Journal
DEEP-SEA RESEARCH PART I-OCEANOGRAPHIC RESEARCH PAPERS
Volume 57, Issue 1, Pages 78-94Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.dsr.2009.10.005
Keywords
Diel vertical migration; ADCP backscatter; Diel and seasonal cycles; Lazarev Sea; Eastern Weddell Sea
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Funding
- German Federal Ministry of Education and Research (Bundesministerium fur Bildung and Forschung, BMBF)
- R/V Polarstem
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Ten-month time series of mean volume backscattering strength (MVBS) and vertical velocity obtained from three moored acoustic Doppler current profilers (ADCPs) deployed from February until December 2005 at 64 degrees 5, 66.5 degrees 5 and 69 degrees S along the Greenwich Meridian were used to analyse the diel vertical zooplankton migration (DVM) and its seasonality and regional variability in the Lazarev Sea. The estimated MVBS exhibited distinct patterns of DVM at all three mooring sites. Between February and October, the timing of the DVM and the residence time of zooplankton at depth were clearly governed by the day-night rhythm. Mean daily cycles of the ADCP-derived vertical velocity were calculated for successive months and showed maximum ascent and descent velocities of 16 and -15 mm s(-1). However, a change of the MVBS pattern occurred in late spring/early austral summer (October/November), when the zooplankton communities ceased their synchronous vertical migration at all three mooring sites. Elevated MVBS values were then concentrated in the uppermost layers (< 50 m) at 66.5 degrees 5. This period coincided with the decay of sea ice coverage at 64 degrees S and 66.5 degrees S between early November and mid-December. Elevated chlorophyll concentrations, which were measured at the end of the deployment, extended from 67 degrees S to 65 degrees S and indicated a phytoplankton bloom in the upper 50 m. Thus, we propose that the increased food supply associated with an ice edge bloom caused the zooplankton communities to cease their DVM in favour of feeding. (C) 2009 Elsevier Ltd. All rights reserved.
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