Marine sediments are a primary reservoir for the long-term storage of organic matter, and the rate of burial and oxidation of this sedimentary organic material help to regulate both atmospheric oxygen and carbon dioxide concentrations. To evaluate the impact of circulating basement fluid on the preservation of deeply buried organic carbon, sedimentary profiles of dissolved and particulate organic carbon (DOC and POC) near the sediment/basement interface were obtained from sediment coring at Site U1363 during Integrated Ocean Drilling Program Expedition 327. Sedimentary DOC increased from 0.25 mM at 1 m below the seawater/sediment interface to a maximum of 0.86 mM at mid-depth (8-11 meters below seafloor [mbsf]), before subsequently decreasing to a minimum of 0.10 mM at the sediment/basement interface (222.7 mbsf). Thus, the oceanic basement appears to be a net sink for sedimentary DOC. Sedimentary DOC and alkalinity profiles were similar and inversely mirror those of sulfate, suggesting that the buildup of DOC in sediment pore water is related to remineralization of sedimentary POC. The sedimentary POC content at Site U1363 ranged from 47 to 391 µmol-C/g, with δ 13 C values from-25.3‰ to-22.4‰. The total particulate nitrogen (PN) content ranged from 4.1 to 32.9 µmol-N/g, with δ 15 N values from 1.8‰ to 7.2‰ and a POC:PN ratio of 12 ± 2 (n = 54). No depthspecific systematic variations in POC, PN, POC:PN ratio, δ 13 C-POC or δ 15 N-PN were detected, and no significant correlations between sedimentary DOC and POC concentrations were observed. Buried particulate organic matter (POM) in the sediment is mobilized to inorganic compounds such as carbon dioxide and ammonium by aerobic and anaerobic respiration and to dissolved organic matter (DOM) by processes including microbial hydrolysis and anoxic fermentation (