Surveying Unexplored Features

August 20, 2009 · Filed Under 2009, Journey

Andy Armstrong, NOAA Office of Coast Survey, Co-chief scientist about USCGC Healy

Today we did some multibeam bathymetric mapping over areas of high seafloor relief on the Alpha-Mendeleev Ridge complex, 625 miles north of the Arctic coast of Alaska. We are still breaking through 9/10 ice (90% of the sea surface covered by ice) in front of the Canadian Coast Guard Ship Louis S. St-Laurent. Although the ice is often 1-2 meters thick, we are generally breaking it fairly easily.

This part of the track is designed to obtain multichannel seismic reflection profiles over seafloor areas from which we dredged rock samples last year (see photos of scientists examining these rocks at http://continentalshelf.gov/newsroom.html). The dredge samples and seismic profiles will help us analyze the geology of the Arctic region and delineate the extended continental shelf.

Our planned route has also taken us within a few miles of an unsurveyed feature that is vaguely depicted on Russian contour maps of the area, and is represented as a single circular contour on the International Bathymetric Chart of the Arctic Ocean. These representations are indistinct probably because they are based on one or two isolated soundings.

So, in an exploratory deviation from our planned track, we are running a bathymetric survey to precisely locate and define the feature. We began mapping a north-south trending, 14-nautical-mile-long ridge that rises abruptly out of the seafloor and stands at least 500 meters tall. Having mapped the eastern flank on our first pass, our path over the next two hours will take us along the spine of the feature and back to our originally planned track line (see image). As we turned to run the northbound leg of our survey, we saw a hint of some additional seafloor relief to the south – but that will have to wait for next year!

Two days ago, over the abyssal plain, we also had an opportunity to pass over another potential feature: an area shown as a deeper spot on Russian bathymetric maps. As we passed over the area, however, we found no change in the depth. We are again reminded that the existing maps and charts of the Arctic are based on very sparse soundings from a wide variety of sources, and depth contours reflect the very subjective judgment of the compiler.