Thursday, November 5, 2009

Surveys of hypox-partner GeoEcoMar at the Romanian Black Sea Shelf

The Romanian Shelf is one of the hypox target sites for hypoxia studies in the Black Sea. For decades, the north-western shelf received particularly high nutrient loads, mainly through the discharge of the Danube. Eutrophication resulted in an increase in deposition of organic matter and seabed oxygen consumption that led to recurrent and widespread seasonal bottom water hypoxia and a deterioation of the of the benthic system: Sea grass, benthic macroalgae communities, and mussel beds disappeared. Thus, in combination with overfishing, eutrophication led to complete collapse of the pelagic and benthic ecosystems. Reduced riverine nutrient discharges following the breakdown of industry and agriculture in eastern European countries led to the decrease in occurrence of large-scale bottom water hypoxia since the 1990’s and allowed for a slow recovery of the pelagic and benthic ecosystems. The Romanian shelf is thus of particular interest to investigate processes that benthic systems undergo upon recovery from previous hypoxia and understand the complex interaction of nutrient input, climate forcing, and oxygen availability.

Already in May (i.e., project month 2) Marian-Trajan Gomoiu and colleagues from the hypox partner GeoEcoMar (National Institute of Marine Geology and Geo-ecology of Romania) conducted a cruise to the Romanian Shelf. Investigations included sampling of the benthic communities as well as mapping of oxygen distributions in shelf waters and at the seafloor. At this time of the year hypoxic conditions with dissolved oxygen concentrations below 63┬Ámol/L or 2mg/L were largely restricted to water depths >100m, i.e., around and below the shelf break. The same sites will be revisited several times within the time course of the project to follow the temporal and spatial dynamic of oxygen distributions and the response of the bethic communities.

Fig. 1: Overview of the stations visited during the GeoEcoMar cruise in May

Fig. 2: An example of the distribution of dissolved oxygen along a transect on the Romanian Shelf

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