HR: 0800h
AN: B21A-1017    [Abstracts]
TI: Massive Organic Matter Fall Processing and Organic Enrichment in Deep Sea Sediments: the Role of Fall Type
AU: * Hannides, A K
EM: hannides@hawaii.edu
AF: Department of Oceanography, SOEST, University of Hawai`i, 1000 Pope Road, Marine Science Building, Honolulu, HI 96822 United States
AU: Smith, C R
EM: craigsmi@hawaii.edu
AF: Department of Oceanography, SOEST, University of Hawai`i, 1000 Pope Road, Marine Science Building, Honolulu, HI 96822 United States
AU: Baco-Taylor, A R
EM: abaco@whoi.edu
AF: Woods Hole Oceanographic Institution, 2-14 Redfield, MS #33, Woods Hole, MA 02543-1050 United States
AB: Resource-limited deep-sea sedimentary settings are occasionally punctuated with massive organic matter (MOM) falls, such as fish and marine mammal carcasses, macrophytes and wood. In the case of whale falls, previous studies have shown that sharp gradients in microbial activity exist within a few meters of these falls. These sites are characterized by intense sulfate reduction and sulfide generation, which are commonly attributed to sedimentary organic enrichment from MOM, and in part support extensive chemosynthetic communities that rely on endosymbiotic oxidation of this sulfide for energy. Enrichment is brought about by the fragmentation and dissemination activities of deep-sea megafauna: scavengers in the case of carcasses and macrophytes, and wood borers in the case of wood.
Differences in MOM fall composition and structure and the subsequent megafaunal processing raise questions concerning the patterns of organic enrichment around these falls and how these patterns vary with fall type. We present an extensive data set of surface sediment organic carbon and nitrogen content at whale, kelp and wood falls of various ages in the California Borderland Basins region. Evidence for organic enrichment around whale falls is lacking, corroborating previous findings. However, distinctly low C:N ratios in surface sediments adjacent to whale falls suggest more complex processing of MOM in this zone. This pattern persists regardless of whale fall age. On the contrary, evidence for organic enrichment around kelp and wood falls abounds. Organic carbon and nitrogen content values adjacent to 3 month-old kelp falls are 25-50 % higher than those 1 m away from the falls and traces of this signal persist for at least 3 more months. In the case of wood falls, 6 month-old falls do not show any significant traces of enrichment, but 3 years after the fall event organic carbon content adjacent to the falls increases by 2-5 times that of background. C:N ratios concomitantly increase to startling levels of 80-100. Comparison of falls of different ages but similar masses reveals that kelp falls result in rapid (<3 months) enrichment peaks, while wood falls only generate significant signals on the order of years. Comparison of organic enrichment patterns with pore water sulfide distributions suggests a role of MOM type or quality in stimulating increases in sedimentary organic matter decomposition rates.
DE: 1050 Marine geochemistry (4835, 4845, 4850)
DE: 3035 Midocean ridge processes
DE: 4805 Biogeochemical cycles, processes, and modeling (0412, 0414, 0793, 1615, 4912)
DE: 4815 Ecosystems, structure, dynamics, and modeling (0439)
DE: 4850 Marine organic chemistry (0470, 1050)
SC: Biogeosciences [B]
MN: Fall Meeting 2005