Celebrating Geodiversity Day with these seabed features

From rocks to soils to mountains to beaches, the non-living parts of our planet and the processes that create and shape them support and sustain us and all other life on Earth. As this year's theme for International Geodiversity Day says, "Geodiversity is for everyone."

Geodiversity is often breathtakingly beautiful. While we can all experience geodiversity on land, experiencing what lies beneath the ocean surface is much more challenging. Yet, across the Atlantic, Arctic, Indian, Pacific, and Southern Oceans, a complex tapestry of marine geological treasures has shaped our lives and planet. Today, in honour of Geodiversity Day, we celebrate just some of the marine geodiversity we have discovered.

Atlantic Ocean: Chicxulub’s little sibling?

Four hundred kilometres off the coast of Guinea, West Africa, lies evidence that at least two meteor impacts may have played a role in the extinction of the dinosaurs 66 million years ago.

The Nadir crater was likely caused by a meteor some 400 metres wide – much smaller than the estimated 10-kilometre diameter meteor that created the Chicxulub crater in the Yucatán Peninsula and the surrounding ocean. Still, the meteor left its mark. "This would have generated a tsunami over 3,000 feet [914 metres] high, as well as an earthquake of more than magnitude 6.5," said University of Arizona's Dr Veronica Bray, co-author of the study outlining the finding. "Although it is a lot smaller than the global cataclysm of the Chicxulub impact, Nadir will have contributed significantly to the local devastation."

The crater has an estimated minimum diameter of 8.5 kilometres, forms a 200-metre dent in the seabed, and has a crater rim reaching between 20 metres and 40 metres above the seabed. Outside the crater is a series of fault planes extending up to 12 kilometres, likely caused by the shockwave produced when the meteor hit the seabed and as the crater took shape.

Arctic Ocean: Holes in the Beaufort Sea seabed

Changes to the seafloor can happen quite quickly. Between 2010 and 2019, four mapping surveys chronicled the appearance and growth of 41 depressions on the seabed in part of the Beaufort Sea. The cause appears to be the thawing of ancient permafrost buried beneath the seafloor and the subsequent collapse of the floor above. On average, these oval or circular depressions are just under seven meters deep. The largest, which spans some 225 metres in length and 95 metres in width, reaches some 29 metres below the seafloor. This particular hole now sits on what used to be a 200-metre-long ridge.

The permafrost melting isn't thought to be related to the current climate crisis. "There isn't a lot of long-term data for the seafloor temperature in this region, but the data we do have aren't showing a warming trend," said Dr Charlie Paull, Senior Scientist with the Monterey Bay Aquarium Research Institute (MBARI), and lead author of a PNAS paper detailing the finding. Rather, the melting is likely driven by the slower changes in our climate since the permafrost first formed in the last ice age. "The changes to seafloor terrain are…being driven by heat carried in slowly moving groundwater systems," Paull explained.

Indian Ocean: The Sunda Trench is as deep as you can go

In the eastern Indian Ocean some 40-100 million years ago, the Indo-Australian Plate slid underneath the Eurasian Plate, generating a 3,200-kilometre-long arc-shaped trench that became host to the deepest part of the Indian Ocean.

Located south and west of Sumatra and Java, the bottom of the Sunda Trench sits some 7,200 metres below the sea surface. When researchers visited the trench in the scientific submersible DSSV Pressure Drop as part of the Five Deeps Expedition, they not only mapped the trench in unprecedented detail, but also found an extraordinary diversity of life. "Applying new technology to the largely unexplored depths of the Indian Ocean produced an extraordinary set of rare and unique discoveries in just five days," said Dr Heather Stewart, a Marine Geologist with the British Geological Survey who was involved in the expedition.

Among the octopodes, decapods, snailfish, and other marine life spotted in and around the soft sediment and scree, communities of bacteria flourished along a portion of the steep slope. "Ideally, we would return and do many more submersible surveys to explore a greater area of sea floor on a variety of geomorphological and geological features," Steward said. "We could then assess how common these chemosynthetic communities are and figure out how important a role they play in the food web at these extreme depths."

Pacific Ocean: A gulf shaped by ancient glaciers

From walrus to sponges to Pacific halibut to black-footed albatross, the Gulf of Alaska is home to a rich abundance of life. While currents and upwellings bring nutrients that support marine life today, ancient glaciers shaped the seafloor features that influence ocean processes and create a home for a multitude of plants and animals.

Clues about the ancient glaciation, which likely took place somewhere between 13,000 and 25,000 years ago, came to light when NOAA researcher Dr. Mark Zimmermann and geospatial analyst Megan Prescott compiled millions of soundings from multiple datasets to create a detailed seafloor map of the Shelikof Strait and western Gulf of Alaska.

By analysing the detailed map, U.S. Geological Survey geologist Dr Peter Haeussler identified some of the more unusual features as having glacial origin. These include moraine crests – ridges of rocks, dust, and other debris that are pushed together by the glacier as it grows; submerged shorelines – ancient shorelines that existed when the sea level was lower during the last glacial period; and iceberg ploughmarks – long grooves in the seabed caused by the bottom of the glaciers scraping along the seafloor, up to seven meters deep.

Southern Ocean: Hydrothermal vents fueling Antarctic marine life

The Southern Ocean, also known as the Antarctic Ocean, may be famous for its chilly sea temperatures, but deep below the sea surface, hotspots do exist. The source of these hotspots? Hydrothermal vents.

Hydrothermal vents start life with cracks in the seafloor. Seawater can enter these cracks, coming close to the Earth's mantle, where it is heated up. The superheated seawater then moves back up towards the seabed where it, along with any dissolved gases or minerals it collects on its way, is expelled back into the colder ocean. Many of the minerals brought up from beneath the seafloor begin to precipitate, falling like rain down to the seafloor. Over time, these minerals build up, creating chimney-like structures around the vent, eventually becoming home to myriad life.

Hydrothermal vents have been discovered in several locations in the Southern Ocean. For example, between South America and Antarctica at the Mermaid's Purse, East Scotia Ridge, researchers have mapped and surveyed vent systems with chimneys up to 15 metres tall, pumping out superheated seawater with temperatures up to 352.6°C. Meanwhile, between Australia and Antarctica, the Australian-Antarctic Ridge hosts at least two vent fields.

Lying some 4,300 kilometres away from the nearest known vent system, these systems are the most geographically isolated vents mapped so far. Nevertheless, the discovery of a Paulasterias starfish species that is genetically very similar to the ones found at the East Scotia Ridge vents and Kiwa (yeti) crabs potentially distantly related to those also found on the East Scotia Ridge suggests some connectivity between the two sites.

This story was written for Seabed 2030