PhD student Emelia Chamberlain sends the following dispatch from Polarstern.
The MOSAiC floe, just prior to break-up.
After 64 days at sea, the RV Polarstern and icy surroundings have officially started to feel like home. I can’t believe how quickly the time has passed, but here we are at the end of MOSAiC Leg 4! A truly special cruise, we witnessed the re-building and complete break-down of an ice camp, the peak and end of the spring under-ice bloom, and were the last to sample from the original MOSAiC floe before that singular, well characterized piece of ice (chosen all the way back in last October!) finally reached the marginal ice zone, and the end of its life as a contiguous floe. It’s really quite incredible to have had the opportunity to contribute to this astounding time series. As part of this expedition, over 200 individual scientists have worked on this one piece of ice, following its drift across the Arctic. Even if we cannot determine the full scope of this project or see all the results just now – it is clear that these data will have an impact for generations to come and, especially as a student, I feel so lucky to have contributed to this legacy.
Polarstern on a sunny day in the ArcticOur home-base, the RV Polarstern is at the heart of this expedition. Summer weather near the sea-ice edge is extremely variable. Our evening weather reports predicted >95% cloud cover almost every day, but we still lucked out with some gorgeous sunny days. But no matter the weather (or distance from which it finally appears out of the fog), the Polarstern after a long day on the ice is always a welcome sight.
When we first arrived at the MOSAiC floe, we were very excited to find enough of it intact to re-establish the Central Observatory ice camp. Very soon, versions 2.0 of all the ice “cities” began popping up across the floe and the science began in earnest. However, every day we had new reminders of the fact that we were decidedly in the Arctic melt season. Melt-ponds became a dominant feature and often, new roads and pathways had to be forged on the fly to get to sampling locations. For example, starting at around 1.5 m the first week, our last first year ice cores were only 90 cm long.
Looking down from the bridge, this was the logistics area of the ice floe on June 19th, the day after our arrival. The research camp has yet to be set up and the area is still fairly dry and melt-pond free.Here is the same view from the bridge on Jul 25th. The logistics area has become ponded and brownish due to sediment melting out of the ice, darkening the surface and enhancing melt. It was not uncommon to find rocks, shells, etc. on our floe – remnants from its origins off the coast of the New Siberian Islands (https://doi.org/10.5194/tc-14-2173-2020). In the foreground is the remote sensing site, followed by the Balloon Town (measuring atmospheric profiles). MET City and Ocean City are behind, hidden in the fog. And now, the same view on Jul 31st, after we hit the marginal ice zone and swell increased to the point of breaking the floe apart.
These melt-dynamics not only provided physical challenges to working on the ice, but also scientific ones as well. How to capture this fresh-water lens and study the impacts of such surface stratification on the biomass blooming beneath the ice? This stratification was seen most clearly in the lead systems surrounding the ship. After several surveys, we were able to characterize 3 clear layers – surface freshwater, a green algal layer (brackish salinities), and the underlying seawater. Over time, the living layer shoaled and went from a happy photosynthetic green, to a clearly dying, particulate organic matter greenish/brown. Capturing this bloom transition was quite exciting for us and I look forward to analyzing how the microbial community in these layers evolved.
Ale taking go pro footage from a lead near ROV Oasis on July 10th. At this point, the biomass layer was around 1m deep and only visible with go-pro on stick or ROV footage.Using the classical “tubing duct-taped to stick” technique, here I am sampling from a lead on the far-side of the floe on July 22nd. At this point, the biomass layer is clearly visible near the surface, reaching a max of 30 cm deep, with lots of dead Melosira (ice-algae) floating in the current.22nd July cont. On the other end of the tubing, Ale fills our sample bottles while the OCEAN and ICE teams continue to survey the lead both from shore (upriser turbulence profiles – Team Ocean) and sea (high resolution CTD profiles by Kayak – Team ICE).
In addition to these opportunistic events, Alessandra D’Angelo (PhD, URI) and I were happy to continue progress on the core MethOx project work, started by Jessie Creamean (PhD, CSU) on Leg 1, and Jeff on Leg 3. When conditions allowed, we were lucky enough to have nearly daily CTD casts from the Polarstern rosette (thank you Team Ocean!) and were therefore never in want of water. With both of us on board we were able to maximize sampling and analysis, collecting almost 278 unique samples for the core project work alone! We measured weekly seawater profiles for microbial community structure in conjunction with ambient methane concentrations/isotopes and ran experimental samples to study potential oxidation/production rates of methane using elevated methane in select incubations.
The MethOx team after a successful deployment of the BGC team’s gas-flux chamber at Remote Sensing.Filling BOD bottles from the CTD for discrete O2/Ar ratios to run on the AWI MIMS.Some of the most promising incubation samples, however, came from the bottom sections of sea-ice cores. In addition to our weekly water column work, I also took part in the interdisciplinary MOSAiC ice-coring Monday to support the sampling effort of these cores. This event included the collection of approximately 25 cores per site (First Year and Second Year ice) per week for a host of parameters: salinity, net primary production, gypsum content, etc. It was great to be able to start every week out on the ice and witness the changes occurring at our floe first-hand.A heavily ponded First Year Ice Coring Site and the bridge we had to build (and re-build… and re-build) to get there.Alison Fong (PhD, AWI) and I preparing to section cores. The tent is used to keep temperatures cool and protect samples from direct sunlight during processing. With air-temperatures hovering between -1 and 1 C for most of the leg, this was key to prevent premature melting of the samples.Ale “fishing” for methane from a hole used for sediment trap deployments near the First Year Ice site. The syringe is used to carefully sample seawater into gas tight bags without incorporating air bubbles – that way we measure the true seawater signal without any atmospheric interference.
BUT – it’s not over yet. Even as I now take this time to reflect on Leg 4, we are quite busy with preparations for Leg 5 where we will head north and witness the re-freeze of the Arctic fall! And although it will be bittersweet to part from our Leg 4 colleagues… the Akademik Tryoshnikov has arrived and the handover must begin. I look forward to continuing on as the Bowman Lab/MethOx Project representative on MOSAiC Leg 5 and can’t wait to see where the RV Polarstern takes us next!
Another bittersweet farewell, the last weather balloon at the MOSAiC floe site on July 31, after the final break-up of the MOSAiC floe.Happy scientists on the ice… even at 1:00 in the morning! This was the midpoint of a 24 hr sampling cycle and I think summarizes the energy brought by the Leg 4 team very well. Pictured left to right: Ale, UiT Post-doc Jessie Gardner, myself, and our fearless bear-guard Tereza Svecova.
