Consequences of Atlantification on a Zooplanktivorous Arctic Seabird

Global warming, combined with an increasing influence of Atlantic Waters in the European Arctic, are causing a so-called Atlantification of the Arctic. This phenomenon is affecting the plankton biomass and communities with potential consequences for the upper trophic levels. Using long-term data (2005-2020) from a high Arctic zooplanktivorous seabird, the little auk (Alle alle), we tested the hypothesis that the Atlantification affects its diet, body condition and demography. We based our study on data collected in three fjords in West Spitsbergen, Svalbard, characterized by distinct oceanographic conditions. In all three fjords, we found a positive relationship between the inflow of Atlantic Waters and the proportion of Atlantic prey, notably of the copepod Calanus finmarchicus, in the little auk chick diet. A high proportion of Atlantic prey was negatively associated with adult body mass (though the effect size was small) and with chick survival (only in one fjord where chick survival until 21 days was available). We also found a negative and marginally significant effect of the average proportion of Atlantic prey in the chick diet on chick growth rate (data were available for one fjord only). Our results suggest that there are fitness costs for the little auk associated with the Atlantification of West Spitsbergen fjords. These costs seem especially pronounced during the late phase of the chick rearing period, when the energetic needs of the chicks are the highest. Consequently, even if little auks can partly adapt their foraging behaviour to changing environmental conditions, they are negatively affected by the ongoing changes in the Arctic marine ecosystems. These results stress the importance of long-term monitoring data in the Arctic to improve our understanding of the ongoing Atlantification and highlight the relevance of using seabirds as indicators of environmental change.publishedVersio

Consequences of Atlantification on a Zooplanktivorous Arctic Seabird

Global warming, combined with an increasing influence of Atlantic Waters in the European Arctic, are causing a so-called Atlantification of the Arctic. This phenomenon is affecting the plankton biomass and communities with potential consequences for the upper trophic levels. Using long-term data (2005-2020) from a high Arctic zooplanktivorous seabird, the little auk (Alle alle), we tested the hypothesis that the Atlantification affects its diet, body condition and demography. We based our study on data collected in three fjords in West Spitsbergen, Svalbard, characterized by distinct oceanographic conditions. In all three fjords, we found a positive relationship between the inflow of Atlantic Waters and the proportion of Atlantic prey, notably of the copepod Calanus finmarchicus, in the little auk chick diet. A high proportion of Atlantic prey was negatively associated with adult body mass (though the effect size was small) and with chick survival (only in one fjord where chick survival until 21 days was available). We also found a negative and marginally significant effect of the average proportion of Atlantic prey in the chick diet on chick growth rate (data were available for one fjord only). Our results suggest that there are fitness costs for the little auk associated with the Atlantification of West Spitsbergen fjords. These costs seem especially pronounced during the late phase of the chick rearing period, when the energetic needs of the chicks are the highest. Consequently, even if little auks can partly adapt their foraging behaviour to changing environmental conditions, they are negatively affected by the ongoing changes in the Arctic marine ecosystems. These results stress the importance of long-term monitoring data in the Arctic to improve our understanding of the ongoing Atlantification and highlight the relevance of using seabirds as indicators of environmental change.publishedVersio

The Response of Tidewater Glacier Termini Positions in Hornsund (Svalbard) to Climate Forcing, 1992–2020

Many Arctic marine-terminating glaciers have undergone rapid retreats in recent decades. Seasonal and year-to-year variations in terminus position act on all tidewater glaciers, but the key controls on those changes vary from region to region. Here, we examined seasonal and decadal changes in termini positions of seven tidewater glaciers in the inner part of Hornsund, the southernmost fjord of Spitsbergen (Svalbard Archipelago), based on a variety of data from 1992 to 2020. Combining satellite imagery, basic meteorological data (air temperature, positive degree day index (PDD), liquid precipitation), sea surface temperature (SST), mean temperature in the glacier forefield bays, fast sea ice cover, and bathymetry near the glacier front, we examined the influence of potential controlling parameters on interannual and seasonal variability of the glacier termini. We found regional synchrony between terminus advance/retreat and climate variables. At a regional scale, annual fluctuation changes are related to PDD and SST, while summer fluctuations are linked to PDD, although individual glaciers are shown to have differing sensitivities to potential climate drivers. We also found that the retreat period in Hornsund generally lasts from June to October-December. Onset of the retreat is related to sea and air temperature, and in some cases follows the disappearance of the ice cover. These results indicate that the expected increase in meltwater runoff in Svalbard, the input of relatively warm Atlantic water to the fjord, and the increasing trend of longer summer and warmer winter periods will have implications for glacier velocity and frontal ablatio