Fernando Gilbes

An episodic chlorophyll plume on the West Florida Shelf

The episodic formation of an extensive pigment plume on the West Florida Shelf was detected using historical Coastal Zone Color Scanner (CZCS) data collected between 1979 and 1986. The phenomenon is confirmed by in situ observations made in March 1992. The plume occurs mainly during spring, when high pigment concentrations persist 1–6 weeks in a pattern which extends >250 km southward along the shelf. In general, the shelf and continental slope had low pigment concentrations during summer and high pigment concentrations during spring. The information currently available is insufficient to determine the cause of the plume with certainty. Plume formation may be associated with one or a combination of the following processes: (1) discharge from small, local rivers along the NW Florida coast; (2) seasonal changes in steric height differences between the shelf and deep Gulf of Mexico waters; (3) circulation of water associated with the Loop Current and upwelling in the DeSoto Canyon; and (4) discharge from the Mississippi and Mobile Rivers.

Physiological Responses of Acropora cervicornis to Increased Solar Irradiance

The effects of increased UV radiation (UV‐B [280–320 nm] + UV‐A [320–400 nm]; hereafter UVR) on the growth, production of photosynthetic pigments and photoprotective mycosporine‐like amino acids (MAAs) were studied in the threatened Caribbean coral Acropora cervicornis transplanted from 20 to 1 m depth in La Parguera, Puerto Rico. The UVR exposure by the transplanted colonies was significantly higher than that at 20 m, while photosynthetically active radiation (PAR) only increased by 9%. Photosynthetic pigments, quantified with HPLC, as well as linear extension rates and skeletal densities, were significantly reduced 1 month after transplantation to 1 m depth, while MAAs increased significantly despite immediate paling experienced by transplanted colonies. While these colonies showed a significant reduction in photosynthetic pigments, there were no significant reductions in zooxanthellae densities suggesting photoacclimation of the coral’s symbionts to the new radiation conditions. The results suggest that while corals might be able to survive sudden increases in UVR and PAR, their skeletal structure can be greatly debilitated due to a reduction in the photosynthetic capacity of their symbionts and a possible relocation of resources.

Validation of SeaWIFS-derived chlorophyll for the Rio de la Plata Estuary and adjacent waters

The South Atlantic Ocean near the Río de la Plata Estuary is a highly dynamic region that encompasses four different water bodies: the Río de la Plata, the continental shelf and the Brazil and Malvinas currents. Bio-optical measurements obtained during 6–11 November 1999 provided the initial field data for validating Sea viewing Wide Field of view Sensor (SeaWiFS)-derived chlorophyll imagery for this region. The turbid waters of the Río de la Plata Estuary showed the highest variability and complexity in water optical properties, while the offshore waters of the Brazil Current had the lowest. In most cases, the estimates of chlorophyll using the SeaWiFS algorithm were higher than in situ measured values.

SeaWiFS helps assess hurricane impact on phytoplankton in Caribbean Sea

Hurricanes can change the biogeochemistry and productivity of coastal regions due to their large impact on river discharge, land runoff, water circulation, and morphological conditions. Such changes are very dramatic, but they can only last from days to a few weeks. The brief span of these events makes a rapid and low-cost assessment of their regional impact very difficult. Remote sensing of ocean color is a promising tool for assessing the impact of hurricane disturbances in coastal areas at relatively low cost.

A probabilistic sensitivity analysis of water-leaving radiance to water constituents in coastal shallow waters

An important step to determine whether certain coastal environment parameters can be estimated from remote sensing measurements is to establish their identifiability from the water leaving remote sensing reflectance. This work addresses the sensitivity analysis of water leaving remote sensing reflectance to water constituents. The model used in the sensitivity analysis is Hydrolight, a radiative transfer code for ocean waters. We use the Morris factor screening method to determine which parameters have a substantial influence on the remote sensing reflectance. From Morris results, we realize a more precise sensitivity analysis focusing on the most influential parameters, using variance decomposition (Sobol method). As an important example of application, we perform a sensitivity analysis of coral reefs in coastal shallow waters, where the concentrations of Chlorophyll, yellow substance and suspended sediments were limited to a feasible range of variability. The results of the sensitivity analysis lead us to the formulation of band relationships for the estimation of water depth and seabed reflectance in coral reefs.

Phytoplankton dynamics in the eastern Caribbean Sea as detected with space remote sensing

The Space Information Laboratory (SIL) of the Tropical Center for Earth and Space Studies of the University of Puerto Rico at Mayagüez (UPRM) has been collecting and processing satellite data since December of 1996. Satellite imagery from the Advanced Very High Resolution Radiometer (AVHRR) and the Sea viewing Wide Field of view Sensor (SeaWiFS) provides us with a new understanding of phytoplankton dynamics in the Caribbean region. SeaWiFS shows the intrusion of waters into the eastern Caribbean Sea from the Orinoco River during fall and from the Amazon River during spring–summer. Strong coastal upwelling in Venezuela produced by the trade winds during winter–spring is detected with the AVHRR. The satellite data suggest that these seasonal events may play an important role in phytoplankton fertilization of the eastern Caribbean Sea. SeaWiFS and hydrological data are also combined to evaluate the impact of hurricanes on phytoplankton distribution. The development of models for estimation of ocean primary productivity using SeaWiFS and AVHRR data is now in progress.

Subsurface detection of coral reefs in shallow waters using hyperspectral data

Hyperspectral Remote Sensing has the potential to be used as an effective coral monitoring system from either space or airborne sensors. The problems to be addressed in hyperspectral imagery of coastal waters are related to the medium, which presents high scattering and absorption, and the object to be detected. The object to be detected, in this case coral reefs or different types of ocean floor, has a weak signal as a consequence of its interaction with the medium. The retrieval of information about these targets requires the development of mathematical models and processing tools in the area of inversion, image reconstruction and detection. This paper presents the development of algorithms that does not use labeled samples to detect coral reefs under coastal shallow waters. Synthetic data was generated to simulate data gathered using a high resolution imaging spectrometer (hyperspectral) sensor. A semi-analytic model that simplifies the radiative transfer equation was used to quantify the interaction between the object of interest, the medium and the sensor. Tikhonov method of regularization was used as a starting point in order to arrive at an inverse formulation that incorporates a priori information about the target. This expression will be used in an inversion process on a pixel by pixel basis to estimate the ocean floor signal. The a priori information is in the form of previously measured spectral signatures of objects of interest, such as sand, corals, and sea grass.