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 AÍ and Fe, biogenic components
opal and organic carbon, and palaco-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.
A geochemical study of marine sediments from the Mac. Robertson shelf, East
Antarctica: initial results and palaeoenvironmental implications
