to the measured current profiles starting at a distance of 0.5 m above the sediment led to inconsistent estimates of both friction velocity and roughness length. Moreover, a phase lag between the current and the turbulent dissipation of 1.5 hours and a persistent maximum in the current profile at a height of 2.5 to 3 m above the sediment were observed. The experimental findings were compared to the results of a k-epsilon turbulence model and showed good agreement in general. Specifically, the inconsistent logarithmic fitting results and the observed phase lag were reproduced well by the model.