Double-Trouble

Global warming causes changes to the sea-ice habitat with yet uncertain consequences for polar marine food webs. Previous research suggests that pelagic food webs in the Central Arctic Ocean (CAO) are highly dependent on ice-associated food sources (Fig. 1), but how prevailing trophic structures will change with ice retreat remains unclear. Superimposed on changing environmental conditions, CAO food-web dynamics are subject to additional sources of stress: Notably, facilitated by sea-ice retreat, increasing influx of Atlantic waters, riverine input and marine traffic will bring more anthropogenic pollutants, even to remote Arctic regions, where they are entrained in water and sea ice, and transferred along the marine food chain. 

Figure 1. Carbon flow in polar ecosystems. Sea-ice algae and phytoplankton represent the base of the food web. Carbon (=energy) is transferred from the primary producers via zooplankton and fish to top predators. Ungrazed algae sink to the seafloor to fuel benthic communities.

Consequences of individual stressors on the structure and functioning of marine food webs have been documented, but information on cumulative impacts of multiple pressures, particularly in the remote CAO, is virtually absent. In this context, Double-Trouble aims at i) assessing trophic structures and the degree of anthropogenic pollution under current environmental conditions and ii) simulating cumulative effects of warming and increasing pollution on future CAO food webs (Fig. 2) to help identify the consequences of ecosystem change for future sustainable fisheries management in the CAO. 

Figure 2. Carbon flow through the CAO food web with unknown changes under sea-ice decline and different sources of anthropogenic pollution threatening current CAO ecosystem structure and functioning: atmospheric pollution of sea ice and water column, sea ice as contaminants source upon melt, risk for contamination from increased human activity (shipping, fishing, tourism).

Additionally, complementary data on trophic relationships and the pollution burden of Antarctic food webs will allow for a comparison of the resilience vs. vulnerability to changing environmental conditions and pollution between both Polar Regions. We will elucidate trophic structures and interactions by applying a state-of-the-art multidimensional trophic marker approach (Fig.3). For example, lipid and stable isotope compositions can inform about the preference for diatom- vs. dinoflagellate-produced carbon as well as the origin of this carbon source, i.e., ice-associated or pelagic, in a consumer. It is crucial to quantify the trophic dependency of the CAO food web on ice algae-produced carbon to assess potential consequences of change to the spatio-temporal availability of ice algae due to warming. Results will depict the status quo of the food-web structure, providing a basis for predictions about the functioning of the CAO ecosystem in the decades to come.

To outline the current pollution burden of the CAO food web, we will identify and quantify major contaminants. This will include legacy Persistent Organic Pollutants (POPs), regulated and partly banned by the Stockholm Convention due to their known adverse effects on ecosystem and health, as well as Chemicals of Emerging Arctic Concern (CEAC), substances with a potential to pose a risk for the environment and ultimately human health, which are not yet controlled by (international) regulations. Additionally, we will assess the distribution of microplastics in the food web. Using field samples and an experimental approach, the aim is to determine the degree of exposure and trophic transfer of anthropogenic pollutants with a potential increase in concentration along the food chain (bioaccumulation, biomagnification). Despite strong scientific interest, our knowledge on the degree and impact of anthropogenic pollution in the Arctic is still in its infancy and the research effort clearly needs to be increased, particularly for poorly studied regions such as the CAO.