Toward an Understanding of Earth System Evolution: Japan National Science Plan for the Integrated Ocean Drilling Program

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2 Toward an Understanding of Earth System Evolution: Japan National Science Plan for the Integrated Ocean Drilling Program OD21 Science Advisory Committee January 2003 Contents: 1. Introduction 2. IODP Science Plan led by Japan 2-1 Mantle processes and Earth system evolution (1) Mantle processes during the Cretaceous period (2) Climate changes from Cretaceous to Cenozoic 2-2 Crustal processes and Earth system evolution (1) Formation of continental crust (2) Formation of oceanic lithosphere (3) Linkage of continent, ocean, and atmosphere in the marginal seas and continental slopes of Asia 2-3 Dynamics and mass circulation in subduction zones and Earth system evolution (1) Carbon cycle and the deep biosphere in accretionary prisms (2) Carbon circulation in accretionary prisms and mechanisms of great earthquakes (3) Biology of microorganisms living in deep accretionary prism environments 2-4 Long-term borehole monitoring 2-5 Strategy for deep biosphere research

3 Toward an Understanding of Earth System Evolution: Japan National Science Plan for the Integrated Ocean Drilling Program OD21 Science Advisory Committee January Introduction In this day and age, people recognize the finite nature of the Earth and seek guidance in planning for the future. One important issue that we must tackle is to understand the nature of Earth system evolution and its relationship to human society. Ocean drilling is the most effective method for addressing this emergent issue (Fig. 1). Scientific ocean drilling began in 1968 as the Deep Sea Drilling Project (DSDP) and then continued with the International Phase of Ocean Drilling (IPOD) and the Ocean Drilling Program (ODP). Scientific ocean drilling now faces a new stage as the Integrated Ocean Drilling Program (IODP) starts in October IODP will operate two types of drilling platform: the Japanese riser drilling vessel "Chikyu"; a riser-less drilling vessel to be provided by the United States; and possibly a third-type of mission-specific platforms to be provided by European countries. Ocean drilling has confirmed the theory of plate tectonics, reconstructed past changes in Earth environments, and recognized the importance of the deep biosphere. Based on these results, significant and fundamental progress in the understanding of the status of changes in the global Earth system, the fundamental causes of these changes, and the interactions between subsystems will be made, and a new view of the Earth will be created in the IODP phase (Fig. 1). Potential scientific targets using riser drilling and associated technical problems were discussed at the Conference on Cooperative Ocean Riser Drilling (CONCORD) held in Tokyo in In addition, the scientific plans for the riser-less drilling vessel were established at the international Conference on Multiple Platform Exploration (COMPLEX) in Vancouver in 1999, and for mission-specific drilling platforms at the international Alternate Platform Conference (APLACON) in Lisbon in The results of these conferences were discussed by the IODP Planning Sub-Committee and incorporated in the IODP Initial Science Plan. The IODP scientific themes are as follows. The Deep Biosphere and the Subseafloor Ocean - Exploring the Deep Biosphere - Nature and Distribution of Gas Hydrates Environmental Change, Processes and Effects - Internal Forcing of Environmental Change - External Forcing of Environmental Change - Environmental Change Induced by Internal and External Processes Solid Earth Cycles and Geodynamics - Formation of Rifted Continental Margins, Oceanic LIPs and Oceanic Lithosphere - Recycling of Lithosphere Into the Deeper Mantle and Formation of Continental Crust - Seismogenic Zone - 1 -

4 Japan is expected to undertake a central role in the accomplishments of the IODP. Therefore, it is important to identify the scientific themes of the Initial Science Plan on which Japanese scientists can be expected to exert the greatest efforts. The science planning working group of the OD21 Science Advisory Committee investigated the Japanese science plan and presents this report on the scientific targets for the Japanese IODP. This science plan is a blueprint for Japanese scientists to participate proactively in IODP, based on the IODP principles, and to develop drilling proposals that will gain broad international support. This document describes what the Japanese science community should achieve, and highlights selected science targets that have a large body of achievements by Japanese researchers. This science plan should be revised as needed, to reflect the collective consensus of the Japanese science community. -2-

5 2-1. Mantle processes and Earth system evolution Many Earth subsystems experienced episodes of substantial change during the mid Cretaceous Period. Several perturbations such as global warming, active volcanism, mantle plume generation, a magnetic superchron, and oceanic anoxic events occurred simultaneously. Therefore, a comprehensive study of the dynamics of the Earth system during the mid-cretaceous greenhouse period is required for understanding the evolution of the Earth system throughout its history and for predicting future changes. By contrast, the formation of ice sheets and global cooling during the Cenozoic Era can be recognized as a transitional process from a greenhouse to the present icehouse environment. Therefore, the cooling process may provide important information for understanding global warming processes. Consequently, we propose two major targets led by Japan in the IODP. Understanding core-mantle processes, by deep drilling into a large oceanic plateau in the western Pacific, and Detailed investigation of material circulation during greenhouse Earth, and the transitional process from greenhouse to icehouse environments, by drilling Cretaceous to Cenozoic sediments in the Pacific. (1) Mantle processes during the Cretaceous period A large oceanic plateau in the western Pacific was formed by magmatic activity about 100 Ma in the South Pacific, where a mantle mega-plume is currently upwelling. The activity of the mantle plume that formed this oceanic plateau possibly had a large impact on the evolution and fluctuations of the Earth system. To understand comprehensively the Cretaceous mantle activity and its influences on the evolution and fluctuations of the Earth system, an outstanding target fot scientific drilling would be the Ontong Java Plateau, the largest plateau in the western Pacific (Fig. 2). To understand the origin and circulation of the mantle plume and to reconstruct mantle evolution, we will analyze the internal structure of the mantle plume based on petrochemical characterization of basaltic rock samples from the large plateau. We will also use these samples to quantitatively estimate the temporal changes in the flux of volatile elements from Earth s interior to the surface, and to evaluate the mantle effects on the formation of the greenhouse Earth. To conduct our drilling research effectively, we are planning the following pre-drilling studies. 1) Integrated research of the geology, petrology, and geophysics of the Ontong Java Plateau and Solomon Islands. 2) Integrated research of the seismology, electromagnetics, petrology, and geochemistry of the hot-spot region in the South Pacific. 3) Development and operation of simulation technology to quantitatively understand the interactions between Earth sub-systems. 4) Integrated research on geomagnetic fluctuations during the Cretaceous nonreversal mode using paleomagnetism, submarine magnetic anomalies, and numerical simulations of the geomagnetic dynamo

6 (2) Climate changes from Cretaceous to Cenozoic The western Pacific is the only place in the world where ocean drilling can provide comprehensive analyses of paleoenvironments in the Mesozoic to Cenozoic Eras. The Cretaceous Period is characterized by various global events, such as a much warmer greenhouse environment, upwelling of a large mantle plume, global deposition of black shale, a magnetic superchron, and formation of subsiding coral reefs. To understand the causes of these various events in each subsystem is one of the most important targets of Earth science. We consider the following research in IODP are important, using continuous sedimentary samples cored by riser drilling: Paleoenvironmental characterization of continuous sedimentary sections recovered from the Pacific region and investigation of the interrelationship of black shale formation, age and course of coral reef subsidence, sea-level changes, and ocean circulation. Detailed paleoenvironmental analyses of sediments recovered from large oceanic plateaus, reconstruction of Earth system activity before and after the formation of the plateau, and investigation of the relationship between mantle activity and the response of the Earth system. Investigation of the mechanism of Cenozoic cooling, especially the roles of the North Pacific and surrounding continents. Comprehensive and detailed investigation of paleoenvironmental changes, carbon and nitrogen circulation, and paleontological evolution, using continuous sediments from the Jurassic to the Cenozoic in age. -4-

7 To conduct our drilling research effectively, we are planning the following pre-drilling studies. Detailed survey and analysis of black shale in the Shimanto Belt Analogue research on modern anoxic areas of the ocean Establishment of high-resolution continuous stratigraphic sections of the Mesozoic-Cenozoic strata in the continental margins and marginal seas of East Asia 2-2. Crustal process and Earth system evolution The crust has played an important role in the evolutionary processes of the Earth system. For example, andesitic continental crust acts as a reservoir for light elements in the solid Earth system. To understand the evolution and differentiation of the solid Earth system, it is important to understand the fundamental processes of continental and oceanic crust formation. Oceanic crust, which is removed into the deep Earth, has had strong effects on mass circulation and chemical evolution in the mantle. The continents also, have made a range of contributions to surface environmental changes. For example, the continents have modified the circulation of chemical elements related to biological activities, and continental margins act as an organic sink in the Earth system. In addition, continental topography can modify atmospheric circulation, and sediments deposited in marginal seas may record the effects. To understand the role of the crust in the evolution of the Earth system, we propose the following three research fields to be led by Japan: Understanding the process of continental crust formation by deep drilling into oceanic arcs, Understanding the process of oceanic lithosphere formation by deep drilling of a bacarc spreading system, and Understanding of continent-ocean-atmosphere linkage, by drilling in the marginal seas and continental slopes of Asia. (1) Formation of continental crust The formation of andesite in the middle crust of oceanic arcs was recently indicated by geophysical experiments in the Izu-Bonin Arc (Fig. 3). This moderately mature arc is therefore, an excellent place to understand the process of active continental crust formation. We believe our strength lies in leading the following research in IODP. Examine the possibility that andesitic middle crust in oceanic arcs is essentially generated from basaltic magma, by investigating the petrogenetic relationship of lower, middle and upper crust material. To clarify the process of continental crust formation through drilling in the Izu-Bonin Arc, we propose the following pre-drilling projects. A detailed geophysical survey in the northern Izu-Bonin-Mariana Arc, where middle crust is well developed

8 An examination of the petrogenesis of andesitic plutonic rocks by on-land geology and drilling in the northern Izu-Bonin-Mariana Arc. Laboratory experiments of crustal re-melting processes in high-temperature and high-pressure environments to clarify the generation of felsic magma. An investigation of the origin of andesitic magma in the northern Japan Arc. (2) Formation of oceanic lithosphere From the perspective of a comparative study of oceanic lithosphere, we identify the following research as an important IODP target to be led by Japan: Characterization of lithosphere material recovered from continuous drilling of backarc basin crust: Investigation of the architecture of backarc crust and its physical and chemical properties compared to ophiolites and mid-ocean ridges. We propose the Japan Sea and Izu-Bonin backarc areas as drilling sites, for the following reasons: Both sites were drilled during the ODP, and the surface structures were well documented. Analyses of magmatism in the associated volcanic arcs (NE Japan and Izu-Bonin Arcs) have provided world- -6-

9 leading achievements. Integrated research of the trench-arc-backarc system can be achieved in conjunction with deep drilling of the arc crust. It will be possible to clarify the influence of spreading rate on the structure and composition of oceanic lithosphere, because the spreading rates of the two systems are quite different (20 cm/yr and 7 cm/yr). To conduct our drilling research effectively, the following pre-drilling studies, led by Japan, are required. Geophysical experiments in southern Izu-Mariana arc and the Japan Sea Integrated research of geology, petrology and geophysics of the Oman Ophiolites, where the process of oceanic lithosphere formation in a backarc spreading system may be well preserved. (3) Linkage of continent, ocean, and atmosphere in the marginal seas and continental slopes of Asia The growth, convergence, and breakup of continents have had great impacts on environmental change in the ocean and atmosphere. To understand the continent-ocean-atmosphere linkage, continuous coring of late- Cenozoic sedimentary sequences deposited in the marginal seas and continental slopes of East Asia is required (Fig. 4). We propose the following two items as selected IODP targets led by Japan. Investigation of the history of ice-sheet development in the northern hemisphere and abrupt climatic changes by drilling in the marginal seas of East Asia. Specifically, 1) formative processes and paleoceanographic changes in the Okhotsk Sea, Japan Sea, East China Sea, and South China Sea, 2) evolution of the Kuroshio and Oyashio Currents, 3) formation of intermediate and deep water in the North Pacific, 4) cooling processes in the Eurasian continent, 5) establishment and evolution of the Asian monsoon and the continent-ocean-atmosphere linkage, will be investigated based on continuous coring and high-resolution analyses. Formation of Himalayan and Tibetan Mountains and understanding the continent-ocean-atmosphere linkage. To understand the monsoon effects on the Earth system, we will reconstruct the uplift of the Himalayan and Tibetan Mountains, the evolution of the Asian and Indian monsoons, and related paleoceanographic changes, by using high-resolution Cretaceous sedimentary sections recovered from the marginal seas and continental slopes of the East Asia and Indian subcontinents. This research requires the following pre-drilling studies led by Japan. Development of new proxies to reconstruct paleoenvironments quantitatively. Improved accuracy of age determinations using isotopes, micropaleontology, and paleomagnetics. Development of model ocean research in the modern analogue environment to develop new paleoenvironmental proxies

10 Development of non-destructive, high-resolution methods for measuring microstructures, chemical composition, mineral distribution, and magnetic properties in drill cores. 2-3 Dynamics and mass circulation in subduction zones and Earth system evolution Subduction zones, where oceanic plates are recycled into the mantle, are the most geologically dynamic areas on the Earth. Essential questions remaining to be solved include: Understanding mass balance, fluid circulation, biological activity, and energy transfer in subduction zones. Understanding the mechanism of crustal deformation in subduction zones. What mechanisms control rock deformation in faults? What is the role of fluids in plate boundary faults? We propose the following research on subduction zones led by Japan: Investigation of the Carbon cycle and the deep biosphere in accretionary prisms, Investigation of the mechanism and cycles of great earthquakes, tectonics, and mass circulation in convergent plate margins, and Biology of extreme microorganisms living in deep accretionary prism environments

11 (1) Carbon cycle and the deep biosphere in accretionary prisms Many energy resource and environmental issues remain to be solved in 21st century. Large amounts of organic carbon are accumulated in forearc basins and continental slopes on the Pacific side of Japan. Gas hydrates, which are drawning attention as a new energy resource, are developed in the formations in those areas. Cold seepage associated with chemo-synthetic biological communities and methane gas, which increase global warming, are observed in the forearc basins and continental slopes. These phenomena strongly suggest that Carbon circulation and deep microbial activities are ongoing, and that generation, accumulation, and dissolution are occurring in accretionary prisms (Fig. 5). In response to the points mentioned above, we propose the following research by riser drilling in the subduction zones along the Japanese Islands: Investigation of mass circulation in accretionary prisms, by transect drilling across the Nankai accretionary prism: Transect drilling across Nankai prism may document the quantity and the distribution of organic materials and microorganisms, and quantify deep microbial activities in the prism. We aim to understand comprehensively, carbon circulation from deposition, dissolution and transportation in accretionary prisms, the generation of hydrates and oils, and the dissolution and recycling of hydrates, and to verify the formative process and hypothesis of oil generation by microorganisms. To conduct our drilling project, the following pre-drilling research led by Japan, is required. 3D shallow seismic imaging of BSR. Estimation of alteration processes and the flux of organic material in the formations. Long-term measurements of fluids and methane flux from the seafloor. Tool development for the long-term monitoring of hydrates. Evaluation of microbial activities related to the generation of methane hydrates. Establishment of research methods for the deep biosphere. Investigation of the relationship between chaotic strata formed by the collapse of hydrate layers and climatic changes

12 (2) Carbon circulation in accretionary prisms and mechanisms of great earthquakes Understanding the mechanisms of earthquake generation and predicting the occurrence of large earthquakes represents a great challenge for mankind in the 21st century. Previous earthquake studies have been based on data from geological records and remote-sensing observations, and have never reached the seismogenic zone itself. With riser drilling, however, we can obtain direct samples for the first time from the area of coupling between continental and oceanic plates, and thus answer many fundamental questions (Fig. 6). The network for geophysical and geodetic observation constructed in Japan currently has the highest quality performance in the world. Also, among the world s subduction zones, the history of earthquakes that have occurred along the Japanese subduction zones is particularly well reconstructed. The Nankai Trough is an especially good target for earthquake research because it has been well documented that the 120-year cyclicity of M8 earthquakes and seismogenic faults are strongly coupled during the inter-seismic period. Moreover, it is notable that modern through to Cretaceous geological records are well preserved in the Nankai accretionary prism. Research objectives for Nankai drilling are: 1) What controls the type of plate coupling in the subduction zone? What energy accumulation causes large earthquakes? Is it possible in theory to predict earthquake magnitudes? 2) How do parameters such as porosity, pore pressure, permeability, chemical processes, physical properties, stress, and strain in a fault zone change the fault properties? What is the mechanism of coupling in faults? To answer the above questions, it is necessary to obtain material from the seismogenic fault zone, which can reveal friction properties and the physical/chemical significance of rupture processes on the faults. It is also

13 important to observe directly the degree of coupling between the plates, the partition of strain energy, and the role of fluids by utilizing in-situ monitoring of stress and strain. Moreover, the integration of data from existing global remote-sensing systems with in-situ monitoring will provide new insights on seismogenic processes. (3) Biology of microorganisms living in deep accretionary prism environments The study of microbial activity in subsurface environments is underway and making good progress. In fact, important information about the origin and evolution of life has been obtained through biological studies of microorganisms in extreme environments (=extremophiles). Since microbes living under the seafloor most likely use specific survival strategies different from those of terrestrial microorganisms, the identification of novel genes, enzymes, and catabolic pathways is expected, and these results will contribute to new biotechnology and industrial applications in the 21st century. From this perspective, we propose to conduct biological research involving the isolation and analysis of new extremophiles from core samples obtained by ocean drilling. Isolation and characterization of extremophiles from below the seafloor Elucidation of cellular dynamic systems in novel extremophiles Isolation of useful extremophiles and elucidation of their functions Utilization of useful functions of extremophiles from below the seafloor

14 2-4. Long-term borehole monitoring In-situ borehole monitoring is an essential method for quantifying and modeling various sub-seafloor processes (Fig. 7). Our abilities to measure seismicity, strain, tilt, fluid pressure, temperature, electro-magnetism, chemistry and microbiological properties should be improved. Furthermore, boreholes should be utilized as subsurface laboratories or incubation systems for microbial cultivation experiments. Such achievements will require significant technological developments. In particular, the development of new downhole tools for high-temperature environments is indispensable for monitoring in deep boreholes, where temperatures can reach C in the seismogenic zone and 400 C in hydrothermal areas. However, current downhole sensors can withstand temperatures of only 180 C. To promote the efficient development of new technology for borehole monitoring, packer and data transmission technology in high-temperature environments should be investigated, and systematic collaboration between scientists and engineers is important. It is also important to explain the necessity of understanding environmental change in the finite Earth. Exploration of physical, chemical, and biological changes in the sub-seafloor ocean that is far removed from our everyday world should be appealing to the public as well as to the science community. 2-5 Strategy for deep biosphere research It is important in Japan for deep biosphere research to play a leading role in IODP from the beginning. Deep biosphere research should focus on the following three topics: How microbial activities relate to environmental formation and change, How microbial activities relate to on-going mass circulation in deep subsurface environments, The effects of deep subsurface environments on microbial evolution. In particular, examination of microbial populations in deep accretionary prism environments and microbial activities related to gas hydrate formation should be emergent subjects. In addition, results from deep-sea hydrothermal vents suggest that research on microbial activity in extreme deep subsurface high temperature environments is one of the most important themes in life science. Mid-ocean ridges, arc-trench systems, and hot spots should therefore, be important drilling targets for the study of biologically active subsurface environments

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16 Editors Hisao Ito Kenji Kato Hiroshi Kitazato Kiyoshi Suyehiro Ryuji Tada Yoshiyuki Tatsumi Senior Research Scientist Institute of Geoscience, National Institute of Advanced Industrial Science and Technology Professor Faculty of Science, Shizuoka University Director IFREE, Japan Marine Science and Technology Center Director Deep Sea Research Department, Japan Marine Science and Technology Center Professor Department of Earth and Planetary Science, University of Tokyo Director IFREE, Japan Marine Science and Technology Center

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