SESSION SUMMARY: 

 GULF OF MAINE SEDIMENT DYNAMICS 



Daniel F. Belknap 



Dept. Geological Sciences and 



Center for Marine Studies 



University of Maine 



Orono, ME 04469 



As part of the overall ecosystem of the Gulf of Maine, 

 sediment dynamics is a critical area of study. Sediments are an 

 important part of the benthic substrate, controlling 

 distribution of organisms to a large degree, and are intimately 

 involved in the food web through transport pathways, substrates 

 for microorganisms, and through storage and recycling of 

 nutrients within the bottom. Besides nutrients, sedimentary 

 particles also transport, store and recycle pollutants, affecting 

 the benthos in less beneficial ways. 



A prime area of current research is the source, transport 

 pathways, and sinks of sedimentary particles. Part of that study 

 is the present distribution of sediment types and the geologic 

 record of past distributions. It is probable that sediments are 

 segregated into deep channels by tide and wave scour, and the 

 action of slumps and turbidity currents. It is clear that there 

 is no simple blanket produced by hemipelagic settling. The 

 redistribution of sediments by slumps, tidal currents and wave 

 action occurs at least seasonally, and probably at a more 

 frequent rate on most ridges and shoals. The rate at which this 

 material is carried to deeper basins has important consequences 

 to benthic communities. On hard bottoms, being swept clear of 

 sediments has a distinct advantage. On muddy bottoms, input of 

 new sediments is advantageous up to a certain rate, since new 

 food is made available. When sediment smothers the bottom to a 

 critical depth, however, macroinvertebrates will be killed, and 

 nutrients will be buried too deeply for excavation. The rate of 

 sediment accumulation and the episodicity of processes thus 

 requires quantification. 



Three major nearshore environments have been identified in 

 the Gulf of Maine: rocky ledge, sandy nearshore ramp, and basin. 

 Rocky ledges are swept clear of sediments, but often have a talus 

 pile of angular rocks at their base. Next to the talus pile are 

 carbonate shell hash-rich gravel aprons, grading into basinal 

 muds or sand. Sandy ramps are reworked paleodeltas or beach 

 shoreface deposits. Sand waves and oscillation megaripples 

 provide evidence for current and wave activity on these surfaces. 

 Basins are usually the sites of former estuaries, produced at the 

 early Holocene low sea stand, and are muddy and abundantly 

 bioturbated. 



141 



