The biogeochemical significance of organic rich aggregates (marine snow) in the vertical flux of organic matter into the oceans' interior and sea floor is widely acknowledged.1'2 The aggregates, which form during phytoplankton blooms and, to a lesser extent, by the resuspension of benthic biofilms, are a primary source of marine snow.3 A considerable part of the aquatic primary production is removed from the surface through processes of particle aggregation and sedimentation.4-6 These aggregates are the most important components of the organic matter flux to the deep sea7 and appear to be hotspots of heterotrophic activity in the water column, being an important carbon source for free-living bacteria throughout their descent.8 After sedimentation and during an extended period of resuspension loops, almost all of the remaining carbon is then remineralized. Nevertheless, a part of this organic matter is too refractory to be recycled, thus becoming buried in ocean sediments, sequestering carbon and so influencing atmospheric carbon dioxide concentrations.9,10 This chapter will concentrate on the fate of organic aggregates in the size range of tens to

©2005 by CRC Press 237

thousands of micrometers, their production and descent through the water column as well as their residence and further modification within the benthic boundary layer. The term "benthic boundary layer" (BBL) is used for the water layers above the sediments although in sedimentological/physical-oceanography terminology "bottom boundary layer" would be the right phrase to use. Most examples will be given from continental margin studies. Continental margins can be defined as the region between the upper limit of the tidal range and the base of the continental slope. The burial of aggregate-associated organic matter in continental margin sediments is directly linked to the global cycles of carbon over geologic time.11 Although continental margins account only for «15% of total ocean area and 25% of total ocean primary production, today more than 90% of all organic carbon burial occurs in sediments built up by particle deposition on continental shelves, slopes, and in deltas.12 In this whole chapter, useful new references are predominantly cited which lead the interested reader to important previous work on the topic.

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