Examining the plankton acoustic response with a vessel mounted ADCP across oceanic fronts located in the Drake Passage

• Main Authors: Blanc, Silvia, Baqués, Michele, Etcheverry de Milou , Marta I.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Asociación Argentina de Geofísicos y Geodestas 2008
• Subjects: ADCP; volume sound scattering; Drake Passage; Antarctic; The Antarctic; Antarctic Peninsula; Antarc*
• Online Access: https://revistas.unlp.edu.ar/geoacta/article/view/13576

On December 2001 and January 2006, during the LMG01-9 and LMG06-1 cruises to Antarctic Peninsula, at-sea oceanographic and acoustic measurements were conducted onboard the R/V L. M. Gould icebreaker along two transects located between (55.15 °S, 65 ºW) and (64.65 °S, 65 ºW) and between (55.15 ºS, 64.91 ºW) and (62.7 ºS, 62.21 ºW), respectively. The scientific crew consisted of researchers from two US institutes, and a scientific observer from the Argentinean Naval Service of Research & Development under the frame of the US National Science Foundation Antarctic Program. The present work accomplishes an alternative application for a vesselmounted Acoustic Doppler Current Profiler (ADCP) with an operating frequency of 153.6 kHz. Volume Acoustic Backscattering Strengths, SV, were computed from the recorded ADCP’s voltages. The obtained values fell in a range of -92 dB to –62 dB, for the layer of the water column comprised between 26 m - 300 m on 2001 and in the range of –93 dB to -58 dB for the water column between 22 m - 300 m on 2006. Depth-averaged, SV, for the upper water column (about the first 150 m) on experiment transects were computed as well as SV values averaged in depth and latitude. Data processing revealed interesting features about the upper ocean acoustic behaviour. On December 2001, a significant non-uniform scattering response in the ensonified water column with quite high values of SV, associated with the diel vertical migration, was obtained. Additionally, a remarkable increment in the scattering response was observed at the estimated location of the Antarctic Divergence (AD). This feature was also observed on January 2006 in addition to remarkable high values of SV, in coastal waters of the Antarctic Peninsula. Plotting and exhaustive analyses of SV (z) profiles enabled the visualisation of three distinct types of qualitative patterns, namely, curves with: (I) two observable maxima, (II) only one maximum, (III) a depth-interval of variable width with a minimum acoustic response. Along the ...