Hard Data and Virtual Plankton — How We Model Ship Traffic’s Impact on the Arctic

The North Atlantic Arctic region is characterized by significant connectivity between its oceanic subregions, driven by both human activity and natural oceanographic processes.

On the one hand, growing ship traffic, particularly along emerging and established Arctic shipping routes connects ports and coastal communities. However, the ship traffic along these connections is also a source of pollutants. For example, by discharging wastewater vessels add nutrients, pharmaceuticals, as well as micro- and nanoplastics to the environment.

On the other hand, powerful ocean currents, like the North Atlantic Drift and the East Greenland Current, create physical and ecological linkages by transporting water masses, heat, nutrients, and marine organisms across vast distances. These same currents also facilitate the long-range transport of pollutants, including contaminants originating far outside the Arctic.

Together, these interconnected pathways shape the region’s environmental health, economic potential, and geopolitical significance.

Ship traffic depends on the season

Shipping activity in the North Atlantic Arctic region follows distinct seasonal patterns, largely dictated by sea ice extent and weather conditions.

Most traffic is concentrated in the ice-free summer and early autumn months, when navigation routes become better accessible. Recent and future changes in sea ice cover may impact these seasonal patterns. Furthermore, tourism-related vessel traffic has become more prominent in recent years, even though the overall number of tourist ships remains relatively low compared to cargo or fishing vessels.

However, the cruise ships tend to have a disproportionately large environmental footprint. These ships generate significantly higher volumes of waste per voyage, including graywater (from sinks, showers, and laundries), as well as black water (from toilets), which are treated differently amongst ships before discharge. This seasonal influx of wastewater adds a layer of environmental pressure to an already sensitive and rapidly changing ecosystem.

How we model the impact on plankton ecosystem

Within ICEBERG, our goal is to resolve some of the potential impacts of these discharges on the marine plankton. In order to do this, we combine model simulations with Arctic Ship Traffic Data (ASTD), provided by the working group Protection of the Arctic Marine Environment (PAME) of the Arctic Council.

These data resolve ship tracks from AIS (automatic identification system) positions and estimated volumes of wastewater discharged by the ships.

The impact on the plankton ecosystem will be simulated and assessed along water masses that are passing through the three ICEBERG case study sites. For this, we use ensembles of model trajectories (pathways of ‘virtual plankton’ drifting with the ocean currents) that cross the respective case study sites during the months between April through October. Along their journey, the growth of the plankton will be affected differently by the ships’ discharges.

Our modelling approach allows us to compare a plankton ecosystem affected by wastewater discharges from marine traffic with a ‘control ecosystem’ that is not perturbed by marine traffic.

Such comparisons enable us to quantify the impact of wastewater pollution associated with ships. It also helps us identify times and locations when and where the discharge—e.g. from cruise ships— has minimal impact or where it should be better avoided.

Written by Markus Schartau and Vanessa Lampe (GEOMAR).

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