CAPE-ROBERTS-PROJECT, ANTARCTICA
Prof. Dr. Werner Ehrmann, Dipl.-Geol. Marco
Neumann, Dipl.-Geol. K. Polozek
National Cooperation:
Alfred Wegener Institute for Polar and
Marine Research, Bremerhaven
Leibniz Institute for Applied Geosciences, Hannover
International Cooperation:
The Cape Roberts Science Team consisted
of scientists from USA, Australia, New Zealand, Great Britain, Italy, Netherlands
and Germany.
German Funding of the Project:
Deutsche Forschungsgemeinschaft, Bonn
Alfred Wegener Institute for Polar and Marine
Research, Bremerhaven
|
| Scientific Background:
Antarctica exerts strong control on the
athmospheric and oceanic circulation patterns of the earth. This makes
the Antarctic ice sheet to one of the most important features controlling
the global climate and sea level. Melting of the Antarctic ice would result
in a sea level rise by about 70 m. For a better understanding of processes
and causes responsible for climate and sea level changes, it is therefore
of high importance to reconstruct the glacial history of Antarctica. The
Antarctic data also gain increasing interest for predicting future climatic
trends.
| Drill Core |
CRP-1 (1997)
|
CRP-2 (1998)
|
CRP-3 (1999)
|
Location
Water Depth
Distance to Coast
Sea Ice Thickness
Participant
First Core
Last Core
Penetration
Core Recovery
Depth to First Core
Quaternary + ?Pliocene
Lower Mioc. + Oligocene
Basement (Devonian) |
77.008°S;
163.755°E
153 m
16.0 km
1.6 m
Ehrmann
17. Oktober
24. Oktober
148 m
86 %
15 m
28 m
105
0 m
|
77.006°S; 163.719°E
178 m
14,2 km
2,0 m
Ehrmann, Polozek
16. Oktober
25. November
624 m
94 %
5 m
22 m
597 m
0 m
|
77.011°S; 163.640°E
295 m
11,8 km
2,0 m
Neumann
9. Oktober
19. November
939 m
97 %
2 m
0 m
821 m
116 m
|
Aim of the Project:
The aim of the Cape Roberts Project was
to recover early Tertiary sediments from the continental shelf of McMurdo
Sound, Ross Sea, Antarctica. The geologists from the University of Leipzig
concentrated on reconstructing the Antarctic glacial history, the climate
of the past some 34 million years (my), and the uplift of the Transantarctic
Mountains. For this purpose, the drill cores were described in detail and
sediment samples were investigated with a variety of complementary sedimentological
methods. |
| The
drill rig of the Cape Roberts Project had a weight of 50 tons. It was mounted
some 15 km off the coast, on 2 m thick sea ice over up to 300 m of water.
Note the Transantarctic Mountains in the background. |
Different
types of sediments from a depth of 125 m in CRP-2/2A. Above: relatively
fine-grained sediments; middle: sediments with a coarse ice-rafted component,
below: conglomeratic sediments deposited just in front of the ice. The
sequence documents a 21.5 my old ice advance, with ice coming from the
Transantarctic Mountains and depositing coarse debris at the drill site.
|
Already
in McMurdo Station, Antarctica, samples were taken from the drill cores.
About 1000 samples were investigated by the geologists of the Institute
for Geophysics and Geology at the University of Leipzig.
|
|
| First Results:
The drill cores of the Cape Roberts Project
are important archives containing a wealth of information on environmental
changes. The sediments mirror sea numerous level changes between 34 and
17.5 my, and they document the climatic and glacial history of Antarctica.
The investigations showed that already 34 my ago ice was present in Antarctica,
but that the size and the volume of the ice shield fluctuated strongly
and frequently. However, no indications were found so far that the ice
totally disappeared from Antarctica at any time, or that the ice at least
retreated from the coast. |
Lithology and interpretation
of the sedimentary sequence at CRP-1, with a reconstruction of the relative
position of the ice margin (Cape Roberts Science Team, 1998). |
| The sediments and the organic remains
document a transisition from a cool-temperate climate at 34 my to a subpolar
climate at 25 my and finally to a polar climate. The clay mineral assemblages
indicate chemical weathering under relatively warm and humid conditions
on the Antarctic continent at 34-33 my. Phases with chemical weathering
alternated with phases with physical weathering between 33 and 32 my. Intense
physical weathering began at 32 my and indicates a cool and dry climate
on a largely ice-covered Antarctic continent. The clay minerals indicate
a further deterioration of the climate at c. 29 my. |
Numerous Oligocene
and Miocene ice advances could be reconstructed. Polythermal or temperate
glaciers expanded out form the Transantarctic Mountains towards the drill
site (red dot), occasionally extending beyond. Diamicts accumulated at
the drill site. During phases of ice retreat, most ice was gone apart from
remnants of valley and tidewater glaciers. Icebergs calved into the sea.
Distal glacimarine sediments such as sandstones and mudstones accumulated
at the drill site (Cape Roberts Science Team, 1998).
During ice advances
in the youngest part of the Early Miocene and the Quaternary, most of the
ice masses came from the south, the region of the present-day Ross Ice
Shelf. During the retreat phases the situation resembled that of the Oligocene
and Miocene, although with most of the icebergs now being derived from
the south. |
| The detrital components are derived from
a variety of different source rocks in the hinterland of the drill site.
Debris from the Transantantarctic Mountains is much more abundant than
debris from the volcanic rocks cropping out in the south of McMurdo Sound.
The systematic analysis of the detrital components indicates that already
34 my ago the Transantarctic Mountains probably were almost as high as
today. In the first instance, erosion removed mainly the upper parts of
the Beacon Supergroup and the volcanic rocks of the Ferrar Group. Since
about 24 my erosion products of the basement areas dominate. The change
in the composition therefore documents the gradual incision of the valleys
into the Transantarctic Mountains.
In a depth of 790 m, the drill core CRP-3
penetrated into more than 350 my old sandstones of the Beacon Supergroup.
The sandstones look very similar as those cropping out in the higher parts
of the Transantarctic Mountains, only 50 km away. The difference in altitude
is more than 3000 m and asks for strong vertical displacement accompanying
the formation of the Transantarctic Mountains and the Ross Sea.
The cored sediments also document the history
of the volcanic activity in the McMurdo Sound area and show that volcanism
similar to that of the McMurdo Volcanic Group already started some 25 my
ago, although the oldest outcrops on land are only 19 my old.
Publications:
The project resulted in several publications
on the bulk mineralogy of the sediments and of the composition and distribution
of the clay mineral and heavy mineral fractions (cf. publication list of
the Geology Division of our institute). |
 |
