DETERMINING MARINE VS. TERRESTRIAL SOURCES OF ORGANIC MATTER (OM) WITHIN SUBMARINE CANYON SEDIMENT USING LIPID BIOMARKERS

The transport and fate of terrestrial organic matter (OM) far offshore is less well understood than the transport of OM to the nearshore environment. Submarine canyons can play a critical role in transporting particulate material from the shelf to the deep sea. These geomorphic features form during sea-level low stand, as fluvial systems erode through the edge of a continental shelf. When sea level rises, the canyon is inundated and fluvial processes cease, leaving behind a steep-sided, deep incision at the edge of the continental shelf and emplacing complex fluid dynamic systems. Sediments within submarine canyons – as well as proximal waters – contain higher concentrations of OM than adjacent continental shelf water column and sediments of comparable depths, indicating that submarine canyons are important conduits of OM to the deep ocean. Variations in the source and concentration of benthic OM also influence both the diversity and abundance patterns of benthic fauna in submarine canyons.

Here we examine lipid biomarkers in sediment samples collected from the Baltimore Canyon in the Mid-Atlantic Region to determine benthic OM sources (marine or terrestrial). Marginal OM can originate from a combination of fluvial systems, marine production, and atmospheric dust, as well as the resuspension of canyon sediments. Multiple geochemical proxies can help identify these OM sources, including bulk composition (isotopes, grain size) as well as organic biomarker composition. Surficial sediment samples were collected along a downcanyon transect of Baltimore Canyon spanning a depth range from ~200 to 1200 m. Sediment characteristics vary widely: average grain size ranged from 0.041-0.211 mm and percent carbon ranged from 0.05-0.67 %. Sediment was solvent extracted and separated into fractions by polarity. Chain length distributions of n-alkanes (long versus short and even versus odd carbon number) and specific sterol compound biomarkers were examined to determine OM origin. By studying sedimentary OM sources along the canyon transect, we uncover trends in the distribution of OM within the canyon. The varied sources of sedimentary OM detected in Baltimore Canyon reveal a complex offshore transport system that may play a role in the bathymetric patterns of species diversity.