A Plan for pre- and post-2003 Drilling

Prepared by

Tectonics and Climate Program Planning Group
 

 Executive Summary  One of the aims of ocean drilling is to obtain a record of past climate fluctuations and understand the mechanisms responsible for such changes.  A number of studies indicate that changes in solid earth boundary conditions (e.g., orography, continental positions, ridge volume, opening and closing of ocean gateways) may have either contributed directly to climate change or influenced geochemical cycling that influenced atmospheric greenhouse gas levels.  The goal of the Tectonics and Climate Panel is to outline a general strategy for ocean drilling that provides needed information for more refined testing of the role of tectonic changes on climate.

 The Tectonics and Climate Panel identified three main research areas as topics for future concentrated effort:  (1) effects of tectonics on climate (and vice-versa), either directly or through its effect on atmospheric carbon dioxide levels; (2) role of ocean gateways in redistribution of heat and their effect on Cretaceous and Cenozoic climate change; and (3) study of key ridge segments or oceanic plateaus that provide critical information on the role of these features in modifying atmospheric CO2 levels.

 The Tectonics and Climate Panel divided specific recommendations into near-term (pre-2003) and long-term (pre-2003) recommendations, with the rationale being that only a limited number of legs are likely to be drilled before the termination of the present phase of ocean drilling and that full implementation of a plan could not be implemented until (and if) a new phase of drilling commences after 2003.  The Panel views the post-2003 phase element of the plan as contributing to the overall scientific justification for post-2003 drilling.

 With respect to pre-2003 drilling the Panel recommends a number of actions:  (1) drilling in the northern Indian Ocean to better understand the role of Tibetan/Himalayan uplift on climate change; and (2) drilling along the Greenland-Scotland Ridge to test the hypothesis that changes in uplift of the ridge have modulated the production rate of North Atlantic Deep Water.

 With respect to post-2003 drilling the Panel recommends several steps:  (1) continued drilling of the northern Indian Ocean and South and East China Seas to delineate the role of the uplift of the Himalayan/Tibetan Plateau complex on the Asian monsoon, weathering, and atmospheric carbon dioxide levels; (2) study of smaller tectonic provinces (e.g., Taiwan, New Zealand, New Guinea, Alaska) where the effects of climate on tectonics could be better isolated; (3) examination of critical ocean gateways (e.g., Indonesia, Drake Passage, central American isthmus, Arctic gateways) to assess their effect on the world ocean circulation and climate; and (4) drilling of key ridge segments or oceanic plateaus that provide critical information on the role of these features in modifying atmospheric CO2 levels.

 The Panel recommends that highest priorities be given to developing:  (1) a better understanding of the inter-relation between tectonic uplift and climate change, particularly with respect to the Tibetan/Himalayan complex and smaller, isolated terrains;  and (2) drilling legs that advance our understanding of the role of changes in deep water circulation on the global climate, in particular the Drake passage and Indonesian straits. These topics have been chosen as highest priority because previous research indicates a natural extension of present emphases into the future.  However, other targets of opportunity should not be ignored and may eventually supercede the importance of the identified priorities.

 With respect to implementation of the plan the committee considers several modifications from existing ODP policy/drilling:  (1) an emphasis on coordinated multi-leg drilling to develop a comprehensive assessment of the role of the above processes;  (2) further interactions (workshops) with the terrestrial tectonics community to better coordinate uplift-gateway related drilling legs with advances on land geology; (3) potential advances in drilling technology to ensure better retrieval of sediments from fan deposits; and (4) development of new geochemical methods for analyzing the history of carbon dioxide and other trace gas variations

 A.  Brief Scientific Background

 One of the aims of the Ocean Drilling Program is to obtain a record of past climate fluctuations and understand the mechanisms responsible for such changes.  This information is useful for several reasons:

 (1) it provides a valued time perspective on past climate change that can be used as a framework for interpreting future projections of climate change;

 (2) paleoclimate data can provide valued constraints on understanding evolutionary changes and geochemical cycling;

 (3) paleoclimate data can be used to test physical and chemical models of the atmosphere and ocean.  Since some of these same models are used in greenhouse gas predictions for the future, the geological data represents an independent test of the ability of the models to function under extreme changes in boundary conditions.

 B.  Charge

 A number of studies indicate that changes in solid earth boundary conditions (e.g., orography, continental positions, ridge volume, opening and closing of ocean gateways) may have either contributed directly directly to climate change or influenced geochemical cycling that influenced the atmospheric greenhouse gas levels.  The charge of the Tectonics and Climate Panel is to outline a general strategy for ocean drilling that provides needed information for on the interaction between tectonics and climate and to encourage submission of proposals relevant to this problem.

 The Tectonics and Climate Panel divided the goals into near-term (pre-2003) and long-term (pre-2003) goals, with the rationale being that only a limited number of legs are likely to be drilled before the termination of the present phase of ocean drilling and that full implementation of a plan could not be implemented until (and if) a new phase of drilling commences after 2003.  The Panel views the post-2003 phase element of the plan as contributing to the overall scientific justification for post-2003 drilling.
 

 C.  Justifications for Principal Research Areas

 Uplift and Climate.    Over the last ten years there has been considerable discussion about the effects of changes in orography and its effect on atmospheric circulation and CO2 levels.  Uplift of the great Tibetan-Himalayan complex has been a particularly widely discussed topic as to its role with respect to development of the Asian monsoon, late Cenozoic climate change, and atmospheric CO2 levels.  Changes in the American Cordillera and Alpine Complex are also important.  Additional discussions have pointed out that climate change can also affect orography by changing erosion rates.  There are a number of key questions that cannot be fully addressed at the present stage and which warrant further investigations:  (1) the need to pin down more precisely the uplift history of the major orographic provinces; (2) the need to link these changes with climate variations; (3) the need to develop more reliable indices of continental weathering in order to better quantify the effect of uplift on atmospheric CO2 levels; and (4) the need to determine the effects of climate change on tectonic complexes.

 Ocean Gateways.   The opening and closing of major ocean gateways has been a topic of discussion for over twenty years but over the last ten years has been stimulated by observational and modeling studies linking some of these changes with major events in climate and the ocean circulation.  In particular closure of the central American isthmus appears to have contributed significantly to salt buildup in the North Atlantic, which is a necessary precondition for North Atlantic Deep Water (NADW) formation.  Changes along the Greenland-Scotland ridge appear to regulate the passage of these waters in regions of active deep water formation.  Development of an active North Atlantic overturning cell may also have had a profound effect on distribution of sediments in the world ocean.  Opening of the Drake Passage should have had a profound effect on the Antarctic Circumpolar Current and the climate of Antarctica.  Closure of the Indonesian straits may have affected development of the Western Pacific Warm Pool and perhaps the El Nino/Southern Oscillation system. The history of the Bering Passage and its influence on northern hemisphere climate is almost unknown. Despite the recognition that these changes have occurred, in some cases the timing of some these changes has not been precisely determined (e.g., Drake Passage).  In other cases the effect of the tectonic changes on the ocean circulation have not been fully determined.

 Changes in Ocean Plateaus and Ridges.    A topic that has received somewhat less attention but which may be very important for changes in atmospheric CO2 levels involves changes in the volume of ocean ridges and plateaus.  Episodic growth of ocean plateaus, such as the Ontong-Java Plateau in the mid-Cretaceous, can lead to increased CO2 release.  Changes in ridge spreading directions may also affect ocean chemistry and perhaps the paths of bottom currents.   For example, the major plate boundary rearrangements in the early Eocene is the time of warmest Cenozoic climates and  major silica deposition and hydrothermal activity (at least at some sits). The major plate boundary rearrangement at 80-85 Ma  bounds the Laramide orogeny. In order to develop a better understanding of the role of these processes on climate additional drilling is required in some of these provinces.
 
 

 D.  Recommended Actions

 The panel divided its recommendations into pre- and post-2003 drilling.  The rationale for this division is that, given the time frame for processing ODP proposals, only a handful of pre-2003 drilling opportunities are feasible.  Therefore, only two specific recommendatios are made with respect to pre-2003 drilling.  With respect to post-2003 drilling the picture is much different and the panel makes a number of general recommendations, with some specific elaborations where some type of concensus was developed.

 i.  Pre-2003 Drilling

 With respect to pre-2003 drilling the Panel examined a number of proposals now under evaluation by JOI that meet the general goals of the Tectonic and Climate Panel; the Panel also contacted several researchers about possible new contributions.  Based on these activities the Panel recommends two actions on pre-2003 drilling:

 (a) drilling of at least one additional leg in the northern Indian Ocean (Arabian Sea, Bay of Bengal and/or 90 E Ridge).  The uplift history of this region is one of long-standing interest.  Sites close to land could be most directly linked to terrestrial changes but distal sites (e.g., 90 E Ridge) could provide more continuous sections and better stratigraphy at the cost of higher resolution.   Either or both of these legs could also provide information from geochemical proxies directly linking changes in sediment delivery to changes in ocean chemical record (and by extension, perhaps atmospheric CO2).

 (b) drilling along the Greenland-Scotland Ridge to test the hypothesis that changes in uplift of the ridge have modulated the production rate of North Atlantic Deep Water. Modeling studies suggest that closure of the central American isthmus may have allowed a salt buildup in the North Atlantic that is a critical precondition for formation of NADW.  Observational studies suggest pulsations of NADW that appear to be linked to pulses of seafloor spreading and uplift of the Greenland-Scotland Ridge.  These two processes may be linked in the sense that closure of the central American isthmus may be critical for salt buildup, but if the passageway to the Norwegian/Greenland Sea is too restricted, it may not be possible to isolate surface water masses to the point where they cool sufficiently to form deep water masses.

 ii.  Post-2003 Drilling

 With respect to post-2003 drilling the Panel recommends some specific steps in the major identified areas:

 Uplift and Climate  This problem has to be addressed from several angles.  First, more information is needed in piecing together marine-based evidence on the effect of the Himalayan/Tibetan Plateau uplift on the Asian monsoon, weathering, and atmospheric carbon dioxide levels. A great deal of research indicates a significant interconnection between uplift, evolution of the monsoon, and weathering rate changes that might affect atmospheric carbon dioxide levels.  Specific areas of interest involve the northern Indian Ocean, with drilling both proximal and distal to the Indus and Bengal fans, perhaps the Irrawaddy Delta, and drainage basins in the South and East China Seas.   Needed is better quantification of the changes in sedimentation in these fans and their  precise relation to tectonic changes on land, evolution of the monsoon, variations in 87Sr/86Sr, 187Os/186Os, d13C in inorganic and organic carbon, and the relation thereof to inferred changes in atmospheric CO2.

With respect to climate-tectonics interactions, interpreting cause and effect from these amalgamated data from complex terrains can be difficult and ambiguous. There is therefore also the need for process studies that examine several tectonically simple, spatially limited, actively deforming areas. Examples of potential areas for such case studies include New Zealand and Taiwan (perhaps New Guinea and Alaska). The reasons to focus on such areas are several: their Late Cenozoic tectonic development is well known; they have experienced large-scale changes in tectonic rates, topography, and erosion during the past 10 Ma; major sediment-source areas (the mountains) feed directly into the bounding oceans with few intervening sediment traps; and the local climate along these ranges has been strongly influenced by orographic effects, such that there are both spatial and temporal contrasts in climate. Changes in sediment flux,  sediment composition, provenance, water chemistry, patterns of basin subsidence, and styles of sediment deposition will reflect these interactions.
 
 Role of Ocean Gateways    Several  ocean gateways (e.g., Indonesia, Drake Passage, central American isthmus, Arctic) have been identified as important for regulating interocean heat exchange and their effects on climate and patterns of sedimentation.  Specific questions involve narrowing the opening (and deepening) times of the Drake and Australia-Antarctic openings, uplift history of the central American isthmus, variations in the Greenland-Scotland Ridge, changes in the history of the Arctic gateways, and closure history of the Indonesian straits.  Data to determine the depth and flow through the passages would be obtained from sites on either side of the passage or in some cases from more remote regions.  These data would include composition of the planktonic and benthonic assemblages, stable isotopes, degree of carbonate dissolution, and sediment grain sizes.  The passages between the Pacific and Atlantic have been sheltered by island arcs which may have interfered with the circulation.  To understand how the present system has come into existence, one would also have to use information from drillsites in the Caribbean and the Scotia Sea.
 
 History of Ocean Plateaus and Ridge Jumps  New or augmented drilling of selected plateaus/rises may be useful in developing case studies of changes in some key provinces., such as Ontong-Java Plateau, Kerguelen Ridge, and Shatsky Rise.  Areas recording information from times  of major ridge jumps, such as the Early Eocene and Late Cretaceous, may also provide valued information about the relation between these changes, tectonic changes on land, and climate.  Because this latter topic has not been extensively explored, the Panel defers from making specific recommendations as to locations of sites and priorities.

 E.  Priorities

 The Panel recommends that highest priorities be given to developing:  (1) a better understanding of the inter-relation between tectonic uplift and climate change, particularly with respect to the Tibetan/Himalayan complex and smaller, isolated terrains;  and (2) drilling legs that advance our understanding of the role of changes in deep water circulation on the global climate, in particular the Drake passage and Indonesian straits. These topics have been chosen as highest priority because of previous research indicates a natural extension of present emphases into the future.  However, other targets of opportunity should not be ignored and may eventually supercede the importance of the identified priorities.
 

 F.  Implementation

 With respect to implementation of the plan the committee considers several modifications from existing ODP policy/drilling:

 (1) an emphasis on coordinated multi-leg drilling to develop a comprehensive assessment of the role of the above processes;   piecemeal drilling of individual legs will simply not provide the comprehensive information needed to accomplish the goals of future ocean drilling.

 (2) improved coordination between scientists working in the marine and terrestrial realms.  This process can be effected in at least two ways:  (a) holding one or more workshops of a general nature where there is sufficient representation from both disciplines to stimulate increased interactions; (b) a strong recommendation that individual proposals include land researchers as part of a drilling/research team in order to ensure presence of land-based expertise on specific projects.

 (3) potential advances in drilling technology to ensure more complete retrieval of sediments from fan deposits

 (4) development of new geochemical methods for analyzing the history of carbon dioxide variations. At present various proxy CO2 measurements have been used to estimate CO2 variations, but the uncertainties are quite large and there has been little intercomparison of techniques.  In order to determine the effects of tectonics on weathering and CO2 it is essential to develop more accurate estimates of past CO2 fluctuations.
 

END OF DRAFT REPORT