Q: I am curious about the dotted lines at the seabed of the Barents Sea region. I found them using Google (Ocean) Maps, and I have not been able to get a plausible explanation.
From Med Vennlig Hilsen
Reply by Prof Tony Watts (University of Oxford)
The lines are, in fact, tracks of research ships that have made measurements of the depth of the seabed using echo sounders. Ideally, the tracks should be invisible and you should just see the different shades of blue that reflect the depth of the seabed. However, when the Google Ocean team gridded up the seabed depth data they do not appear to have taken into account the irregular spacing of the original data.
The reason I can be so certain that the lines are ship tracks is that I was actually onboard one the ships in the Barents Sea when the depth measurements were made! The ship was R/V Vema and we were carrying out marine geophysical surveys between Bodo and Stavanger. The red lines on the image highlights a portion of V3011 ship track. The cruise was memorable because it was very cold and it included a 24 hour stopover in Murmansk, Russia. We were, in fact, the first US research ship to enter a Russian port and although it was dark the entire time we were there, we were very well looked after by our Russian hosts.
You may have also noticed on the seabed map some small crater-like depressions along some of the ship tracks. These are called pockmarks and they are believed to represent places where gas (probably methane) is erupting on the seabed. The origin of the gas is not clear, but it may have formed by the decomposition of gas hydrates in the underlying sediments, following the collapse of the Barents Sea ice sheet about 20,000 years ago.