E. V. Stanev(1,2)*, A. Palazov(3), Y. He(2), E.Peneva(1) ,S. Grayek(2), A. Boetius(4), M.Milanova(1), A.Gencheva (2)
(1) : University of Sofia "St. Kliment Ohridski", Sofia, Bulgaria
(2) : Helmholtz-Zentrum Geesthacht
(3) : Institute of Oceanology “Fritjof Nansen” Bulgarian Academy of Sciences
(4) : Alfred Wegener Institute, Bremerhaven, Germany
Black Sea is a region of particular interest, as it is rather sensitive to climate and anthropogenic influences. It is a deep sea with maximal depth of 2200 m. The Black Sea receives drainage from almost one-third of the continental Europe (five times its own surface) which includes significant portions of 17 countries, 13 capital cities and some 160 million people. The Black Sea is virtually isolated and hence a vulnerable water basin with 87% of its volume affected by anoxia. Of all the basins in the world ocean, the environmental degradation in the Black Sea is the most severe.
Specific European interests in the European regional seas require enhanced monitoring there, including in its whole depth range. Argo floats are capable to measure not only the thermohaline characteristics, but also the dissolved oxygen concentration and water quality. This automatically obtained information could be then used for satellite data validation and calibration, initialization and assimilation in the ocean forecasting models, assessment of physical processes and circulation, thus the Argo floats regular measurements are unique tool on the way towards operational oceanography in the region.
First Argo floats were deployed by the US scientists (see Korotaev et al., 2006). At the moment there are five operating floats. The BulArgo contribution to the establishment of the future Black Sea Argo system will be 5 Argo floats deployed in three years period. The inventory of the Argo data in the Black Sea is done in cooperation with the research in the frame of FP7 HYPOX Project and BulArgo (2010-2012) project in Bulgaria. BulArgo is funded by the Bulgarian National Science Fund and the Ministry of Education, Youth and Science, which aims to establish a national research infrastructure in the frame of Euro-Argo activities. The partners in BulArgo project are the Bulgarian Institute of Oceanology, Sofia University “St. Kliment Ohridski” and the National Institute of Meteorology and Hydrology.
In 2005, four APEX floats have been deployed by the US Argo project with a parking depth at 1500 dbar and a profile depth at 1550 dbar. Their average lifetime was about 3 years. In December 2009 and April 2010, in a frame of a collaborative effort with France, Bulgaria deployed two Provor (#1901200 and #5902291). PROVOR float (#5902291) was deployed in the deep part of the Black Sea, but ceased operating after only 24 cycles. Helmholtz-Zentrum Geesthacht (HZG, previous GKSS) and Max-Planck-Institut fuer Marine Mikrobiologie in Bremen conjointly deployed in 2010 two NEMO froats with oxygen sensors during a research cruise with R/V Maria Merian in the frame of HYPOX Project. One of them ceased operating on 28 December 2011. Then after the start of the Bul-Argo project in March 2011, three additional APEX floats (#6900803, #6900804, #6900805) were deployed in the Black Sea. This activity was performed by the researchers in the project on board of the R/V Akademik. Apart from the standard CTD measurements, one of the floats (#6900804) was equipped by an oxygen sensor. All BulArgo floats are equipped with a SBE-41 type CTD and an ARGOS telemetry system, and are programmed with a 5-days cycle, a parking-depth at 750 dbar and a profile depth at 1500m.
Figure 1. Argo Floats trajectories in the Black Sea between December 2009 and February 2012 -
(pink) : Provor #1901200 ; (blue) : NEMO-floats #0144 and #0145, (white) : Apex #6900803, (green) : Apex #6900804 and (red) : Apex #6900805
The data from the floats deployed under the BulArgo project are available at the Institute of Oceanology website (http://www.gisserver.io-bas.bg/Web_argo). The standard procedures for real time data processing and quality control are performed at the French Argo Data Centre (www.coriolis.eu.org). Collaboration with the scientists at MedArgo data center is ongoing to allow for processing data also in MedArgo. At the moment, the data quality procedures are being revised by the competent staff to account for the Black Sea regional characteristics.
First diagnosis on the evolution of the thermohaline characteristics in the Black Sea have been possible thanks to Argo floats. The Provor #1901200, programmed with a 5-days cycle and 200 dbar (resp.1550 dbar) parking (resp.profiling) depths, is still active with a total of 188 cycles. Figure 2 shows the evolution of its temperature and salinity measurements with time. The associated trajectory is plotted in pink color in figure 1. Those first diagnosis show clear physical signals such as a cold water transformation during winter and a seasonal thermocline during summer.
Figure 2. Temperature (top panel) and Salinity (bottom panel) evolution with time for the PROVOR Float #1901200 in the Black Sea.
Two NEMO-Floats have been deployed in the Black Sea during the first leg of R/V Maria S.Merian Cruise Nr.MSM 15(07.04.2010 - 29.07.2010) with Andera optode in order to provide oxygen in addition to temperature and salinity measurements. Results are shown in figure 3 and again, some signals appear clearly. Both floats show an oxygen maximum occuring in the first 50m-depth, just above thin suboxic zone at the base. A persistent cold intermediate layer (CIL) is extanding during all year, from 50 to 150m-depth in some regions. Important vertical gradients in salinity appear especially in summer around 100m-depth.
Figure 3. Oxygen (top), Temperature (middle) and Salinity (bottom) function of depth and time for NEMO-Float #0144 (left column) and #00145 (right column).
The BulArgo contribution to the establishment of the future Black Sea Argo system will be 5 Argo floats deployed in 2 years period. After 2012, Bulgaria plans to join the Euro-Argo research infrastructure, deploying 3 Argo floats in the Black Sea per year. In addition, it will be necessary to work on several key issues taking into account Black Sea peculiarities: technical (float technology, data management and delivery system) and organizational (logistics for deployment) issues. Significant efforts will be dedicated to consolidate and broaden the user community and to demonstrate the impact and utility of Argo floats in the Black Sea via scientific exploitation of data.
- Korotaev, G., Oguz, T., Riser, S. : Intermediate and deep currents of the Black Sea obtained from autonomous profiling floats. Deep-Sea Research II 53 1901–1910, 2006.
- Palazov A., Stanev E., Korchev G., Peneva E. and Slabakova S. : Development of National research infrastructure as a Bulgarian component of the Euro ARGO network - Bul ARGO, Geophysical Research Abstracts Vol. 13, EGU2011-3790, 2011.