Baltic Marine Environment Protection Commission

Transcription

1 Baltic Marine Environment Protection Commission Helsinki Commission Helsinki, Finland, 3-4 March 2015 HELCOM Document title Special Report from a Cruise - Great Inflow to the Baltic Sea Code 6-1 Category INF Agenda Item 6 Any other business Submission date Submitted by Poland Reference Action required The Meeting is invited to take note of the attached cruise report submitted by Poland. Page 1 of 1

2 INSTITUTE OF METEOROLOGY AND WATER MANAGEMENT NATIONAL RESEARCH INSTITUTE Maritime Branch in Gdynia GDYNIA Waszyngtona 42 tel. (+48) fax (+48) Special Report from a Cruise Great Inflow to the Baltic Sea Vessel: r/v Baltica Cruise No: 1 (156) Date: 4 5 February 2015 Supervised by: Chief Inspectorate of Environmental Protection Financed by: National Fund for Environmental Protection and Water Management

3 By the end of December 2014, there was a great inflow of salt water from the North Sea into the Baltic Sea. The previous phenomenon of a similar scale was observed in The transport of salt and oxygenated water takes place from the west to the east through the major deeps of the Baltic Sea (Fig. 1). PL Basen Arkoński Basen Bornholmski Rynna Słupska Basen Gotlandzki Basen Gdański Arkona Basin Bornholm Basin Słupsk Trough Gotland Basin Gdańsk Basin EN Fig. 1. Inflow course determined on the basis of the newest measurement data. The white arrows stand for the likely direction of further movement of inflow waters. Between 2 and 7 February 2015, the Maritime Branch of the Institute of Meteorology and Water Management National Research Institute carried out a monitoring cruise in accordance with the programme for Polish Baltic Sea zone monitoring, in the framework of an agreement with the Chief Inspectorate of Environmental Protection. The main objective of the studies was to measure the physical and chemical parameters of the marine environment in order to determine the winter biogen pool. As the date of the cruise coincided with an extraordinary inflow of salt waters, it was possible to perform studies that allow collecting information on a natural phenomenon that is of utmost importance to the condition of bottom waters, both in the area of the Bornholm Deep and the Gdańsk Deep. In order to quantify the inflow and the change in the thermohaline structure of waters, and to determine the characteristics of hydrodynamic processes connected with the inflow, the

4 temperature and salinity of water, as well as oxygen concentration were measured in the entire area of elevated salinity waters, including at set monitoring stations. At the same time, the speed and direction of currents was registered using an ADCP RDI Doppler acoustic current log from the sub-surface layer to the bottom layer, along the set profiles (Fig. 2).

5 Fig. 2. Location of CTD probes and ADCP transects during the inflow. The colourful dots stand for permanent monitoring measuring stations. The information gathered in this way allowed to perform an initial assessment of the speed and reach of the head of the salty front (Fig. 3). On the basis of the data collected during SMHI cruises (cruise report Aranda) and the cruise by the Institute of Meteorology and Water Management National Research Institute, the speed of inflow waters was preliminarily estimated. It was concluded that within three weeks, the inflow moved from Hano Bay (13 January 2015) through Bornholm Deep to Słupsk Trough (5 February), filling in also the Bornholm Basin south of Bornholm up till isobath 40 m (Fig. 1). The thin layer of the inflow head was pushed beyond the eastern border of the Słupsk Trough, reaching the southern edge of the Gotland Basin to the depth of ca. 84 m (Fig. 3). The minimum speed of inflow water transport can thus be estimated at ca. 16 cm s-1. The effects of the inflow were the most visible in the Bornholm Basin and the Słupsk Trough. The hydrological situation in these sea areas changed radically compared to what was observed during the cruise in November Highly saline and well oxygenised waters moving from Kattegat caused a considerable increase in salinity and oxygen concentration in bottom layers of these sea areas. The highest salinity (19.65 PSU) was detected in the Bornholm Deep at the bottom of station P5. It was much higher than salinity observed at that station in November 2014 (16.16 PSU). Inflow waters filled the Bornholm Basin in the bottom layer, whose upper limit reaches the depth of ca m.

6 The effects of the inflow became visible also by disappearance of the oxygen deficit layer (<2 ml/l). During the cruise in question, the highest oxygen concentration (6.06 ml/l) was detected at the bottom of Bornholm Deep, while in November last year it was only 1.1 ml/l. At the bottom of Słupsk Trough, the oxygen content increased from 2.69 ml/l in November 2015 to over 4 ml/l in February The visible border marked by differences in salinity and oxygen concentration at the bottom between stations TS16 and P140 allows determining the location of the inflow head in this area (Fig. 1). No visible effects of the inflow have been detected in Gdańsk Basin yet.

7 PSU OXYGEN TEMPERATURE SALINITY Fig. 3. Vertical distribution of salinity, temperature and oxygen along the main profile running through monitoring stations in 2014 and 2015.

8 Fig. 3. Location of the main profile Prepared by: N. Drgas, W. Krzymiński