Cold Seeps of Scott Inlet

Though not the final station for all operations, the arrival of the CCGS Amundsen at the Scott Inlet site on August 4th marked the last few dives with the Amundsen's new Comanche 38 remotely operated vehicle. There were three days of ROV dives planned for the site, as well as the usual array of water, sediment, bottom mapping, and faunal sampling operations. The first and third days of diving were the main scientific dives of the site; the goal of which was to explore the methane seeps of the area.

Sampling microbial mats growing on the sea floor at a methane seep at Scott Inlet (Photo taken by the Comanche 38 remotely operated vehicle via Amundsen Science)

Situated on a fault line, Scott Inlet has been surveyed on previous Amundsen cruises, which - as with many of the stations - revealed more sites of interest in the immediate area, and gave a better understanding of where to explore next. A methane seep is similar to a naturally-occurring undersea oil spill - methane is slowly released up and out of the sea floor from a source deep in the earth, creating a completely different ecosystem where it comes up. Since these communities contain organisms that break down the resulting compounds, they are of great interest for comparing against the communities of microbes that might respond to man-made oil spills that could happen at the surface of the Arctic Ocean.

In order to get the full picture of the seeps, there are a number of measurements to be taken. The meteorological tower at the ship's bow takes readings of the atmospheric methane, while down below, at the seep itself, targeted sediment cores are taken by the ROV. Between these two extremes, water samples are taken up through the water column, and with all of this information, it can be determined how much the surface chemistry and microbial community changes in response to what the seep produces below.

The meteorological tower at the bow of the CCGS Amundsen (Photo taken via drone footage by David Cote, Fisheries and Oceans Canada)

The water sampling done at Scott Inlet and throughout the Amundsen cruise is done with a rosette - an 8-foot tall cylindrical frame holding 24 Niskin bottles that can be closed at specific depths, bringing a full sample of the entire water column up to the ship. The frame is also outfitted with instruments that can measure other water parameters, such as the water currents just above the sea floor - something that is very important to know before sending the remotely operated vehicle down. In 2019, a rosette was lost at Scott Inlet during a cruise, and one of the goals for the site this year was to use the ROV to locate and - hopefully - retrieve it. Navigating the sea floor with only the coordinates of the ship at the time of the loss to go off of, the ROV team not only successfully located the still-functional rosette, but attached a line that they then carried back up to the surface to recover the rosette back onto the ship.

Recovery of the lost 2019 CTD-rosette (Photo taken by the Comanche 38 remotely operated vehicle via Amundsen Science)

A resounding success, the Scott Inlet site was the longest the ship remained at a station, for a total of just over 68 hours of operations. Though the end of the ROV dives, the operations were not yet over - and the ship turned to head into the adjacent fjords.

Written by Sophie Wolvin