Acoustic evidence for an intense plankton bloom primarily in the
northern sector of the Southern Ocean GLOBEC broad-scale survey grid in
the austral fall of 2002
Peter H. Wiebe, Carin J. Ashjian, Scott M. Gallager, Cabell
BIOMAPER-II was deployed from the stern of the RVIB N.B. Palmer and towyo'd between most of the broad-scale survey stations on the 2002 fall broad-scale survey. Multi-frequency acoustic data (43, 120, 200, 420, and 1000 kHz) were collected between the surface and near bottom while video images and environmental data were collected between the surface and bottom of towyo's (max 250 to 300 m) along the towyo path in much of the survey area.
On NBP02-02, at a number of
locations along the mid- and outer shelf areas, and offshore waters, the 1 MHz
transducers had high backscattering levels in the 0-60 m depth interval that
correlated with very high algal mats, chain forming diatom and radiolarian concentrations
that were observed on the Video Plankton Recorder (see Ashjian
et al. abstract). A diatom bloom of
significant proportions was occurring in the northern and central portion of
the SO GLOBEC survey grid and this was most evident in the 1 MHz echograms, but
also in the 420 kHz echograms. This high backscattering was not observed in
A similar fall bloom was reported by Uli Bathmann during the German survey work on the RVIB Polarstern (13 April to 7 May) in the GLOBEC region shortly before the RVIB N. B. Palmer arrived for work on cruise NBP01-03 in April 2001. It apparently had disappeared by the time of our arrival, although highest fluorescence levels on that cruise were present in the northern portion of the survey grid.