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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 111, C07009, doi:10.1029/2005JC003214, 2006

Optical determinations of suspended sediment dynamics in western Long Island Sound and the Connecticut River plume

Steven G. Ackleson

Office of Naval Research, Arlington, Virginia, USA


Abstract

The magnitude of beam attenuation attributed to suspended sediments, c p , and the slope of the log-transformed attenuation spectrum, γ, were used to investigate the properties and dynamic nature of matter suspended in the waters of western Long Island Sound (LIS) and the adjacent Connecticut River plume (CRP). Within the LIS, c p and γ indicate a robust relationship between sediment concentration and particle size distribution (PSD). As concentration increased, the PSD shifted to larger particles. The highest concentrations and particle sizes were found in a nepheloid layer adjacent to the sound floor. Within the adjacent CRP, sediments were observed to shift towards smaller particles at the lateral plume boundary, where current shear stress may have disrupted large particle aggregates, relative to sediments in the more quiescent plume interior. A strong linear correlation between γ and salinity was also found, indicating that mixing between the two water masses may also have altered the PSD of the plume sediments. A suspended sediment attenuation model based on Mie theory, a power law form of the PSD, and a single sediment source indicates that the observed changes in LIS c p and γ are consistent with sediment removal as particles settle with size-dependent rates. In contrast, within the CRP, the model supports the hypothesis that turbulence-induced aggregate disruption at the lateral plume boundary is responsible for the observed variability in c p and γ. However, mixing between the LIS and CRP particle populations would violate the single source requirement of the model and necessitate a more complicated set of particle dynamics in order to correctly interpret the observed variability in particulate attenuation.

Received 9 August 2005; accepted 27 March 2006; published 11 July 2006.

Keywords: suspended sediment; light attenuation; Long Island Sound.

Index Terms: 4558 Oceanography: Physical: Sediment transport (1862); 4264 Oceanography: General: Ocean optics (0649); 4211 Oceanography: General: Benthic boundary layers; 4528 Oceanography: Physical: Fronts and jets.

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Citation: Ackleson, S. G. (2006), Optical determinations of suspended sediment dynamics in western Long Island Sound and the Connecticut River plume, J. Geophys. Res., 111, C07009, doi:10.1029/2005JC003214.