Historical seabird population dynamics and their effects on Arctic pond ecosystems: a multi-proxy paleolimnological study from Cape Vera, Devon Island, Arctic Canada

Rapid environmental changes occurring in polar regions may pose a significant threat to the similar to 10 million seabirds currently inhabiting the Canadian Arctic. However, a paucity of long-term data on seabird population dynamics makes effective management difficult. As top predators in the oceanic pelagic foodweb, seabirds provide marine-derived nutrients to freshwater habitats via their guano, causing trophic cascades that may be tracked using paleolimnological techniques. Diatoms (Bacillariophyceae) are the most commonly used bioindicators in paleolimnological studies and, because they are known to respond sensitively to changes in trophic status, may be effective proxies for tracking changes in seabird population dynamics. Here, we present diatom data obtained from sediment cores in seabird-affected ponds near Cape Vera, Devon Island, High Arctic Canada. We also report on additional sedimentary proxies that can be used to track seabird influence, namely stable isotopes of nitrogen (delta N-15) and spectrally-inferred chlorophyll-a. Sedimentary delta N-15 appears to track well the proximity of the ponds to the seabird colony, as seabird wastes are elevated in delta N-15 relative to terrestrial and freshwater sources. Interpretations are less straightforward for sedimentary chlorophyll-a profiles and diatom-inferred changes, which show no consistent relationship to one another or to shifts in sediment delta N-15. Diatom proxies show changes consistent with delta N-15 where there have been large shifts in delta N-15 through time, but no clear pattern where delta N-15 inputs have remained relatively stable. As such, diatom assemblage changes alone may be too blunt a tool to reconstruct bird populations at Cape Vera. Our results support previous research findings that diatom assemblages do not respond in a simple manner to prolonged nutrient enrichment in high Arctic ponds, which is in part related to the overriding influence of climate on aquatic biota in these ice-dominated systems.