Cape Roberts Project

The international Cape Roberts Project ( CRP) has drilled in the years 1997 to 1999 with the participation of Australia, Germany, Great Britain, the Netherlands, Italy, New Zealand and the United States up to 1000 m long cores for reconstruction of Antarctic glacial history. Determined according to seismic Vorerkundungen geophysicist as suitable position the area off Cape Roberts in the Ross Sea at 77 ° 0 ' 0 " S, 163 ° 43' 0" E - 77163.71666666667 on the edge of the Transantarctic Mountains. The wells were drilled with a conventional, clad against the harsh climate rig through the 2 m thick sea ice in water depths of 150-300 m. Four overlapping holes reflect the last 34 million years of geological history and Antarctic glaciation in unprecedented quality. As logistical and scientific basis served the nearby U.S. McMurdo Station and New Zealand's Scott Base. Supplying the hole was on the ice with snowmobiles and snow Bullis, exchange of personnel with helicopters. The logistical costs were approximately four million U.S. 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

Antarctica is an essential part of the global " climate machine ". Today's atmospheric and oceanic circulation patterns and their changes in the course of the earth are also controlled by the Antarctic ice sheet. Changes in the size and volume of the ice sheet thus also have an effect on the climate and sea level. A prerequisite for the understanding of these processes and thus to predict future events in the future, knowledge of the history of the Antarctic ice sheet. The geology thus provides the historical contribution to the current debate on climate change and to the modeling of future developments.

Of the drill

Objectives

The Cape Roberts Project aimed with the help of three stratigraphically overlapping holes on the continental shelf in the Ross Sea in Antarctica to erbohren early Tertiary sediments. The geological sequence should provide new comprehensive information about the history of Antarctic glaciation and the climate of the last 34 million years, as well as 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

• 34-25 Ma ( million years): Subpolar climate with tundrenähnlicher vegetation; first icebergs calve from glaciers and the growing ice sheet. There is no evidence that the ice after the ice had begun to have withdrawn at any time again completely from the Antarctic, or even from the coast. The sediments and their organic content ( microfossils ) document a change from a cool - temperate climate before 34 Ma to a subpolar climate before 25 Ma and finally to a polar climate.

• 24-17 Ma: Colder phase with an already extensive overlying ice sheet.
• The current volcanic activity in the area of ​​McMurdo Sound (Mount Erebus ) began about 24 Ma.
• The Transantarctic Mountains reached its present height before 34 Ma.
• The lowering of the Victoria Land conducted in the period 34-17 Ma.

Clay minerals show in the period 34-33 Ma chemical weathering under relatively warm and moist conditions. Between 33 and 32 Ma alternated with phases of chemical weathering and physical weathering phases. 32 Ma ago, began intensive physical weathering and points to a cool, dry climate on a at least largely ice-covered continent. Ma ago, about 29 a further tightening of climate and weathering conditions took place.

The detrital components point to a variety of different delivery rocks in the vicinity of the drill site. Detritus from the Transantarctic Mountains dominates detritus from the volcanic rocks in the south of McMurdo Sound. The analysis shows that the Transantarctic Mountains probably had nearly reached its present height before 34 Ma. However, the erosion distant at first mainly the higher overlying sediments of the Beacon Supergroup and the volcanic rocks of the Ferrar Group. Since about 24 Ma erosion products dominate from the basement areas. The change in the mineral assemblage documented how deepened the valleys in the Transantarctic Mountains.

At a depth of 790 m CRP -3 came across about 350 Ma old sandstones ( Beacon sandstones ), as they can now be found on the tops of just 50 km from the Transantarctic Mountains. The difference in height of more than 3000 m shows the extent of vertical movements that have accompanied the formation of the present-day Transantarctic Mountains and the Ross Sea.

The sediments of the holes also document the history of volcanic activity in the McMurdo Sound and show that volcanism similar to the McMurdo Volcanic Group dates back to 25 Ma, so much further than outcrops on land prove (19 Ma).

For the Oligocene and Miocene bottom numerous ice advances have been reconstructed, where the ice from the East Antarctic Coming flowed through the Transantarctic Mountains and up close to the drilling position (red dot) approach, or over them, lay on the ground. During these times Diamikte were deposited.

During the Oligocene and Miocene retreat phases of the ice had retreated to the valleys of the Transantarctic Mountains into it. From the glaciers calving icebergs and drifted out into the open sea. At the drill site distal glazialmarine sediments such as sands, silts and clays came to deposit.

When the ice advances of the youngest part of the Untermiozäns and the Quaternary, most of the ice from the south came from the area of present-day Ross Ice Shelf. During the retreat quaternary phases, the situation was similar during the Oligocene retreat phases, with the difference that now the icebergs almost all came from the south.

Pictures

The approximately 50 -ton derrick of the Cape Roberts Project. He stood about 15 km off the coast of Antarctica, only two meters thick sea ice. Was drilled in up to 300 m water depth. In the background the Transantarctic Mountains can be seen.

Sampling of the cores was already at McMurdo station in Antarctica instead. Each flag marks the position of a sample. About 1000 samples went to the sedimentological processing at the Institute for Geophysics and Geology, University of Leipzig.

Various glacial sediments that have been encountered at a depth of about 125 m in drill core CRP-2/2A. Above: relatively fine- grained sediments; Middle: iceberg sediments transported components; Below: conglomeratic sediments that were deposited directly in front of a mass of ice. The sequence documents a Eisvorstoß from the Transantarctic Mountains before about 21.5 million years ago, in which the ice was deposited coarse products of erosion from the mountains.

CRP rig on the sea ice

Core segments from 900 m deep (sandstone)

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