A PILOT EXPERIMENT ON THE TEMPORAL VARIABILITY OF THE NEPHELOID AND DYNAMICAL STRUCTURES IN THE BESOS CANYON (NW MEDITERRANEAN SEA) [1] Instituto de Ciencias del Mar, CSIC, Barcelona, España, [2] P.P. Shirshov Institute of Oceanology, Russian Academy of Sciences, Moscow, Rusia, Emelianov M. 1, Font J. 1, Puig P. 1, Martín J. 1, García Ladona E. 1, Salat J. 1 and Ostrovskii A. 2, Zatsepin A. 2, Kremenetskiy V. 2, Shvoev D. 2, Soloviev V 2, Tsibulskiy A. 2 INTRODUCTION The project Intraseasonal Variability of Water Dynamics, Thermohaline Structure and Vertical Exchange in the Northeastern Black Sea and the Northwestern Mediterranean: A Comparative Study nicknamed VID (Variabilidad Intraestacional y Dinamica) is a part of collaboration between CSIC (Institut de Ciencies del Mar) and Russian Academy of Sciences (P.P. Shirshov Institute of Oceanology). In the framework of VID, the field experiment for investigation of the nepheloid and dynamical structures of the North Balearic sea over the Barcelona continental slope was carried out by using the new moored profiler Aqualog in March-April EQUIPMENT AND METHODS The mooring was deployed at the depth of 808 m at the Besos canyon axis (Fig. 1) on March 23, The mooring system (Fig. 2) featured two AANDERAA RCM current meters with Seapoint turbidimeters at fixed depths as follows: one RCM was attached to the mooring line below the subsurface floatation at the depth of 42 m and the other was fixed at 4-5 m above the bottom anchor. The moored profiler Aqualog regularly 6 times a day carried out measurements within the depth range of m (Fig. 3). The profiler operated until April 3 (Fig. 3). The total distance of the autonomous profiling amounted to 92 km. During the experiment the profiler speed was m/s. The profiler carried the Nortek Aquadopp acoustic Doppler current meter, the SBE 52MP CTD probe and the Seapoint Turbidimeter. When the carrier was moving the profiles of pressure, conductivity, temperature and turbidity were measured with a vertical resolution of m, while the vertical resolution of the current velocity and the acoustic backscatter was about 1.05 m. Fig. 1: Location of the mooring. Fig. 2: The mooring system. Fig. 3: The profiler track. RELIMINARY RESULTS Comparison of the current meter data obtained by the profiler at the topmost profiling depth with those of the upper RCM showed very good correlation both for the current speed and the current direction. The current speed usually differed by less than 0.02 m/s within the subsurface layer at m depth. The current structure of the bottom layer was much more complex. At the depth of 4-5 m above the bottom, the flow often was times stronger than that at the depths 13 m higher. No evidence of the bottom Ekman spiral was observed; at the depths of m and m, the currents were usually directed coherently either northwestward or southeastward. Fig. 4: The Aqualog’s Aquadopp data versus the AANDERAA Fig. 5: Comparison of the SBE CTD 911 data of the cast at 10 a.m. Fig. 6: ,S-plot based on RCM 11 data: current speed (left) & current direction (right) with those of the Aqualog profile at 4 p.m : the Aqualog CTD data of temperature (left), turbidity ( center), dissolved oxygen(right) In order to validate the Aqualog profiler measurements, the CTD probe SBE 911 with Seapoint Turbidimeter and the dissolved oxygen sensor SBE 43 was used to obtain the reference data several hours before the start of the profiler survey (Fig. 5). The feasibility study showed that the Aqualog data were of high quality. The T,S diagram (Fig. 6) indicated three water masses, typical for the NW Mediterranean. The upper m were occupied by relatively warm and less saline surface water mass (Fig. 7). In the depth range between 150 m and 500 m, the Winter Intermediate Water (WIW) was found. This water was characterized by relatively low temperatures and salinity. Below the WIW between 500 m and 800 m, the warmer and salty Levantine Intermediate Water was observed. Fig. 7: The temporal variability of vertical distributions of the temperature (left) and Fig. 8: The temporal variability of vertical distributions of the zonal (left) the salinity (right). and meridional (right) current velocity. The current speed did not exceed 0.2 m/s during the survey. The upper layer dynamics was dominated by the inertial oscillations (Fig. 8). In the pycnocline at m depth, the interpycnocline eddies having time scale of about 2 days were observed. The deep eddies, occupying the water column from near-surface layer down to 600 m depth, occurred twice during the survey. Fig. 9: The temporal variability of Fig. 10: The temporal variability of vertical vertical distribution of turbidity distributions of distribution of the acoustic backscatter as as observed by the turbidimeter observed by the Aquadopp current meter installed at the Aqualog profiler. installed at the Aqualog profiler. Thin lines indicate isolines of Sigma θ. The nepheloid structure became evident in the turbidity profiles and the acoustic backscatter profiles (Fig. 9, 10). Above the pycnocline, the vertical distribution of the acoustic backscatter was in agreement with that of the turbidity. The acoustic backscatter was at minimum in the cold intermediate layer. The lower boundary of this layer undergone huge oscillations with amplitude of up to 250 m. The amount of the sound backscatterers suspended in the water was usually largest at m depth. The eddies carried large amount of particulate matter from the near-surface layer throughout the deep sea. Several times during the survey the amount of the suspended sediments increased rapidly in several hours in the layer between 600 m and 800 m. Acknowledgements: This joint CSIC-RFBR research project was funded by CSIC 2010RU0063 and Russian Fund for Basic Research INIS_а. We are grateful to Instrumentation Service personal J. Pozo, M. Lloret y J. Salvador, to Cpt. and the crew of R/V “García del Cid” Russian Academy of Sciences P.P.Shirshov Institute of Oceanology Profiler Aqualog