 Proxy
ice volume records from deep-sea sediments, and studies of glacimarine
and terrestrial sediments and surfaces around the Antarctic
margin have indicated that the present ice sheet has provided
permanent ice cover on East (Greater) Antarctica for the last
15 million years. Prior to this time, however, when planetary
temperatures were 4 to 5ºC warmer, drill cores from the Antarctic
margin indicate that the ice sheet was more dynamic, with large
and possibly frequent variations in size and extent. In addition,
deep-sea oxygen isotope records from 35 to 15 million years
ago show oscillations, commonly on a 40,000 year time scale,
which are regarded as representing variations in ice volume.
These were most likely from the Antarctic ice sheet of the time,
though a direct connection has yet to be established. Oscillations
resulted directly from fluctuations of the ice-sheet margin
have also been inferred from sequences recognised in numerous
seismic records from offshore strata around the Antarctic margin.
However, the timing and scale of these oscillations, and their
effect on the environment (climate, erosional/depositional environment)
remains unknown because a lack of dating and lithological data
from these strata.
 As
part of a joint project with CRP Chief Scientist, Peter Barrett
of Victoria University, GNS scientists Tim Naish and Stuart
Henrys propose to investigate strata from CRP drilling, which
are sited in a location and setting that can resolve these
issues . It is proposed to focus the research on a set of
three of the thicker and more complete sequences (sequences
9, 10 and 11 from 130 to 307 mbsf in CRP-2A) . They have a
total time span of 400,000 years (23.7 to 24.1 Ma including
known unconformities), determined from a combination of radiometric
ages on volcanic ash beds, microfossil biostratigraphy and
magnetostratigraphy.
The study will attempt to increase the detail of textural
analyses and relate them to other core features and trends
through the three sequences. Additionally, the study will
aim to establish the geometry of each sequence by tracing
them for hundreds to thousands of metres in both coast-parallel
and coast-normal directions, and to relate erosional and depositional
features in the seismic records to core features. Finally,
spectral analysis techniques will be used to determine frequency
and magnitude of environmental changes recorded in the drill
hole data, and to separate the role of external (orbital)
and internal (local) forcing mechanisms on ice sheet dynamics
and global sea level.
The outcome of this work will be to characterise the frequency
and style of Antarctic ice margin fluctuations in the distant
and warmer past. When combined with plant microfossil data
for contemporaneous climate on land, the results will be used
to obtain more realistic scenarios for ice sheet behaviour
from regional ice sheet models, and also to test Antarctic-wide
ice sheet models for a warmer planet.
Contact Tim Naish here |
