@article{demopoulos_smith_demaster_fornes_2003, title={Evaluation of excess Th-234 activity in sediments as an indicator of food quality for deep-sea deposit feeders}, volume={61}, ISSN={["1543-9542"]}, DOI={10.1357/002224003322005096}, abstractNote={Deep-sea deposit feeders selectively ingest large volumes of sediment. Knowledge of the nature of this selectivity will help to elucidate the limiting nutritional requirements and geochemical impacts of these abundant animals. Shallow-water and theoretical studies suggest that deep-sea deposit feeders should select particles rich in protein, bacterial biomass, and/or chloropigment concentrations. Recent studies indicate that deep-sea megafaunal deposit feeders exhibit strong gut enrichment of excess (xs) 234 Th activity, even though 234 Thxs lacks nutritional value. To explore the significance of selective ingestion of 234 Thxs activity, we evaluated the correlations between 234 Thxs activity and three potential tracers of deposit feeder food quality: chlorophyll a (chl a), enzymatically hydrolyzable amino acids (EHAA), and adenosine triphosphate (ATP). Surface sediments from three quiescent bathyal basins off Southern California (San Nicolas, Santa Catalina, and San Clemente) were collected by a multiple corer and analyzed for 234 Thxs activity, chl a, EHAA, ATP, and total organic carbon and nitrogen. 234 Thxs activity was positively correlated with chl a and phaeopigment concentrations and negatively correlated with EHAA concentrations. Excess 234 Th was not linearly correlated with concentrations of ATP, organic carbon, or total nitrogen. The results suggest that deep-sea deposit feeders select sediments with high 234 Thxs activity because it is associated with recently settled phytodetrital material. There is no evidence that this 234 Thxs-rich material has particularly high concentrations of labile amino acids or microbial biomass. Phytodetrital material may be an important source of some other limiting nutrient to deep-sea deposit feeders, e.g., polyunsaturated fatty acids, labile organic carbon and/or vitamins.}, number={2}, journal={JOURNAL OF MARINE RESEARCH}, author={Demopoulos, AWJ and Smith, CR and DeMaster, DJ and Fornes, WL}, year={2003}, month={Mar}, pages={267–284} }
 @article{demaster_thomas_blair_fornes_plaia_levin_2002, title={Deposition of bomb (14)C in continental slope sediments of the Mid-Atlantic Bight: assessing organic matter sources and burial rates}, volume={49}, ISSN={["0967-0645"]}, DOI={10.1016/S0967-0645(02)00134-0}, abstractNote={As part of the Ocean Margins Program (OMP), organic carbon 14C measurements have been made on benthic fauna and kasten core sediments from the North Carolina continental slope. These analyses are used to evaluate the nature and burial flux of organic matter in the OMP study area off Cape Hatteras. Despite the fact that surface sediment 14C contents ranged from −41 to −215 per mil, the benthic fauna (primarily polychaetes) all contained significant amounts of bomb-14C (body tissue 14C contents ranging from +20 to +82 per mil). Bomb-14C clearly is reaching the seabed on the North Carolina slope, and the labile planktonic material carrying this signal is a primary source of nutrition to the benthic ecosystem. The enrichment of 14C in benthic faunal tissue relative to the 14C content of bulk surface-sediment organic matter (a difference of ∼150 per mil) is attributed to a combination of particle selection and selective digestive processes. Organic carbon burial rates from 12 stations on the North Carolina slope varied from 0.02 to 1.7 mol of C m−2 yr−1, with a mean value of 0.7 mol of C m−2 yr−1. The accumulation of organic matter on the upper slope accounts for <1% of the primary production in the entire continental margin system. The North Carolina margin was deliberately selected because of its potential for offshore transport and high sediment deposition rates, and even in this environment, burial of organic carbon accounts for a very small fraction of the primary production occurring in surface waters.}, number={20}, journal={DEEP-SEA RESEARCH PART II-TOPICAL STUDIES IN OCEANOGRAPHY}, author={DeMaster, DJ and Thomas, CJ and Blair, NE and Fornes, WL and Plaia, G and Levin, LA}, year={2002}, pages={4667–4685} }
 @article{fornes_demaster_smith_2001, title={A particle introduction experiment in Santa Catalina Basin sediments: Testing the age-dependent mixing hypothesis}, volume={59}, ISSN={["0022-2402"]}, DOI={10.1357/002224001321237380}, abstractNote={The occurrence of age-dependent mixing, a process by which recently deposited, food-rich particles undergo more intense bioturbation than older, food-poor particles, could dramatically alter patterns of organic-matter diagenesis in deep-sea sediments. To explicitly test for age-dependent mixing, an in-situ particle introduction experiment was conducted on the bathyal Santa Catalina Basin floor. Mixtures of radioisotope-tagged particles representing a food quality gradient were dispersed in small amounts on the seafloor and sampled over periods of 0 to 594 days. Introduced particle types were all similar in size and included fresh diatoms (young particles), surface sediments (intermediate-age particles), and particles from 30-cm deep in the sediment column (old particles). This approach permitted evaluation of particle mixing intensity for several particle ages and provided an independent check on mixing coefficients determined from naturally occurring radioisotopes ( 234 Th xs and 210 Pb xs ). All particles experienced rapid (<6 h) transport into the upper 2 cm of the seabed resulting from passive deposition down burrows or extremely rapid bioturbation. Intense bioturbation on 4-d time scales included both biodiffusive and nondiffusive (bioadvective and nonlocal) transport. Bioturbation of tracers exhibited time (or age) dependence in two ways: (1) Diffusive mixing intensity for all tracer types decreased with time (4-d D b = 293 cm 2 y -1 , D b at 520 d = 2.6 cm 2 y -1 ), and (2) The nature of bioturbation changed over this period with more efficient bioadvection and nonlocal exchange giving way to slower diffusive mixing. Both changes are consistent with the age-dependent-mixing hypothesis. Biodiffusive mixing was not measurably selective, with no significant preference for a single particle type. In contrast, nondiffusive transport, likely caused by deposit-feeding cirratulid polychaetes, exhibited distinct particle selectivity, especially over 4-d time scales, with the diatom tracer transported most rapidly to depth. Degradation of the labile organic carbon in diatoms most likely led to decreasing selection of diatoms by deposit feeders until diatoms and old sediment particles experienced comparable mixing intensities.}, number={1}, journal={JOURNAL OF MARINE RESEARCH}, author={Fornes, WL and DeMaster, DJ and Smith, CR}, year={2001}, month={Jan}, pages={97–112} }