HR: 1330h
AN: B52B-1037    [PDF]
TI: The Search for Organics ($\delta^{13}$C and $\delta^{15}$N) Throughout a Sub Basement Fossil Soil (Ocean Drilling Program, Leg 197): Implications for Earth/Mars deep subsurface
AU: * Bonaccorsi, R
EM: bonaccor@units.it
AF: University of Trieste - Department of Geological, Environmental and Marine Sciences (DiSGAM), Via E. Weiss, 2, Trieste, 34127 Italy
AB: Detecting organics buried deep beneath the surface of a planet is a fundamental step to constrain the presence and evolution of life on a planet. This is especially true for Mars with barren-life surface owing to extreme settings (UV flux, P atm and T). However, organics and/or viable microbes could still preserved at some deeper locations on Mars [e.g.,1]. This work presents the first nitrogen isotope ($\delta^{15}$N) data for deeply buried Early Tertiary fossil soil Unit (Core 197-1206A-40R; 307.5-309.9 mbsf). They were RCB-cored from the volcanic basement at Site 1206 (Koko Seamount, ~34$\deg$56' N; ~172$\deg$9' E) during the ODP Leg 197 (Emperor Seamounts, north Pacific). These Fe-rich, palagonite-bearing soils were formed on the top of subsiding atolls and subsequently buried by lava flows in a near shore environment {[2]}. Burial rates higher than average subsidence rates ensured the isolation of these fossil soils in a present-day sub-basement setting and their decoupling from the ocean and the atmosphere for likely $>$54 Ma. Leg 197 soils contain very low, but reliable amounts of total organic carbon (TOC=0.01-0.12 %wt, $\pm$ 0.02%, N=36; {[2-3]}). The single fossil soil unit has stable isotope values more negative (i.e., $\delta^{13}$C-org. = $-25.3 \permil$ to $-26.2\permil$;{[4]}) and $\delta^{15}$N-tot = $-9.5\permil$ to $+2.5\permil$ than those of exposed Hawaiian counterparts (i.e., $\delta ^{15}$N-tot = >=0$\permil$ to +8.5$\permil$). This isotopically lighter Ntot could be interpreted as bacterial fractionation throughout the N-cycle either occurred in the past (Early Eocene/Late Paleocene) and changing organic source (C-3, C-4-plants, bacterial) and N-cycle associated processes. However the existing data-set {[2-4]} need to be compared with microbiological data to establish the potential for these soils to serve as a suitable analog for a possible Mars near-surface/deep biosphere. \\ \noindent {[1]}Mancinelli, R.L, 2000. Planet. Space Sci., 48:1035-1043; {[2]} Shipboard Scientific Party, 2002, Proc. ODP, Init. Repts. 197: College Station, TX; {[3]} Bonaccorsi, R., 2002. EOS Trans AGU, 83(47), Fall Meet. Suppl. Abstract;{[4]}Meyers, P.A., 1997. Org. Geochem., 27, 5/6:213-259.
DE: 0400 Biogeosciences
DE: 1040 Isotopic composition/chemistry
DE: 1055 Organic geochemistry
DE: 6225 Mars
DE: 9810 New fields (not classifiable under other headings)
SC: Biogeosciences [B]
MN: 2003 Fall Meeting