INTRODUCTION 



Particle maxima, especially bottom nepheloid layers (BNL) , 

 are ubiquitous features in the world's oceans (McCave, 1986) . 

 They are hypothesized to be biologically enhanced over the 

 surrounding clear water layers and to be major sites where 

 organic matter degrades (Garfield et al., 1983; Karl et al., 

 1984; Fowler and Knauer, 1986). In the Gulf of Maine there are 

 two or three particle maxima, depending in part on the presence 

 of certain water masses (Spinrad, 1986) . At deeper stations 

 these include surface and intermediate particle maxima and a BNL, 

 while at shallow stations only the surface maxima and BNL are 

 observed. Organic material produced at the surface must pass 

 through and be altered by these particle maxima before becoming a 

 food resource for benthic organisms and demersal fishes. 

 Accordingly, some organisms may feed selectively in particle 

 maximum layers, due to the nutritional enhancement. In 

 particular, the degree of biological and nutritional enhancement 

 in the BNL may be a major factor affecting benthic productivity. 



The nutritional quality and biological enhancement of 

 particle maxima, especially the BNL, were determined at three 

 sites in the Gulf of Maine in 1985 and 1986. In 1986, the major 

 field year, Jordan Basin (A, Fig.l) was sampled on two dates and 

 a station off Mt. Desert Island (B, Fig. 1) was sampled in the 

 interim. The Jordan Basin station (approximately 250 m deep) is 

 at the center of a cyclonic gyre which minimized horizontal 

 advection. It is well stratified in the summer with low primary 

 productivity in the surface and typically three particle maxima. 

 The Mt. Desert Island station, in contrast, is much shallower 

 (approximately 100 m) , is well mixed with strong tidal currents 

 near the bottom, has generally higher surface productivity and 

 has only two particle maxima. In 1985 a station was taken in 

 Sheepscot River estuary (C, Fig. 1, approximately 80 m depth) to 

 sample very near the bottom. During 1985 sampling was 

 accomplished with the Johnson Sea-Link submersible, but in 1986 

 sampling was conducted from a surface ship, the R.V. Oceanus , 

 with sampling gear. 



It was hypothesized that the surface layer, where primary 

 production occurs, would be the most biologically enhanced. At 

 the more nearshore Mt. Desert Island station it would be more 

 enhanced than at the Jordan Basin station. The relative 

 enhancement of the intermediate particle maximum cannot by 

 hypothesized because it has been studied so little. Our efforts 

 concentrated on the BNL. The strong gradients in particle 

 concentration near the bottom suggest that there should be 

 similar gradients in nutritional and biological enhancement and 

 chemical composition. The BNL should be biologically enhanced 

 over the clearer waters above. Due to constant resuspension of 

 bottom sediments by tidal currents at the Mt. Desert Island 

 station, it was hypothesized that the BNL there would be less 

 biologically enhanced than at the Jordan Basin station, despite 

 the higher surface productivity and shallower depth at the 



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