A Geochemical Study of Marine Sediments from the Mac. Robertson Shelf, East Antarctica: Initial Results and Palaeoenvironmental Implications

• Main Authors: Sedwick, Peter N., Harris, P. T., Robertson, L. G., McMurtry, G. M., Cremer, M. D., Robinson, P.
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: ODU Digital Commons 1998
• Subjects: Southern Ocean; Weddell Sea; Productivity; Antarctic continental margin; Palaeoenvironmental; Quartenary; Holocene; Geochemistry; Oceanography and Atmospheric Sciences and Meteorology; Paleontology; Sedimentology; Antarctic; East Antarctica; Mac. Robertson Land; The Antarctic; Weddell; Antarc*; Antarctica; Mac Robertson Land
• Online Access: https://digitalcommons.odu.edu/oeas_fac_pubs/141; https://digitalcommons.odu.edu/cgi/viewcontent.cgi?article=1150&context=oeas_fac_pubs

Sediments from the Antarctic continental margin may provide detailed palaeoenvironmental records for Antarctic shelf waters during the late Quaternary. Here we present results from a palaeoenvironmental study of two sediment cores recovered from the continental shelf off Mac. Robertson Land, East Antarctica. These gravity cores were collected approximately 90 km apart from locations on the inner and outer shelf. Both cores are apparently undisturbed sequences of diatom ooze mixed with fine, quartz-rich sand. Core stratigraphies have been established from radiocarbon analyses of bulk organic carbon. Down-core geochemical determinations include the lithogenic components Al and Fe, biogenic components opal and organic carbon, and palaeo-redox proxies Mn, Mo and U. We use the geochemical data to infer past variations in the deposition of biogenic and lithogenic materials, and the radiocarbon dates to estimate average sediment accumulation rates. The Holocene record of the outer-shelf core suggests three episodes of enhanced diatom export production at about 1.8, 3.8 and 5.5 ka BP, as well as less pronounced bloom episodes which occurred over a shorter period. Average sediment accumulation rates at this location range from 13.7 cm ka-1 in the late Pleistocene-early Holocene to 82 cm ka-1 in the late Holocene, and suggest that the inferred episodes of enhanced biogenic production lasted 100- 1000 years. In contrast, data for the inner-shelf core suggest that there has been a roughly constant proportion of biogenic and lithogenic material accumulating during the middle to late Holocene, with a greater proportion of biogenic material relative to the outer shelf. Notably, there is an approximately 7-fold increase in average sediment accumulation rate (from 24.5 to 179 cm ka-1 ) at this inner-shelf location between the middle and late Holocene, with roughly comparable increases in the mass accumulation rates of both biogenic and lithogenic material. This may represent changes in sediment transport processes, or reflect real increases in pelagic sedimentation in this region during the Holocene. Our results suggest quite different sedimentation regimes in these two shelf locations during the middle to late Holocene.