The short-term fate of fresh algal carbon in continental slope sediments

Emplacement of a tracer mixture containing C-13-labeled green algae on the sea floor of the continental slope offshore of Cape Hatteras, North Carolina, elicited a rapid response over 1.5 d from the dense benthic community. Certain deposit-feeding annelids (e.g. Scalibregma inflatum and Aricidea quadrilobata) became heavily labeled with C-13 as a result Of ingestion of the algae. C-13-labeled organic matter was transported to a depth of at least 4-5 cm into the seabed during the 1.5-d period, presumably as a consequence of a feeding-associated activity. Nonlocal transport produced subsurface peaks in organic C-13 at 2-3 cm. Dissolved inorganic C-13, produced by the oxidation of the labeled algae, penetrated to 10-cm depth. The transport of highly reactive organic matter from the sediment surface at initial velocities greater than or equal to 3 cm d(-1) is expected to be an important control of subsurface benthic processes in slope environments characterized by abundant macrofaunal populations. Anaerobic processes, which are enhanced on the Cape Hatteras slope relative to adjacent areas, may be promoted by the rapid injection of reactive material into subsurface sediments. The transport, in turn, is a consequence of the dense infaunal populations that are supported by the rapid deposition of organic carbon in this region.