Abrupt Holocene climate change as an important factor for human migration in West Greenland

Abstract

West Greenland has had multiple episodes of human colonization and cultural transitions over the past 4,500 y. However, the explanations for these large-scale human migrations are varied, including climatic factors, resistance to adaptation, economic marginalization, mercantile exploration, and hostile neighborhood interactions. Evaluating the potential role of climate change is complicated by the lack of quantitative paleoclimate reconstructions near settlement areas and by the relative stability of Holocene temperature derived from ice cores atop the Greenland ice sheet. Here we present high-resolution records of temperature over the past 5,600 y based on alkenone unsaturation in sediments of two lakes in West Greenland. We find that major temperature changes in the past 4,500 y occurred abruptly (within decades), and were coeval in timing with the archaeological records of settlement and abandonment of the Saqqaq, Dorset, and Norse cultures, which suggests that abrupt temperature changes profoundly impacted human civilization in the region. Temperature variations in West Greenland display an antiphased relationship to temperature changes in Ireland over centennial to millennial timescales, resembling the interannual to multidecadal temperature seesaw associated with the North Atlantic Oscillation.

Fig. 1.

(A) Site map identifying Kangerlussuaq and other locations in West Greenland mentioned in the text. (B) Map of the Søndre Strømfjord region showing locations discussed in the text. (C) Map of the North Atlantic region noting the locations of Kangerlussuaq, Crag Cave (38), and the Bermuda Rise (39). Coloration indicates the modern temperature pattern observed during the positive mode of the North Atlantic Oscillation, where red is warm and blue is cool.

Fig. 2.

(A) C₃₇ alkenone flux to Braya Sø lake bottom determined using interval sediment traps. (B) Temperature calibration developed for this study using in situ from Braya Sø water filters collected during summer 2007 (red diamonds) and 2009 (blue squares) and a previously published calibration (12) from Europe (black circles).

Fig. 3.

(A) Alkenone-based lake water temperature reconstruction for Lake E (gray) and Braya Sø (red), Kangerlussuaq, West Greenland. The time series have been visually aligned within the 2σ error of the calibrated ¹⁴C dates. Error bars show standard error of estimation (S.E.) from the calibration and the analytical uncertainty (2σ) (B) The Kanger Stack was developed by resampling and calculating the arithmetic mean of the individual temperature reconstructions from Braya Sø and Lake E at 20-y intervals. Blue shading represents uncertainty from averaging the two records. (C) The loss-on-ignition paleoproductivity record from lake SFL4-1 (21), near Kangerlussuaq. (D) Temperature reconstruction from the Greenland Ice Sheet Project Two ice core, Summit, Greenland (23).

Fig. 4.

(A) Alkenone-based Kangerlussuaq lake water temperature reconstruction (blue curve). Error bars depict the standard error of estimation (S.E.) from the calibration and the analytical uncertainty (2σ) (B) δ¹⁸O record from speleothem CC3, southwestern Ireland (38) (red curve; lower δ¹⁸O values reflect colder temperatures). (C) δ¹⁸O record from Sargasso Sea (39) (black curve, lower δ¹⁸O values reflect warmer temperatures). (D) Difference between normalized time series (Greenland-Ireland) after 21-point smoothing.