Sea-ice Buoy Retrieved After a Long Trek Across the Arctic
31 March 2021
The thermistor buoy (2018T52) was installed in the Arctic on 14.09.2018, where it continued to transmit data until 04.07.2020 (see Figure 1). After an impressive journey through the Central Arctic, its return to Bremerhaven makes for an equally exciting story!
When was the buoy deployed and how far did it travel?
As part of a German-Russian-American collaboration (project name: NABOS / TRANSDRIFT / TICE), the buoy designated 2018T52 was deployed in the Russian sector of the Arctic Ocean during the ARKTIKA 2018 expedition on board the Russian icebreaker Akademik Tryoshnikov, which continued from 18 August 2018 to 29 September 2018. We’ve already reported here on the buoys that were installed during the expedition.
The aim of the monitoring programme (Multidisciplinary Ice-based Distributed Observatory - MIDO) was to install buoys in what are known as arrays (measuring fields) on the ice in the northern Laptev and East Siberian Seas (see Figure 2). In one such array, ice mass balance buoys, including 2018T52, and snow buoys were placed on a total of three small floes (100 - 200 m diameter). Complex, multi-layer bio-optical buoys and a snow buoy were installed on a larger central floe located between the three smaller ones. Setting up the systems took up to three hours on the smaller floes, and up to eight hours on the larger ones.
Between 11.09.2018 and 16.09.2018, two complete arrays with a total of 19 buoys were deployed in the East Siberian Sea. The region lies in the southern Makarov Basin, east of the Lomonosov Ridge and ca. 610 km southeast of the position where the MOSAiC expedition began its drift roughly one year later, at 85.08°N, 134.43°E. Buoy 2018T52 was deployed on the ice by Miriam Hansen (University of Kiel / GEOMAR), Simon Hummel (AWI) and H. Jakob Belter (AWI) on 14.09.2018 (position: 80.76°N, 163.18°E) (Figure 1, centre and right) and continued to transmit data until 04.07.2020. After a long journey with the Transpolar Drift, covering a linear distance of ca. 2240 km, but an actual drift distance of ca. 4920 km, it finally reached Fram Strait roughly four months before the MOSAiC floe, despite having been installed more than a year before the start of the MOSAiC expedition (Fig. 3).
Finding the buoy
Thermistor buoys do not float and normally sink into the sea as soon as the ice is no longer able to support their weight. As a result, most of them can’t be recovered and are lost. However, on 04.07.2020, buoy 2018T52 reached Jan Mayen, a small volcanic island roughly 550 km north of Iceland in the Greenland Sea (see Fig. 3). There it was discovered on a beach by Pål Lunde and Jared Elgvin, head technicians at the weather station in Olonkinbyen, the island’s only settlement. They contacted Jakob Belter from the Alfred Wegener Institute, and sent the case and measuring unit back to Bremerhaven (Photos 1 and 2). The buoy arrived there on 01.03.2021, exactly 900 days after being installed on the ice. “I was surprised when I received the call! It’s unusual to say the least for one of these buoys to survive the ice melting after such a long time drifting, and then to be found after washing up on a beach! As a result, the buoy’s not only provided an extensive and valuable dataset; it’s also a very special memento,” says Belter. “We can learn from this buoy and its story, and design future buoys to float, so that we’ll hopefully get them back more often.”
Using the data
Even before 2018T52 arrived back in Bremerhaven, Simon Hummel, who was among those who installed it in 2018, had begun processing the ice-thickness data from the buoys deployed back then. A student assistant on board the Akademik Tryoshnikov at the time, he is now analysing the data as part of his master’s thesis. His aim is to determine, on the one hand, the thermodynamic ice growth during the drift, and on the other (drawing on positioning data), how the buoys drifted relative to one another and from that the dynamic ice growth component. In addition, he is using the data to validate sea-ice growth models, which will help to improve future forecasts of the Arctic sea ice along the Transpolar Drift.
Background information on buoy-based monitoring
Monitoring systems installed on the sea ice of the Arctic and Antarctic, so-called Lagrangian buoys, are especially important in terms of understanding the polar climate system. They are used to document developments in the sea ice and especially how it responds to changes in atmospheric and oceanic conditions, offering a better ‘big picture’ of the system.
Frequently employed sea-ice buoys include comparatively simple GPS drifters (also called “surface velocity profilers”), and more complex snow and sea-ice mass balance buoys, which, along with meteorological parameters, constantly measure ice and snow thickness. These instruments represent the ideal complement to satellite-based observations, which offer broader spatial coverage. Data from these buoys is also available at meereisportal.de. Here, both the drift trajectories and the individual parameters can be viewed in near-real time and downloaded.
In addition, sea-ice-based buoys play a vital part in weather predictions for the polar regions. They measure e.g. the atmospheric pressure and temperature over the polar oceans and transmit this data, together with their GPS coordinates, to the Global Telecommunications System (GTS) and the WMO (World Meteorological Organisation) within a matter of minutes. From there, the measurements are freely available to the public – a fact that especially the prediction models used by various weather services and meteorological organisations profit from.
Thermistor buoys make it possible to distinguish between air, ice and water on the basis of their respective thermal conductivities. To do so, first the regular temperature is recorded. The thermistors are then briefly heated and the temperature measured again after a few seconds. The difference between the two values depends on the medium’s ability to transport the heat created, and as such provides information on its thermal conductivity. As a result, depth profiles include spikes in the temperature difference, which indicate boundary layers between various media, e.g. between snow and ice or between ice and water. Employing this method makes it possible, from the profiles, to determine the conditions on the underside of the ice even in summer, when the temperatures of the sea ice and surrounding ocean are almost identical. Measuring conductivity also provides information on the snow thickness (see Figure 1, right).
Lei, R., M. Hoppmann, B. Cheng, G. Zuo, D. Gui, Q. Cai, H. J. Belter, W. Yang, 2021. Seasonal changes in sea ice kinematics and deformation in the Pacific sector of the Arctic Ocean in 2018/19, The Cryosphere, 15, 1321-1341, doi.org/10.5194/tc-15-1321-2021
Dr H. Jakob Belter (AWI)
Dr Renate Treffeisen (AWI)
Dr Klaus Grosfeld (AWI)