Abstract
Abstract. Holocene permafrost from ice wedge polygons in the vicinity of large seabird breeding colonies in the Thule District, NW Greenland, was drilled to explore the relation between permafrost aggradation and seabird presence. The latter is reliant on the presence of the North Water Polynya (NOW) in the northern Baffin Bay. The onset of peat accumulation associated with the arrival of little auks (Alle alle) in a breeding colony at Annikitisoq, north of Cape York, is radiocarbon-dated to 4400 cal BP. A thick-billed murre (Uria lomvia) colony on Appat (Saunders Island) in the mouth of the Wolstenholme Fjord started 5650 cal BP. Both species provide marine-derived nutrients (MDNs) that fertilize vegetation and promote peat growth. The geochemical signature of organic matter left by the birds is traceable in the frozen Holocene peat. The peat accumulation rates at both sites are highest after the onset, decrease over time, and were about 2-times faster at the little auk site than at the thick-billed murre site. High accumulation rates induce shorter periods of organic matter (OM) decomposition before it enters the perennially frozen state. This is seen in comparably high C∕N ratios and less depleted δ13C, pointing to a lower degree of OM decomposition at the little auk site, while the opposite pattern can be discerned at the thick-billed murre site. Peat accumulation rates correspond to δ15N trends, where decreasing accumulation led to increasing depletion in δ15N as seen in the little-auk-related data. In contrast, the more decomposed OM of the thick-billed murre site shows almost stable δ15N. Late Holocene wedge ice fed by cold season precipitation was studied at the little auk site and provides the first stable-water isotopic record from Greenland with mean δ18O of -18.0±0.8 ‰, mean δD of -136.2±5.7 ‰, mean d excess of 7.7±0.7 ‰, and a δ18O-δD slope of 7.27, which is close to those of the modern Thule meteoric water line. The syngenetic ice wedge polygon development is mirrored in testacean records of the little auk site and delineates polygon low-center, dry-out, and polygon-high-center stages. The syngenetic permafrost formation directly depending on peat growth (controlled by bird activity) falls within the period of neoglacial cooling and the establishment of the NOW, thus indirectly following the Holocene climate trends.
Highlights
The Thule District of Northwest Greenland (Fig. 1) is notable for its large seabird colonies along the coast, especially the little auk, Alle alle (e.g., Boertmann and Mosbech, 1998), and the thick-billed murre, Uria lomvia (e.g., Kampp, 1990), both belonging to the auk family (Alcidae)
The mainly piscivorous thick-billed murre and the planktivorous little auk both depend on the resources from the productive North Water Polynya (), which is situated in northern Baffin Bay (Stirling, 1980; Davidson et al, 2018)
The ice content is high in the frozen core with a mean value of 80 ± 4 wt %, while the moisture content of the active layer decreases to 39 wt % in the uppermost sample
Summary
The Thule District of Northwest Greenland (Fig. 1) is notable for its large seabird colonies along the coast, especially the little auk, Alle alle (e.g., Boertmann and Mosbech, 1998), and the thick-billed murre, Uria lomvia (e.g., Kampp, 1990), both belonging to the auk family (Alcidae). The area is especially important for the little auk as > 80 % of the global breeding population of the species, corresponding to approximately 33 million pairs, is estimated to breed Wetterich et al.: Permafrost and seabird presence in NW Greenland and Mosbech, 1998; Kampp et al, 2000; Egevang et al, 2003) This has been linked to an exceptional abundance of their preferred zooplankton prey (Calanus hyperboreus and C. glacialis), which is available in the throughout the little auk breeding season (Møller et al, 2018). The thickbilled murre population of the Thule District is estimated to be approx. 225 000 breeding pairs, accounting for 68 % of the Greenlandic breeding population of the species (Merkel et al, 2014)
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