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Prolonged drying trend coincident with the demise of Norse settlement in southern Greenland - PubMed

  • ️Sat Jan 01 2022

Prolonged drying trend coincident with the demise of Norse settlement in southern Greenland

Boyang Zhao et al. Sci Adv. 2022.

Abstract

Declining temperature has been thought to explain the abandonment of Norse settlements, southern Greenland, in the early 15th century, although limited paleoclimate evidence is available from the inner settlement region itself. Here, we reconstruct the temperature and hydroclimate history from lake sediments at a site adjacent to a former Norse farm. We find no substantial temperature changes during the settlement period but rather that the region experienced a persistent drying trend, which peaked in the 16th century. Drier climate would have notably reduced grass production, which was essential for livestock overwintering, and this drying trend is concurrent with a Norse diet shift. We conclude that increasingly dry conditions played a more important role in undermining the viability of the Eastern Settlement than minor temperature changes.

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Figures

Fig. 1.
Fig. 1.. Temperature profiles from southern Greenland and the related driving factors.

(A) Summer insolation anomaly at 61° N (21). (B) Arctic summer temperature anomaly based on a synthesis of multiple Arctic records (20). (C) Our brGDGT-inferred summer water temperature from Lake 578. Gray shading represents the calibration errors of ±0.52°C (19). The dashed line represents the linear trend. Note that the temperature reconstruction is truncated at 7 cm because of the unconstrained “core-top cooling” for the sedimentary MBT′5ME index (Supplementary Materials). (D) Southern Greenland region glacier extent. The solid squares are 10Be-dated moraine age near Narsarsuaq (23), and the thick line indicates the readvanced period of the south Greenland ice margin (22). (E) Principal component analysis (PCA) scores of the Lake Igaliku chironomid samples (8). (F) δ18O values of Scoop Lake chironomids (11). (G) Biogenic silica from Lake N14 (10). (H) Diatom-based August SSTs from core MD99-2322 from the SE Greenland shelf (24). (I) Reconstructed August SSTs from core Rapid 21-COM, the Reykjanes Ridge (25). Orange bar indicates the time span of Norse settlement. The red lines are 5-point running mean. See fig. S1 for site locations.

Fig. 2.
Fig. 2.. Hydroclimate profile from Lake 578, southern Greenland.

(A) Leaf wax δ2H of C23 (aquatic) and C29 (terrestrial) n-alkanes from Lake 578. The black and red shading represents 1 σ proxy uncertainty. (B) DYE-3 ice core oxygen isotopes (34). The thick violet line is the 5-point running mean. (C) ΔRH reconstruction from Lake 578 based on leaf wax δ2H and the dual-biomarker model (31). Blue shading represents the 90% confidence interval (CI), and the thick blue line is the 5-point running mean. (D) The optimum Nuussuaq (NU) ice cap accumulation history and the 10% least complex interval denoted with gray shades (35). (E) Concentrations of organic carbon from Lake 578 (Supplementary Materials). Higher values indicate a high organic matter (OM) content. (F) RABD660;670 index (relative absorption band depth centered in 660 to 670 nm) from Lake 578, indicates the intensity of lake productivity (Supplementary Materials). The thick brown line is the 10-point running mean. Orange bar indicates the time span of Norse settlement. VSMOW, Vienna Standard Mean Ocean Water.

Fig. 3.
Fig. 3.. NAO in southern Greenland and its connection to summer precipitation [June, July, and August (JJA)].

(A) Spatial correlation between summer NAO and precipitation from 1950 to 2020; dashed lines include areas of significant correlations (P < 0.005). The precipitation data are based on the CRU TS 4.04 precipitation dataset from the Climate Explorer (

climexp.knmi.nl

). (B) The correlation between summer NAO and measured precipitation from the Narsarsuaq weather station (1961–2020) (fig. S1B). The red line is the linear fit, and the shaded area represents the 95% CI. (C) Time series of the annual mean and JJA mean NAO index plotted from 1950 to 2020. Brown columns [corresponding to brown squares in (B)] indicate recently observed and documented summer droughts that led to a notable decrease in grass, crop, and hay production (15). NAO index in all figures is excerpted from the “NAO (rotated EOF of Z500, 1950-now, CPC)” dataset from the Climate Explorer (

climexp.knmi.nl

).

Fig. 4.
Fig. 4.. The reconstructed climate conditions from southern Greenland and the Norse diet transition.

(A) BrGDGT-inferred summer water temperature (SWT) from southern Greenland. An error bar of ±0.52°C from the calibration (19) is shown with the gray shading. (B) Leaf wax hydrogen isotope-inferred ΔRH from southern Greenland. Blue shading represents the 90% CI. The thick blue line represents 5-point running mean. (C) Percentage of marine sourced food in the Norse diet (46). (D) The ratio of marine to terrestrial mammal bones [number of identified specimens (NISP)] from a Norse farm in Qassiarsuk (47). Orange bar indicates the time span of Norse settlement.

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