Coherence of Thin Layers in Space and in Time  
Temporal and spatial coherence are the critical properties that set Thin Layers apart from micro-patches. The example shown below depicts a Thin Layer which meets these criteria. In this data set, two or more replicate profiles were collected at each of four stations along the longitudinal axis of East Sound, WA. Replicate profiles of chlorophyll-a measurements are shown in the left and right panels. A layer less than one meter thick was observed in all replicate casts at all four stations. Peak chl-a concentrations in the Thin Layer ranged from 27 µg/L in the northern part of the sound to 12 µg/L in the southern part of the sound. These values are 3 to 10 times higher than the average concentrations of chl-a throughout the rest of the water column. Profiles collected at the northern most station showed that the layer persisted for 24 hours. The combination of dense concentrations of phytoplankton (indicated by high chlorophyll-a levels) coupled with the temporal and spatial coherence of this Thin Layer provides migrating zooplankton with an elevated food resource throughout the sound. As a result, Thin Layers probably affect not only zooplankton distributions, but also their feeding and growth.  

OPTICAL PROFILES SHOWING COHERENCE OF A THIN LAYER IN EAST SOUND, WA.

From top to bottom: profiles along a north to south transect in East Sound
From left to right: replicate casts at each statiion

upper x-axis = Chlorophyll-a, in µg/L
lower x-axis = sigma theta
y-axis = depth, in meters

© P.L. Donaghay

  

East Sound, WA

East Sound is a fjord in the San Juan Islands, Washington. It is oriented northwest to southeast, and is about 12 km long.
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31 August 1999