MOSAiC Leg 3

Where to begin… I started writing this post several days ago on a nearly empty plane flying from Charlotte, N.C. to San Diego. That flight marked the end of MOSAiC Leg 3 for me, though Leg 3 will continue for several more weeks. We were supposed to be done on April 4, however, the COVID-19 pandemic and dynamic sea ice conditions pretty well hashed that plan. I took advantage of a single opportunity to leave the Polarstern early (meaning only a couple of weeks late) to help with the childcare situation at home. The remaining brave and dedicated crew and scientists are expected to return by ship to Europe in late May.

Our journey began in Tromsø, Norway in the innocent days of January when COVID-19 seemed like a regional rather than global problem. We had several Chinese expedition members on Leg 3, but they all made it out just fine and – though they were concerned about the situation back home – we figured things would improve in due time. After a week of safety training we were transported to the Russian icebreaker Kapitan Dranitsyn for what we thought would be a 2-3 week voyage to the Polarstern.

A lot of thought and effort went into determining how the MOSAiC scientists and crew would reach Polarstern throughout the drift. During the winter a conventional icebreaker of Dranitsyn‘s class is not the best way to reach a location in the central Arctic, however, it was the best among the affordable and available options. And in the end it did the job. I’m not sure of the history, but I’m fairly certain that its feat of reaching Polarstern in the dead of winter is unprecedented.

We spent a week in a pleasant fjord just outside of Tromsø waiting for a weather break to cross the Barents Sea to the pack ice. The Barents Sea is notoriously stormy, and we needed wave heights below 4 m to attempt the crossing. Ice breakers don’t ride well in heavy seas, and there were refrigerated shipping containers carrying (our) food for Polarstern stored on deck in the bow. We couldn’t take big waves on the bow, nor could we tolerate much ice formation on the chilling units. Both happened anyway. But at least the crossing was relatively short, and within 72 hours we were in the pack ice.

The Dranitsyn ended up being a bigger part of Leg 3 than any of us imagined at the time. Had our departure from Polarstern gone as expected, we would have been in transit on Dranitsyn as long as we were doing science on Polarstern. It was an interesting experience. Scientists are pretty good at keeping themselves busy; most of us have a long backlog of analyses to complete and papers to write, in addition to fielding emails from students and colleagues, and handling administrative matters. Absent the internet or email, however, a lot of these responsibilities disappeared. I worked on a proposal and finished a (3 year overdue) paper. Much of the rest of the 5 weeks we were on Dranitsyn I spent in discussion with my Leg 3 colleagues. It was something like an extended MOSAiC workshop. We covered everything from synthesizing across different science themes, to how time and on-ice resources would be shared between groups in a typical week.

The roughly 2 week delay in reaching the Polarstern was due in large part to ice conditions. Despite previously expeditions onboard icebreakers I hadn’t really thought out it this way before, but the ice compresses and relaxes in response to tides, winds, and other external forces. When the ice is compressed it’s incredibly difficult for an ice breaker to break; there’s simply no place for the ice to be displaced to. Under a relaxed state more leads are open, and there’s more space within the pack ice accommodate the displaced ice as the ship moves through. Temperature also plays a role. Icebreakers are more typically used during the spring summer and fall, when maritime shipping in the Arctic is active and more research activities are taking place. Spring, summer, and fall sea ice is naturally much warmer than winter sea ice. Warmer sea ice is softer and breaks more easily, and the surface of the ice has less friction. This means an icebreaker can more easily ride up and over the ice to break it. With temperatures low and the ice in a “compressed” state it was a tough grind, as this video from our embedded videographers from the UFA production company shows:

Despite the conditions and some weeks of uncertainty we did eventually make it to Polarstern. Seeing that little point of light appear on the horizon after all those weeks of travel made me appreciate how alone we were up there at that time of year.

After we reached Polarstern it took nearly a week to transfer cargo, exchange the scientists and crew, and become familiar enough with our tasks and the surroundings to take over. Many of the MOSAiC observations take place in what’s called the central observatory. This is an aggregation of relatively stable floes around Polarstern that house a number of on-ice installations. These include the colloquially named Met City, Balloon Town, Ocean City, and Droneville sites, among others. Beyond the central observatory are various “pristine” sites for snow and ice sampling, and beyond those lie the nodes of the less frequently visited distributed observatory. The distributed observatory is critical because it provides some spatial context to the intensive observations of the central observatory.

We had about a week of “normal” operations before the central Arctic started throwing plot twists at us. The ice was surprisingly dynamic. The reasons behind this will, I think, be an important science outcome of MOSAiC. Thinner, rougher sea ice? More wind stress? Whatever the cause the ice cracked a lot. By chance we were located in what ice dynamicists call a “shear zone”, an area of enhanced kinetic energy within the pack. Here’s the first emergence of a crack, on March 11. You can see the logistics team scrambling to move the snow machines to a safer location. Over the next few weeks this crack grew into a major and ever-evolving lead.

By April everyone was pretty used to cracks, leads, and ridges in the central observatory. Overall I was impressed with the resilience of the various team as different installations were threatened, and in some cases destroyed. For the ATMOS (atmospheric sciences) team in particularly, Leg 3 should have been relatively easy – low temps not withstanding. Everyone expected consolidated ice and stable, well-established instruments and protocols. Instead, for a period of time there was a near-daily scramble to maintain power and infrastructure at the Met City site. The adjacent Remote Sensing site was enveloped by a large ridge system and had to be relocated to near the logistics area. Setting up these sites is something that took specialists on Leg 1 many days, on Leg 3 systems had to be dismantled and re-established on the fly. Because spring is a particularly interesting time for atmospheric chemistry in the Arctic the clock was ticking every time a site or instrument went down. The dedication and ingenuity of the scientists at the Met City and the Remote Sensing sites was great to observe. The rest of us helped where we could, but we had our hands pretty full with other problems.

At the top of the problems list was the loss of the hole for the main CTD/rosette system. The CTD is an instrument package that measure conductivity, temperature, and pressure (depth) along with other parameters. It is the fundamental tool in ship-based oceanography. The CTD is attached to a long conductive wire, and embedded within a rosette of sample bottles. The sample bottles are fired at specific depths to collect water for a number of analyses and experiments. Lots of parameters and projects were dependent on this sampling system, and a huge amount of effort had been expended to construct and maintain a hole in the ice for deploying it. On March 15, however, the ice shifted, pushing Polarstern forward. This caused superficial damage to the Weatherhaven covering the hole, but more significantly placed the hole out of reach of the crane that operates the CTD/rosette. Just like that we lost all of our capacity to sample below 1000 m (the central Arctic Ocean is deeper than 4000 m in most places) and to collect large volumes of water from any depth. All sampling had to shift to a much smaller system at the Ocean City site.

Why couldn’t we simply make a new hole? It’s worth remembering that the ice in March is near its maximum thickness. It was roughly 160 cm thick when access to the main CTD hole was lost. This discounts any rafting of multiple ice floes, which was probable, and could easily double or triple the thickness. Assuming only a single layer of ice, the way to make a hole big enough for the CTD is with a chainsaw. The thickness of the ice that you can cut is limited by the size of the chainsaw bar. Maybe commercial logging operations have a 2 m bar, we certainly did not! You can cut the ice out in layers – I’ve had to do this in the Antarctic before – but the problem is that you create a bathtub as soon as you start cutting the final layer. To finish the job you’d need a snorkel for yourself and the chainsaw!

All our water column sampling had to shift to Ocean City, and focus on the upper 1000 m of the water column. Ocean City is the main site for the physical oceanography team. It was designed to accommodate a small team taking ultra-high resolution measurements of the surface ocean. The physical oceanographers went above and beyond sharing their space and resources, and I ended up thoroughly enjoying the time that I spent out at Ocean City. The below video was made on April 20 by lowering a GoPro through the CTD hole at Ocean City while one of the physical oceanographers is conducting high resolution profiling of temperature and salinity. You can see the microstructure profiler used for this near the end of the sequence.

In addition to the water column sampling we carried out sea ice sampling, when conditions allowed. To minimize the impact of light pollution from the vessel on the growth of sea ice algae our preferred ice coring sites were located some distance from the ship. Through the spring and summer, most of the photosynthesis taking place in the central Arctic occurs in the ice itself, rather than the water column. The ice algae have more consistent access to light than their planktonic counterparts, and are famously sensitive to even the lowest levels of light. Ambient light from the ship is more than enough to induce growth in the vicinity during the long polar night. Distance from the ship combined with the dynamic ice conditions created some access challenges.

Despite the access challenges we got some great ice core samples. We fielded two ice coring teams, one for first year ice and one for second year ice. I had the pleasure of working with the second year ice coring team. It was a great US-German-Russian collaborative effort, and we had some good times out there!

The original plan for exchanging Leg 3 with Leg 4 involved flying us all out on ski equipped Antonov An-74 aircraft. This would have been a slick and expedient way to carry out the exchange. It also requires a pretty long runway and permissive global travel. By mid-March it was clear that both of these things were going to be an issue. I’ll be honest, there were some tense weeks where it wasn’t clear when and how Leg 3 would end, and what the future of MOSAiC would be. Kudos to cruise and expedition leadership for navigating us through the ups and downs. In particular AWI logistics had the difficult task of designing and scoping the possible solutions. They did an amazing job of iteratively working through a huge range of options to come up with the one that maximized science and minimized impacts on individual lives. But of course it was a compromise.

The current plan involves the Polarstern leaving the central observatory in mid-May for a rendezvous with one or more ships near Svalbard. The Leg 4 personnel (including Bowman Lab member Emelia Chamberlain) are already under strict quarantine in Bremerhaven, Germany. They’ll remain under quarantine until they depart for Svalbard at roughly the same time Polarstern leaves the central observatory. Once the crew has been exchanged, Leg 3 will sail for Germany and Leg 4 will begin the difficult task of re-establishing observations at the central observatory. An advantage of this plan is that it doesn’t require a complete breakdown of the central observatory. It will require, however, that many of the installations be partially disassembled for safety while Polarstern is away from the floe.

There was one opportunity to leave Polarstern before the official Leg 3-4 exchange. After agonizing over it for a couple of days I decided I needed to take advantage of the opportunity. After an epic few weeks our project was in decent shape, and with two young kids and no school or daycare, attention needed to shift to the home front. On April 22 I stepped onto a Twin Otter operated by Kenn Borek Air Ltd. to begin the long flight home with six other expedition members. We flew to Station Nord in Greenland, then across the Canadian Arctic via Eureka-Resolute-Arctic Bay-Churchill-Toronto, and finally to the US.

Immigration: “You’re coming from where?”

Me: “Resolute”

Immigration: “What were you doing in Resolute”

Me: “Just passing through, we were only there for a few minutes”

Immigration: “So where were you before that?”

Me: “Greenland, but again not very long. See there’s this ship…”

Immigration: “Uh, nevermind. Here’s your passport.”