Abstract
MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 354:21-34 (2008) - DOI: https://doi.org/10.3354/meps07222 Phytoplankton thin layers caused by shear in frontal zones of a coastal upwelling system J. P. Ryan1,*, M. A. McManus2, J. D. Paduan3, F. P. Chavez1 1Monterey Bay Aquarium Research Institute, Moss Landing, California 95039, USA 2Department of Oceanography, University of Hawaii, Honolulu, Hawaii 96822, USA 3Naval Postgraduate School, Monterey, California 93943, USA *Email: ryjo@mbari.org ABSTRACT: Using multidisciplinary observations from regional- to small-scale, we examined the development of thin phytoplankton layers in water mass frontal zones of a coastal upwelling system. Two fronts developed successively in the same region of Monterey Bay, California, USA, during August and September 2003: (1) when warm, fresh offshore waters flowed into the bay following relaxation and reversal of upwelling favorable winds, and (2) when a cold upwelling filament flowed into the bay after upwelling favorable winds resumed. Thin phytoplankton layers were observed during the presence of both fronts. The layers exhibited peaks in chlorophyll fluorescence and optical backscattering, indicating biomass maxima in the layers. Maximum chlorophyll concentrations in the layers ranged from 11 to 37 µg l–1 and were 4 to 55 times greater than background levels. Layer vertical thickness ranged from 1 to 5 m, averaging 2.3 m. All thin layers were in the thermocline, near the 12.5°C isotherm, and the depth of the layers varied between 12 and 33 m, in parallel with variations in thermocline depth. Synoptic mapping of the first frontal zone shortly before the thin layers developed showed strong phytoplankton patchiness. The role of vertical shear in thin layer formation from phytoplankton patches is supported by multiple results: (1) most thin layers (92%) were associated with sharp changes in the direction of horizontal currents; (2) layer thickness was significantly (p < 0.03) negatively correlated with shear; (3) the median shear profile, computed from all thin layer velocity profiles, peaked sharply at the center of thin layers. KEY WORDS: Phytoplankton · Thin plankton layers · Coastal upwelling system · Shear · Thermocline Full text in pdf format PreviousNextCite this article as: Ryan JP, McManus MA, Paduan JD, Chavez FP (2008) Phytoplankton thin layers caused by shear in frontal zones of a coastal upwelling system. Mar Ecol Prog Ser 354:21-34. https://doi.org/10.3354/meps07222 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 354. Online publication date: February 07, 2008 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2008 Inter-Research.
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