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HYPOX - Open seas

HYPOX activities in open seas comprised three different areas: the Black Sea, the Baltic Sea and the Artic Sea. Main results of marine environment monitoring in each site are briefly described:

Black Sea monitoring: three different sites were studied:

  • Bosporus / Istanbul Strait: the monitoring work in this area aimed to identify a characteristic phenomenon where the inflow of Marmara Sea water (MSW) along the bottom of the Strait replenishes the salt that is lost through the surface outflow of brackish water leaving the Black Sea as a consequence of the positive water balance of the basin. Two different cruises with 9 and 54 sensing casts were carried out; during the first cruise, strong evidences of Marmara Sea intrusions were found (temperature, salinity, and oxygen anomalies), whereas in the second cruise these evidences were not found. This clearly demonstrated that monitoring time series are needed in future attempts to quantify the oxygen supplied by the Marmara Sea.
  • Crimean Shelf: this zone is characterised by a lateral oxygen gradient that generates neighbouring oxic, hypoxic and anoxic areas, which makes the area ideal for analysing the effect of oxygen conditions on benthic communities and processes. Investigations took place at two different sites, where different in situ chemical sensing approaches and platforms were used to characterize spatial patterns and temporal dynamics of oxygen distribution. Results revealed that the expected depth-dependent oxygen gradient had superimposed a temporal component, with different scales. Long temporal scale dynamics were attributed to wind-driven currents, whereas small temporal changes are probably driven by internal waves.
  • Romanian Shelf: this zone has been exposed to overexploitation, pollution and eutrophication for several decades. As a consequence, a seasonal depletion of oxygen contents has been shown for more than 20 years, resulting in a deterioration of its benthic system. A long time monitoring of oxygen, temperature, turbidity, salinity and currents speed and direction was carried out at two levels (0.5 m and 3.5 m above sea floor). This information was complemented by measurements of benthic nutrients fluxes from the sediment to water. All these analysis provided a deeper insight into the mechanisms that control hypoxia on the shelf.

Baltic Sea monitoring: the Gotland Basin was selected as the main site for making measurements. A Biogeochemical Observatory BIGO was used for measuring major element fluxes and total oxygen uptake rates. Conversely, a DOS lander equipment was used for long-term O2 measurements, and an eddy flux correlation for the short-term measurements. Additional oxygen micro-profiles were also obtained. Data analyzing revealed strong oxygen flux fluctuations that ranged from almost zero up to 20 mmol O2 m-2 d-1, with O2 fluxes lower than 5 mmol O2 m-2 d-1 in most cases.

Artict Sea monitoring: work was carried out at the deep-sea long-term observatory HAUSGARTEN. An optode with multiple oxygen sensors was used, as well as two single optodes for measuring oxygen levels at approximately 2 m above the seafloor. Data from measurements conducted during the annual cruises in the summers 2008 to 2009 are archived in the World Data Center for Marine Environmental Sciences / Pangaea (http://www.wdc-mare.org/).

Related references:

  • McGinnis DF, Cherednichenko, Sommer S, Berg P, Rovelli L, Schwarz R, Glud R, Linke P (subm.) Simple, robust eddy correlation amplifier for aquatic dissolved oxygen and hydrogen sulfide flux measurements. Limnol. Oceanogr. Methods.
  • Sommer S, Linke P, Pfannkuche O, Schleicher T, v. Deimling JS, Reitz A, Haeckel M, Flögel S, Hensen C (2009) Seabed methane emissions and the habitat of frenulate tubeworms on the Captain Arutyunov mud volcano (Gulf of Cadiz). Mar Ecol Prog Ser. 382: 69–86.
  • Sommer S, Schorp T, McGinnis DF, Bertics V , Dale AW, Pfannkuche O (2011) In situ fluxes of major nitrogen species, phosphorus, oxygen and silicate across the benthicboundary layer of the oxic to anoxic Gotland Basin (Baltic Sea). Aquatic Sciences Meeting. ASLO Conference, San Juan, Puerto Rico, 2011.

 

Source:
Deliverable D6.1: Installation and operation of in situ observatories for monitoring oxygen depletion and associated parameters in shelf and open seas (Black Sea, Baltic Sea, Fram Strait) and collection of data into the HYPOX web portal