Chair: Colin W. Devey
Working Group Members:
Russia - Georgiy A. Cherkashev
USA - Bernard J. Coakley
USA - Kathleen Crane
France - Olivier Dauteuil
Russia - Vladimir Glebowsky
Iceland - Karl Gronvold
Canada - H. Ruth Jackson
Korea - Young Keun Jin
Germany - Wilfried Jokat
Norway - Yngve Kristoffersen
USA - Peter J. Michael
UK - Neil C. Mitchell
Germany - Hans Albert Roeser
Japan - Hideki Shimamura
Japan - Yoshifumi Nogi
USA - Cindy Lee Van Dover
The goal of this working group was to coordinate planning efforts for mapping and sampling the Arctic Ridges. This group was formed in 1994 and in 2004, fused with the South West Indian Ridge Working Group in 2004 to form the Ultraslow Spreading Ridge Working Group.
2001 - Arctic Working Group Update
The planning for the joint American-German two-ship cruise to the Gakkel Ridge (Arctic Ocean) is entering the final stages. The ships will leave Tromso, Norway in late July for a two-month geophysical/petrological expedition to this previously virtually unstudied ridge (the rationale behind the cruise is outlined in the InterRidge workshop reports). The major aims are to achieve a first-order sampling of a major portion of the ridge and to collect geophysical information relevant to the crustal production processes occurring on this slowest-spreading of all ridges. An overview of the cruise plan is presented in this volume (see page 45). Some information on the petrological aspects of the cruise are available at http://www.mpch-mainz.mpg.de/~geo/Arctic Of further interest to the Arctic Ridge working group are the IODP (successor to ODP, designated starting date October 2003) plans for alternative drilling platforms. There is a strong thrust in Europe (lead, amongst others, by Prof. Jörn Thiede, Alfred-Wegner-Institute for Polar Research, Bremerhaven) to build an ice-breaking drill ship, capable of drilling in the high arctic. This ship could make many fascinating targets of InterRidge significance accessible.
1999 - Arctic Working Group Update
The Arctic Ridges Working group convened a workshop in Hannover, Germany, on 16-17 October 1998 to advance plans to sample and survey the ridge which crosses the Arctic Ocean (formally named the Gakkel Ridge). This workshop was a follow-up to an InterRidge workshop in 1994 during which a series of clear goals for the study of the Gakkel Ridge were drawn up. The aim of the 1998 workshop was to establish a time-frame and methodological approach to achieve at least some of these goals within the next five years. The Gakkel Ridge is of great interest to the InterRidge community for a number of reasons:
# Its spreading rate is appreciably lower than that of any other ridge on Earth.
# In contrast to the slow-spreading Southwest Indian Ridge, for example, ridge offsets on the Gakkel Ridge are rare and spreading is orthogonal.
# The rift valley is extremely deep and appears to be underlain by very thin crust.
# The Gakkel Ridge (and also the Knipovitch Ridge further south) could be the home to unique vent communities due to both the presence of Iceland as a block to migration of hydrothermal-dependent species along the ridge axis into the Arctic and the lack of sedimentation from the surface.
All of these features combine to make the Gakkel Ridge an extremely attractive target for petrological, geophysical, hydrothermal and biological studies. The extreme working conditions presented by the permanent ice cover mean, however, that up to present ridge research here has been restricted mainly to bathymetric mapping from nuclear submarines and some geophysical experiments. The working group«s major priority is to redress this position and facilitate the first sampling and observation programs. This goal has been moved markedly closer through the SCICEX program which has, for the first time, provided bathymetry with sufficient resolution and coverage to make pre-cruise identification of sampling targets possible.
The workshop succeeded in establishing a list of priorities and plans to guide the ridge studies. These are:
# The European end of the Gakkel Ridge (as opposed to the end which abuts the Laptev Sea) should be studied first. The reasons for this are logistical (relatively easy access from the N. Atlantic), diplomatic (international waters), bathymetric (SCICEX has good coverage here) and sedimentologic (the rift valley is apparently relatively sediment-free).
# The Laptev Sea end, in view of its extremely low spreading rates, is interesting in its own right and should remain a high-priority goal. Sampling its volcanics will be a more challenging task both logistically and geologically.
# Two ships will be needed to carry out any reasonable sampling and observational program. Although both ships should have the capability to carry out scientific work, the control of the science plan must be clearly in the hands of one of the vessels.
# Existing technology is sufficient to accomplish most sampling goals in the Arctic, however developments to minimize time in the water would be advantageous and make the program much more cost-effective.
Following the workshop a proposal was submitted by the Alfred-Wegner-Institut, Bremerhaven, Germany to request the Polarstern for 2001 to begin this sampling. International support for the Polarstern cruise in the form of contributions towards charter costs for the second ice-breaker will be essential for the success of this proposal. Other opportunities for continuing the Arctic sampling program will be presented when the icebreaking reseaarch vessel USCG Healy is fully operational in the Arctic, perhaps in 2002.
A workshop report was produced by the InterRidge Office in time for the Fall AGU meeting in December 1998. Copies of this report are available to all interested parties by contacting the InterRidge Office.
Mapping the Gakkel Ridge: SCICEX 98 achievements and plans for SCICEX 99 on the USS Hawkbill
Reprinted from InterRidge News 8.1 (March, 1999)
Bernard Coakley 1 , James R. Cochran 2 , and Margo Edwards 3
1 Department of Geology, Tulane University, New Orleans, LA 70118, USA
2 Lamont-Doherty Earth Observatory, Columbia University, 61 Route 9W, PO Box 1000, Palisades, NY 10964, USA
3 Hawaii Institute of Geophysics, University of Hawaii at Manoa, 2525 Correa Road, Honolulu, HI 96822, USA
Since 1995 the US Navy has provided a Sturgeon-class fast attack submarine for an annual unclassified scientific cruise in the Arctic Ocean. The SCICEX program has utilized the mobility of the submarine, which is independent of surface conditions, to explore this largely unknown ocean basin. Designed to be quiet and stable, the submarine provides an ideal platform for the efficient acquisition of underway sonar data, particularly swath mapping and sub-bottom profiler data. Due to the constraints imposed by the circulating ice pack, this information cannot be efficiently collected by any other means in the Arctic.
In 1996, the Arctic Natural Sciences Program of the National Science Foundation, with support from the Palisades Geophysical Institute, the Geological Survey of Canada and Lamont-Doherty Earth Observatory (LDEO), funded the fabrication of a unique set of active sonar instruments for future SCICEX missions. The Seafloor Characterization and Mapping Pods (SCAMP) includes an Arctic optimized SeaMARCTM type Sidescan Swath Bathymetric Sonar (SSBS), a swept frequency ("chirp") High Resolution Sub-bottom Profiler (HRSP), a Bell BGM-3 gravimeter and a Data Acquisition and Quality Control System (DAQCS). SCAMP is an integrated geophysical data acquisition system for underway mapping of the seafloor derived from proven technologies, optimized for under hull operation on a submarine in ice covered waters. SCAMP was installed and tested on the USS Hawkbill for SCICEX 98.
The Gakkel Ridge is the slowest spreading section of the global mid-ocean ridge system (total rates of 0.6-1.3 cm/yr), an important end-member for the study of magmatic and tectonic processes at ridge. It may be a unique hydrothermal and biological environment as well. Although the development of the Eurasian basin is well-understood in the context of global plate tectonics, we know very little about the morphology, structure, magmatism, petrology or distribution of sediments on the Gakkel Ridge. We have no information on the existence or distribution of magmatic activity, hydrothermal vents or benthic vent communities. To remedy this situation, one of the primary objectives for SCICEX 98 and 99 has been SSBS mapping of the Gakkel Ridge.
Building on work that was done during SCICEX 96 from the USS Pogy (Coakley and Cochran, 1998), approximately 3300 track km of data were collected along axis of the Gakkel Ridge during SCICEX 1998 (Fig. 1) using SCAMP. Two segments of the ridge, totaling about 250 km in length, were mapped out to 50 km on either side of the axis (approximately anomaly 5). One segment from this data set, showing roughly 120 km of data along the axis was shown at Fall 98 AGU (Chayes et al., 1998) and reproduced on the back cover of the recent InterRidge report on the meeting of the Gakkel Ridge working group (Wilson, 1998). In this data, the pattern observed in the 1996 narrow-beam profile data (Coakley and Cochran, 1998) is evident. The ridge axis is quite deep, more than 5000 meters in some locations and segmented by inter-axial highs. The flanks are characterized by a blocky morphology with high relief. There may be persistent asymmetry across the axial zone, but there are no obvious transform offsets.
This quality of the data, collected during the first deployment of the SSBS, is encouraging. Additional processing is underway at the University of Hawaii to elimnate artifacts in the grid shown last fall.
There were also some problems with the SSBS hardware during SCICEX 98, which prevented acquisition of the starboard-side data and may have diminished the quality of the port side data as well. Dale Chayes from LDEO spent much of early January working on these problems, identifying the primary cause as flooding in four of the 10 sub-arrays that make up the transducer arrays of the SSBS. Repositioning two of the failed sub-arrays into the fore and aft positions in the transducer pod to maintain the weight distribution and pod fairing results in a slight reduction in transmit power and along-track resolution, compared to the design specifications for the SSBS. Data collected off Hawaii during a recent shakedown cruise demonstrate that the repair of the SSBS was successful. We expect to have very good swath bathymetry and backscatter data to complement the excellent gravity anomaly and HRSP data that will be collected again this year.
The SCICEX 99 cruise, again on the USS Hawkbill , will sail on March 15, 1999 from Pearl Harbor for approximately 40 days of oceanographic and geophysical data acquisition in the deep Arctic Basin. Margo Edwards will be chief scientist. During SCICEX 1999 cruise, we plan to sail along the axis of the Gakkel Ridge east to the edge of the SCICEX operational area to image the youngest seafloor formed at the slowest spreading rates in the submarine's operational area. We also plan to complete the mapping begun during SCICEX 98 further to the west along the ridge axis. This will result in complete coverage of the axial zone in the operational area as well as roughly 600 km of continuous swath mapping data along the faster spreading portions of the ridge to 50 km on either side of the axis. This data will help answer questions about seafloor spreading (Coakley and Cochran, 1998) and magmatism (Reid and Jackson, 1981) at ultra-slow rates as well as providing the basis for planning a proposed cruise for geophysics and seafloor sampling on the German icebreaker Polarstern in 2001.
References
Coakley, B. J., and J. R. Cochran, Gravity Evidence of very thin crust at the Gakkel Ridge (Arctic Ocean), Earth Planet. Sci. Lett., 162, 81-95, 1998. Chayes, D., G. Kurras, M. Edwards, R. Anderson and B. Coakley, Swath Mapping the Arctic Ocean from US Navy Submarines; Installation and Performance Analysis of SCAMP Operations During SCICEX 1998, EOS Trans. AGU, 79, F854, 1998. Reid, I., and H. R Jackson, Oceanic spreading rate and crustal thickness, Mar. Geophys. Res., 5, 165-172, 1981. Wilson, C. (ed.) Mapping and Sampling the Arctic Ridges: A Project Plan. Report from the InterRidge Workshop on Mapping and Sampling the Arctic Ridges held in BGR, Hannover, Germany, Oct. 1998. InterRidge, Paris, 25 pp., 1998. Questions about this instrumentation, known collectively as the SCAMP (Seafloor Characterization and Mapping Package), can be directed to Bernard Coakley at LDEO (bjc@ldeo.columbia.edu or +1 (914) 365-8552). Questions about the SCICEX program and future cruises can be directed to either Odile de la Beaujardiere at the Office of Polar Programs at NSF (odelab@nsf.gov or +1 (703) 306-1033) or Mike Van Woert at the Office of Naval Research (+1 (703) 696-4720)
1998 - October - Arctic Working Group Update
Roland Rihm was no longer able to continue chairing the InterRidge Arctic Ridges working group, and at the InterRidge Steering Committee meeting in September Colin Devey was appointed chair.
InterRidge first formally focussed its attention on the Arctic Ridges when it convened the 1994 workshop entitled "Arctic Ridges: Results and Planning" in Kiel. The aim of this workshop was to collect together as much Arctic ridge data as was available at the time and to initiate dialogue between the many researchers with ridge-related interests north of Iceland. The ensuing workshop report, published in 1997, provided a clear overview of the state of Arctic ridge research at that time and contained several clear recommendations for how Arctic ridge studies should progress. Studying the Gakkel Ridge was identified as the overriding priority, as up until that time it had been the subject of several geophysical studies but had been sampled, both for its rocks and sediments, only rarely. The 1994 workshop recommended that both reconnaissance-scale sampling of rocks, sediments and life forms (30-50 km sample spacing) and further geophysical work be carried out urgently.
InterRidge held another workshop "The Arctic Ridges: Mapping and Sampling" convened by Wilfried Jokat, Peter Michael and Hans Roeser October 16-17, 1998. The objective of the workshop was to formulate clear plans for getting these priority targets fulfilled. To achieve this aim the Workshop began with an update of the state of knowledge, after which participants contributed towards the formulation of clear and practicable plan for studying the Gakkel Ridge, including the identification of research platforms (ships, submarines, aircraft) for carrying out the studies and time windows for their use, the identification of specific experiments that should be conducted, and a clear time-frame in which these goals will be achieved over the next five years. This project plan will be published by the end of November. Hopefully future updates will report on funded or scheduled work on the Gakkel Ridge as a result of this workshop.
1998 - April - Arctic Working Group Update
Last Fall the report from the 1994 InterRidge Arctic Ridges: Results and Planning Workshop held in Kiel was published. This 78 page report summarizes the existing knowledge and data about the Arctic Ridges, and details some of the logistical concerns involved with Arctic research. The major conclusion of the Kiel Workshop was that the Gakkel Ridge should be the highest priority for future geophysical and geochemical studies in the Arctic.
The next step in coordinating international research on the Arctic Ridges is to develop a Program Plan to direct future studies. Towards this aim, there will be an InterRidge workshop on Mapping and Sampling the Arctic Ridges held next October 16-17 in Hannover, Germany. The objectives of this workshop will be twofold - to bring participants up to date on work done since the 1994 workshop, and to draft a Program Plan. Participants will be selected by the organizing committee to include broad representation of different relevant disciplines ranging from biology to geophysics.
Arctic Geophysical Data Acquisition from US Navy Submarines
Reprinted from InterRidge News 5.2 (Fall, 1996)
M. Langseth and B. Coakley
Lamont-Doherty Earth Observatory, Columbia University, Palisades, NY 10964, USA
Since 1993 the US Navy has made a Sturgeon-class nuclear powered attack-submarine available for annual unclassified science cruises to the Arctic Ocean. These cruises have collected water samples and CTD casts from surface stations as well as collecting underway oceanographic and geophysical data across the entire deep Arctic Ocean. Approximately 30,000 km (approximately 20,000 km more should be collected during the cruise of the USS Pogy, which is presently underway) of underway gravity anomaly and narrow beam bottom sounder data have substantially expanded the unclassified database for the Arctic Ocean. Three more cruises in 1997, 1998 and 1999 will complete the planned SCICEX program.
It has been widely recognized that the stability, silence, range and independence from surface conditions render a Sturgeon-class submarine a nearly ideal platform for geophysical measurements. Floating pack ice, which covers most of the Arctic Ocean, restricts or prohibits access to much of the basin. The submarine's independence from surface ice is a particular advantage in the Arctic permitting the first ever systematic bathymetric surveys in the basin.
While the "silent service" has traditionally abhorred active sonar, the Navy has responded to the enthusiasm of the scientific community for additional data from the once-in-a-lifetime opportunity of unrestricted access to the deep Arctic Ocean. Additional instrumentation for future cruises requires funds for study, acquisition, testing and implementation. NSF's Office of Polar Programs supported an initial engineering study last year and has agreed to fund the fabrication and testing of a SeaMARC-type Side-scan Swath Bathymetric Sonar and a Data Acquisition and Quality Control System. In support of NSF's commitment, a private organization, the Palisades Geophysical Institute, is funding acquisition of a chirp, swept-frequency sub-bottom profiler. The transducers for these sonars will be mounted in a instrument "pod" attached to the keel of the submarine. This equipment should be ready for the next SCICEX cruise, which is scheduled to get underway in late July or early August of 1997.
If all goes according to plan, the SCICEX program will collect co-registered backscatter, bathymetry, chirp sub-bottom profiler and gravity anomaly data during the remaining unclassified Arctic cruises. If previous cruises are an indication of what we can expect in the future, the next three cruises in this program will collect approximately 60,000 km of additional underway data and approximately 1,000,000 km2 of swath imagery by the end of the 1999 trip.
Four organizations are collaborating to make these plans a reality. Lamont-Doherty Earth Observatory (LDEO) is acting as lead institution, managing acquisition, integration and testing of the instruments and computer data logging system. Alliant Techsystems of Mukilteo, Washington has been contracted to fabricate the Arctic-optimized SeaMARC-type side-looking sonar. The Hawai'i Mapping Research Group (HMRG) will adapt their software for the MR-1 towed side-looking sonar for the submarine application. The Arctic Submarine Lab (ASL) of San Diego, California is developing a design for the transducer "pod" that will be mounted on the submarine keel and preparing the engineering documentation required by the Navy for this installation. Once completed, LDEO will act as caretaker for the instrumentation, maintaining, repairing and improving it as necessary or desirable. ASL will be responsible for the annual installation and demobilization of the instruments. LDEO and HMRG will operate the system and archive and reduce the data to a consistent standard over the three year life of the program in support of PIs funded under the SCICEX program and for the community at large.
