HR: 1330h
AN: B12B-0779    [PDF]
TI: The MICROBE (Microcosm Investigation of Carbonate Reef/Ocean Microbial Biogeochemistry \& Ecology) Project
AU: * Hannides, A K
EM: hannides@hawaii.edu
AF: Department of Oceanography, University of Hawai`i, 1000 Pope Road, Marine Sciences Building, Honolulu, HI 96822 United States
AU: Gaidos, E J
EM: gaidos@hawaii.edu
AF: Department of Geology and Geophysics, University of Hawai`i, 1680 East-West Road, Honolulu, HI 96822 United States
AU: Sansone, F J
EM: sansone@soest.hawaii.edu
AF: Department of Oceanography, University of Hawai`i, 1000 Pope Road, Marine Sciences Building, Honolulu, HI 96822 United States
AB: We present a methodology to manipulate carbonate reef sediments in order to study the geochemical and microbiological response of reef systems to perturbations. We specifically plan to study the effects of changes in the atmospheric partial pressure of CO$_{2}$. Our laboratory set-up will consist of cores containing carbonate reef sediments and overlying water. These microcosms are designed to replicate the gross hydraulic and geochemical characteristics of sediments in a natural tropical reef patch. This is achieved by reproducing the advective transport of water and particulates in and out of the sediments induced by tides and surface waves. Seawater from nearby reefs is to be introduced into the cores with reversible peristaltic pumps. The pumps will vary the overlying water column and simulate the changes in hydrostatic head that accompany waves and tides. The parameters characterizing these oscillations will be set at values reflecting those at nearby natural settings. Sediment column characteristics will be determined non-destructively through openings at various depths down the sediment cores. These openings are fitted with rubber septa and shut-off valves, which allow gas-tight sampling of porewaters. An additional set of openings allows for the removal of small amounts of sediments using augers. Our porewater analyses will include dissolved O$_{2}$, CO$_{2}$, CH$_{4}$ and alkalinity, ammonium, sulfide, and iron and manganese ions. Our solid phase analyses will include carbonate composition and framework structure, and iron and manganese abundances in the carbonate phases. We will measure microbial abundance in porewater and the sediment particles by DAPI cell counts and will assay community composition using Denaturing Gradient Gel Electrophoresis (DGGE). Our goal is to use this methodology to observe and record carbonate precipitation and dissolution by microbiota under varying carbon dioxide regimes. pCO$_{2}$ concentrations will be manipulated by bubbling a N$_{2}$/CO$_{2}$ mixture through the overlying water column and will be regulated by a CO$_{2}$ detector connected to the column's head space. Settings will reflect a range of concentrations between pre-industrial (280 ppmv) and predicted future (700 ppmv) levels. Analyses and observations in microcosms exposed to different carbon dioxide levels will be crucial in elucidating the impact of the on-going carbon dioxide increase in the atmosphere on carbonate dissolution and precipitation in coral reef sediments during early diagenesis. Our prediction is that increased pCO$_{2}$ will lead to a decreased efficiency of recycling of organic matter and nutrients in a reef, lower productivity and, potentially, attenuated reef biodiversity.
DE: 0315 Biosphere/atmosphere interactions
DE: 1050 Marine geochemistry (4835, 4850)
DE: 4805 Biogeochemical cycles (1615)
DE: 4806 Carbon cycling
DE: 4840 Microbiology
SC: Biogeosciences [B]
MN: 2003 Fall Meeting