In support of efforts to establish an extended continental shelf under the auspices of the Law of the Sea Treaty, the United States and other nations have been collecting high-resolution multibeam sonar data in many previously unmapped regions of the Arctic., The U.S. has conducted eight dedicated mapping cruises since 2003 (four in collaboration with Canada) in the mostly ice-covered waters north of Alaska as far north as 83.5o N (Mayer et al., 2010) using the USCG Icebreaker HEALY equipped with a 12-kHz multibeam sonar. Given the generally heavy ice conditions in this region (the ice-edge was typically encountered at about 75o N), most of the surveys involved single multibeam swaths that cover specific targets relevant to a Law of the Sea submission (e.g., the 2500-m isobath or the foot of the slope). During the 2012 record-setting ice minimum, however, we found the ice margin at about 80oN that left large areas of open water available for mapping using more traditional overlapping multibeam survey techniques (Mayer and Armstrong, 2012). The complete coverage surveys carried out during 2012 revealed a remarkable, previously unknown submarine channel (informally named “Weather Channel”), most likely, the northern-most submarine channel ever mapped.

Description

The channel is approximately 160 km long, first appearing at a depth of about 3300 m on a relatively flat basin floor in what is most likely a pull-apart basin that separates the northern extension of Chukchi Rise from Chukchi Cap (Brumley et al., 2009). The channel lies in the middle of the basin approximately 13 km north of the base of Chukchi Cap and 9 km south of the topographic highs of the northern extension of Chukchi Rise (Fig. 1a and c). The bathymetry rises on both the north and the south to depths as shallow as 2750 m approximately 60 km north of the channel and depths of 2600 m 45 km to the south (Fig. 1a and c). The area where the channel is first seen is approximately 110 km east of the base of the Mendeleev Ridge (also at a depth of approximately 3250 m) and about 240 km east of the top of Mendeleev Ridge with a depth of approximately 1600 m. The channel appears to drain to the east with an average gradient of 0.18˚ over the 160 km that the channel can be traced to its exit into an embayment of Canada Basin at a depth of approximately 3800 m. The channel is incised only 10 m deep where first mapped in the eastern portion of the pull-apart basin but deepens to the west to a maximum depth of more than 80 m deeper than the surrounding seafloor about mid-way between the head of the channel and its termination in Canada Basin. The incision of the channel then decreases from its deepest point to its termination in Canada Basin (Fig 1a and c).  The channel consists of three relatively linear segments, the first approximately 90 km long that trends 112o, the second approximately 50 km long that trends 070o, and a 20 km long third segment that trends 038o with a number of small tributaries and bifurcations.  In some areas, a bifurcation creates a double channel (Figs. 1a and c). The channel flanks are typically asymmetric with the southern flank typically significantly shoaler (20 to 100 m) than the northern flank (Fig. 1c).

Interpretation

Submarine channels have been mapped worldwide although many questions still remain about their origin and evolution (Wynn et al., 2007). These channels are the primary conduits of density-driven sediment flows across continental margins that build submarine fans. Sediment is typically supplied by river input or margin-failure processes; in high latitudes, a number of glacial processes can lead to flows, including meltwater outbursts (Piper and Normak, 2009) and hyperpycnal flows resulting from sea-ice formation (Dowdeswell, et al., 2002). For the most part, submarine channels run down-dip across the continental slope and follow the trend of maximum downslope gradient. However, the “Weather Channel” runs orthogonal to the proximal steep relief to the north and south of it and transits at least 160 km over a gradient of less than 0.18˚, raising the question of where is the source (or sources) of the flow(s) that created the channel?  Given the general east-west orientation of the channel, a source for the channel on Mendeleev Ridge might be implied.  However, the first appearance of the channel is approximately 240 km from the top of the ridge and 110 km from its base.  Although multibeam sonar data are sparse in this area (and collected with an older system with less resolution than the system used in 2012 and in sometimes heavy ice conditions), there is no indication of a channel that connects Mendeleev Ridge to Weather Channel (Fig. 1c). Several tributary channels are seen that come from the south but still no connection can be found to the bathymetric highs of Chukchi Cap (Figs. 1a and c). Using extreme vertical exaggeration and strong sun-illumination, a very small (5 to 10 m deep, less than 500 m wide) channel is seen that flows south from the bathymetric high north of the basin and connects into the main channel (Fig. 1d). Although this shows a connection to the main channel, it is located well to the east (downstream) of first appearance of the channel. It may very well be that connecting channels exist but that they are just below the resolution of the multibeam sonar. Given the limited data available, we propose that small turbidity currents that flow off bathymetric highs on both the north and the south of channel are fed to the center of the basin and then are bathymetrically constrained, particularly by the large sediment lobe at the base of Chukchi Cap (Fig. 1a).  The implication is that the large asymmetry seen in the channel (Fig. 1a) is not so much the result of levee building but rather indicative of a bathymetric feature that constrained flows. Whether or not there are also sources on Mendeleev Ridge will have to await more detailed surveys.

References

BRUMLEY, K., MAYER, L.A., COAKLEY, B., & MILLER, E.L., 2009, Tectonic Geomorphology of the Chukchi Borderland, Arctic Ocean:  Constraints for Tectonic Reconstruction Models, GSA Penrose Conference Tectonic Development of the Amerasia Basin, October, 2009.

DOWDESWELL, J.A., O’COFAIGH, C, TAYLOR, J., KENYON, N.H., MIENERT, J., & WILKEN, M, 2002, On the architecture of high-latitude continental margins: The influence of ice-sheet and sea-ice processes in the Polar North Atlantic, in Dowdeswell, J.A., and O’Cofaigh, eds., Glacier-influenced sedimentation on  high-latitude continental margins: Geological Society of London Special Publication 203, p. 33-54.

MAYER, L.A., ARMSTRONG, A. A., CALDER, B. & GARDNER, J. V., 2010, Seafloor mapping in the Arctic: support for a potential U.S. extended continental shelf, International Hydrographic Review, No. 3, pp. 14 – 23.

MAYER, L. A., AND ARMSTRONG, A. A, (2012), U.S. Law of the Sea Cruise to Map and Sample the US Arctic Ocean Margin, University of New Hampshire (UNH), Center for Coastal and Ocean Mapping (CCOM)/Joint Hydrographic Center,(JHC),p.159 . http://ccom.unh.edu/sites/default/files/publications/HEALY1202_FINAL_CRUISE%20REPORT.pdf

PIPER, D.J.W., and Normark, W.R., 2009, Processes that initiate turbidity currents and their influence on turbidites: A marine geology perspective: Jour. Sedimentary Research, v. 79, p. 347-362.

WYNN, R.B., CRONIN, B.T., AND PEAKALL, J., 2007, Sinuous deep-water channels: Genesis, geometry and architecture: Marine and Petroleum Geology, V. 24.,p. 341-387.