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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.


 
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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.
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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).