Welcome to another foggy night on the SWERUS-C3 expedition... since several days, thick fog is hanging over us, but at least the ice has started to get thinner, and we are slowly picking up some speed. The last days have been challenging though: to reach some to our desired station locations through the ice, to position the ship in a sufficiently ice-free spot and still catch interesting features like seep sites. The challenge here is to capture a
feature seen in the online-geophysical data with as many as possible sampling platforms – CTD, GoFlo, submersible pump and sediment corers. At the current shallow depths, it is possible to put several things in the water at the same time, but then ice conditions have to be watched continuously, and the ship can’t maneuver away from ice if several devices are hanging from different sides of it. The thinner ice is actually a large challenge than the thick ice when it comes to “parking” the ship – if there is thick ice, the ship basically “gets stuck”, so there is not much drifting during a station. In thin ice conditions, however, we have to be very careful – first, we might drift away from the interesting feature that made us stop at this place in the first place, and then also smaller ice pieces can drift towards us, and endanger the equipment hanging into the water. But we are getting quicker and more efficient in our deployment, and also manage to do things with less people (so things can happen simultaneously).

At one station, we really manage to catch signals from a flare with all sampling devices more or less at the same time. In general, we managed to characterize a small source region with high methane levels and quite some bubble flares – and in the 5 days prior to arriving at the source region, we have been seeing continuously rising methane levels in the surface and midwater – not so much in the bottom, so this seemed to be the signal
transported from the source region. It will be interesting to look at the isotope data from this transect to get a better understanding how far the influence of local methane sources can reach.

For the practical point of work, our team is doing a lot of GoFlo-sampling, mainly from the aft deck because of the ice conditions, and now we work completely together with the submersible pump team – I become Emma’s
winchdriver for the pump, and she is my GoFlo person, this also helps a lot in speeding up the deployment and sampling of both devices. I am not adding more GoFlo- and pump action pictures to this post, as my fellow
bloggers have done that excessively (even Brett has been drawn down to the “lower decks” to become our cable watcher)... instead I want to say a word about two activities that are really important for the work of my methane
team and that I haven’t talk so much about before: The first activity is the sediment sampling – I guess I mentioned at some point that the sediment team takes samples for my radiocarbon measurements of CH4.

Now that I have been on the aft deck a bit more, I have seen them also in action, instead of just coming mud-covered into my lab to hand me the sample. As the methane concentrations in the sediments were somewhat lower than we expected, we had to change the sampling method for that during the cruise, so I get bigger samples. This ended up in quite some extra work for the sediment team, first they sometimes had to do an extra cast just for me, and then they have to quickly get my samples in the “sample jars” to not lose any methane and still manage to seal the containers leak-tight for the subsequent stripping. Thanks for doing a great dirty job, sediment team! The other sediment person I have to thank is a member of my own team: Denis is taking samples for methane concentration profiles in the sediment, and these are not only important by themselves to give us a better understanding of the general methane sources and processes, but his results give me also a guideline whether I have enough methane in my jars to start the stripping. For him, it is also quite some extra stress, as now sediment and water sampling often happen at the same time, so he is running between the bow and the aft to get all samples, and then he measures them quickly – so that I know whether I can use them or if we give them to another colleague for other measurement (every sample is precious).

The other “methane” hero I want to mention today is Marc. You have read in earlier posts – both by me and also by some others – about the continuous methane measurements from the seawater intake, and Marc is the one running (and having developed) this system that is very useful to guide us to good spot for sampling and to enhance the spatial resolution of our measurement in between stations.

Picture 1: Pete, Tommaso and Lisa filling the sample containers, picture 2: Jorien and Tommaso sealing them and picture 3: ongoing sediment stripping.