Monday 22 August 2005

PB1
1550-1710 hours

098
An acoustic insight into Drake Passage oceanography
Blanc, Silvia¹, Baqués, Michele¹, De Milou, Marta Etcheverry¹
1 Argentinean Naval Service of Research And Development, Vincente Lopez, Argentina
Author email: silblanc@yahoo.com
An Argentinean researcher with Naval Service of Research and Development was invited to embark Lawrence M. Gould icebreaker on December 2001 during LMG01-9 cruise to Antarctic Peninsula, under the frame of US National Science Foundation Antarctic Program. Hence, the international duty of having a local scientific observer on board with the consequent supply of raw at-sea measurements, was fulfilled. Although the main purposes pursued by the two abroad research teams involved in the expedition, were out of local interest scope, focused in Ocean Acoustics, oceanographic measurements held during south and north-bound crosses of the Drake Passage, led to valuable information that could be successfully used as input data to examine sound volume scattering effects mainly due to zooplankton. Data processing of depth, temperature and salinity measurements and vector current velocity determinations from frequency shifts, recorded with a hull-mounted Acoustic Doppler Current Profiler -ADCP- operating at 150 kHz, at 65°W between 55°S and 65°S, revealed interesting features about the upper ocean behaviour. Sound velocities were computed. Location estimates of Subantarctic and Polar Fronts, eddies and jets were achieved. Moreover, an alternative application for the ADCP recorded voltages, corresponding to emitted and backscattered acoustic signals, was attempted for the first time in the experiment area. Determinations of relative values of Acoustic Volume Backscattering Strength, Sv, as a function of depth and horizontal distance, are reported. Plotting of Sv profiles provided three qualitative types of patterns depending on latitude. This fact led to suspect a correlation between the type of pattern and one of the following regions: (I) Antarctic Convergence zone; (II) between Polar Front and Antarctic Divergence; (III) between Antarctic Divergence and Antarctic Continent. Distinctive features obtained for each region suggested the feasibility of correlating Sv behaviour not only to planktonic biomass but to oceanic fronts and eddies' presence.

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