Year: 2006
Type: dissertation
Abstract: The West Florida Shelf (WFS), typically characterized as being oligotrophic, is\none of the most productive continental shelves in the United States. In addition to\nsupporting a large fishing industry, the WFS also supports high biomass blooms of the\ntoxic dinoflagellate\nKarenia brevis. Because of the large ecological and economic\nimpacts these blooms have on the area, the ECOHAB: Florida program was developed to\ngain a better understanding of red tides and their initiation, maintenance, and dispersal.\nThis interdisciplinary program consisted of monthly cruises from June 1998 through\nDecember 2001, with a hiatus from January through March of 2001. Hydrography,\nnutrients, chlorophyll\na, phaeopigments, and a wide variety of other factors were\nmeasured during the cruises. In this paper chlorophyll\na and phaeopigment\nconcentration, nutrients, and hydrographic data were examined to explain the temporal\nand spatial distribution of chlorophyll on the shelf.\nAverage surface chlorophyll values were 0.55 mg/m\n3 with near bottom values\naveraging 0.85 mg/m\n3. Chlorophyll was found to be highest near the estuaries of Tampa\nBay and Charlotte Harbor with a decreasing gradient seaward. Near bottom chlorophyll\nvalues were generally two to fourfold greater than surface values. Midshelf stations (35-\n50 m) were characterized by high near bottom chlorophyll, whereas the offshore stations\n(86-200 m) were characterized by a subsurface chlorophyll maximum ranging between\n40 to 80 m deep. Nutrients were generally low across the shelf except for 1998 when a\nsubsurface intrusion of nutrient rich slope water reached to the 20 m isobath.\nTemperatures ranged from 14.00\n° C to 31.47° C. Salinity ranged from 30.5 to 37.50 in\nthe study area.\nFour blooms of\nKarenia brevis, lasting several months, contributed to the high\nchlorophyll concentrations along the inner shelf. Maximum chlorophyll concentrations\nof 27.10 mg/m\n3 were a result of the October 1999 to March 2000 red tide. Blooms of\nTrichodesmium\nand diatoms also were contributors to patterns seen on the shelf.\nMaximum chlorophyll values were generally highest in the late summer and fall except\nfor offshore values which showed little to no seasonality. Inshore of the 50 m isobath,\naverage phaeopigments comprised from 43 to 68 percent of the measured Chl\na, while\noffshore values were from 68 to over 100 percent.\nInshore chlorophyll distributions were attributed to riverine and estuarine flux of\nnutrients, localized upwelling, and recycling of nutrients aided by salinity and\ntemperature fronts. Midshelf distributions were attributed to the movement of\nbiologically important material through the bottom Ekman layer from offshore to the\ninshore regions of the shelf. Offshore distributions were attributed to Loop Current\nupwelling and synoptic scale processes associated with seasonal meteorological forcing.
Author: Danylle N. Ault
Language: English
Subfield: Oceanography
Field: Earth and Planetary Sciences
Domain: Physical Sciences
SDG: Life below water
Open Access status: green
OpenAlex ID: W1487137746