Antarctic Drilling Program

 

Date of this Version

2002

Comments

Published by ANDRILL Science Management Office (SMO), Contribution 1. University of Nebraska–Lincoln, Lincoln, NE. vi+301 pp.

Abstract

ANDRILL (ANtarctic DRILLing) is a multinational initiative with the objectives to recover stratigraphic core records for use in interpreting Antarctica’s climatic, glacial and tectonic history over the past 50 million years and at varying scales of age resolution (0.1 to 100 thousand years [k.y.]). A key motivation of ANDRILL is that the role of the Antarctic cryosphere (ice sheets, ice shelves and sea-ice) in the global climate system is complex and poorly known. Understanding the past history of ice volume variation in Antarctica and associated physical changes in this region is critical to proper assessment of the global climate system and interaction of ice sheets with the ocean, atmosphere and biosphere. High-quality sedimentary archives of past ice sheet behavior have become available recently from the Cape Roberts Project (CRP) (Naish et al., 2001), unfortunately these are too few in number to allow a comprehensive understanding of Antarctica’s influence on global climate. Through the collection of geological data and their input into climate and ice sheet models, the ANDRILL Initiative will address this issue. ANDRILL proposes to drill a portfolio of sites—the McMurdo Sound Portfolio (MSP)—in order to recover critical intervals of Earth’s past climate history, where the dynamic behavior of ice sheets, ice shelves and sea-ice on Antarctica is thought to have influenced global ocean and atmospheric circulation and global sea-level elevation. In doing so, we acknowledge that efforts to understand the role of Antarctic drivers on global climate variability require a fundamental knowledge of Antarctic cryospheric evolution not only in recent times, which is plainly vital, but also for past times when global temperature and atmospheric CO2 were last similar to that which might well be reached by the end of this century.

Limited exposures of Cenozoic strata in Antarctica (due to the ice cover), the low number of stratigraphic drillholes on the continental margin, and the short time that Antarctica has been explored, led geologists to rely on information derived from lower latitude proxy records. The oxygen isotope record from deep-sea cores, and eustatic changes inferred from sequence stratigraphic records on passive continental margins have been leading paradigms for the interpretations regarding Antarctic ice sheet history. However, interpretations based on these proxy records of glacio-eustasy have little direct confirmation from geologic records in Antarctica, and in numerous cases have led to conflicting interpretations (Harwood et al., 1991, 1993; Moriwaki et al., 1992; Wilson, 1995; Miller and Mabin, 1998). The ANDRILL initiative will help to remedy this situation with the recovery of new direct records of Cenozoic strata from locations proximal to the ice sheet that are ideally suited for recording and dating ice sheet oscillations, and associated oceanic and climatic variations. These will contribute to a better understanding of the global climate system and clearer linkage between the high and low latitude records.

The basins ANDRILL will target have been the focus of several drilling projects; the most successful of which have been the Deep Sea Drilling Project (DSDP) (Hayes, Frakes, et al., 1975), Cenozoic Investigations in the Western Ross Sea (CIROS)-1 (Barrett, 1989; Wilson et al., 1998) and the international Cape Roberts Project (CRP)-1, 2/2A, 3 (Cape Roberts Science Team [CRST], 1998a, b, 1999, 2000; Hambrey, et al., 1998; Barrett, et al., 2001). Despite the success of these projects, numerous critical intervals which hold many of the keys to understanding climate evolution in Antarctica, remain uncovered. These missing stratigraphic intervals are to be targeted in the ANDRILL program (Section 5.0). Completion of the ANDRILL targets will provide an unrivalled sedimentary record spanning some 40 m.y., extending from the pre-glacial conditions in the Eocene, through the onset and growth of temperate ice sheets with interglacial/glacial cycles in the Oligocene, to the cold ice sheet of today. Efforts are underway to develop an integrated, high-precision chronostratigraphy for the Antarctic margin and Southern Ocean that will enable linkage of Antarctic events to global records for comparison and identification of drivers in Earth’s Cenozoic system at key time intervals. Most important is societal need to recognize and address potential future climate and sea-level changes, which can be approached through an integrated analysis of geological and historical records from Antarctica within the framework of climate and glacial model testing.

Stratigraphic drilling by the DSDP played a major role in developing modern theories of Earth processes on many fronts, but particularly in establishing plate tectonics as a unifying theme of the geosciences. This initiative continues to enhance our understanding of Earth history through the Ocean Drilling Project (ODP) and the planned Integrated Ocean Drilling Program (IODP, 2001). Other scientific drilling initiatives planned for the Arctic (Nansen Arctic Drilling – NAD) and past Antarctic drilling programs (McKelvey, 1991) such as the Dry Valley Drilling Project (DVDP) (McGinnis, 1981), McMurdo Sound Sediment and Tectonic Studies (MSSTS) (Barrett, 1986), Cenozoic Investigations in the Western Ross Sea (CIROS) (Barrett, 1989; Wilson et al., 1998) and the recently completed Cape Roberts Project–– (CRP International Steering Committee, 1994; Barrett and Davey, 1992; Webb and Wilson, 1995; Davey et al., 2001) will help to bring high-latitude records of Cenozoic climate change into the global picture (Webb, 1990).

Determination of the scale and rapidity of changes affecting large ice masses is of vital importance because (i) icevolume variations lead to changing sea levels, (ii) ice sheets influence sea-ice distribution, Earth’s albedo, and latitudinal climatic gradients, and (iii) ice shelves generate cold bottom-water that ventilate the world’s oceans. General circulation models (GCMs) indicate that the Polar Regions are the most sensitive regions to climatic warming, thus the projected global rise in temperature of 1.4–5.8˚C by 2010 (Intergovernmental Panel on Climate Change, [IPCC], 2001) is likely to be even greater in the Antarctic. In order to validate climatic models, we need to look to archives of climatic change preserved in the ice core record (100,000 year time scale) and in the sedimentary record (10 million year time scale), to determine the relationship between ice sheet fluctuations and climatic change.

ANDRILL proposes to recover sedimentary cores using a drilling rig positioned on the floating fast-ice, ice shelf, or land based sites, using and enhancing the technology employed during the CRP (Fig. 1), which during its last season recovered 98% of a 939 m drillcore at the CRP-3 drillsite. Such high rates of core recovery are in contrast to that of ODP and DSDP (Section 5.0), which are unable to operate efficiently on the Antarctic margin with recovery rates between 6 to 60%. The McMurdo Sound Portfolio (MSP) is the first of a series of portfolios that will be developed to address key questions related to Antarctic geology and global climate issues using this technology. Cruise objectives of DSDP and ODP legs into Antarctic waters highlight science objectives in the Antarctic arena, but have largely been unable to answer key questions because of the poor core recovery inherent in drilling glacigene sediments using current ODP technology.

The development of a better understanding of Antarctic climate and glacial history and this region’s influence on global climate are critical to the science that will result from the new IODP, 2001. ANDRILL will complement and expand the ability for IODP to succeed in its mission. The Shallow Drilling (SHALDRIL) and ANDRILL projects are complementary, with similar goals, but able to reach different stratigraphic targets around the Antarctic margin. A proposed Scientific Committee on Antarctica Research (SCAR) initiative, ACE (Antarctic Climate Evolution [http://www.ace.scar.org//]), will provide an important vehicle to integrate the information gained from these drilling projects and expand their value as data are incorporated into glacial and climate models. The overlapping membership in steering committees that direct these initiatives will help integrate objectives and results obtained from these geological tools. The science program presented in the following chapters continues to develop. It is in line with scientific themes and objectives highlighted in numerous recent workshops and international planning documents (for example: Webb and Wilson, 1995; Webb and Cooper, 1999; Barker et al., 1998; Kristoffersen et al., 2000; Florindo and Cooper, 2001).

This report summarizes the results of the first ANDRILL Workshop, held at Oxford University, UK, from April 5 to 7, 2001. The workshop was attended by thirty-nine scientists and technical experts from seven nations — Australia, Germany, Japan, New Zealand, United Kingdom and United States. The aim of the Workshop was to develop a science plan and organizational structure to best meet the above scientific and societal needs. An ANDRILL consortium has been established, comprising five countries – Germany, Italy, New Zealand, United Kingdom and United States. Other interested nations are welcome to join this initiative.

This Workshop brought together an international team of interested scientists and technical advisors and called for the organization of national workshops and scientific groups, which at the time of this printing have all been completed. The ANDRILL Initiative evolved considerably over the past 2 years since the completion of the final CRP Workshop in Columbus, Ohio (September, 2000), and will continue to evolve and mature. This document reflects ideas and concepts developed at the Oxford Workshop, at subsequent national workshops, and through the efforts of the ANDRILL International Steering Committee (ASC).

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