Recent occupation by Adélie Penguins (Pygoscelis adeliae) at Hope Bay and Seymour Island and the ‘northern enigma’ in the Antarctic Peninsula

Abstract

We excavated active and abandoned Ade ´lie Penguin (Pygoscelis adeliae) colonies at Seymour Island and Hope Bay, Antarctic Peninsula, to determine an occupation history for this species at these sites. Previous research at Hope Bay has indicated an occupation there since the middle Holocene, based on a sediment record from Lake Boeckella. Excavations revealed only shallow and relatively fresh ornithogenic soils in the active colonies at the two localities. At least 53 abandoned pebble mounds were located at Hope Bay of which nine were excavated and four were sampled by probing to recover organic remains to determine their age. Radiocarbon dating of egg membrane, feather, and bone from both sites revealed a young occupation dating to less than *600 years after correcting for the marine carbon reservoir effect. The mismatch in the geologic record of Ade ´lie Penguin occupation in the northern Antarctic Peninsula, including Lake Boeckella sediments and geologic deposits and lake sediments on King George Island, with more direct evidence of breeding colonies from ornithogenic soils from active and abandoned colonies is hereby referred to as the 'northern enigma' as it does not occur in other regions of Antarctica including the southern Antarctic Peninsula, East Antarctica, or the Ross Sea, where the penguin record extends to the early to middle Holocene and matches well with the geologic record of deglaciation and penguin occupation. As yet, there is no convincing explanation for the 'northern enigma'.

Holocene occupation history of pygoscelid penguins at Stranger Point, King George (25 de Mayo) Island, northern Antarctic Peninsula

“…yr BP (Emslie et al, 2011; Figure 1). Although there was only minimal movement of juvenile penguin bones from breeding sites on the terrace near the Pingfo I beach deposits, ornithogenic soils from these former colonies are absent, adding to the mismatch with depositional records for penguin breeding (including those in lake sediments, beach deposits, and glacial moraines) that has been termed the 'northern enigma' (Emslie et al, 2018). Only one active breeding colony of Adélie penguins at the Danger Islands, Weddell Sea (Figure 1), has produced an older age of ornithogenic soils at ~2800 cal.…”

“…Roberts et al (2017) reported the recovery of juvenile Gentoo penguin bones from Ardley Lake, Ardley Island, dating to ~7400–7200 cal. yr BP, though no ornithogenic soils have been found near this lake or on Ardley Island that also date to this period (Emslie et al, 2018). Tatur (1989) also reported ~2 m of alluvial deposits of sands and gravels that included at the base a ~40 cm thick phosphatic mud containing abundant juvenile Adélie and Chinstrap penguin bones from Penguin Ridge, Thomas Point, King George Island.…”

“…Two pebble mounds, one on the lower beach and one on the upper terrace, were excavated at Stranger Point to recover penguin remains for analysis. Excavations were completed following the methods of Emslie et al (2018). A 1 × 1 or 0.5 × 0.5 m test pit was placed on each mound and excavated in arbitrary 5 cm levels until reaching the bottom of the ornithogenic deposits, or until permafrost prevented further excavation.…”

“…Three pygoscelid penguin species (Adélie, Gentoo, and Chinstrap penguins) are widely distributed at breeding colonies throughout the northern Antarctic Peninsula. Despite this presence, radiocarbon dates on penguin tissues from ornithogenic soils at active and abandoned colonies so far indicate a relatively young age for these sites at ~1100 BP for Gentoo penguins (Pygoscelis papua), and only 500-600 BP for Adélie (Pygoscelis adeliae) and Chinstrap (Pygoscelis antarctica) penguins (Emslie et al, 2011(Emslie et al, , 2018. However, older beach and lake deposits have produced pygoscelid penguin bones dating to the early to middle Holocene on Ardley and King George Islands, South Shetland Islands.…”

“…In the Ross Sea and East Antarctica, however, ornithogenic soils have been identified as old as 27,000 BP (Baroni and Orombelli, 1994; Emslie et al, 2007). This mismatch in age of ornithogenic soils and the penguin fossil record in the northern Antarctic Peninsula does not occur in other regions of Antarctica and has been referred to as the ‘northern enigma’ (Emslie et al, 2018).…”