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. Holocene permafrost from ice wedge polygons in the vicinity oflarge seabird breeding colonies in the Thule District, NW Greenland, wasdrilled to explore the relation between permafrost aggradation and seabirdpresence. The latter is reliant on the presence of the North Water Polynya (NOW)in the northern Baffin Bay. The onset of peat accumulationassociated with the arrival of little auks (Alle alle) in a breeding colony atAnnikitisoq, north of Cape York, is radiocarbon-dated to 4400 cal BP. Athick-billed murre (Uria lomvia) colony on Appat (Saunders Island) in the mouth of theWolstenholme Fjord started 5650 cal BP. Both species providemarine-derived nutrients (MDNs) that fertilize vegetation and promote peatgrowth. The geochemical signature of organic matter left by the birds istraceable in the frozen Holocene peat. The peat accumulation rates at bothsites are highest after the onset, decrease over time, and were about2-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 incomparably high C∕N ratios and less depleted δ13C, pointing to a lowerdegree of OM decomposition at the little auk site, while the oppositepattern can be discerned at the thick-billed murre site. Peat accumulationrates correspond to δ15N trends, where decreasing accumulationled to increasing depletion in δ15N as seen in the little-auk-related data. In contrast, the more decomposed OM of the thick-billed murresite shows almost stable δ15N. Late Holocene wedge ice fed bycold season precipitation was studied at the little auk site and providesthe 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. Thesyngenetic ice wedge polygon development is mirrored in testacean records ofthe little auk site and delineates polygon low-center, dry-out, andpolygon-high-center stages. The syngenetic permafrost formation directlydepending on peat growth (controlled by bird activity) falls within theperiod of neoglacial cooling and the establishment of the NOW, thusindirectly following the Holocene climate trends.

Stable isotope signatures of Holocene syngenetic permafrost trace seabird presence in the Thule District (NW Greenland)