Abstract
Abstract. Regions of milky white seas or "whitings" periodically occur to the west of Andros Island along the Great Bahama Bank where the bottom sediment consists of fine-grained aragonite mud. We present measurements of inherent optical properties within a sediment whiting patch and discuss the potential for monitoring the frequency, extent, and quantity of suspended matter from ocean colour satellite imagery. Sea spectral reflectance measured in situ and remotely from space revealed highly reflective waters elevated across the visible spectrum (i.e., "whitened") with a peak at 490 nm. Particulate backscattering was an order of magnitude higher than that measured at other stations throughout the region. The whiting also had one of the highest backscattering ratios measured in natural waters (0.05–0.06) consistent with water dominated by aragonite particles with a high index of refraction. Regular periodicity of 40 and 212 s evident in the light attenuation coefficient over the sampling period indicated patches of fluctuating turbidity on spatial scales that could be produced from regular rows of Langmuir cells penetrating the 5-m water column. We suggest that previously described mechanisms for sediment resuspension in whitings, such as tidal bursting and fish activity, are not fully consistent with these data and propose that wind-driven Langmuir cells reaching the full-depth of the water column may represent a plausible mechanism for sediment resuspension and subsequent whiting formation. Optics and remote sensing provide important tools for quantifying the linkages between physical and biogeochemical processes in these dynamic shallow water ecosystems.
Highlights
The Bahama Banks represent an extensive carbonate depositional system that rises sharply from the deep western tropical Atlantic seafloor to a broad shallow platform whose water depth ranges from 4–8 m
On 28 March 2004, a whiting event was encountered at 25◦03.090 N, 78◦42.324 W 16:55 Greenwich Mean Time (GMT) on the western arm of the Great Bahama Bank, approximately 30 km west of Andros Island, the largest island of the Bahamas archipelago (Fig. 1a)
Sediment whitings are not merely isolated turbidity events, but have implications for the formation of aragonitic muds found on the western bank of the Great Bahamas Bank near Andros Island (Milliman et al, 1993) and the global carbon cycle
Summary
The Bahama Banks represent an extensive carbonate depositional system that rises sharply from the deep western tropical Atlantic seafloor to a broad shallow platform whose water depth ranges from 4–8 m. The region west of Andros Island on the Great Bahama Bank has relatively low wave-energy and is dominated by fine lime mud and pellet mud sediments (Purdy, 1963). The seas overlying these muds are well known for episodic, highly turbid events that produce milkywhite coloured waters, historically referred to as “whitings” (Cloud, 1962). Whitings cover from tens to hundreds of km and have an average suspended sediment concentration of 10 mg L−1 (Shinn et al, 1989) These whitings are so distinct that the dramatic white waters have been observed and enumerated from photography taken by astronauts aboard the Space Shuttle (Robbins et al, 1997). Little is known about the inherent and apparent optical properties of the particles within whitings and the mechanism forming these whiting events still remains to be identified (Broecker, 2009)
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