Meridional and interannual variations of the seasonally modulated Zooplankton diel vertical migration in the Lazarev Sea and their possible physical-biological controls

• Main Authors: Strass, Volker, Cisewski, Boris
• Format: Conference Object
• Language: unknown
• Published: 2014
• Subjects: Lazarev Sea; polar night; Sea ice
• Online Access: https://epic.awi.de/id/eprint/36242/; https://epic.awi.de/id/eprint/36242/1/StrassCisewski_SCARposter1529.pdf; https://hdl.handle.net/10013/epic.47952; https://hdl.handle.net/10013/epic.47952.d001

Acoustic Doppler current profilers (ADCPs) not only take measurements of the water velocity components but also of the backscatter strength, which can be used to infer distribution patterns of zooplankton and small nekton. Here we present results obtained from ADCPs that were moored at 64°S, 66.5°S and 69°S along the Greenwich Meridian during the three-years period February 2005 until March 2008. A diel vertical migration (DVM) pattern – downward at dawn and upward at dusk - of two distinct groups of migrators persisted during most part of the years at all moorings sites, closely related to the astronomical daylight cycles. While the DVM was symmetric around local noon, the annual modulation of the DVM was asymmetric relative to the summer/winter solstices at the three mooring sites. This annual asymmetry resulted from a change in the migration behaviour that occurred in late spring (October - November), when the DVM ceases for around three months. In contrast to many previous studies in other regions, DVM at our observation sites persisted throughout winter, even at the highest latitude during the polar night. Using in-situ physical and biological data collected during deployment and recovery of the moorings, ice-thickness time series measured by Upward Looking Sonars, and satellite maps of remotely sensed sea ice coverage and surface chlorophyll concentration we can explain part of the seasonal to interannual variations in the inferred zooplankton distribution patterns by environmental cues. For a more complete explanation of the observed organisms’ behaviour, however, we hypothesize controls by internal drivers that need also be taken into account.