Icebergs are a major threat to shipping in the North Atlantic, particularly around the Grand Banks of Newfoundland where shipping lanes are densely populated. The importance of monitoring icebergs has become clear since the tragic sinking of the Titanic in 1912. However, the drift of these masses of ice from Greenland is complex to model because of the various interactions with the ocean, the atmosphere and the pack ice. A new approach is currently being considered and tested in Baffin Bay.
by Laurie Henry
Baffin Bay is a coastal sea in the Arctic Ocean, located between Greenland and north-eastern Canada. A team of researchers from the Canadian universities of Manitoba,Alberta,Ottawa and Carleton, led by J.M. Marson, has published a study in the Journal of Geophysical Research: Oceans that highlights the improvement of a numerical model using a Sea Ice Locking (SIL) mechanism. This new configuration makes it possible to better predict iceberg drift, especially in winter when Baffin Bay is covered in thick pack ice.
Innovative modelling to understand iceberg drift in winter conditions
To study the effects of pack ice locking (SIL) on iceberg drift, the researchers incorporated this mechanism into the NEMO-ICB ocean model. This model simulates iceberg drift by taking into account various natural forces: the force of ocean currents, wind pressure and, in this particular case, the resistance exerted by the pack ice on the icebergs.
The SIL mechanism represents a breakthrough by modelling the force required for the pack ice to ‘lock’ an iceberg, preventing it from moving freely under the effect of currents. Unlike other models that apply a uniform drag force, SIL adjusts this force according to the local characteristics of the pack ice, such as its thickness and concentration, making it possible to better simulate the specific conditions in Baffin Bay, where dense pack ice plays a decisive role in iceberg movements.
Map showing the bathymetry of most of the sub-polar North Atlantic. The arrows indicate the general pattern of ocean circulation, where orange represents relatively warm currents and blue/black relatively cold currents.© J. M. Marson et al., 2024
The researchers carried out this study using two simulation configurations over a period of 15 years (2002-2017): a control configuration (CTL) based on the classic model without the locking mechanism, and another configuration incorporating the SIL.
In the CTL configuration, the pack ice simply acts as a drag force proportional to its density, without taking into account the possibility of locking. In the SIL configuration, on the other hand, the forces exerted by the pack ice on the icebergs vary according to the concentration and thickness of the ice. When the pack ice exceeds a certain threshold of concentration (90%) and resistance, it ‘captures’ the iceberg and causes it to drift in synchronisation with it. This configuration has enabled researchers to simulate and observe the trajectories of icebergs captured in different ice conditions in winter.
To assess the accuracy of these simulations, the team used observation data from satellites and tracking beacons attached to icebergs. These beacons, called Cryologger ITBs, recorded the position of the icebergs hour by hour, providing a detailed view of the actual trajectories of the icebergs in Baffin Bay. The satellites provided information on the concentration and speed of the pack ice. The researchers then compared the trajectories simulated by the model with those observed in reality. They found that, when the SIL mechanism was activated, the modelled trajectories were more closely aligned with those observed in winter, as the icebergs moved more often with the pack ice when it reached a high concentration, thus modifying their usual drifting behaviour and their interaction with the currents.
Altered trajectories and an extended lifespan for icebergs
The integration of the pack-ice locking mechanism into the drift models has led to a better understanding of the winter trajectories of icebergs in Baffin Bay. More specifically, the researchers found that when icebergs are locked in by pack ice, they tend to move away from the Baffin Island coastal current and drift further south-eastwards. Without the SIL mechanism, the icebergs mainly follow the cyclonic circulation of the bay, remaining concentrated along the current. The data show that, in the scenarios with SIL, there is a significant increase in the number of icebergs moving away from this current, which explains their increased presence in Newfoundland waters in winter. In addition, the lifespan of the icebergs is extended, from 220 to 241 days, because the pack ice protects these masses of ice from the rapid melting caused by waves and winds.
(a) Map showing the net number of icebergs drifting faster (red) or slower (blue) than pack ice in the CTL simulation (2002-2017). The dotted lines mark the main areas where icebergs drift more slowly. (b) Speed of icebergs relative to pack ice under conditions of high ice concentration for the CTL simulation. (c) Direction of iceberg drift in Baffin Bay in winter (January-March) for CTL (in blue) and SIL (in red). The size of the bars indicates the frequency of movement in each direction.. © J. M. Marson et al., 2024
These results have important implications for maritime safety and risk management. Currently, around 400 icebergs cross the 48th parallel north each year, a critical point for transatlantic shipping routes. The study revealed that the application of the SIL mechanism makes it possible to better predict the peak passage of icebergs at this point. The seasonal forecasts are adjusted by one month, and the number of predicted passages is revised upwards (from 347 to 390), which corresponds more closely to actual observations. By anticipating these movements, the authorities can plan shipping routes more safely, minimising the risk of collision with ships converging on the Grand Banks of Newfoundland, where several international routes are concentrated.
Map showing the difference in iceberg distribution between the SIL and CTL simulations (SIL – CTL), indicating the areas where icebergs drift more (in red) or less often (in blue) with the ice pack locking mechanism (SIL) compared with the traditional simulation (CTL). The black dotted line encircles the main region where a decrease in the presence of icebergs is observed. © J. M. Marson et al., 2024
The study also points out that the blocking by pack ice modifies the distribution of iceberg meltwater in the sub-polar North Atlantic. Simulations have shown that icebergs protected by pack ice discharge this meltwater closer to the Canadian coast, particularly around Baffin Bay, Lancaster Sound and the Labrador coast, rather than dispersing into the interior of the bay and the Labrador Sea.
This increased concentration of melt may have repercussions on the local circulation of ocean currents and the distribution of salt, potentially influencing marine ecosystems and regional ocean dynamics. For climate management, these observations are crucial as they could help refine models of the distribution of freshwater masses in the North Atlantic Ocean and potentially improve maritime safety by better anticipating areas at risk.
Source : Marson, J. M., Myers, P. G., Garbo, A., Copland, L., & Mueller, D. (2024). “Sea ice-driven iceberg drift in Baffin Bay”. Journal of Geophysical Research: Oceans, 129, e2023JC020697.