Monday, 27 May, 2024 / Edition 9

The undersea is a mysterious world. I once listened to a TedTalk that mentioned that less than 10 percent of the ocean floor has been mapped in some detail. This edition of Core Elements includes some interesting stories about marine geology—from the North Sea to the East Antarctic. Our first stop is the Antarctic Ocean.

Rasoul Sorkhabi

Editor, Core Elements

How Seals Helped Map the Antarctic Ocean floor

Courtesy of Clive McMahon

An article in Communications Earth & Environment describes how a group of Australian researchers used seals to map the details of the East Antarctic Shelf. And here I mean the blubbery animal-type seal, not U.S. Navy SEALs.

What they did: Researchers attached small satellite-linked devices to seals, which measured depth, temperature, and salinity of the ocean as the seals swam. This study beneath the East Antarctic Shelf has been ongoing since 2005 and includes data collected from more than 500,000 individual seal dives.

What they found: The information gathered by the seals showed surprising results. For instance, some deep canyons were found adjacent to glaciers, where some seals dove 200–1000 meters deeper than where researchers had previously thought to be the “ocean floor.”

Why it matters:

• Mapping ocean-bottom canyons and channels is crucial to understanding how the East Antarctic Ice Shelf—which houses 80 percent of the global glaciers—behaves in the face of global warming.

• Mapping sea canyons and channels for water flow into and out of Antarctica is crucial for this purpose. 

The bottom line: Next time you see a seal, remember: they make excellent field assistants.

Go deeper: Read the full article here and watch a clip to learn more here.     

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The Mystery of Seafloor Pits in the North Sea Solved

Ayman Shalaby/Shutterstock.com

For years, thousands of mysterious pockmarks, or small depressions in sediments, on the floor of the North Sea have captured the attention of scientists and environmentalists. What are they?

The common understanding is that these are created by methane gases seeping from beneath the seafloor sediments. But is this true?

This question engaged Jens Schneider von Deimling, a German geoscientist at Kiel University, for many years, and he finally decided to investigate.

What researchers did:

• Schneider worked with biologists, oceanographers, and satellite data scientists.

• The researchers utilized multibeam echosounder technology with a resolution down to centimeters to image the pockmarks.

• Navigating over thousands of miles in German research vessels, the researchers collected millions of echosoundings from the sea floor and analyzed the data.

What they found:

• The data did not support methane seeps.

• The seafloor pockmarks were small pits that averaged 11 cm deep and corresponded to the breeding sites of sand eels, a kind of fish which spends most of the year buried in shallow sediments.

• The pits are also the hunting grounds of porpoises and other sea animals who feed on sand eels.

• This suggests the seafloor pits are created by these sea animals and then scoured out by bottom currents.

What they are saying: “Our results,” says Jens Schneider von Deimling, “show for the first time that these depressions occur in direct connection with the habitat and behavior of porpoises and sand eels and are not formed by rising fluids.”

Why it matters:

• These pockmarks are also found in many other seas and oceans, so this study could have applications across several sites.

• If the pockmarks are made by greenhouse methane gases spewing from the underlying sediments, they will have adverse effects on marine environments and climate.  

Go deeper: Read the article here. Information is also available on the website of Kiel University.

Natural Oil Seeps in the Aegean Sea

Michal Bednarek/Shutterstock.com

Studies of offshore oil seeps have largely been reported from the Gulf of Mexico, the Caspian Sea, and the West African Margin. A recent article looks at seeps in the Aegean and explores the possible roles of fault lines in developing them.

About the Aegean: The Aegean Sea is a back-arc marine basin developed above the northward subduction of the East Mediterranean segment of the African plate. It has a complex geology, including an active volcanic arc and many faults.

What researchers did:

• The study, conducted by French scientists, used satellite-based synthetic (antenna) aperture radar (SAR) data.

• To create a SAR image, pulses of radio waves are transmitted to a target zone, and their echoes are received and recorded.

• A single beam-forming antenna mounted on a satellite (or an aircraft) is used for this purpose.

• You can learn more about this process here.

What they found:

• The study revealed the presence of a massive oil seepage system, consisting of 33 seep sites, in the northern part of the Aegean Sea.

• The oil seeps cluster in two geological zones: (1) The Limnos and Saros pull-apart basins. The seeps are aligned along the North Anatolian Fault; and (2) The Skyros-Edremit region in the vicinity of the Skyros-Edremit Fault.

• Both of these faults are strike-slip faults originating on the Anatolian plate. It appears that faults play a major role in the formation of these natural oil seeps.

• Oil flow rates range from 0.6 to 65.3 cubic meter per year, with a total volume of 500 cubic meter per year for all seeps.

Why it matters: Satellite imagery of natural oil seeps in offshore areas has applications in several fields, including:

1. Mapping and characterizing offshore oil expulsion sites in relation to faults, seismicity, and basin stratigraphy

2. Exploration of offshore petroleum prospects

3. Investigations of the hydrocarbon seepage impact on marine chemistry and ecology

Go deeper: Read the full article in Vast Oil Seeps here.

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