Precise timing of abrupt increase in dust activity in the Middle East coincident with 4.2 ka social change

Stacy A. Carolin; Richard T. Walker; Christopher C. Day; Vasile Ersek; R. Alastair Sloan; Michael W. Dee; Morteza Talebian; Gideon M. Henderson

doi:10.1073/pnas.1808103115

New Research In

Edited by Glen M. MacDonald, University of California, Los Angeles, CA, and approved November 16, 2018 (received for review May 10, 2018)

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Fig. 1.
Correlation maps of archeological site Tell Leilan (black “+”) rainfall with European Centre for Medium-range Weather Forecasts Re-Analysis Interim (ERA-Interim) model forecast total precipitation (resolution ∼80 km) (41). White areas indicate areas where P > 0.10. The ERA-Interim model forecast record at (37°N, 41.5°E) was used to represent Tell Leilan rainfall. (A) Correlation map using annual precipitation records, constructed by calculating the 12-mo average of each year centered on winter, i.e., July 1979 to June 1980, July 1980 to June 1981, etc. (B) Upper uses only winter months October through March, and Lower uses only spring and summer months March through August, to create yearly records highlighting a particular season. A also shows the direction and relative speed in arrow size of 850-mb-level winds from July 5, 2009, 12:00 GMT (41), an example time period of a severe dust event in Tehran, Iran, in which dust was sourced from the Mesopotamia region (25, 28). The locations of paleoclimate records discussed in the text are marked with circles; labels are provided in A. Source area of 92% of contributions of PM₁₀ (fine dust with particles smaller than 10 μm) in Tehran (50 km from location 9; this study) during 2009–2010 dusty episodes are shown by dotted boxed area in A (28).
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Fig. 2.
Mid-to-late Holocene records of climatology in the Mesopotamia region. (A) Marine records: 1, Red Sea sediment core GeoB 5836-2 shallow dwelling foraminifera Globigerinoides ruber δ¹⁸O (5); 2, Gulf of Oman Core M5-422 eolian dolomite concentration (percent weight) (3). Terrestrial records: 3, Buca della Ranella RL4 stalagmite δ¹⁸O record (6, 19); 4, Sofular cave So-1 stalagmite δ¹⁸O record (42); 5, Jeita J-1 stalagmite δ¹⁸O record (43); 6, Soreq cave multiple stalactite and stalagmite δ¹⁸O records (8, 44); 7, Qunf cave Q5 stalagmite δ¹⁸O record (45); 8, Tonnel’naya cave TON-2 stalagmite δ¹⁸O record (46). Locations of the caves are shown in Fig. 1. (B) Local climate proxies, Mg/Ca (millimoles per mole) and δ¹³C (per mil), measured in the Buca della Ranella RL4 stalagmite (6, 19), are plotted with our high-resolution δ¹⁸O (per mil) record (19), all on the updated age model (19). A gray dotted line in both A and B indicates the location of date 4.2 ka before 1950 CE.
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Fig. 3.
GZ14-1 age v. depth plot with OxCal Poisson process deposition age model 68% (black) and 95% (dark gray) confidence ranges (30, 31). Original individual U-series samples’ ages are plotted as black “x” shapes. Individual samples’ modeled age distributions are shown in dark gray (68%) and light gray (95%). (Inset) GZ14-1’s mean extension rate (micrometers per year), plotted as a 20-y moving average of the annually interpolated OxCal mean extension rate, is included as a subset.
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Fig. 4.
Timing of environmental changes in Middle East region compared with archeological settlement records. (A) Proxy records of Mesopotamia-sourced dust event activity: i, GZ14-1 Mg/Ca (millimoles per mole) (this study); ii, Gulf of Oman Core M5-422 eolian dolomite concentration (percent weight) (3), plotted on an updated age model (SI Appendix). Time resolution of GZ14-1 is an average of ∼2 y during fast growth and an average of ∼10 y to 15 y during slow growth, with slow growth period found within intervals highlighted in gray (growth rate shown in Fig. 3). In both records, greater Mg/Ca or dolomite % wt indicates more dolomite-containing eolian dust deposits. (B) Proxy records of aridity climate: i, GZ14-1 δ¹⁸O (this study), with more positive values interpreted as drier conditions to an unknown magnitude on interannual timescales; ii, Jeita cave stalagmite δ¹⁸O record as in Fig. 2A, with more enriched δ¹⁸O interpreted as drier conditions (43); iii, Soreq cave multiple stalactite and stalagmite sample δ¹³C records, with more enriched δ¹³C interpreted as drier conditions (8, 44); iv, Red Sea sediment core GeoB 5836-2 G. ruber δ¹⁸O, as in Fig. 2A, with more enriched δ¹⁸O interpreted as greater evaporation and thus drier climate (5). (C) Graphical representation of the evolution of rain-fed agricultural settlements in north Mesopotamia, which became urbanized around 4.5 ka, were imperialized by Akkad around 4.26 ka, and then were suddenly abandoned at 4.19 ± 0.018 (1σ) ka (17), coincident with the decline of the Akkadian empire. Settlements returned at 3.90 ± 0.026 (1σ) ka (17). Modeled U/Th mean ages (blue circles) and 95% confidence ranges are plotted above each record. For the two GZ14-1 records, A, i and B, i, the ages are plotted only above A, i. The two vertical gray bars across all panels begin when Mg/Ca ratio in the GZ14-1 record rises greater than 3σ from the average ratio of the record for >10 y, and end when Mg/Ca returns to background levels (see Event Timing and Errors).