Expedition PS101 tests, deploys and recovers several new types of instrumentation for the observation of ice, ocean and seafloor processes in the Central Arctic. A main aim is to observe and analyse the changes in the sea ice cover, and its causes and consequences for ocean and life.
Besides the work with new technologies, the fourth week of the Expedition PS101 has kept us busy working at the hydrothermally active mound of Gakkel Ridge at 87°N and 55°E, as well as at the large seamounts of Langseth Ridge at 86°N and 60°E. We have retrieved important samples for the geological and biological programs, which we will report on next week. This weekly report deals with the new instrumentation implemented during this expedition as contribution to the infrastructure program FRAM - Frontiers in Arctic Ocean Monitoring. The sea ice researcher Marcel Nicolaus together with the FRAM Team reports on the progress made with new and “old” technologies.
Increasing autonomy, and flexibility for the integration of various sensors for multifunctional research platforms build the basis of modern observatories for polar research. Such technologies allow the progression from classical point measurements to data sets with much higher spatial and temporal resolutions. But at the same time, it is essential to maintain the quality of each single measurement and to ensure that new methods are consistent with previous methods and results. The Helmholtz infrastructure program FRAM has supported the development of such new methods and measurement systems during the last two years. During PS101, we are testing some of these multisensor systems under the real, harsh polar conditions. This includes comparisons of results with measurements from established “classical” methodologies. Also our research ice breaker Polarstern was promoted to act as a complex sensor platform, carrying various “underway” measurements, including an autonomous water sampler and filtration unit that derives a suite of biological and geochemical parameters along the cruise track. The new under-ice ROV (remotely operated vehicle) “Beast” is equipped with a suite of sensors for interdisciplinary sea ice research. Similar sensors are also used for advanced autonomous ice tethered platforms (buoys) and moorings in the deep ocean. The ice buoys provide continuous year round observations while they drift through the Arctic Ocean when no ship can be around. A new sea ice information system (IceGIS) on board is of great benefit for navigation through the sea ice and for station planning under complicated ice conditions and low visibility.
The main work carried out at our ice stations during PS101 was performed by the new under-ice ROV “Beast”. The “Beast” enables us to study the properties of sea ice and the upper ocean as well as their spatial variability. Its distinctive interdisciplinary payload, enables the measurement of physical, biological, and geochemical parameters simultaneously. Different cameras on board document all dives. The results from the combined data sets of all sensors will enable us to learn more about the Arctic climate- and eco-systems, and how these systems interact. Using the new ROV, we operate one of the worlds leading platforms for research into sea ice covered oceans. This will strongly improve our abilities to study ice-ocean interaction in more detail across different scales. The ROV observations are complemented by measurements of sea ice thickness, snow cover, and surface properties. This gives a more complete picture of the ice cover under the current freeze-up conditions.
Another important aspect of our work on board is the deployment of buoys on the ice. These buoys measure atmospheric, snow, sea ice, and ocean parameters over the coming months. Similar to the ROV, we are advancing these systems by integrating new and further develop sensors and units. The new sensors fullfil the increasing need for more interdisciplinary data sets. The measurements are transmitted into international data networks right after acquisition. Thereby they contribute to daily weather forecasts and drift information as well as valuable information about the state of the Arctic ocean system. Simultaneously, we receive data here on Polarstern and integrate them directly into our IceGIS, contribution to our sea ice drift forecasts.
Very few ships can break ice and access the ice-covered Arctic Ocean. And even those that can, including our icebreaker Polarstern, need a lot of information as to the sea ice state, the wind and drift, to navigate the ship through open leads, thin ice, or to reach particular sites in due time. During this expedition we are testing a new system to combine all of this information into a geoinformatic system “IceGIS” for enhanced sea ice navigation. The majority of observations and point measurements at the sea floor that we carry out on PS101 require a particularly good knowledge of the sea ice and its drift. Once the instruments are deployed on a wire by the ship’s winches, no active navigation and positioning of the vessel is possible anymore. Polarstern drifts with the ice, while we try to hit a sampling spot smaller than the size of a football field in depths of up to 3000m. Impossible, some may say. The new IceGIS supports this challenge. It visualizes different satellite data, weather forecasts, and sea ice observations. The data are provided via our internet link from different sources on land with shortest possible delay, and they are integrated into one information system producing maps. Additional forecasts of the vessel’s drift are generated on board. Through a combination of all these different information, we have substantially increased our speed of operations in the ice. Precious ship time may be used more efficiently and fewer resources are used than usual.
The observed rapid decline in summer sea ice extent has led to a freshening of surface waters. This exacerbates the temperature-dependent stratification of the ocean and potentially reduces the supply of nutrients from deeper waters. The reduction in ice cover also allows for more light penetration and longer growth seasons, potentially stimulating algae blooms consuming nutrients in the water (Nitrate, Nitrite, Silicate, and Phosphate). Based on these changes, one could expect the Arctic Ocean to move from a predominantly light-controlled (ice-covered) to a more nutrient-controlled (open water) system. But in order to judge this balance and potential ecological consequences, the biogeochemistry of the Arctic system has to be better understood. The dynamics of this system become progressively more important under these environmental change conditions, and a better knowledge of carbonate chemistry and nutrient concentrations is needed.
The established standard method is to take water samples and process them by filtering and chemical analyses, to obtain insight about the presence of different organisms and nutrient concentrations. But this method is mostly limited to a coarse seasonal and spatial resolution. Hence, we use modern underway-measuring systems, installed on Polarstern. The main system consists of a sensor and filtration platform with in-situ sensors for long-term deployments in the Arctic. A pump, pipes, and a water inlet in the ship’s hull are used to supply our underway sensors with a continuous stream of water samples. At the same time, we operate in-situ sensors, submersed in the ocean to measure profiles or time series for more than a year. Unfortunately, these in situ sensors are less precise compared to the on-board chemical analyzes. The reasons for uncertainties and errors in the measurements are diverse. They range from the measuring principle itself over temperature influences to biofilm formation on the sensors which may compromise their results. To evaluate the reliability of the data sets, we compare these underway systems with conventionally analysed water samples. This also provides new insights into possible offsets or long term drifts of the sensors.
Besides the mobile platforms, we also have fixed point observatories with multisensory modules, two of which were successfully recovered during this mission. Besides new innovations like ADCP systems that monitor currents based on the movement of particles in the water column, we use more conventional sensors like CTDs to obtain conductivity and temperature data at certain depths. To get information about biological and chemical parameters, we deploy sediment traps and novel types of water samplers which allow collection of year-round nutrient data. Sediment traps are very useful for quantifying the composition and amount of biomass sinking down from the surface to the seafloor. The water sampler (type RAS500) was deployed for the first time in the central Arctic and successfully recovered during this cruise. It provides 48 reference water samples for sensor calibration and further chemical analyses back in the institute, that help us understand better the seasonal dynamics of biogeochemical processes in the ice, and the consequences the sea ice retreat will have.
With best greetings from Polarstern Expedition PS101, Marcel Nicolaus and the FRAM team