Zooplankton in Langmuir Cells Observed from FLIP
Abstract
We sought to test the hypothesis of Stommel and others that Langmuir cells (LCs) foster pattern in the distribution and abundance of zooplankton in the open ocean. To this end, one of us (DMC) participated in the 1995 Marine Boundary Layer (MBL) Experiment in which FLIP was deployed in deep water off Monterey in springtime. Atmospheric and wave forcing of LCs was measured by MBL participants. Periodically, we profiled continuously at 1 meter per second for hours to days within the upper ocean with a package containing a CTD and Optical Plankton Counter. Throughout, we deployed a CTD and Acoustic Doppler Velocimeter at a mean depth of 6 then 8 m. On occasion, simultaneous collections were made with a plankton pump and net system and the samples were microscopically enumerated. The resultant data were analyzed for pattern using geostatistics. Conditions progressed over a period of two weeks from benign, with a stratified upper ocean, to strong winds and high waves, with well-developed LCs, followed by abatement. Forcing was quantified by estimating LC convergent velocity from wind stress and wave height time series. LCs were manifest in the temperature distribution of our profiler data. In particular, in the time-depth domain, sections within LCs showed cool water apparently entrained upward from the base of the mixed layer to the surface. These patterns persisted on the scale of hours. Temperature at a single depth within well-developed LCs varied in a periodic fashion over a range of the order 0.02 deg C. Such measurements provide the physical context in which to interpret our biological observations. Variograms were used to assess spatial pattern of temperature and plankton. Significant pattern existed for temperature in LCs in the horizontal but not along profiles in the vertical, within the mixed layer, consistent with our observations of LCs in the time-depth domain. The fixed and profiling CTDs yielded consistent time series, confirming the accuracy of the profiler temperature data and, thus, existence of LCs. No significant pattern existed in LCs in the horizontal for zooplankton-sized particles sensed by the profiling OPC. Similarly, no structure, thus pattern, existed in LCs in the horizontal for zooplankton collected with the plankton pump. Conversely, during benign conditions, pattern was evident in the zooplankton sensed by the profiling OPC and collected by the pump. Residual velocities of LCs we observed in the open ocean appear to exceed the swimming speed of individual zooplankters. Hence, whereas LCs caused pattern in temperature, they mixed the plankton. FLIP remains a unique and excellent platform for interdisciplinary studies of plankton and air-sea interactions. Future work might use include the use of video to study the plankton and marine snow (particle aggregates) in a range of forcing conditions. Collaboration between the disciplines is enhanced by FLIP's tight quarters. This work was supported by the Office of Naval Research.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2002
- Bibcode:
- 2002AGUFMOS61B0217C
- Keywords:
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- 3339 Ocean/atmosphere interactions (0312;
- 4504);
- 4504 Air/sea interactions (0312);
- 4855 Plankton;
- 4894 Instruments and techniques