THE ROLE OF NEPHELOID LAYERS IN BENTHIC-PELAGIC COUPLING 



Quay Dortch 

 Louisiana Universities Marine Consortium 



David W. Townsend 

 Bigelow Laboratory for Ocean Sciences 



Richard W. Spinrad 

 Office of Naval Research 



Lawrence M. Mayer 

 University of Maine 



ABSTRACT 



Particulate organic matter (POM) formed at the surface of 

 the Gulf of Maine is concentrated as it sinks to the bottom in 

 subsurface particle maxima and the bottom nepheloid layer ( BNL ) . 

 The hypothesis that these particle maxima are layers of 

 intensified biological activity where substantial changes occur 

 in the quantity and quality of the sinking POM is being tested by 

 comparing the numbers of organisms, the chemical and biochemical 

 composition and the physical and optical properties of the 

 particles in the particle maximum layers with the intervening 

 particle minimum layers. During a test dive in 1985 in the 

 Sheepscot River estuary, chlorophyll, protein, bacterial numbers 

 and SPM were measured on water samples taken at cm to m depth 

 intervals above the bottom nepheloid layer (BNL) using the 

 Johnson Sea-Link . In 1986, the particle maxima, BNL, and clearer 

 water in between were sampled in Jordan Basin (250 m) and off Mt. 

 Desert Island (100 m), using a bottom-tripping sampler with 

 three, 30 1 Niskin bottles or a rosette with CTD, beam 

 transmissometer, and 24, 5 1 Niskin bottles (from the R.V. 

 Oceanus ) . Measurements included acetone-extracted chlorophyll, 

 total and biologically available protein, CHN, ATP, respiratory 

 electron transport activity, particle volume and size analysis, 

 and counts of bacteria, autotrophic and heterotrophic 

 nanoplankton, micro- and meso-zooplankton. 



Some biological enhancement of almost all the particle 

 maxima was observed. Since protein concentrations were the most 

 consistently elevated, these particle maxima may be 

 nutritionally enhanced. There was considerable variation in the 

 biological and chemical properties of particles in the BNL 

 between the two stations, between dates at the same station, and 

 between replicates taken within several hours at the same 

 station. Some of the variation could be explained by differences 

 in hydrography or environmental conditions, and some is probably 

 related to the dynamic nature of the processes in the BNL. 



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