scientific drilling beneath the oceans solves earthly problems · scientific drilling beneath the...

Scientific drilling beneath the oceans Australian Journal of Maritime and Ocean Affairs (2010) Vol 2(2)

Scientific drilling beneath the oceans solves earthly problems Neville Exon*

Abstract

Australia and New Zealand are partners in the world’s largest international geoscience program, the Integrated Ocean Drilling Program (IODP), which involves both geoscientists and microbiologists. IODP takes sediment and rock cores from as deep as several kilometres below the sea bed, in order to explore how the Earth has worked in the past and how it is working now. Many ocean drilling expeditions have been carried out in our region since the early 1970s and a great amount of fascinating scientific knowledge of global significance has been gained.

______________________________________________

The importance of ocean drilling to a marine audience

The Integrated Ocean Drilling Program (IODP) is a program of exciting science but some parts of that science are of more immediate interest to a general audience than others; of especial interest are the studies of past changes in climate, ocean currents and sea level, which can help us better predict the future. Ocean drilling is complementary to the study of ice cores, which provides information about past atmospheric changes but not oceanic changes, and which is limited to very high latitudes (Antarctica and Greenland), whereas ocean drilling has and is being carried out from the Equator to Antarctica and the Arctic Ocean. The other area of high general interest is the study of natural hazards; the history of volcanic outbursts can inform our understanding of future hazards and the planning for them. The drilling study of the mechanisms of earthquakes associated with oceanic trenches, including instrumenting the fault zones, can help us to better understand how the earthquakes occur and hopefully to help predict them in the long term.

Australia and Marine Science

Australia is a small but influential player in international marine science, including its role within IODP.

* Professor Neville Exon is the Program Scientist in charge of the Australian and New Zealand IODP Office at the Research School of Earth Sciences at the Australian National University in Canberra. He has wide experience in land geology and marine geology and geophysics, and has written successful proposals for and participated in past ocean drilling expeditions. He is also part of the Technical Advisory Group for the new deepwater Australian research vessel The Investigator. He can be contacted at [email protected] or by phone on 02 6125 5131.

We have one of the world’s largest marine jurisdictions (larger than onshore Australia) to study and manage, and marine geoscience plays a key role in both environmental and resource assessment. Australia has present claims to about 14 million km² of offshore territory,1 consisting of 11.65 million km² off Australia that is accepted by the Commission of the Limits of the Continental Shelf, and our Extended Economic Zone off Antarctica of 2.21 million km²; the maximum potential claimable area is about 15 million km². Under the United Nations Convention on the Law of the Sea 1982 arrangements, we need to understand and manage our offshore jurisdiction; the understanding must be based largely on marine science. For this purpose we actually need more scientists than we have, specialised equipment that we do not have, and vessels with capabilities that Australian research agencies do and will not possess. The planned Australia research vessel, The Investigator, will improve our situation considerably but will still not be capable of some important research activities.2 There is a new government emphasis on marine matters as exemplified by recent initiatives such as the recently released A Marine Nation: National Framework for Marine Research and Innovation report.3

1 Philip Symonds, Mark Alcock and Colin French, ‘Setting

Australia’s limits: understanding Australia’s marine jurisdiction’, AUSGEO News 93, March 2009, p. 7, <www.ga.gov.au/image_cache/GA13583.pdf> (26 July 2010).

2 CSIRO media release 09/82, $120 million for new Marine Research Vessel, 12 May 2009, <www.csiro.au/news/New-marine-research-vessel> (26 July 2010).

3 See Australian Government Oceans Policy Science Advisory Group, A Marine Nation: National Framework for Marine Research, Bureau of Meteorology, Melbourne, 2009, <www.opsag.org/pdf/opsag-marine-nation-01.pdf> (26

37


We have natural advantages in marine geoscience because, along with New Zealand, we are probably the major players in the southern hemisphere and are the only IODP members in this hemisphere. Fortunately, international research institutes are already heavily involved in cooperation with Australian groups (government agencies and universities) in the field. It should be noted that there is strong cooperation between geoscience and other disciplines such as physical oceanography and marine biology.

The Nature of Marine Geoscience

Marine geoscience involves examining the nature of the sea bed and the processes shaping it, and the nature and mineral resources of all that lies beneath the sea bed. The nature of the sea bed is of vital importance to the food chain that is based on it and hence to our wild fisheries and aquaculture. The sediments below the sea bed tell us about past environments, and host resources such as petroleum, metallic ore deposits of various types, and sand and gravel that are vital to our future. Offshore petroleum is one of Australia’s largest export earners, and its discovery depends on geoscience.

Much geoscience work involves remote sensing, such as acoustic swath mapping to map the sea bed, reflection seismic profiling to reveal the structures (and by inference, resources) below the sea bed, and the taking of sediment cores to study climate history. It also includes taking sea bed samples on steep slopes where the ancient strata of sedimentary basins are exposed, thus giving us a better understanding of those basins and their petroleum potential.

A completely different field is the study of active and extinct volcanoes in island arcs and adjacent to oceanic trenches, both to better understand them and the hazards they present, and also to study modern gold and copper deposits, not only for their own worth but also to better understand and predict ancient deposits that formed in the ocean but that are now on land.

IODP coring is the ultimate tool to study many of these matters deep below the sea floor. For example, off Japan the hazards from earthquakes are well known and devastating. There, IODP will place geophysical, pressure and chemical sensors in bore

July 2010); and Kate Wilson, Providing a framework for our Marine Nation, Australian Government Oceans Policy Science Advisory Group, <www.opsag.org/powerpoint/ 090617-AmericanChamberOfCommerce-OPSAG-KWilson. ppt> (26 July 2010).

holes across fault zones that generate earthquakes and tsunamis, with the aim of better understanding earthquakes, and ideally predicting them and thus saving untold numbers of human lives. This technology could perhaps be used later west of Sumatra – we all know of the devastating earthquakes and tsunamis generated there.4

What is IODP?

The sediments and rocks beneath the world’s oceans contain a remarkable story of how the Earth works now and has worked in the past, and suggestions about how it may work in the future. Australian geoscientists and microbiologists are involved in studies of cores taken through these sediments and rocks, using the latest technology from the IODP, which is the world’s largest multinational geoscience program.5 The rationale for these studies includes the realisation that the past is often a key to the future of the Earth.

IODP controls drill ships worth roughly US$1 billion, and has an annual working budget of about US$210 million for the United States fiscal year.6 The primary exploration tools are dynamically-positioned Japanese and American coring vessels but, where the primary vessels are not suitable, the European Union through the European Consortium for Ocean Drilling Research (ECORD) charters other coring platforms. The available equipment can take continuous sediment or rock cores in all oceans, in most water depths and up to 5000m below the sea bed. Deepwater drilling has been likened to drilling into the pavement with a string of spaghetti from the top of the Empire State Building.

Onboard ship, an average of 30 scientists and 30 technicians from around the world works around the clock on the cores. They have an array of laboratory and other research equipment aboard the primary vessels that few Australian university departments can match. A single two-month expedition can recover thousands of metres of cores, which keep 30 or more scientists busy for several years. A host of publications appear in the open scientific literature 2-3 years after each expedition, and the IODP’s own scientific reports on expeditions are publicly

4 Phil Cummins and Mark Leonard, ‘The Boxing Day 2004

Tsunami – a repeat of 1833?’, AUSGEO News 77, March 2005, pp. 3-5, <www.ga.gov.au/image_cache/GA6137.pdf> (26 July 2010).

5 See the Integrated Ocean Drilling Program website <www.iodp.org> (2 July 2010).

6 IODP, Annual Program Plan FY2009, pp 7-8, <www.iodp.org/index.php?option=com_docman&task=doc_download&gid=2416> (26 July 2010).

38


Figure 1: Map showing the locations of IODP scientific drilling until mid 2010.

Courtesy H.C. Larsen, IODP-MI

available,7 and an example of a mature publication covers the results of scientific drilling off Tasmania in 2000.8

IODP’s main research fields are:

• Environmental change processes and effects. This covers past rapid climate change and extreme climates, climatic cycles, and the evolution of oceanic currents and boundaries. Ocean drilling has been and will be a key to understanding past climate change on all time scales and at many locations, and hence in helping to predict future climate changes.

• Solid earth cycles and geodynamics. This deals with continental breakup and sedimentary basin formation, which is especially important in petroleum exploration; large igneous provinces like the Kerguelen Plateau southwest

7 See IODP Scientific Publications <www.iodp.org/scientific-publications> (26 July 2010).

8 NF Exon, JP Kennett, MJ Malone (eds), The Cenozoic Southern Ocean: Tectonics, Sedimentation and Climate Change between Australia and Antarctica. American Geophysical Union, Geophysical Monograph Series 151, 2004.

of Australia; drilling to the earth’s mantle; and understanding earthquakes and tsunamis.

• The deep biosphere and ocean floor. ‘Extremophile’ microbes have been shown to live deep beneath the sea floor. In total they have an enormous biomass, and they could be of industrial importance. Accumulations of frozen gas hydrates (largely methane) beneath the sea floor are a huge potential energy resource and their release has been shown to trigger bursts of global warming in the past.9

Studies of past changes in climate and global sea level, and of past volcanic eruptions, are obviously of great immediate societal relevance. In this area the past can illuminate the future. Climate change and sea level rise are pressing issues, and some of the best evidence about past variations and what appears to have driven them comes from ocean drilling cores. Evidence of the size, damage caused by, and frequency of past volcanic eruptions can

9 Integrated Ocean Drilling Program Initial Science Plan, 2003-

2013, Earth, Oceans and Life: Scientific Investigation of the Earth System using Multiple Drilling Platforms and New Technologies, <www.iodp.org/isp> (2 July 2010).

39


Table 1. ANZIC participants on IODP expeditions

Expedition Date Participant

NanTroSeize 1: 316 Nankai Trough Faulting

December 2007 - February 2008

Chris Fergusson (University of Wollongong), sedimentology

PEAT 1: 320 Eastern Pacific environments

5 March - 5 May 2009

Christian Ohneiser (Otago University), palaeomagnetism

Bering Sea: 323 Connections from Pacific to Arctic

5 July - 4 September 2009

Kelsie Dadd (Macquarie University), sedimentology of volcanic ash

Shatsky Rise: 324 Volcanic buildup: NW Pacific

4 September - 4 November 2009

David Murphy (QUT), petrology of volcanics

NanTroSeize 2: 319 Nankai Trough deep observatory

10 May - 31 August 2009

Gary Huftile (QUT), structural geology

NanTroSeize 2: 322 Nankai Trough Subduction

5 September - 10 October 2009

John Moreau (Melbourne University), microbiology

Great Barrier Reef: 325 environmental change caused by post-glacial sea level rise

11 January - 5 March 2010

Jody Webster (Sydney University), Co-Chief Scientist, reef formation

Canterbury Basin: 317 sea level fluctuations in last 20 million years

4 November 2009 - 4 January 2010

Bob Carter (JCU), Simon George (Macquarie), Greg Browne, Martin Crundwell (GNS), Kirsty Tinto (Otago)

Wilkes Land: 318 climate and oceanographic changes in last 53 million years

4 January - 9 March 2010

Kevin Welsh (Queensland) and Robert McKay (Victoria University, Wellington), both sedimentology

South Pacific oceanic gyre microbiology. East of New Zealand

8 October - 12 December 2010

Jill Lynch (Melbourne University), microbiology

Louisville Seamount geodynamics. Southeast of Tonga

12 December 2010 - 11 February 2011

Ben Cohen (Queensland University), volcanic petrology, David Buchs (ANU), volcanic sedimentology

also be found in such cores and used to help predict the future. Although IODP is designed as a program of pure science, a better understanding of the sedimentary sequences of poorly known continental margins is important to the petroleum exploration industry. Previous ocean drilling in the Exmouth Plateau off the Australian northwest shelf, and off Tasmania, has helped companies better understand some aspects of the petroleum potential of these regions, thus better focusing their efforts on petroleum search. Successful petroleum search is in the nation’s interest, because it increases our self sufficiency and decreases our import costs.

IODP coring tests global geoscientific theories that are often developed largely on the basis of remote sensing. New technologies and concepts in geoscience are continuously being developed through IODP. Proposals for drilling are rigorously assessed under intense international competition and

only those that address global problems in particularly suitable areas have any chance of success. The membership of IODP is led by the United States, Japan and Europe, and the other countries involved are Australia, Canada, China, India, New Zealand and the Republic of Korea.

A map showing the location of IODP drilling since 2004 indicates just how geographically widespread were the various expeditions. Before the present phase of ocean drilling ends in 2013, more work will be done in the Pacific, Atlantic and Indian oceans.

The Australian and New Zealand IODP Consortium

Australia and New Zealand form the Australian and New Zealand IODP Consortium (ANZIC), and the two countries have access to all IODP activities including shipboard and post-cruise research,

40


participation in planning committees and groups, and visits from outstanding scientific speakers. The Australian involvement is supported by the Australian Research Council (ARC), 14 universities (Adelaide, ANU, Curtin, James Cook, Macquarie, Melbourne, Monash, Newcastle, Queensland, QUT, Sydney, Tasmania, Western Australia, and Wollongong), CSIRO, ANSTO and AIMS, and MARGO (a marine geoscience peak body). The Australian annual budget is almost $2.2 million, of which the ARC provides $1.55 million.10

Membership of IODP helps Australia and New Zealand maintain our leadership in southern hemisphere marine research. For geographic, climatic, oceanographic and plate tectonic reasons, our region is vital to addressing various global science problems, and some of them cannot be addressed elsewhere. Accordingly, the Australasian region has seen a great deal of ocean drilling since 1968, when the first program was established.11 Although drilling in the Australian region has ended for the time being, our scientists have and will be involved in a variety of expeditions elsewhere in the world, addressing global scientific problems. Australian scientists gain in various ways: through shipboard and post-cruise participation in cutting edge science, by building partnerships with overseas scientists, by being research proponents and co-chief scientists who can steer programs and scientific emphasis, and by early access to key samples and data. Post-doctoral and doctoral students have an opportunity of training in areas of geoscience and microbiology that could not be obtained in any other way.

Early Days: The Deep Sea Drilling Project

Between 1968 and 1983, the Deep Sea Drilling Project (DSDP) began the study of the deep ocean sediments and rocks using the Glomar Challenger. DSDP was funded by the US National Science Foundation but welcomed foreign scientists, including Australians and New Zealanders, to its drilling campaigns. This ship started to build a story about what was happening and had happened in the 70 per cent of the Earth’s crust that lies beneath the oceans. Its major achievements included:

• Drilling and dating the oceanic basalts that form on the sea floor as continents drift apart and are

10 See the Australian Integrated Ocean Drilling Program website <www.iodp.org.au> (2 July 2010).

11 Integrated Ocean Drilling Program Initial Science Plan, 2003-2013, Earth, Oceans and Life: Scientific Investigation of the Earth System using Multiple Drilling Platforms and New Technologies, <www.iodp.org/isp> (2 July 2010).

later covered in sediment, thus contributing greatly to the concept of plate tectonics.

• Proving that the oceanic rocks existing at present have all formed in the last 200 million years, and showing that such rocks are continuously poured out at mid-oceanic ridges and destroyed at oceanic trenches. Continental rocks, by contrast can be billions of years old. Many of these ‘continental rocks’ are, in fact, ancient sedimentary and volcanic rocks that formed in the ocean but have been accreted to the continents.

• Providing a detailed history of the climate and oceanographic changes that have affected the world’s oceans in the last 200 million years.

This was the exploration phase of ocean drilling, with holes being drilled in most parts of the world’s oceans to test existing ideas and also to see what actually was there. A great deal was learned about the volcanic ridges and the intervening sedimentary basins that characterise the sea floor in our region, and about the plate tectonic history of Australia. It was shown that other Gondwanan continents broke away from Australia, starting about 160 million years ago, with Australia moving north from Antarctica in the last 90 million years.

Early Maturity: The Ocean Drilling Program

In 1985, a larger and more capable new drilling vessel, the JOIDES Resolution, replaced the Glomar Challenger in the new Ocean Drilling Program (ODP). This phase of ocean drilling was still largely funded by the United States, but considerable funds were provided by European countries and Japan, and Australia joined as an associate member in a regional consortium in 1988.12 Although scientists from member countries took up most positions on vessels, scientists from countries that were not members, but where drilling was taking place, also participated. Australian scientists were heavily involved both before Australia joined and afterward, and New Zealand scientists were commonly involved near New Zealand although New Zealand was not a member. By the time ODP ended in 2003, there had been 17 two-month expeditions in our region (13 in Australian waters), 71 Australian scientists had participated in expeditions, and 7

12 Elaine Baker and Jock Keene, Full Fathom Five – 15 years of

Australian involvement in the Ocean Drilling Program, WYSIWIG DESIGN, Sydney, 2004.

41


Figure 2: Chikyu at sea. This huge drillship can drill in water 2500m deep, and is designed to take cores up to 6000m below the sea bed.

Australian scientists had acted in the key position of co-chief scientist.13

This was a phase of ocean drilling which aimed to solve global scientific problems, rather than one of curiosity-driven exploration like DSDP. Numerous Australians were proponents of successful proposals and the Australian geoscience research vessel, Rig Seismic, was instrumental in carrying out the detailed site surveys that were essential for successful proposals. When Rig Seismic was disposed of by the Australian Geological Survey Organisation (AGSO) in 1998, Australia no longer had the world-class seismic profiling capability needed for most site survey work.

Maturity: The Integrated Ocean Drilling Program

IODP has access to more drilling platforms than the one that ODP had, but the JOIDES Resolution is still a very important part of the drilling capability, along with the larger and more capable (for some

13 Integrated Ocean Drilling Program Initial Science Plan, 2003-2013, Earth, Oceans and Life: Scientific Investigation of the Earth System using Multiple Drilling Platforms and New Technologies, <www.iodp.org/isp> (2 July 2010).

purposes) Chikyu.14 The Europeans charter specialised drilling vessels for occasional expeditions where neither of the other two vessels has the right capability.15 This means that drilling in the Arctic Ocean and in shallow reefal areas, for example, is now possible.

Recent IODP expeditions: western Pacific Ocean and Southern Ocean

Australians and New Zealanders have recently been involved in various expeditions using three vessels.

In 2009, six Australian scientists and one New Zealander sailed on expeditions in the northern Pacific. An Australian led the microbiological program on an expedition off Japan – the first Australian to sail in this role in the history of ocean drilling. The giant Japanese drillship, Chikyu, has and will be drilling south of Japan to investigate the geology of the oceanic trench where the Pacific Ocean crust is plunging beneath the Japanese islands, causing devastating earthquakes and

14 See American vessel JOIDES Resolution

<http://joidesresolution.org/> (2 July 2010); Japanese information on the drill vessel Chikyu and its program <www.jamstec.go.jp/chikyu/eng/Expedition/NantroSEIZE/index.html> (2 July 2010).

15 See the ECORD website <www.ecord.org> (2 July 2010).

42


resultant tsunamis. A better grasp of the geology, and the installation of seismometers and other analytical instruments deep beneath the seabed, will help scientists understand and perhaps even predict earthquakes.

Figure 3: JOIDES Resolution in Hobart. This drillship can drill in water 6000m deep, and take cores up to 2000m below the sea bed.

The large American drillship, JOIDES Resolution, has recently drilled on two expeditions in our region. The first is studying past climates and global sea level fluctuations over the last 15 million years in the especially suitable Canterbury Basin east of New Zealand. This expedition is described in some detail later.

The second, in the Australian-claimed Wilkes Land region south of Australia off Antarctica, is studying the onset of Antarctic glaciation about 33 million years ago, and the fluctuations in glacial history since then. Senator Kim Carr, Minister for Science and Innovation, visited the JOIDES Resolution in Hobart in March. He made the point that the government strongly supports marine science through its funding for building the new deepwater research vessel, The Investigator, through its support for IODP, and in other ways.16 This expedition is also described in some detail later.

Another drilling expedition has recently used the smaller GreatShip Maya to investigate the history of the 120m sea level rise in the Great Barrier Reef since the last glaciation about 18,000 years ago, and the associated changes in water properties and in the composition of the reef as it migrated landward. It is clear from seabed mapping that from time to time the reef suddenly stepped back westward to a new position, and it is probable that this was caused by a sudden rise in sea level followed by slow rise. Understanding what has happened to the reef as the ocean warmed and sea level rose can surely help us better understand what might happen to the reef in a future warming world.

Canterbury Basin expedition: initial results

The Canterbury Basin Expedition (317), carried out in late 2009 in a sedimentary basin east of New Zealand’s South Island, was designed as one of several ocean drilling expeditions carried out worldwide, to look at the details of how the world’s sea level has varied over many millions of years. The vessel used was the JOIDES Resolution. The co-chief scientists were Craig Fulthorpe from the University of Texas in Austin, and Koichi Hoyanagi

16 Senator the Hon. Kim Carr, Research Ship Arrives with 54-

million-year old climate samples, Media Release, Department of Innovation, Industry, Science and Research, Canberra, 12 March 2010.

of Shinshu University in Japan. Among the scientific party were Bob Carter of James Cook University, Simon George of Macquarie University, George Brown and Martin Crundwell of GNS Science in Wellington, and Kirsti Tinto of Canterbury University. The following text is drawn largely from the Preliminary Report.17

This expedition was devoted to understanding the relative importance of changes in global sea level versus local tectonic (uplift and erosion) and sedimentary processes in controlling continental margin sedimentary cycles. The expedition recovered sediments deposited offshore in the last 35 million years, with a particular focus on the sedimentary cycles of the last 10 million years, when global sea level change was dominated by the waxing and waning of huge ice sheets on Antarctica and, in the last 5 million years, in the northern

17 Integrated Ocean Drilling Program Expedition 317

Preliminary Report: Canterbury Basin sea level, February 2010 <www.iodp.org/preliminary_report/317/317PR.PDF> (2 July 2010).

43


hemisphere. Drilling in the Canterbury Basin takes advantage of high rates of sediment supply, which preserve a high-frequency (0.1-0.5 million years) record of depositional cycles. The applied value of this research is that such sedimentary cycles are related to global sea level changes. The global cycles are used in petroleum exploration to help interpret local cycles seen in seismic reflection profiles (cross-sections through the strata). If the cycles are better understood and better dated, petroleum exploration becomes more efficient.

The expedition results allow the study of the complex interactions of the processes responsible for preserving the sedimentary sequences, in a region where an uplifting and eroding mountain chain (the Southern Alps) provides large volumes of derived sediment, and strong ocean currents erode and deposit those sediments. Currents have locally built large, elongate sediment drifts or wedges. Expedition 317 did not drill into one of these elongate drifts, but currents are inferred to have strongly influenced deposition across the basin, including in locations lacking prominent mounded drifts.

Sedimentary sequences covering the last 10 million years were cored in a transect of three sites on the continental shelf (landward to basinward), and one site on the continental slope. The transect provides a record of depositional cycles across the shallow-water environments that were most directly affected by sea level change. The boundaries of different sedimentary sequences, provisionally correlated with seismic reflectors, have been identified in cores from each site. These help in understanding the origins of sequences identified by seismic profiling, which provide cross-sections through the earth. This record will be used to estimate the timing and amplitude of global sea level change and to document the sedimentary processes that operate during sequence formation. Superb sections through the last 3 million years of sediments will yield high-resolution records of recent glacial cycles in a continental shelf setting.

Continental slope Site U1352 has a complete sedimentary section from modern land-derived sediment to hard marine Eocene limestone, with all the associated sedimentary, biological (fossil), physical, geochemical, and microbiological information. The site also provides a record of ocean circulation and fronts during the last 35 million years. A break in sedimentation about 30 million years ago (the Marshall Paraconformity), was the deepest drilling target of the expedition and is believed to represent intensified current erosion (or non-deposition) associated with the initiation of

thermohaline circulation. This new mode of ocean circulation, caused by a much greater temperature gradient from the equator to the poles, followed the separation of Australia and Antarctica and the freezing of Antarctica. It and the changes in land configuration, largely caused by plate tectonics, drive a very different pattern of ocean currents, the ones with which we are familiar today.

Expedition 317 set a number of technological ocean drilling records:

• The deepest hole drilled in a single expedition and second deepest hole in the history of scientific ocean drilling (Hole U1352C, 1927m).

• The deepest hole drilled by the JOIDES Resolution on a continental shelf (Hole U1351B, 1030m).

• The shallowest water depth for a site drilled by the JOIDES Resolution for scientific purposes (Site U1353, 84.7m water depth).

• The deepest sample taken by scientific ocean drilling for microbiological studies (Site U1352, 1925m).

Expedition 317 supplements previous drilling of sedimentary sequences for sequence stratigraphic and sea level objectives, particularly drilling on the New Jersey margin of America, and in the Bahamas, but includes an expanded Pliocene (2-5 million years old) section. Completion of at least one transect across a geographically and tectonically distinct siliciclastic-dominated (quartz, feldspar and other rock grains) continental margin was the necessary next step in deciphering the strata on this continental margin. Expedition 317 also complements ODP Leg 181, which focused on drift development in deeper water areas of the Eastern New Zealand Oceanic Sedimentary System. Plans are underway for another complementary drilling expedition on the northwest shelf off Australia.18

Wilkes Land expedition: initial results

The full scientific results of the Wilkes Land expedition (318) will not be known for several years, but the following is drawn largely from the Preliminary Report.19

18 See Proposal 667 on the Integrated Ocean Drilling Program

website <www.iodp.org/index.php?option=com_docman& task=doc_download&gid=487> (26 July 2010).

19 Integrated Ocean Drilling Program Expedition 318 Preliminary Report: Wilkes Land Glacial History level, April 2010 <www.iodp.org/preliminary_report/318/318PR.PDF> (2 July 2010).

44


The international team of scientists worked for two months aboard the JOIDES Resolution in early 2010, and took cores of sediments and sedimentary rocks from the seafloor near the coast of Antarctica, at four drill sites. Despite negotiating icebergs, near gale-force winds, and snow and fog, they managed to recover approximately 2000m of sediment core. Wilkes Land lies due south of Australia, and is believed to be one of the more climate-sensitive regions of the polar continent. The new core samples collected during the expedition are unique because they provide a direct record of the waxing and waning of the ice sheet in this region of Antarctica. These sediments preserve the history of how the ice sheets formed and interacted with changes in the climate and the ocean.

In response to growing concerns about our planet’s changing climate, rising global temperatures and sea levels, and increasing concentrations of atmospheric carbon dioxide (CO ), many scientists are looking to Earth’s past to help predict its future. This research expedition will provide critical clues to understanding one of the most dramatic periods of climatic change in Earth’s history – and a glimpse into what might lie far ahead in our climate’s future.

2

The poles control much of our global climate. Giant ice sheets in Antarctica behave like mirrors, reflecting the sun’s energy and moderating the world’s temperatures. The waxing and waning of these ice sheets contribute to changes in sea level and affect ocean circulation, which regulates our climate by transporting heat around the planet. Despite their present cold temperatures, the poles were not always covered with ice. Like a history book, the sediment cores tell the story of how, approximately 53 million years ago, Antarctica had a warm, sub-tropical environment covered in forest. During this same period, known as the ‘greenhouse’ or ‘hothouse’ world, atmospheric CO2 levels were ten times as high as those of today.

Then quite quickly, about 33.5 million years ago, Antarctica’s lush environment changed into an icy realm not much different from the present one. In only 400,000 years – a mere blink of an eye in geologic time – concentrations of atmospheric carbon dioxide decreased greatly. Global temperatures dropped. Ice sheets developed. Antarctica became ice-bound. How did this change happen so abruptly and how stable can we expect ice sheets to be in the future?

Combined, the cores will tell the story of Antarctica’s transition from an ice-free, warm, ‘greenhouse’ world to an ice-covered, cold, dry ‘icehouse’ world. Sediments and microfossils

preserved within the cores will document the onset of cooling and the development of the first Antarctic glaciers and the growth and recession of Antarctica’s ice sheets. Cores from one shallow site contain sediment alternations that can be used like tree rings to sort out environmental changes – alternating bands of light and dark sediment record seasonal variability during the last de-glaciation, which began some 10,000 years ago.20

Understanding the behaviour of Antarctica’s ice sheets plays a fundamental role in our ability to build robust, effective global climate models, which are used to predict future climate. ‘These models rely on constraints imposed by data from the field’, the co-chiefs pointed out. ‘Measurements of parameters such as age, temperature, and carbon dioxide concentration provide invaluable inputs that help increase the accuracy of these models. The more we can constrain the models, the better they’ll perform – and the better we can predict ice sheet behaviour.’

What's next? The science team now embarks on a multi-year process of onshore analyses to further investigate the Wilkes Land cores. Age-dating and chemistry studies among other analyses are expected to resolve changes in Antarctica’s climate over unprecedentedly short timescales (50-20,000 years). Data collected from the expedition will complement previous research from ocean drilling operations conducted elsewhere in the Antarctic over the last 40 years. Together, this research will provide important age constraints for models of Antarctic ice sheet development and evolution, thereby forming the basis for models of future ice sheet behaviour and polar climatic change.

Great Barrier Reef Environmental Change

The Great Barrier Reef Environmental Change (GBREC) Expedition (325) was carried out in early 2010. It used the dynamically positioned drilling vessel, GeatShip Maya, and the program was approved and closely monitored by the Great Barrier Reef Marine Park Authority. The following description is drawn largely from the Scientific Prospectus and a post-cruise scientific press release.21 The expedition was designed to study the


Preliminary Report: Wilkes Land Glacial History level, April 2010 <www.iodp.org/preliminary_report/318/318PR.PDF> (2 July 2010).

21 Integrated Ocean Drilling Program Expedition 325 Scientific Prospectus: covering the Great Barrier Reef Environmental Change expedition, August 2009, <www.publications.iodp.org/scientific_prospectus/325/325SP.pdf> (2 July 2010); and ECORD media release, Great Barrier Reef corals unveil sea-level changes and climate

45


Figure 4: GreatShip Maya in the Great Barrier Reef. This smaller drillship is designed to work in relatively shallow water, and took cores in carbonates in water as shallow as 30m on this expedition. (Photograph courtesy of ECORD).

sea level rise and sea-surface temperature warming since the peak of the last glaciation about 20,000 years ago. This will help our understanding the dynamics of the melting of large ice sheets and what happened as they turned to water. Before this expedition, the only sea level records covering the whole de-glaciation came from offshore drilling of Barbados and Tahitian coral reefs. IODP Expedition 310 (Tahiti Sea Level), which was successfully completed in 2005 and 2006, recovered a near-complete record of sea level change since the last glaciation.22

GBREC was designed to establish the course and effects of the last de-glaciation in a reef setting in a tectonically inactive area. Offshore sites were cored along transects on the Great Barrier Reef.

history, 19 July 2010 <www.ecord.org/p/gbrec-osp_press_release.pdf> (26 July 2010).

22 Integrated Ocean Drilling Program, Tahiti Sea Level: Expedition 310 of the mission-specific drilling platform from and to Papeete, Tahiti, French Polynesia, Sites M0005–M0026, 6 October-16 November 2005, <http://publications.iodp.org/proceedings/310/310title.htm> (26 July 2010).

• The first objective was to reconstruct the de-glaciation curve of sea level rise for the period 20,000 to 10,000 ago in order to establish the minimum sea level during the Last Glacial Maximum and to assess the validity, timing, and amplitude of a number of known glacial meltwater pulses. These are thought to have disturbed the general oceanic circulation, which was driven by temperature and salinity, and hence changed global climate. The meltwater pulses, when ice dams confining great northern hemisphere glacial lakes burst, are also believed to have caused at least three periods of accelerated sea level rise, about 19,000, 13,800 and 11,300 years ago. A series of drowned reef terraces had been identified before the expedition, and those between 120m deep (about 20,000 years ago), and 30m deep (about 10,000 years ago) were cored away from living coral. The terraces presumably correspond to periods of relatively slow sea level rise, with the sudden jumps upslope related to meltwater pulses.

46


design the next ten-year phase of IODP from 2013. Several Australians played key roles at INVEST, and Australia and New Zealand produced a white paper before it. Richard Arculus of ANU is a member of the post-INVEST New Science Plan Writing Committee, as is New Zealander Peter Barrett, showing the scientific regard in which we are held. Chris Yeats of CSIRO is the only representative on a key structural planning group from outside the United States, Japan, and the European IODP consortium. Geoff Garrett, former CSIRO Chief Executive and now Chairman of the ANZIC Governing Council, was on another important committee investigating how well the scientific arrangements in IODP have worked in the last three years, and making suggestions for the future.

• The second objective was to establish the sea-surface temperature variation accompanying the sea’s transgression at each transect. These data will allow the researchers to examine the impact of sea level changes on reef growth, geometry, and biological makeup, especially during reef drowning events, and will help improve the modelling of reef development.

• The third major objective was to identify and establish patterns of short-term paleoclimatic changes that are thought to have punctuated the transitional period between present-day climatic conditions following the Last Glacial Maximum. It is proposed to quantify the variations of sea-surface temperatures using high-resolution isotopic and trace element analyses on massive coral colonies. When possible, the researchers will try to identify specific climatic phenomena such as El Niño-Southern Oscillation in the time frame prior to 10,000 years ago.23

At a recent meeting in Cambridge, California, the Science Plan Writing Committee decided on the tentative titles for four overarching themes for the next phase of ocean drilling:

The cores from the expedition were sampled in July 2010 in Bremen, Germany, and detailed scientific work is to start now. Enough is already known of the cores to suggest that much of the planned science will be achieved. The post-cruise scientific press release, produced after the sampling program, stated that cores had come from 34 holes in three key locations on the outer edge of the Great Barrier Reef.24 Altogether 225m of material were recovered, including 191m of fossil coral reef whose age varies from 30,000 to 9000 years.

• Earth's Climate Systems: Extremes, Linkages and Sensitivity.

• The Crust below the Ocean: Window to the Inner Earth.

• Limits of Life: Deep Life, Extreme Environments and External Forcing.

• Earth in Motion: Sub-seafloor Observatories.

Ocean drilling has proved hugely successful in revealing past and present Earth processes, and there is a strong drive to continue this work in existing and new directions. The aim is to have a new ten-year plan in existence when IODP terminates in 2013. Australian and New Zealand science has profited greatly from ocean drilling, and the geoscientists and microbiologists who have been involved in the work thus far are dedicated and enthusiastic supporters of our continuation in the future program.

Future Plans for Ocean Drilling

Ocean drilling will continue in the South Pacific Ocean east of New Zealand late this year and early next year. Then the JOIDES Resolution will move away eastward from our region, but return to the Indian Ocean until the present phase of ocean drilling ends in 2013. The Chikyu will continue to drill in the Japanese region, and an alternative platform may be used to drill ancient and deeply drowned Hawaiian reefs next year.

In September 2009, there was a very large scientific meeting (INVEST) in Germany, which started to


Scientific Prospectus: covering the Great Barrier Reef Environmental Change expedition, August 2009, <www.publications.iodp.org/scientific_prospectus/325/325SP.pdf> (2 July 2010).

24 ECORD media release, Great Barrier Reef corals unveil sea-level changes and climate history, 19 July 2010 <www.ecord.org/p/gbrec-osp_press_release.pdf> (26 July 2010).

47

scientific drilling beneath the oceans solves earthly problems · scientific drilling beneath the...

Documents