Whiting Events Off Southwest Florida: Remote Sensing and Field Observations

“Whiting” is a term used to describe a sharply defined patch of water that contains high levels of suspended, fine-grained calcium carbonate (CaCO3). These features are named for their bright (at times white) appearance when compared to surrounding waters, and have been found to occur globally, persisting for multiple consecutive days. Although whitings have been widely studied using chemical, biological, geological, and physical techniques, there has been little effort to document their spatio-temporal distributions in a systematic way, not to mention the lack of consensus on what generates whitings and allows them to persist for days to weeks at a time. In particular, although fishermen and aircraft pilots have reported whiting-like features off southwest Florida (e.g., a sighting off the Ten Thousand Islands was reported on October 29, 2013), there has been no targeted study on these features in this area. Therefore, the objective of this study is two fold: 1) to document the spatial-temporal distributions of whitings in southwest Florida (SWFL) coastal waters from 2003 through 2015 using satellite imagery to study how their occurrence is related to several environmental variables and 2) to conduct field and laboratory measurements to determine the particle composition and water characteristics in and outside the whiting features. To achieve objective one, a multi-year time series from 2003 through 2015 was developed over SWFL using Moderate Resolution Imaging Spectroradiometer (MODIS) observations. Customized processing was used in order to removed clouds and other artifacts and to delineate the surface whiting features. From this, statistics and distribution maps of whiting occurrence were generated. Annual mean whiting coverage peaked in 2011 (11 km2), when whiting reached a maximum daily visible coverage of 92 km2 on February 23. For the entire time series, the highest daily coverage observed was 126 km2 on December 6, 2008. Over all, whitings had higher spatial coverage during the spring and autumn, with 88% of all whiting coverage occurring within 40 km of the coastline. Images of average seasonal spatial distributions showed that over 90% of whitings located between 40 and 70 km of shore occurred specifically during the winter and autumn. A multivariate linear regression was performed, which found little to no correlation between annual whiting coverage and environmental factors such as sea surface temperature (SST), wind, and river discharge. This analysis was also applied to spatial distributions of whiting events within and outside of 20 km and 40 km from shore. The only statistically significant result was that of SST, as well as SST with river discharge and whiting events distributed more than 20 km from shore. In order to accomplish objective two, several field campaigns were conducted to collect in-situ data and water samples of pre-, post-, and occurring whiting event conditions to provide information on composition, driving forces, and variables that cannot be derived via satellites. Samples were collected for taxonomic identification, chemical analysis, bottom sediment grain size fractionation, in-situ remote sensing reflectance (Rrs), particle backscattering (bbp), chlorophyll-a concentration ([chl-a]), particulate absorption (ap), and gelbstoff (otherwise known as color dissolved organic matter, or CDOM) absorption (ag). Taxonomic identification of marine phytoplankton within whiting water revealed the presence of a dominant, small (\u3c5 \u3eμm), centric diatom species during a sampled whiting event. Through the use of scanning electron microscopy (SEM), these were identified as Thalassiosira sp. Amorphous to fully formed crystals of calcium carbonate were present, attached to cells of Thalassiosira sp., localized to the girdle bands. All other diatom species were devoid of similar growths. In comparing the waters within a whiting area to outside waters, no significant differences were found in ap, ag, nor [chl-a]. The carbonate parameters of whiting water differed from outside water, however due to low sample numbers these results are inconclusive. Average backscattering was twice as high within whiting waters compared to non-whiting water, and measured in-situ Rrs was higher at all wavelengths (400 – 700 nm) within whiting water, with a spectral shape similar to outside waters. Overall, this is the first time that SWFL whiting events have been characterized systematically using satellite imagery, field and laboratory as well as meteorological data to diagnose whiting causes and maintenance mechanisms. Although these results are inconclusive, they add new information to the existing literature on this phenomenon