Marine Science Report No 100 2016

Abstract

The Baltic Sea is a complex ecosystem characterized by a strongly fluctuating, fragile balance between high freshwater runoff and saline water inflows, a stable stratification and a topography composed of connected basins. The sensitivity of the system “Baltic Sea” amplifies climatological fluctuations on the decadal scale. Such changes may be irrelevant in the open ocean but constitute significant indicators in the Baltic Sea. Salt and nutrients in the Baltic Sea remain present there for 20 and more years before being flushed to the Atlantic along with the freshwater export. This long residence time attenuates short-time fluctuations in environmental conditions, but highlights systematic, even small long-term anomalies.

The maps in this publication allow a visual evaluation of inflow events, of the progress of oxygen-consuming processes and of the development of hydrogen sulphide distribution over longer periods of time. The currently used method is a database- and software-based, transparent and reproducible way to represent the distribution of hypoxic and anoxic waters in the near-bottom layer of the Baltic Sea. The datasets of IOWTOPO and RANGS form the framework for all created maps. The oceanographic database IOWDB serves as the standard primary data source and contains harmonized, quality-controlled oxygen and hydrogen sulphide data from the regular monitoring cruises that have visited the western and central Baltic Sea since 1969. The final graphic is created in XML-based format SVG and is editable in any text editor. Furthermore SVG is a vector graphic that is editable with any software application capable of processing vector graphics.