TY - JOUR
T1 - Organic carbon accumulation and preservation in surface sediments on the Peru margin
AU - Arthur, Michael A.
AU - Dean, Walter E.
AU - Laarkamp, Kirsten
N1 - Funding Information:
We gratefully acknowledge the captain and crew of the R/V Seward Johnson and the pilots and crew of the DS/V Johnson Sealink II for their outstanding support during the 1992 Peru expedition (SJ 1092). We thank Lisa Pratt and Tim Lyons for thoughtful reviews of an earlier draft of this paper, and Tim Lyons and Kay-Christian Emeis for reviews of this manuscript. This research was supported by NOAA-NURP and NSF OCE 9014801 (Arthur) and by the USGS Global Change Program (Dean). K. Laarkamp participated in the research as an undergraduate at Penn State University.
PY - 1998/11/16
Y1 - 1998/11/16
N2 - Concentrations and characteristics of organic matter in surface sediments deposited under an intense oxygen-minimum zone on the Peru margin were studied in samples from deck-deployed box cores and push cores acquired by submersible on two transects spanning depths of 75 to 1000 m at 12°and 13.5°S. The source of organic matter to the seafloor in these areas is almost entirely marine material as confirmed by the narrow range of δ13C of organic carbon obtained in the present study (-20.3 to -21.6‰; PDB) and the lack of any relationship between pyrolysis hydrogen index and carbon isotope composition. Organic carbon contents are highest (up to 16%) on the slope at depths between 75 and 350 m in sediments deposited under intermediate water masses with low dissolved oxygen concentrations (< 5 μmol/kg). Even at these low concentrations of dissolved oxygen, however, the surface sediments that were recovered from these depths are dominantly unlaminated. Strong currents (up to 30 cm/s) associated with the poleward-flowing Peru Undercurrent were measured at depths between 160 and 300 m on both transects. The seafloor in this range of water depths is characterized by bedforms stabilized by bacterial mats, extensive authigenic mineral crusts, and (or) thick organic flocs. Constant advection of dissolved oxygen, although in low concentrations, active resuspension of surficial organic matter, activity of organisms, and transport of fine-grained sediment to and from more oxygenated zones all contribute to greater degradation and poorer initial preservation of organic matter than might be expected under oxygen-deficient conditions. Dissolved-oxygen concentrations ultimately may be the dominant affect on organic matter characteristics, but reworking of fine-grained sediment and organic matter by strong bottom currents and redeposition on the seafloor in areas of lower energy also exert important controls on organic carbon concentration and degree of oxidation in this region.
AB - Concentrations and characteristics of organic matter in surface sediments deposited under an intense oxygen-minimum zone on the Peru margin were studied in samples from deck-deployed box cores and push cores acquired by submersible on two transects spanning depths of 75 to 1000 m at 12°and 13.5°S. The source of organic matter to the seafloor in these areas is almost entirely marine material as confirmed by the narrow range of δ13C of organic carbon obtained in the present study (-20.3 to -21.6‰; PDB) and the lack of any relationship between pyrolysis hydrogen index and carbon isotope composition. Organic carbon contents are highest (up to 16%) on the slope at depths between 75 and 350 m in sediments deposited under intermediate water masses with low dissolved oxygen concentrations (< 5 μmol/kg). Even at these low concentrations of dissolved oxygen, however, the surface sediments that were recovered from these depths are dominantly unlaminated. Strong currents (up to 30 cm/s) associated with the poleward-flowing Peru Undercurrent were measured at depths between 160 and 300 m on both transects. The seafloor in this range of water depths is characterized by bedforms stabilized by bacterial mats, extensive authigenic mineral crusts, and (or) thick organic flocs. Constant advection of dissolved oxygen, although in low concentrations, active resuspension of surficial organic matter, activity of organisms, and transport of fine-grained sediment to and from more oxygenated zones all contribute to greater degradation and poorer initial preservation of organic matter than might be expected under oxygen-deficient conditions. Dissolved-oxygen concentrations ultimately may be the dominant affect on organic matter characteristics, but reworking of fine-grained sediment and organic matter by strong bottom currents and redeposition on the seafloor in areas of lower energy also exert important controls on organic carbon concentration and degree of oxidation in this region.
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U2 - 10.1016/S0009-2541(98)00120-X
DO - 10.1016/S0009-2541(98)00120-X
M3 - Article
AN - SCOPUS:0032466112
SN - 0009-2541
VL - 152
SP - 273
EP - 286
JO - Chemical Geology
JF - Chemical Geology
IS - 3-4
ER -
