Cape Roberts Project
Between 1997 and 1999, the international Cape Roberts Project (CRP), with the participation of Australia, Germany, Great Britain, the Netherlands, Italy, New Zealand and the USA, drilled up to 1000 m long drill cores to reconstruct the history of the Antarctic glaciation. After preliminary seismic explorations, geophysicists identified the area off Cape Roberts in the Ross Sea at 77 ° 0 ′ 0 ″ E , 163 ° 43 ′ 0 ″ E on the edge of the Transantarctic Mountains as a suitable position . The boreholes were sunk through the 2 m thick sea ice in water depths of 150 to 300 m with a conventional derrick, which was clad against the harsh climate . Three overlapping boreholes reflected the last 34 million years of geological history and glaciation of the Antarctic in a quality that had not been achieved before. The nearby American McMurdo Station and New Zealand's Scott Base served as the logistical and scientific base . The drilling was supplied via the ice with snowmobiles and snowmobiles, and personnel exchanged with helicopters . The logistical costs were approximately four million US dollars .
Germany was represented in this project by the Alfred Wegener Institute , the Federal Institute for Geosciences and Natural Resources and the Institute for Geophysics and Geology, University of Leipzig .
background
The Antarctic is an essential part of the global "climate machine". Today's atmospheric and oceanic circulation patterns, as well as their changes over the course of the Earth's history, are also controlled by the Antarctic ice sheet . Changes in the size and volume of the ice sheet therefore also affect the climate and sea level . Knowledge of the development history of the Antarctic ice sheet is a prerequisite for understanding these processes and thus also for predicting the future. Geology thus provides the geological contribution to the current climate discussion and to the modeling of future developments.
Data of the holes
| drilling | CRP-1 (1997) | CRP-2 (1998) | CRP-3 (1999) |
|---|---|---|---|
| position | 77,008 ° S, 163,755 ° E | 77.006 ° S, 163.719 ° E | 77,011 ° S, 163,640 ° E |
| Water depth | 153 m | 178 m | 295 m |
| Distance to the coast | 16.0 km | 14.2 km | 11.8 km |
| Sea ice thickness | 1.6 m | 2.0 m | 2.0 m |
| Period of drilling | October 17th to October 24th | October 16 to November 25 | October 9th to November 19th |
| Drilling depth | 148 m | 624 m | 939 m |
| Core profit | 86% | 94% | 97% |
aims
The Cape Roberts project aimed with the help of three located stratigraphically overlapping drilling on the Antarctic continental shelf in the Ross Sea in a time frame from the middle Cenozoic ( Eocene - Oligocene transition) sediments to drill. The geological sequence should provide new comprehensive insights into the history of the Antarctic glaciation and the climate of the last 34 million years and help to reconstruct the history of the rise of the Transantarctic Mountains .
Results
The results of the extensive geological investigations of the cores show among other things
- 34–25 mya (million years): Sub-polar climate with tundra-like vegetation; first icebergs calve from glaciers and the growing inland ice. There is no evidence that, after the glaciation began, the ice retreated completely from Antarctica or even from the coast at any time. The sediments and their organic content ( microfossils ) document a change from a cool, temperate climate 34 Ma ago to a subpolar climate 25 million years ago and finally to a polar climate.
- 24–17 mya: colder phase with an already extensive ice sheet
- approx. 24 mya: beginning of today's volcanism in the area of McMurdo Sound ( Mount Erebus )
- approx. 34 mya: The Transantarctic Mountains reached their current height
- 34–17 mya: Lowering of the Victorialand
Clay minerals show chemical weathering under relatively warm and humid conditions in the period 34–33 mya . Between 33 and 32 mya phases with chemical weathering and phases with physical weathering alternated . 32 mya set in intensive physical weathering and indicates a cool, drier climate on a continent that is at least largely ice-covered. Approx. 29 mya there was a further worsening of the climate and weathering conditions.
The detritic components indicate a variety of different delivery rocks in the vicinity of the drilling site. Detritus from the Transantarctic Mountains dominates over detritus from the volcanic rocks in the south of McMurdo Sound . The analysis shows that the Transantarctic Mountains had probably already reached 34 mya almost their present height. However, the erosion initially removed primarily the higher-lying sediments of the Beacon Supergroup and the volcanic rocks of the Ferrar Group. For about 24 mya, erosion products from the basement areas have dominated. The change in the mineral spectrum documents how the valleys in the Transantarctic Mountains deepened.
At a depth of 790 m, CRP-3 encountered sandstones (beacon sandstones) over 350 Ma old , as they can be found today on the peaks of the Transantarctic Mountains, only 50 km away. The difference in altitude of more than 3000 m shows the extent of the vertical movements that accompanied the formation of today's Transantarctic Mountains and the Ross Sea .
The sediments from the boreholes also document the history of volcanic activity in McMurdo Sound and show that volcanism similar to that of the McMurdo Volcanic Group goes back to 25 mya, i.e. much further than outcrops on land show (19 mya).
Numerous ice advances were reconstructed for the Oligocene and the Lower Miocene , in which the ice, coming from East Antarctica , flowed through the Transantarctic Mountains and rested on the subsoil close to or above the drilling position (red point). During these times, diamictite was deposited.
During the Oligocene and Miocene retreats, the ice had retreated into the valleys of the Transantarctic Mountains. Icebergs calved from the glaciers and drifted out into the open sea . Distal glacial marine sediments such as sands , silts and clays were deposited at the drilling site .
During the ice advances of the youngest part of the Lower Miocene and the Quaternary , most of the ice came from the south , from the area of today's Ross Ice Shelf . During the Quaternary withdrawal phases, the situation was similar to that during the Oligocene withdrawal phases, with the difference that now the icebergs almost all came from the south.
photos
|
The approximately 50-ton derrick of the Cape Roberts project. It stood about 15 km off the coast of Antarctica , on sea ice only two meters thick . The drills were up to 300 m deep . The Transantarctic Mountains can be seen in the background . |
The sampling of the drill cores already took place in the McMurdo station in Antarctica. Each flag marks the position of a sample. Around 1000 samples were sent to the Institute for Geophysics and Geology at the University of Leipzig for sedimentological processing . |
Various glacial sediments encountered at a depth of approximately 125 m in core CRP-2 / 2A. Above: relatively fine-grained sediments; Middle: sediments with components transported by icebergs; Below: conglomerate sediments deposited directly in front of an ice mass. The sequence documents an ice advance from the Transantarctic Mountains about 21.5 million years ago, during which the ice deposited coarse erosion products from the mountains. |
Peter Barrett, senior scientist
CRP derrick on the sea ice
Core segments from 900+ m depth (sandstone)
CRP logo
literature
- Peter J. Barrett: Cape Roberts Project - Science Plan . 1998, p. 99ff. ( PDF ; 30 MB).
- Peter J. Barrett, Christopher R. Fielding, Sherwood W. Wise: Initial report on CRP-1, Cape Roberts Project, Antarctica . In: Terra Antartica 5, Heft 1, 1998, pp. 187ff.
- Christopher R. Fielding, MRA Thomson: Studies from the Cape Roberts Project, Ross Sea Antarctica, Initial Report on CRP-2 / 2A . In: Terra Antartica 6, Heft 1/2, 1999, p. 173ff. ( PDF ; 14 MB).
- Peter J. Barrett, M. Sarti, Sherwood W. Wise: Studies from the Cape Roberts Project, Ross Sea, Antarctica, Initial Reports on CRP-3 . In: Terra Antartica 7, Heft 1/2, 2000, pp. 209ff.
- Scientific results were published in articles in the magazine Terra Antartica ( ISSN 1122-8628 ); see volumes 5 (3), 1998, 7 (3 + 4), 2000, and 8 (4), 2001.
- Further articles can be found in international journals, e.g. B. via Cold Regions Bibliography Project (search for "Cape Roberts Project").
- Drill core analysis data are available in the PANGEA database .
- GEO magazine . February 1998 edition, pp. 138–142.
Web links
- Cape Roberts Project, Antarctica (official website)
- Institute for Geophysics and Geology Leipzig (German website)
