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1 Arctic Ocean Drilling HR Jackson Geological Survey of Canada

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1 Arctic Ocean Drilling HR Jackson Geological Survey of Canada Powered By Docstoc
					                                      Arctic Ocean Drilling

                                           H.R. Jackson
       Geological Survey of Canada Atlantic, Box 1006, Dartmouth, NS, B2Y 4A2 Canada
                                 E-mail: jacksonr@agc.bio.ns.ca




        Deep sea drilling has been done in all the oceans but the Arctic. This is due to the ice
cover that restricts existing scientific drilling platforms and makes collecting seismic profiles
required for site surveys difficult. The principle scientific objectives of Arctic Ocean drilling are
to determine climatic, paleoceanographic and tectonic
evolution. The Arctic Ocean plays a fundamental role
in global climate (NAD, 1992). The sedimentary
record of the Arctic Ocean holds the history of past
climates but only 2% of the Cenozoic record is
represented by core material and less for the Mesozoic
(Fig. 1). The shortage of samples prohibits
understanding of long and short term northern
hemisphere cooling. Knowledge of how climate varied
in the past and predicting future change is of societal
interest.
        A recent proposal to drill on the Lomonosov
Ridge has been selected for external evaluation by the
Ocean Drilling Program (ODP) (Backman et al., 1999).
The principal objectives for the central Arctic Ocean
related to the dynamics of the environment are the
climatic history including the development of ice cover,
the circulation and ventilation of the ocean, and the
sediment flux history.                                        Figure 1. The temporal distribution of
                                                                        core material from the Arctic
        The origin of the central Arctic Ocean is not                   Ocean from NAD (1992).




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understood and particularly the history of its major topographic features the Alpha and
Lomonosov ridges. For the Alpha Ridge, limited information indicates a magmatic origin and
suggests a large igneous province. The adjacent Lomonosov Ridge is interpreted to be a
continental fragment. Its relatively shallow water depths and its accessibility compared to the
Alpha Ridge make it a good target for scientific drilling and the new data acquired on this ridge
will be useful for planning drilling sites in other parts of the Arctic Ocean.
       The Lomonosov Ridge drilling proposal has two objectives related to the dynamics of the
earth’s interior. They are the composition and origin of the pre-Cenozoic bedrock and the rifting
and subsidence history of the ridge. This ridge is 1500 km long and less than 150 km across. If
proven to be continental, it will provide information on the relative strength of continental and
oceanic lithosphere (Backman et al., 1999).
       Recent developments have created circumstances that make drilling possible. Ice
breakers have demonstrated the ability to keep station while drilling in the Arctic Ocean and new
high quality seismic data are available for site selection. Continuous coring using riserless
techniques used by ODP are anticipated. The holes would not need re-entry capability because
an offset drilling strategy with about 200 m deep drill holes is planned. Site surveying in the
Arctic has improved due to strategies that have been developed to enable airgun arrays to be
towed behind ice breakers and the collection of swath bathymetry and high resolutions seismic
profiles from submarines (Rothrock et al., 1999).
       For the Lomonosov Ridge proposal submitted to ODP, a three vessel approach is
presented. A large ice breaker is required to lead the vessels through the ice and to deflect the
ice during drilling. The second ice breaker is the main support for the drilling platform and
would also collect seismic profiles. The third vessel is an ice strengthened drilling platform.
The Swedish Polar Secretariat has committed three weeks of ice breaker support.




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Backman, J., Coakley, B., Edwards, M., Forsberg, R., Jackson, R., Jakobsson, M., Jokat, W.,
   Kristoffersen, K., Mayer, L., and Musatav, E., 1999. Paleoceanographic and tectonic
   Evolution of the Central Arctic Ocean, Ocean Drilling Proposal 533-Full, 19 p.
Nansen Arctic Drilling Program NAD Science Conunittee, 1992. The Arctic Ocean Record:
   Key to Global Change (Initial Science Plan), Polarforschung, 61/1, 1-10.
Rothrock, D., Maslowski, W., Chayes, D., Flato, G., Grebmeier, J., Jackson, R., Sambratto, R.,
   Smethie, W., Steiberger, W., Swift, J., Tarduno, J., and Thorndike, A., 1999. Arctic Ocean
   Science from submersibles - report from the SCICEX 2000 workshop, Proceedings of the
   SCICEX 2000 workshop held at the Airlie convention center, Warrengten, Virginia, 5-9
   October, 1998, 33 p. 2.




Biographical Note
       Ruth Jackson graduated with a B.Sc. from Dalhousie University in l972, a M Sc. from
Durham University in 1978, and a Dr. Philos from the University of Oslo in 1988. She has been
employed at the Geological Survey of Canada since 1972. She has worked on the Arctic Ocean
and its margins. She is involved in producing a series of physiographic, gravity and magnetics
maps along eastern Nunavut. She has also studied the crustal structure of the margins of eastern
Canada and published on the crustal properties of the Gulf of St. Lawrence.




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