The Challenges of Arctic Ice in December!

The Ultima Thule expedition lead by CDeepSea on the R/V Kronprins Haakon left Longyearbyen on November 26, 2024 with the main objective to map and sample in the Lena Trough, including the Ultima Thule vent field at 81° North. Ultima Thule was located on the seafloor during the GoNorth 2023 cruise. Despite multiple attempts to reach the main target area, heavy ice restricted further progress approximately 10 nautical miles south of our northernmost target. However, while in the ice, several geological structures further south in the Lena Trough were mapped and rock and sediment samples collected by the remotely operated vehicle Ægir 6000. This work will help to understand the nature of spreading in the Lena Trough and constrain the southern extension of the Lucky Ridge. As the cruise was scheduled to depart very late in the year, it was predicted that we had a low chance of succeeding in our main objectives. Hence, the cruise had multiple secondary objectives in the Molloy area and around the Jøtul vent field further south where conditions are typically ice-free, or at least manageable this time of year.

At the time of this research cruise, the Lena Trough was covered with thick and challenging ice conditions. However, we were able to map and investigate some of the structures in the southern part of the trough as we were trying to reach Ultima Thule. The first challenge in the ice was to position the ship where desired – as the ice was too thick to break, we could only navigate through leads in the ice. This limited the possibilities in terms of which structures we could aim for. The second challenge was the ice drift, both direction and speed. The ice drift was quite unpredictable, changing both its direction and speed throughout the day. When the drift exceeds 0.8 knots, it is not safe to do seafloor observations and sampling with the ROV because it is too difficult for the ROV to catch up with the ship and safely dock in the TMS. Additionally, in terrain with high relief, there is insufficient time to lift the TMS and ROV to avoid crashing into seafloor structures. Prior to the multibeam echosounder (MBES) surveys carried out during this cruise, the available bathymetric maps of the area were limited to 100-200 m resolution maps. To improve the resolution, as well as providing safer navigation for the ROV, we mapped using the ship’s MBES while simultaneously surveying and mapping with the ROV while it was taking samples during dives in the area. Even with the challenges mentioned above, we were -- thanks to a highly skilled ship and ROV crew -- able to perform ROV dives at different structures that have not been investigated before.

Further south in and around the Molloy deep, we mapped and sampled material from various geological structures in order to get a better understanding of the structural architecture and evolution in the area. Further, we aimed to locate, map and sample a seepage area identified on the edge of the northern basin by multibeam echosounder during a previous MAREANO expedition. The objectives in this area were to address questions related to the geochemical composition of the seeping gas and fluids, its origin, and potential impact on the surrounding marine ecosystem.

Several other areas were also explored and sampled before the Ultima Thule expedition safely arrived back in port in Longyearbyen on December 11. All the scientists and most of the ROV crew left the ship in Svalbard before the RV Kronprins Haakon returned to sea for the final leg transiting towards Tromsø.

The team leaders are thankful to all the funders that helped make the expedition possible, including the University of Bergen, the University of Tromsø and the Norwegian Offshore Directorate.