A 7300-yr-old environmental history of seabird, human, and volcano impacts on Carlisle Island (the Islands of Four Mountains, eastern Aleutians, Alaska)

Abstract

We present the results of multiproxy study of a peat deposit from Carlisle Island (the Islands of Four Mountains, Aleutians). Vegetation on the initial stage of the peat is characterized by heath vegetation dominated by Ericales indicating cold conditions at 7300–6100 cal yr BP. The appearance of Betula and Alnus is the result of long-distance transportation attributable to strong winds at this time. Sedge-grass (Cyperaceae and Poaceae) communities began replacing heath vegetation at 6100 cal yr BP because of the climatic amelioration. C/N ratios and pollen spectra remain relatively stable at 6100–2450 cal yr BP. For the CR-03 peatland, volcanic tephra contributed significantly to the Fourier transform infrared spectroscopy spectral data. Volcanic input created overlap of an aluminosilicate signal with carbohydrate vibrations. Significant changes occurred at approximately 2450 cal yr BP when there is the some evidence of cooler and wetter conditions of the Neoglacial. High values of δ15N observed at 7100–7000 cal yr BP reflect the fertilizing effect of seabird nesting colonies. A decrease in δ15N ca. 6900 cal yr BP may indicate initial settlement on Carlisle Island corresponding with harvesting seabirds. Human predation continued until a series of volcanic eruptions, which deposited Okmok II and CR-02 tephra layers at ca. 2000 and 1050 cal yr BP, respectively.

Hunter-gatherers subsistence and impact on fauna in the Islands of Four Mountains, Eastern Aleutians, Alaska, over 3000 yr

“…Because storm petrels are especially vulnerable to human predation because they nest in burrows and establish dense colonies, the human recolonization of Carlisle Island had a severe impact on the bird colony. Our assumption of island abandonment before 500 cal yr BP is supported by: (1) the lack of sites identified in the IFM archaeological sequence (Hatfield et al, 2019) and (2) the evidence that both the birds’ colony development and the human occupation history are supported by isotopic data from Carlisle peat deposits (Kuzmicheva et al, 2019).…”

“…This evidence suggests that, on Carlisle, a local event unconnected with environmental changes occurred throughout the Aleutian Islands. Changing nitrogen stable isotopes ratios of the 7000-yr-old peat deposit on Carlisle Island suggests that a large sea bird nesting colony arose on Carlisle Island after 2000 cal yr BP (Kuzmicheva et al, 2019). According to δ 15 N dynamics, the bird colony reached its peak of development at 750–500 cal yr BP (Kuzmicheva et al, 2019), following a large eruption of Cleveland volcano on neighboring Chuginadak Island (CR-02 tephra fall, 1050 cal BP; Okuno et al, 2017).…”

Geomorphic processes influence human settlement on two islands in the Islands of Four Mountains, Alaska

“…In the east Tana valley, the presence of hydrothermally altered bedrock facilitated the development of distinct LIA and Neoglacial moraines and influenced the moraine morphology through high rates of diffusion that created more rounded crests and large solifluction lobes. If human settlement predating 3.7 ka did occur in the IFM, as suggested indirectly by peat bog nitrogen isotopic compositions (Kuzmicheva et al, in press), the earliest IFM sites may be deeply buried in sediment fan deposits or filtered from the extant record through coastal erosion associated with eustatic sea level rise. Alternatively, the initial westward settlement of the Aleutian Islands may have bypassed the IFM 7–9 ka because small size of the islands and their unstable fan surfaces offered little terrain suitable for long-term settlement.…”

“…Unexpectedly, the archaeological record of the IFM does not substantiate the direct physical presence of people until ~3.7 cal ka BP (Hatfield et al, 2016). Yet Kuzmicheva et al (in press) interpret low stable nitrogen isotopic compositions of soil as evidence of human impact on IFM bird populations by ~6.9 cal ka BP, a time frame for settlement more consistent with expectations raised by well-dated archaeological sites on adjacent island groups. Could the >3000 yr gap between the geochemical and physical records of human habitation result from geomorphic controls constraining landscape stability?…”

“…Despite the relatively warm temperatures, abundant rainfall, and fertile soil, the IFM are treeless because of the persistent strong winds. The vegetation of islands consists of dense shrubs including crowberry (Empetrum nigrum), grasses (Poaceae), and sedges (Cyperaceae) (e.g., Kuzmicheva et al, in press).…”