Unveiling the Deep – Ocean Floor Topography: What is that?

What is out there? A view from one of the cabins on the R/V Marcus Langseth

It has been said that humankind knows more about the Moon than the oceans. If we think for a bit, the Moon is within sight for everyone on Earth, which makes it easier for anyone with a telescope to look at it. For the seafloor it works differently, as we have to go there, or at least be as close as possible, to view it. Many difficulties come into play when mapping the bottom of the ocean, such as weather, available budget, finding the right crew to join the cruise, having the right equipment, and spending many days at sea. So it is not a trivial task to do without a real purpose. No one wants to be drifting out on the open ocean, waiting to find something, as there are too many uncertainties and risks. But, the recovery cruise for the AACSE OBS deployment has shown a great opportunity to map unexplored patches of the ocean bottom! Would you join us in an open sea adventure? In this post, I would like to share an interesting discovery among many others! Check out our first post here [link to Ginevra’s post].

After we left Kodiak, there was not much to see besides a relaxing and beautiful view of the sea and cloudy skies. As soon as we hit open water, the views have been dependent on the weather (my view was of my bedroom ceiling after getting seasick in the most recent storm). In general, we have found ourselves in a big pound of water where it does not matter where you look. After looking at the same landscape over and over again, with some luck, we have seen some sea animals, but there have been times that we have sadly stopped looking outside at all. However, aboard a research vessel like the R/V Marcus Langseth, there is much more to see if we turn our heads and look down, deep into the water.

To be able to see what is laid down in the underwater realm we have to use special tools, because the sunlight only shines a few meters down, leaving everything below that in completely darkness. Luckily, the Langseth is equipped with a different set of eyes which can draw us some pictures of what is hidden down where we can’t see, a seabed scanner called a Multibeam system. It works similarly to a bat’s echo sounding, but with many powerful bats lined up in an array. This seabed scanner – or our bats – works 24 hours per day, 7 days a week, with the exception of when we are recovering an OBS, since it may affect our communication with it. So, most of the time, the scanner can give us a real-time image what is under the ship as we transit between OBSs.

Rising from the deep, buried in 3600 meters of water, a roughly 35km-long and 900m-high ancient volcano chain is mapped above. The yellow line shows the ship survey path.

Along our path to recover the OBSs, we have faced different water depths ranging from a few hundred meters to more than 6km. The underwater realm looks similar to what we see on land but more wet. We can see completely flat areas similar to the flat areas of the Midwest, mountains, and even strange artifacts. Recently, we found something different on our way to OBS WD64. After many hours of mapping a constant depth of around 4600 meters, with a few small hills showing up, our bats started telling us that we had started going up a very steep slope, around 300km away from the Shumagin islands. Rising from the deep ocean, a roughly 900 meters high, 35km-long, and 7km wide mountain chain appeared on our radar. Previously available topography data for this region showed a big low-resolution bean-shape structure in the middle of a flat area, with not a lot information about it. But now, we can see what it is actually about!

A 3-D view from the previous image. What kind of creatures live there? Is it still active? Special thanks to Bill Danforth, the multibeam specialist on the cruise, for making this figure and processing the multibeam data.

From a 2-D figure, we can see some craters, but the most evident one is in the middle. This gave us a hint of what that mountain chain is about, perhaps an ancient volcano. To have a better sense of whether or not what we are looking at is real, we processed the data and removed the noise. We ended up with a 3-D image of not only one ancient volcano, but at least four! This structure is similar to what we see today in the Hawaiian Islands, but on a smaller scale. It is very likely to be inactive, but the nearby OBS stations may give us a hint of whether earthquakes are still occurring there. This was one question among many others that came up like: how old is it, why is it there? If it’s not active, when did it stop? However, only time and future research can give us the answers. How would you feel flying over undiscovered volcanoes? Tell us in the comments! This is Igor, your today’s post host. Stay up for the next posts and I hope to see you in the next ones. Cheers!


Bonus: Who is there?

Sometimes we see artifacts that are not real, and our minds can be tricky. Look at the figure bellow and try to find anything strange.

A map view from our seabed scanner not yet processed at a different site. It looks like an old TV with scatter signal, but can you see a face in the image?

Thanks Ginevra for reviewing this post!

Igor Eufrasio – AACSE apply to sail participant; graduate student at Northwestern University, IL.




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