Churning of the seafloor: On-going growth and collapse of ice cored submarine pingos

A multipronged, 12-year study has revealed a complex, submarine morphology dotted with pingos which are continually changing due to ongoing freezing and thawing of brackish groundwater seeping up from buried ancient permafrost. Multibeam mapping surveys on both sides of the Mackenzie Trough in the Canadian Beaufort Sea were repeated in 2025, 8 and 12 years after the initial mapping surveys. Differencing 1-m-scale bathymetry grids collected using Autonomous Underwater Vehicles reveals the tops of pingos experience up to 1.5 m of upwards growth between surveys, documenting of upwards growth approaching 20 cm per year of submarine pingos for the first time. Up to 5 m of down drops were also observed on the crest of some submarine pingos. Areas that experience 1.5 m of growth are less than 10 m from areas that experienced 2.0 m of down drops. Remotely Operated Vehicle (ROV) based low altitude surveys using stereo cameras, multibeam, a laser scanner, and vision-based Simultaneous Localization and Mapping navigation mapped sections of this dynamic morphology at sub-cm resolution providing extraordinary detail on the on-going seafloor deformation associated with submarine permafrost. An ice layer exposed in the wall of an <8-year-old crater on the top of a pingo was sampled using a ROV-deployed drill. This ice sample and gravity cores show that segregated ice and ice bounded sediment exist at and just beneath the seafloor on these uplifted structures. Down-core freshening of pore waters from sediment cores taken on the tops of features also confirms that brackish water exists near the seafloor at these sites. ROV measurements show that the bottom water temperatures are <-1° C. At this temperature, fluctuating temperature and salinity of seeping brackish ground waters causes their freezing and thawing and results in the crest of ice cored pingos both growing and collapsing. This latest work broadens the known extent of active submarine permafrost deformation to include submarine pingos on the Arctic shelf. The on-going upwards growth and seafloor collapse at submarine groundwater seeps result in churning-up the seafloor and show that submarine permafrost formation represents an unanticipated geohazard threat to submarine infrastructure.