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Hydrocarbons that originated from Deepwater Horizon were observed at the surface along west Florida’s northern coastline in June 2010. The farthest eastward advance nearly to Cape San Blas occurred during the last week of June before the surface oil retreated back westward and dissipated. Surface oil was not observed on the portion of the West Florida Continental Shelf (WFS) situated to the southeast of Cape San Blas. Nevertheless, there were numerous anecdotal occurrences of reef fish caught on the WFS with lesions and other deformities. Subsequent systematic sampling of WFS reef fish provided additional evidence for damage that extended as far south as the Dry Tortugas. Here we examine the possibility that hydrocarbons of Deepwater Horizon origin transited to the WFS beneath the surface. We use a numerical circulation model simulation run for the entirety of 2010 and quantitatively gauged against in situ observations. A passive tracer is introduced into the model to mimic the movement of subsurface hydrocarbons, either dissolved or of sufficiently small particle size to effectively be dissolved. The tracer, driven primarily by an anomalously strong and persistent upwelling circulation, eventually covered most of the WFS. Using reasonable estimates of what the initial tracer concentration may have been with respect to hydrocarbons, we conclude that the transport of subsurface hydrocarbons to the WFS is both plausible and consistent with the observed distribution of fish lesions, fish liver chemistry and other chemical and ecological evidence. [ABSTRACT FROM AUTHOR]

Harmful algal blooms of the dinoflagellate Karenia brevis require an upwelling circulation to manifest along the coastline of the West Florida Continental Shelf. Too much upwelling, however, can impede bloom formation by increasing inorganic nutrient levels to the point where faster growing phytoplankton such as diatoms may out-compete the slower growing K. brevis , as occurred in 1998 and 2010. Both 2012 and 2013 experienced persistent upwelling, but only 2012 exhibited a robust harmful algal bloom. Here we examine the subtle differences in the coastal ocean circulation between those two years that led to the disparate bloom evolutions. [ABSTRACT FROM AUTHOR]

Over the past two decades, the two most anomalous years for water properties on the west Florida continental shelf were 1998 and 2010. In both instances, the shelf was ventilated by relatively cold, nutrient-rich waters of deep ocean origin, which reset the background state underlying shelf ecology. The ventilation in both of these years derived from prolonged interactions of the Gulf of Mexico Loop Current with the shelf slope near the Dry Tortugas located on the southwest corner of the shelf. By contacting relatively shallow isobaths, the boundary current interactions there set the entire shelf into motion, facilitating upwelling across the shelf break, even to DeSoto Canyon some 500 km away, and then across the shelf to the near shore. Such prolonged and intense upwelling of nutrient-rich water in 2010 contrasted with the more typically occurring locally wind driven upwelling conditions, whereby waters upwelled at the near shore are from the inner shelf, versus the deep ocean. Thus not all upwelling scenarios have similar consequences. Whereas the typical wind driven upwelling scenario is necessary for Karenia brevis red tide blooms to manifest along the coastline, the rarer, deep ocean induced upwelling scenario (as occurred in 1998 and particularly in 2010) acts to suppress K. brevis red tides because of the elevated inorganic nutrient conditions that they facilitate. Hence, minimal cell counts above background were observed in 1998, and no cell counts above background were observed in 2010. We conclude that the lack of red tide along the west coast of Florida in 2010 was due to anomalously large and protracted upwelling of nutrient-rich waters of deep ocean origin caused by Loop Current and eddy interactions with the shelf slope. [ABSTRACT FROM AUTHOR]

Concurrently operated on the West Florida shelf for the purpose of observing surface currents are three long-range (4.9 MHz) Coastal Ocean Dynamics Applications Radar (CODAR) SeaSonde and two median-range (12.7 MHz) Wellen Radar (WERA) high-frequency (HF) radar systems. These HF radars overlook an array of moored acoustic Doppler current profilers (ADCPs), three of which are presently within the radar footprint. Analyzed herein are 3 months of simultaneous observations. Both the SeaSonde and WERA systems generally agree with the ADCPs to within root-mean-square differences (rmsd) for hourly radial velocity components of 5.1-9.2 and 3.8-6.5 cm s−1 for SeaSonde and WERA, respectively, and within rmsd for 36-h low-pass filtered radial velocity components of 2.8-6.0 and 2.2-4.3 cm s−1 for SeaSonde and WERA, respectively. The bearing offset and tidal and subtidal currents of total velocities are also assessed using the ADCP data. Despite differences in a variety of aspects between the direction-finding CODAR SeaSonde (long range, effective depth of 2.4 m, integration time of 4 h, and idealized antenna patterns) and the beam-forming WERA (median range, effective depth of 0.9 m, and integration time of 1 h), both HF radar systems demonstrated good surface current mapping capability. The differences between the velocities measured with the HF radar and the ADCP are sufficiently small in this low-energy shelf that much of these rmsd values may be accounted for by the expected measurement differences due to the horizontal, vertical, and temporal sampling differences of the ocean current observing systems used. [ABSTRACT FROM AUTHOR]

Abstract: The performance of coastal altimetry over a wide continental shelf is assessed using multiple-year ocean current observations by moored Acoustic Doppler Current Profilers (ADCP) and high-frequency (HF) radar on the West Florida Shelf. Across-track, surface geostrophic velocity anomalies, derived from the X-TRACK along-track sea level anomalies are compared with the near surface current vector components from moored ADCP observations at mid shelf. The altimeter-derived velocity anomalies are also directly compared with the HF radar surface current vector radial components that are aligned perpendicular to the satellite track. Preliminary results indicate the potential usefulness of the along-track altimetry data in contributing to descriptions of the surface circulation on the West Florida Shelf and the challenges of such applications. On subtidal time scales, the root-mean-square difference (rmsd) between the estimated and the observed near surface velocity component anomalies is 8–11cm/s, which is about the same magnitude as the standard deviations of the velocity components themselves. Adding a wind-driven Ekman velocity component generally helps to reduce the rmsd values. [Copyright &y& Elsevier]

Abstract: The seasonal variations of the West Florida Continental Shelf (WFS) circulation and sea level are described using observations of velocity from an array of moored acoustic Doppler current profilers and various ancillary data. With record lengths ranging from 3years to over a decade, a robust seasonal cycle in velocity is found, which varies across the shelf in a dynamically sensible way. Over most of the inner shelf these seasonal variations are primarily in response to local forcing, through Ekman-geostrophic spin-up, as previously found for the synoptic scale variability. Thus the inner shelf circulation is predominantly upwelling favorable from fall to spring months (October–April) and downwelling favorable during summer months (June–September). Seaward from about the 50m isobath, where baroclinicity becomes of increasing importance, the seasonal variations are less pronounced. Over the outer shelf and near the southwestern end of the WFS, the seasonal variations are obscured by the deep ocean influences of the Gulf of Mexico Loop Current and its eddies. The seasonal variations in sea level are also robust. But unlike the velocity, these extend across the entire WFS and into the deep Gulf of Mexico. These seasonal sea level variations arise from two influences, one static, the other dynamic. The static influence projects onto the WFS by the static seasonal rise and fall of the Gulf of Mexico sea level due to heating and cooling (also occurring on the shelf). On climatological average, this ranges by about 0.12m, with a minimum in February and a maximum in August and deriving primarily from the density variations over the upper 100m of the water column. Such climatologically averaged variation due to temperature and salinity is also seen in satellite altimetry. An additional dynamic influence of about 0.06m occurs over the inner shelf by the Ekman-geostrophic spin up to the seasonally varying winds. Together, the static and dynamic ocean responses result in a climatologically averaged coastal sea level variation at the central (vicinity of Tampa Bay to Charlotte Harbor) region of the WFS of about 0.18m after adjustment for the inverted barometer effect, which adds about another 0.06m for a total climatologically averaged annual sea level range of about 0.24m. [Copyright &y& Elsevier]

Three long-range (5 MHz) Coastal Ocean Dynamics Application Radar (CODAR) SeaSonde HF radars overlooking an array of as many as eight moored acoustic Doppler current profilers (ADCPs) have operated on the West Florida Shelf since September 2003 for the purpose of observing the coastal ocean currents. HF radar performance on this low-energy (currents and waves) continental shelf is evaluated with respect to data returns, the rms differences between the HF radar and the ADCP radial currents, bearing offsets, and radial velocity uncertainties. Possible environmental factors affecting the HF radar performance are discussed, with the findings that both the low-energy sea state and the unfavorable surface wave directions are the main limiting factors for these HF radar observations of currents on the WFS. Despite the challenge of achieving continuous backscatter from this low-energy environment, when acquired the data quality is good in comparison with the ADCP measurements. The rms differences range from 6 to 10 cm s−1 for hourly and from 3 to 6 cm s−1 for 36-h low-pass-filtered radial currents, respectively. Bearing offsets are in the range from −15° to +9°. Coherent variations of the HF radar and ADCP radial currents are seen across both tidal and subtidal frequency bands. By examining the HF radar radial velocities at low wave energy, it is found that the data returns decrease rapidly for significant wave heights smaller than 1 m, and that the rms differences between the HF radar and ADCP radials are degraded when the significant wave height is smaller than 0.3 m. [ABSTRACT FROM AUTHOR]

An Ensemble Optimal Interpolation (EnOI) system is built to assimilate underwater profiling glider observations into a West Florida Shelf (WFS) coastal ocean model. The Floating Temporal Window (FTW) technique is incorporated into the EnOI scheme to generate and update associated ensemble members, which are directly extracted from the model output states from previous output cycles. The model performance is validated against independent observations from moorings located near the glider tracks. The EnKF, traditional EnOI and the FTW-EnOI schemes are compared in terms of error covariance evolution and model performance at mooring locations. It is found that all three assimilation schemes provide significant (2–3 times) better fit to the mooring data compared with the free model run. Although the EnKF scheme produces the best results, the FTW-EnOI should be considered as an alternative method given the low computational cost and the flow-dependent information embedded in the algorithm. [ABSTRACT FROM AUTHOR]

Highlights: [•] A Karenia brevis bloom was observed on the West Florida Shelf in late 2011. [•] Combination of in situ, satellite, and glider data provided insights into the three-dimensional structure of the bloom. [•] Analysis indicated that the bloom could have been initiated offshore. [•] This study shows the significance of an integrated observing system for harmful algal blooms. [ABSTRACT FROM AUTHOR]