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Offshore forcing on the “pressure point” of the West Florida Shelf: Anomalous upwelling and its influence on harmful algal blooms
Author(s) -
Liu Yonggang,
Weisberg Robert H.,
Lenes Jason M.,
Zheng Lianyuan,
Hubbard Katherine,
Walsh John J.
Publication year - 2016
Publication title -
journal of geophysical research: oceans
Language(s) - English
Resource type - Journals
eISSN - 2169-9291
pISSN - 2169-9275
DOI - 10.1002/2016jc011938
Subject(s) - upwelling , oceanography , submarine pipeline , forcing (mathematics) , algal bloom , bloom , environmental science , continental shelf , phytoplankton , geology , red tide , climatology , nutrient , ecology , biology
Gulf of Mexico Loop Current (LC) interactions with the West Florida Shelf (WFS) slope play an important role in shelf ecology through the upwelling of new inorganic nutrients across the shelf break. This is particularly the case when the LC impinges upon the shelf slope in the southwest portion of the WFS near the Dry Tortugas. By contacting shallow water isobaths at this “pressure point” the LC forcing sets the entire shelf into motion. Characteristic patterns of LC interactions with the WFS and their occurrences are identified using unsupervised neural network, self‐organizing map, from 23 years (1993–2015) of altimetry data. The duration of the occurrences of such LC patterns is used as an indicator of offshore forcing of anomalous upwelling. Consistency is found between the altimetry‐derived offshore forcing and the occurrence and severity of WFS coastal blooms of the toxic dinoflagellate, Karenia brevis : years without major blooms tend to have prolonged LC contact at the “pressure point,” whereas years with major blooms tend not to have prolonged offshore forcing. Resetting the nutrient state of the shelf by the coastal ocean circulation in response to deep‐ocean forcing demonstrates the importance of physical oceanography in shelf ecology. A satellite altimetry‐derived seasonal predictor for major K. brevis blooms is also proposed.

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