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

Wetterich, Sebastian; Davidson, Thomas A.; Bobrov, Anatoly; Opel, Thomas; Windirsch, Torben; Johansen, Kasper L.; González-Bergonzoni, Ivan; Mosbech, Anders; Jeppesen, Erik

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 inline-formulaC∕N ratios and less depleted inline-formulaδ13C, 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 inline-formulaδ15N trends, where decreasing accumulation led to increasing depletion in inline-formulaδ15N as seen in the little-auk-related data. In contrast, the more decomposed OM of the thick-billed murre site shows almost stable inline-formulaδ15N. 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 inline-formulaδ18O of inline-formula M7inlinescrollmathml - normal 18.0 ± normal 0.8 58pt10ptsvg-formulamathimg84d3a8dfe750b52b9d22d7c9a0873899 bg-16-4261-2019-ie00001.svg58pt10ptbg-16-4261-2019-ie00001.png  ‰, mean inline-formulaδD of inline-formula M9inlinescrollmathml - normal 136.2 ± normal 5.7 64pt10ptsvg-formulamathimg659243ef4eabe62c7c90b7a82c5fbdc2 bg-16-4261-2019-ie00002.svg64pt10ptbg-16-4261-2019-ie00002.png  ‰, mean inline-formulad excess of inline-formula7.7±0.7 ‰, and a inline-formulaδ18O-inline-formulaδD 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.

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Wetterich, Sebastian / Davidson, Thomas A. / Bobrov, Anatoly / et al: Stable isotope signatures of Holocene syngenetic permafrost trace seabird presence in the Thule District (NW Greenland). 2019. Copernicus Publications.

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