Researchers investigate mysteries of underwater pockmarks with unique biology

October 24, 2016

About the series: This is the first part of a three-part series on a recent research cruise to better understand species and processes in the Chukchi Borderlands, the complex transition area from the shallow Chukchi Sea shelf to the deep Arctic Basin. Currently, the region is not well understood. The cruise supported international researchers, including a team of professors and graduate students from the University of Alaska Fairbanks, on the U.S. Coast Guard Cutter Healy, an icebreaker capable of conducting extreme Arctic research. The research was funded by a National Oceanic and Atmospheric Administration Ocean Exploration grant, which sends researchers to explore the unknown and ask new questions.

UAF researchers studied unsolved mysteries in unusual landforms during a summer 2016 cruise on the USCGC Healy icebreaker.

The researchers came upon one pockmark that was speckled with anemones. Photo courtesy of Katrin Iken, University of Alaska Fairbanks.

During the 2016 research cruise, scientists collected data on a multitude of organisms in the Chukchi Borderlands, including bacteria in sea ice, tiny zooplankton animals in the water column and on the seafloor, and large marine mammals. They set out to better categorize known and unknown Arctic species, and to study how some mystery species interact with the environment.

Many components of the 2016 cruise mirrored an exploratory cruise that took place in 2005, where the research team first noticed a variety of unknown species and unique topography that helped them narrow down the questions they wanted to address, according to Katrin Iken, a marine biology professor with the UAF College of Fisheries and Ocean Sciences.

Eleven years later, technological advances in field equipment, especially on the remotely operated vehicle used for detecting, collecting and documenting species, have made it possible for researchers to discover and describe unknown species. “The cameras are now able to take photos of such high resolution that you can blow up a photo to see individual hairs on a copepod, which we typically need to look through a microscope to get a good look at,” Iken said.

Iken spearheaded a seafloor-focused team to map out seafloor biology in the Chukchi Borderlands. She was particularly interested in studying the small pockmarks that line the seafloor — bowl-shaped depressions that are about 50 meters deeper than surrounding areas and a few hundred meters in diameter. Iken and her team set out to learn whether these pockmarks have a unique biology compared to the rest of the seafloor.

They observed that the pockmarks typically were dominated by only a few species, while the surrounding areas were much more diverse. “One pockmark had a little anemone forest,” Iken said. “Around the pock, we saw brittle stars, sea stars and shrimp, but you go a few meters down into the pockmark and just see this anemone forest. In another one we saw sea spiders. It was like we were in a prehistoric environment where these gigantic sea spiders were crawling slowly around us.”

A pockmark thriving with sea spiders almost seems like it belongs in a different era. Photo courtesy of Katrin Iken, University of Alaska Fairbanks.

The researchers first noticed the pockmarks in 2005 but had limited opportunities to investigate them. Even after the 2016 cruise, Iken's team doesn't know exactly how they formed or what could be causing such contrasting biology with the outlying areas.

“The marks are not terribly large or deep, but they are fairly distinct,” Iken said. “These perfectly round depressions in the seafloor have a different species composition than the areas around them, and we aren’t sure why. Being 50 meters deeper doesn’t matter to these organisms, so it is not depth alone that causes these distinct species assemblages.”

Pockmarks are typically formed through gas or liquid seepage, which can create a depression in the seafloor. As far as Iken’s team can tell, these pockmarks are not actively bubbling gas anymore. Without knowing exactly how the pockmarks formed and what the current conditions are inside, it makes it even trickier to parse out the influence they have on seafloor biology.

The data collected on the 2016 cruise will provide important baseline information for many aspects of the biology and productivity of the Chukchi Borderlands. With the new insight from the cruise, the researchers look forward to further investigating the organisms and their habitat.

Parts two and three of this series will be published on Wednesday, Oct. 26, and Friday, Oct. 28.

More information from this research cruise, including photos and videos, can be found on the NOAA Ocean Explorer website.