Abstract
Optically-active constituents vary over short time and space scales in coastal waters, and they are impacted by a variety of complex, inter-related forcing processes. As part of the Integrated Coastal Bio-Optical Dynamics (ICoBOD) project, we conducted a field campaign in Mississippi Sound in the northern Gulf of Mexico during spring 2018 to examine the impact of the passage of atmospheric and tidal fronts on fine-scale physical and bio-optical property distributions in a shallow, dynamic, coastal environment. During a 25-day experiment, we deployed eight moorings over a roughly 7 × 7 km box encompassing a frontal zone, to collect a time series of physical and bio-optical measurements. We describe changes in diver visibility related to the passage of a short-duration, high-turbidity surface plume and nepheloid layer development/decay during a tidal cycle. Maximum nepheloid layer development was observed during low tide and lasted about 9–12 h. The strongest turbidity signal extended about 4–5 m above the bottom (approximately half of the water column), although anomalously elevated values were observed all the way to the surface. In addition, high-resolution (50 m) hydrodynamic model simulations provide insight into the frontal dynamics and aid interpretation of the observed patterns. Mooring observations confirmed model-predicted heat flux changes associated with the passage of an atmospheric cold front.
Highlights
Active constituents (OACs) in water, both dissolved and particulate, and the water itself, attenuate light through absorption and scattering processes and thereby control the intensity and spectral quality of the penetrating light [1,2]
Previous surface current data (2001) collected with a Coastal O4 coef a2n2 Dynamics Applications RADAR (CODAR) system indicated the development of regular, persistent ntiodrathl ecornnvGeurglfeonfceMferoxnictos.nTeiadresthienpthasiss rbeegtiwoneeanreShpirpedaonmd iHnaotrenlyIsdlaiunrdnsailn
Salinity, waves, currents, and turbidity data sets collected by multiple moorings demonstrated temporal variability related to tides and winds, with differences observed between the surface and bottom layers even in these shallow waters (11 m depths and less)
Summary
Active constituents (OACs) in water, both dissolved and particulate, and the water itself, attenuate light through absorption and scattering processes and thereby control the intensity and spectral quality of the penetrating light [1,2]. The intensity and spectral quality of the penetrating light in turn impact the OACs, for example, through the regulation of primary production (and the abundance and species composition of the phytoplankton) [3,4] and the photobleaching of CDOM [5,6]. The apparent optical properties (AOPs), such as remote sensing reflectance (Rrs) and the diffuse attenuation coefficient (Kd), depend on both the OACs and the ambient light field. Satellite estimates of Rrs are commonly used in bio-optical inversion algorithms to retrieve the water IOPs [7]
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