Cruise report from R/V Aranda week 2-3, 2015

Type: Report
Author: Karin Wesslander


The expedition was part of the Swedish regular marine monitoring programme and covered Kattegat, the Sound and the Baltic Proper. Mapping of winter nutrients were performed in Kattegat. Skagerrak could not be visited due to the storm Egon. Extra sampling was made to follow up  the inflow from December 2014 when ca. 200 km3 entered the Baltic.  Data presented in this report have been subject to preliminary quality control procedures only.

The water temperature in the surface layer was still above normal in Kattegat but normal in the Baltic Proper. Surface nutrients showed, for the season, almost normal values, except for silicate and phosphate in the Baltic which were elevated, while the Hanö Bight was exceptional with lower silicate concentration.

The effect of the large inflow in December was during the expedition most evident in the Hanö Bight. During the last expedition in December 2014, acute hypoxia (<2 ml / l) was present in the bottom water of Hanö Bight. During this expedition the oxygen concentration was as high as 6.21 ml/l. In the central parts of eastern Gotland Basin, BY15, acute hypoxia was present from depths exceeding 60 meters and complete anoxic conditions were found from depths exceeding 175. However, at 235 meter oxygen was present in small concentrations, 0.11 ml/l. At station BY29, in the northern Baltic Proper, hydrogen sulphide occurred already from 70 meters. In the western Gotland Basin the oxygen situation was serious as acute hypoxia started from 70 meters and acute hypoxia was present ca. 90 meters depth.