Date Published: March 7, 2018
Publisher: Springer Netherlands
Author(s): Thomas A. Davidson, Sebastian Wetterich, Kasper L. Johansen, Bjarne Grønnow, Torben Windirsch, Erik Jeppesen, Jari Syväranta, Jesper Olsen, Ivan González-Bergonzoni, Astrid Strunk, Nicolaj K. Larsen, Hanno Meyer, Jens Søndergaard, Rune Dietz, Igor Eulears, Anders Mosbech.
The North Water (NOW) polynya is one of the most productive marine areas of the Arctic and an important breeding area for millions of seabirds. There is, however, little information on the dynamics of the polynya or the bird populations over the long term. Here, we used sediment archives from a lake and peat deposits along the Greenland coast of the NOW polynya to track long-term patterns in the dynamics of the seabird populations. Radiocarbon dates show that the thick-billed murre (Uria lomvia) and the common eider (Somateria mollissima) have been present for at least 5500 cal. years. The first recorded arrival of the little auk (Alle alle) was around 4400 cal. years bp at Annikitsoq, with arrival at Qeqertaq (Salve Ø) colony dated to 3600 cal. years bp. Concentrations of cadmium and phosphorus (both abundant in little auk guano) in the lake and peat cores suggest that there was a period of large variation in bird numbers between 2500 and 1500 cal. years bp. The little auk arrival times show a strong accord with past periods of colder climate and with some aspects of human settlement in the area.
The North Water polynya (NOW) marine ecosystem is host to the largest seabird populations in Greenland. The community is diverse with 14 regular breeders and a few more species occurring as non-breeding summer visitors. The seabirds are almost exclusively present in the spring and summer, with the exception of some black guillemots (Cepphus grylle), which can winter in the NOW. Here, we focus on the three most abundant seabird species: the little auk (Alle alle), the thick-billed murre (Uria lomvia), and the common eider (Somateria mollissima) (Fig. 1). These species have the largest biomass and the greatest importance of the locally harvested seabird species. The breeding population of the little auk in the NOW region is immense, estimated at 33 million pairs (Boertmann and Mosbech 1998; Egevang et al. 2003) and corresponding to more than 80% of the global breeding population. The thick-billed murre colonies along the Greenland coast of the NOW consist of approximately 225 000 breeding pairs (Merkel et al. 2014) representing two thirds of the breeding population in Greenland. Currently, the NOW is the only area in Greenland where the thick-billed murre population is not in decline. The common eider breeding population in the NOW was estimated at 25–30 000 pairs in 2009, and has had a fivefold increase between 1997 and 2009 (Burnham et al. 2012). This increase is related to the stricter harvest regulations which came into force in 2001, especially the restricting of spring harvest near the colonies, which sparked a general population increase in all West Greenland populations following a decline in the 20th century related to overharvesting (Merkel 2010). Thus, despite the large uncertainties in the estimates, the NOW is clearly of great international importance to the species.Fig. 1Overview map of the coring sites and breeding colonies of little auk, Qoororsuaq (Søkongedalen—SD1), Annikitsoq, Great Lake—GL-3 and Kuukkat (Robertson fjord—RF1), Qeqertaq (Salve Ø—NOW5a) thick-billed murre (Saunders Ø—SI-1) and common eider Booth Sund—BS-1 and Iterlassuup Qeqertaarsui (Three Sister Bess—TSB-2). For the latter two species, colony sizes are given as number of breeding pairs. Colony data come from Boertmann and Mosbech (1998) and The Greenland Seabird Colony Register, maintained by Danish Center for Environment and Energy, Aarhus University, and Greenland Institute of Natural Resources. The estimated date of arrival is the median cal. ka years bp calculated from 14C dates and age modelling (see “Materials and methods”)
Identification of the point of arrival of seabirds in a particular catchment is relatively straightforward as the transport of marine-derived nutrients (MDN) transforms the landscape (González-Bergonzoni et al. 2017; Mosbech et al. 2018). The estimated time of arrival can be determined by dating basal samples from peat cores, or the point of marked increases of δ15N in lake sediments. Values of δ15N in organic matter in lake sediments not affected by seabirds from the High Arctic are generally not higher than 3‰ and seldom rise higher 4–5‰ (e.g. Janbu et al. 2011; Perren et al. 2012). A rise in δ15N of 2–3‰ δ15N has been used in other studies to track millennial scale change in sockeye salmon population in Alaska (Finney et al. 2002) and increases to levels similar to those reported here, up to and > 20‰, have been used to track human influence on fresh waters, via transport of MDN, on the Canadian side of the NOW (Michelutti et al. 2013). Furthermore, there is an almost total absence of peat accumulation in the NOW region outside bird colonies (Mosbech et al. 2018), and in addition, the δ15N values of the peat cores, though variable between sites, are much higher than values reported for non-bird driven peat accumulation (Skrzypek et al. 2008). Thus, the combination of data presented here provides an unequivocal marker of bird arrival. The evidence indicates that the earliest arrival of the little auk in the NOW region was around 4400 cal. years bp, whereas the thick-billed murre and the common eider have been present for at least 1500 years longer. The three species discussed here breed in completely different habitats and landscape settings, so there is no possibility of a change in bird community at a particular site.
This study is the first to investigate the long-term patterns in the presence, absence, and abundance of seabird colonies in the NOW across multiple locations and to provide direct evidence of the timing of the onset of colony formation of the three of the key sea bird species the region. The data, particularly when synthesised together, provide indirect evidence on the state, or ‘strength’ of the polynya through time. Some remarkable correlations between cold periods, bird arrival, and number, inferred polynya condition, and major human demographic events are evident. We should caution that these are inferred polynya conditions, and that there are no simple one-to-one relations between the polynya and demographic developments. For example, periods where the polynya is inferred to be large and productive appear coincide with the absence of humans. The present study certainly encourages further investigations along the same lines and in collaboration with other disciplines exploring polynya formation.