SPATIAL AND TEMPORAL SAMPLING SCALES 



a. Shallow-water sediments. Sediments of the shelf and upper slope probably experience 

 seasonality in temperature, light penetration, and flux of organic carbon. To test for temporary 

 storage of newly produced organic matter in these sediments, we will need to contrast samples 

 collected in productive and non- productive seasons. 



Spatially, our preliminary data suggest trends over latitude, with sediments becoming finer 

 and more carbon-rich from north to south within the field area. We need additional samples to 

 better define gradients over latitude, probably emphasizing depths > 75 m. 



b. Deep-water sediments (depth > -400 m). Temporal distribution of sampling should be less 

 critical for these water depths, although newly-produced organic matter is probably more likely 

 to be detected or intercepted in transit during the first few months after major blooms. Spatial 

 variability must be assessed on small and large scales. Extreme bottom roughness, generally 

 visible as downslope ridges and valleys, must influence transport and deposition of organic 

 matter. We need closely- spaced samples, with precise control over sample location, to 

 understand the effects of this topography; some of this sampling may require use of submersibles. 

 On a larger scale, we need to test for intensification of sediment transport and accumulation 

 southward toward Cape Hatteras; a very high accumulation rate has been reported for one site 

 near Cape Hatteras, but there are too few data in the field area to place this number in 

 perspective. For depths exceeding 1000 m, there are very few data on sediment properties or 

 accumulation rates; because seaward transport could result in deposition of organic matter on the 

 lower slope or upper rise, we shall need to do at least survey sampling in this province. 



METHODS AND PLATFORMS 



We collect most of our sediment samples from surface ships, using grab- or 

 core-samplers. Most ships are capable of handling this equipment. However, while we have our 

 own sediment grabs and a device which collects short (< 25 cm) cores, we rely upon ships to 

 provide equipment for collecting longer cores (box cores, gravity cores, piston cores, Kasten 

 cores, etc). Ships which do not routinely sample sediments may be poorly equipped to do so; 

 for example, in May 1993 box-coring from the Gyre was usually unsuccessful. 



Because of the time involved in subsampling sediment cores, sediment sampling in the 

 OMP field area (short transits between stations) is advantageously combined with other ship uses. 

 Since we are collecting samples for measurement of natural levels of 14-C, however, it is 

 desirable that we not share cruise time with investigators who perform 14-C tracer experiments 

 at sea. 



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