Eleven gravity cores (maximum penetration 102 cm) were obtained in December 1977 below the Ross Ice Shelf at Site J9. The sediments proved to be middle Miocene glaciomarine mud. The sediments may reflect a recent grounding of the Ross Ice Shelf which probably resulted in the erosion of the Pliocene-Pleistocene section. The sediment cores contained two lithologic units: an upper, light olive-gray unit from 5 to 20 cm thick, and a lower darker unit.

Concentrations and stable isotope compositions of the total organic carbon were determined for 13 samples in two of the cores. Three samples from the upper unit contained 0.17, 0.18, an 0.19% organic carbon with ^dgr¹³C_PDB compositions of -25.5, -25.3, and -24.3^pmil, respectively. Ten samples from the lower unit contained more than twice as much organic carbon, ranging from 0.35 to 0.46%, and slightly lower ^dgr¹³C_PDB values, ranging from -25.1 to -26.1^pmil. The amounts and isotopic compositions of the organic carbon in these sediments are probably controlled by the relative amounts of kerogen derived by erosion of rocks from the Transantarctic Mountains and organic carbon fixed by photosynthetic organisms in the Miocene ocean.

End_of_Article - Last_Page 779------------