Ocean Drilling Research: An Arctic Perspective (1999)

The Polar Research Board, a unit of the National Research Council charged to promote excellence in polar science and enhance understanding of polar regions, is aware that cooperative international scientific efforts for deep-earth sampling in the marine environment conducted under the auspices of the Ocean Drilling Program (ODP) are scheduled to end in October 2003. In spring 1999, there will be a major international conference (Conference on the Scientific Objectives of Ocean Drilling in the 21st Century, to be held in Vancouver, Canada) to examine whether ocean drilling should be continued and, if so, define the scientific objectives that might be accomplished should the program be extended or another program begun. The conference will target the scientific goals for non-riser drilling and will complement a recent conference focused on ocean riser drilling, which defined the scientific initiatives for use of a riser-equipped drilling vessel.

Conference organizers have requested input from the scientific community about the possible objectives, importance, and necessity of a continued drilling program. This report contains comments from the Polar Research Board to provide conference organizers and participants with an arctic perspective. Like the planned conference itself, we address the possible scientific goals of a continued drilling program; we do not address funding or priority-setting, issues that are beyond the scope of this short report. We do recognize that the cost implications of factors such as high operating costs and technology development needs would have to be considered in making a decision to include arctic ocean drilling in any future program.

The Ocean Drilling Program is the direct successor to the Deep Sea Drilling Project (DSDP), which ran from 1968 to 1983. DSDP was the first broad scientific effort to sample the seafloor around the globe by coring and downhole logging, and the research was critical in supporting the then-new hypotheses of seafloor spreading and plate tectonics. Although DSDP began as a U.S. effort, it evolved into an international activity with five partners.² By 1981, when the

DSDP drillship GLOMAR Challenger was reaching the end of its useful life, many of the world's leading earth scientists met to plan the future of ocean drilling and recommended that a new program be formed—the Ocean Drilling Program (ODP). The ODP began in 1985 when the larger and more capable ship JOIDES Resolution was modified to meet the special requirements of scientific ocean drilling. With this capacity, scientists could then drill deeper and into more difficult rock formations and use more sophisticated measuring tools.

Since 1985, the Ocean Drilling Program (ODP) has continued as an international partnership of scientists and research institutions organized to explore the evolution and structure of Earth. Funding for the program is provided by eight international partners representing 21 countries.3 ODP provides researchers around the world access to a vast repository of geological and environmental information recorded far below the ocean surface in seafloor sediments and rocks. This information yields insights that improve our understanding of Earth's past, present, and future (NRC, 1998). As a result of DSDP and ODP activities, thousands of seafloor sites have been occupied and drilled and thousands of kilometers of ocean sediment and crustal samples have been obtained from every major ocean basin except the Arctic Ocean. Interpretation of these samples has provided a record of ocean crustal spreading as well as insights into the origin and history of different ocean basins. In addition, our knowledge of seawater chemistry, marine biology, marine geology, and the origin of submarine structures grew dramatically because of Ocean Drilling Program activities, making this one of the most important oceanographic research projects of the 20th century.

Although it has long been recognized as potentially valuable⁴, technical and logistical difficulties associated with drilling in an ice covered ocean forced the ODP, and the DSDP before it, to exclude the Arctic Ocean. In addition, lack of sound geophysical surveys, crustal maps, and seismic understanding of the Arctic Ocean have made it difficult to select sites for drilling in the north. This exclusion has left a significant gap in our understanding of the world's seafloors and leaves an important reservoir of information about global change untapped. If we wish to understand the character and evolution of the Arctic Ocean⁵, it is

essential to recover a complete sedimentary sequence. As discussed in the next section, drilling in the Arctic could contribute to geophysics, structural geology, and our understanding of plate tectonics, including spreading rates and the onset of spreading at various locations. In addition, biogeochemical based studies of organisms and their products preserved in the sediment can provide proxies for past climate change. Understanding current ecosystem processes influencing the state of biological and biogeochemical proxies in the sediment coincident with analyses of sediment from deep cores from the Arctic Ocean will enable interpretation of past climatic systems that have influenced down core sediment records.

Any justification for the perpetuation of scientific ocean drilling in general should be based at least in part on the need for drilling in the Arctic Ocean. The Arctic Ocean is the last frontier for scientific ocean drilling. It alone of Earth's oceans has never been drilled, and as a consequence has a largely unknown climatologic and geologic history or record. In addition, it contains the largest essentially unexplored geologic feature on Earth, the Alpha-Mendeleyev Ridge system (Weber and Sweeney, 1990). Because of these factors, the relationship of the Arctic Ocean to other Earth structures has never been more than partially understood, and the Arctic Ocean's precise role in Earth's climate and geologic development remains enigmatic.

What we do know about Earth's crust and paleoclimate in the Arctic is limited. Short sediment cores taken from floating ice-islands and, more recently, multi-national icebreakers, have provided a partial view of Arctic Ocean history (Clark et al., 1980; Jackson et al., 1985; Poore et al., 1994; Phillips and Grantz, 1997; Bischof and Darby, 1997). The only information on the older Arctic Ocean is based on four piston cores taken from ice-islands over the Alpha Ridge. Three of these cores recovered Late Cretaceous (Maastrichtian) sediment, while the fourth is Early Cenozoic (middle Eocene). The Cretaceous cores are the oldest indigenous deep Arctic Ocean sediment known and in the absence of any other data, alone define the minimum age of the ocean. These Cretaceous cores consist of biosiliceous as well as organic rich palynomorph-bearing sediment, indicating that the Arctic Ocean of approximately 70 million years ago had no ice-cover and thus was relatively warmer than today (Dell'Agnese and Clark, 1994; Firth and Clark, 1998). In addition, the fossils of these cores indicate that vigorous upwelling conditions existed in at least one part of the Arctic Ocean during the Late Cretaceous (Kitchell and Clark, 1982). The Early Cenozoic core contains a rich biosiliceous sediment and this suggests that the same climate

and upwelling conditions as that of the Late Cretaceous existed during the middle Eocene. From these four cores we can conclude that from at least 73 million years ago to approximately 45 million years ago, the Arctic Ocean was ice-free with high production of algae and other protists nurtured by upwelling, and must have been a major factor in Earth climate.

But how did this “warm” Arctic Ocean form? Was it ice-free throughout the Mesozoic? How was its origin related to that of the modern Pacific and Atlantic oceans? How did the temperature of the Arctic Ocean influence Earth climate during this warm geologic interval? And what were the climatic and oceanographic conditions that have resulted in the present permanent ice-cover? No deep Arctic Ocean sediment older than the Maastrichtian or for the interval of approximately 45 million years to 5 million years has been recovered. From the sedimentary record, we only know that the Arctic Ocean must have formed sometime prior to the Maastrichtian. Geophysical evidence suggests an earlier, perhaps Jurassic age for the Arctic Ocean origin (see geophysical reviews by Grantz et al., 1990, and Lawver and Scotese, 1990). In addition, it was during the Eocene that Earth's warm climate began a dramatic change that has led to the modern climate. What was the Arctic Ocean's role in this important transition? Was the Arctic Ocean involved in the development of Earth's present climate or did it only respond to the change (Alley, 1997)? A sedimentary record of relationship of Earth's climatic and oceanographic history in the Arctic would be invaluable for comparisons and understanding of similar research in the North Atlantic and elsewhere.

Regardless of past interactions between the Arctic Ocean and the World Ocean, modern thermohaline circulation in the North Atlantic is directly affected by Arctic Ocean water and its circulation, and may be the immediate control for major shifts in Earth's modern climate (Broecker and Peng, 1982; Broecker, 1998). Arctic drilling should provide important new insights into the origin and development of modern arctic circulation with its major variations in fresh versus saline-rich water discharge, and the control it has exerted on the “conveyor belt” thermohaline circulation of the World Ocean. Recent studies that indicate dramatic changes in the Arctic's salinity and ice-content (Levi, 1998) can best be understood in the context of the developmental history of the present condition, and this information is available only in the Arctic Ocean sediments.

The origin and evolution of the Arctic Ocean and its contribution to, or control of, Earth's modern climate can be interpreted from the results of Arctic Ocean drilling. For example:

• Knowledge of how and when the Arctic Ocean formed may be determined from a study of systems such as the Alpha-Mendeleyev Ridge system

• Knowledge of Arctic Ocean circulation, venting, and other oceanographic factors may be gained from study of the Lomonosov Ridge, a high standing barrier to oceanic circulation in the Arctic.

Drilling of broad arctic ridges at moderate depth should provide very high-resolution stratigraphic records of arctic oceanographic and climatic history that will address the most fundamental issues of paleoceanographic development of the Arctic Ocean and Earth climate. Such sites would be isolated from the strong turbidite deposition found in all basinal areas in the Arctic, and would be isolated from strong currents that truncate the stratigraphic record on shallower ridge crests, and above the CCD. It is clear that the Arctic, the least studied of Earth's oceans, is key to understanding fundamental aspects of the geologic, oceanographic, and climatic conditions of the modern Earth. Without scientific drilling, an enormous gap in our knowledge of Earth will remain unfilled.

Additional objectives of Arctic Ocean drilling are discussed in the Nansen Arctic Drilling Implementation Plan (1997) and the NSF strategy document, Marine Science in the Arctic (Aagaard, 1999). Any inclusion of Arctic Ocean drilling as part of future scientific ocean drilling should be coordinated with the plans of these projects.

The main obstacles preventing deep ocean drilling at sites in the Arctic have been technical. As noted in a 1991 PRB report (NRC, 1991), even with icebreaker support, existing drill ships (including the ODP's JOIDES Resolution) are not suffciently ice strengthened to maneuver safely within the main polar ice pack. In addition, many potentially important arctic drilling sites are in water greater than 4 km deep. In addition to expense, the semi-continuous movement of the mainly wind-driven ice pack limits drilling in deep water, because it requires continuous coring and with that the necessity of holding position against the drift of the ice pack for significant periods of time. Such methods have been developed for shallow areas of arctic shelves, but are lacking for the deep-water areas of the basin (NRC, 1991).

Now, however, arctic experience suggests that an ice-strengthened ship with a dynamic positioning system to maximize drilling time, in the company of an icebreaker, probably could maintain position in 2-3 m ice for drilling operations, at least in shallower depths. The sites of the oldest known Arctic Ocean sediment on the Alpha Ridge include some in water of less than 1500m. In addition, submersible drilling rigs similar to the Russian GNPP Sevmorgeo might be usable in the Arctic Ocean (Nansen Arctic Drilling Implementation Plan, 1997). Also, new technology is being developed by some of our Scandinavian colleagues which could be available sometime early in the 21st Century, in time for a new scientific ocean drilling program. This includes drilling in maximum water depth with anticipated sub-bottom penetration. If there is a commitment to Arctic Ocean drilling as part of any new scientific ocean drilling program, the technology should be available to accomplish many important objectives. For example, the new USCGC Healy will be available for support of deep Arctic Ocean drilling after 2001. Also, it has an announced potential to recover 30m

piston cores, which, if true, is a good example of developing technology that will benefit deep Arctic Ocean drilling.

Another problem is related to the fact that deep ocean drilling commonly is preceded by site surveys that identify the optimum locations for meeting the drilling objectives. Such surveys still are lacking in the Arctic Ocean basin, although some recent bathymetric data may be available from the Navy. While traditional methods of site surveys would be difficult in an ice-covered ocean, alternatives are now available. For example, the geophysical capabilities of the Submarine Ice Experiment (SCICEX) provide a novel but effective means of survey, if the program is continued. More important, seabed coring performed during the past 20 years from the various ice-platforms (T-3, CESAR, LOREX icebreakers) has recovered sediment cores that can provide much of the information necessary for site selection. From the previous piston coring, we know four sites where there is little Cenozoic sediment cover and would be ideal for coring Cretaceous and older sediment to the crust. From the short 3-4 m sediment cores (more than 500 of which are available from the T-3 project alone and at least 150 more from U.S. icebreakers), we also have learned the general sedimentary facies that will be encountered in Arctic Ocean drilling. These include the basinal turbidite facies, generally at depths in excess of 3000m, the Cenozoic glacial-marine sediment facies, common at depths of 1000 to 3000 m on most of the Arctic Ocean ridges, and the mixed facies, common in the Eurasian Basin but also including some of the Chukchi Cap sediment. This information could be considered as preliminary site surveys. The scientific case for Arctic Ocean drilling is so compelling that it should proceed in spite of less than perfect site survey information.

The Polar Research Board believes that the continuation of an organized international program of scientific drilling is valuable because it will continue to provide important insights about Earth's past, present, and future. If such a program is continued, we recommend that it include drill sites in the Arctic Ocean. These would help us understand the origin, age, and history of the only ocean not included in previous drilling programs and fill significant gaps in our knowledge of Earth's ocean basins. This knowledge is critical to understanding the role of the Arctic Ocean in Earth's tectonic evolution, especially its involvement in the structural evolution of the North Atlantic and North Pacific Oceans. In addition, the role of the Arctic Ocean in the evolution of Earth's climate needs better definition in relationship to both thermohaline circulation in the North Atlantic-Arctic Ocean transition area and the climatic impact of an alternately ice-free and ice-covered Arctic Ocean.

Researchers drilling at Arctic Ocean sites will face challenging conditions, but recent technological developments, the considerable experience gained in shallow coring in the Arctic, and advances that are likely in the next few years

can provide solutions to many of these problems if there is an international commitment to the task. Much has changed in the past few decades since the GLOMAR Challenger, with icebreaker support, ventured into the high southern latitudes to drill on Antarctica's continental shelf. There is more knowledge of the pack ice because of satellite photography, new technologies and drilling platforms, and even evidence of thinning of the pack ice. The geopolitical and national security climate has changed as well, with great relevance to the Arctic. This combination of factors strengthens the case for incorporating some Arctic Ocean drilling into any new program that might evolve.