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Climate change and the collapse of the Akkadian Empire:
Evidence from the deep-sea

Heidi M. Cullen, P. B. deMenocal, S. Hemming, G. Hemming, F. H. Brown*, T. Guilderson**, and F. Sirocko***

  Lamont-Doherty Earth Observatory of Columbia University, Palisades, NY 10964
*University of Utah, Park City, UT
**Lawrence Livermore National Laboratory, Livermore, CA 94551
***Max Plank Institut, Meinz, Germany		  

(Reference: Cullen, H.M., P.B. deMenocal, S. Hemming, G. Hemming, F.H. Brown, T. Guilderson, and F. Sirocko, Climate change and the collapse of the Akkadian Empire: Evidence from the deep-sea, Geology, 28 (4), 379-382, 2000; PDF))


Abstract


The first civilization to develop complex city-state societies, the Akkadian Empire ruled Mesopotamia from the headwaters of the Euphrates-Tigris Rivers to the Persian Gulf during the late third millennium B.C. Archeological evidence has shown that this complex civilization collapsed abruptly near 4170±150 cal. years ago, perhaps related to a shift to more arid conditions (Weiss et al., 1993). Detailed paleoclimate records to test this assertion from Mesopotamia are rare, but changes in regional aridity are preserved in adjacent ocean basins. Here, we document Holocene changes in regional aridity using mineralogic and geochemical analyses of a marine sediment core from the Gulf of Oman, which is directly downwind of Mesopotamian dust source areas and archeological sites. Our results document a very abrupt increase in eolian dust and Mesopotamian aridity which is AMS radiocarbon dated to 4025±125 cal. years BP and which persisted for approximately 300 years. Radiogenic (Nd and Sr) isotope analyses confirm that the observed severalfold increase in mineral dust was derived from Mesopotamian source areas. Geochemical correlation of volcanic ash shards between the archeological site and marine sediment record establishes a direct temporal link between Mesopotamian aridification and social collapse, implicating a sudden shift to more arid conditions as a key factor contributing to the collapse of the Akkadian Empire.

SEAWIFS image of a dust storm over the Middle East (May, 2000)

View looking to the northwest, up the Gulf of Oman and over to the Persian Gulf.

Photo was taken approximately 10 days after photo on left.

Figure 1. Location of core M5-422 in the the Gulf of Oman (24° 23.40'N, 59° 2.50'E, 2,732 m deep) and the Tell Leilan archeological site in NE Syria. Mean atmospheric circulation of the regional surface wind field is shown, including the northwesterly "Shamal" winds which entrain and transport abundant mineral dusts from the Tigris and Euphrates floodplain dust source areas to the southeast over the Persian Gulf, Gulf of Oman, and northern Arabian Sea (Al-Bakri et al., 1984; Al-Ghadban, 1990; Sirocko and Sarnthein, 1989; Sirocko et al., 1991). Location of the Tell Leilan archeological locality and Arabian Sea core KL-74 (are also shown.

 
Figure 2. Core M5-422 (24° 23.40'N, 59° 2.50'E, 2,732 m deep) from the Gulf of Oman documenting an abrupt increase in eolian dolomite and CaCO3 between 4194-3626 cal. yr BP. AMS radiocarbon age control was based on analyses on samples of G. bulloides using a 560-year reservoir correction (open symbols; Table 1) which were calibrated to calendar ages using the Calib 3.0.3 program (closed symbols). Conventional bulk (>150µm fraction) radiocarbon analyses are shown with error bars. CaCO3 was measured on 2 cm samples (~100 year resolution) by coulometry and dolomite was measured by quantitative X-ray diffraction; respective analytical precisions are shown.

Figure 3. Radiogenic isotope (eNd and 87/86Sr) data measured for Core M5-422, Tell Leilan (NE Syria), and samples of atmospheric mineral dust fallout collected in Bagdad, Iraq (Summer, 1995); data are listed in Table 2. The Zagros, Indus, and Mesopotamian terrigenous eNd and 87/86Sr endmember compositions are indicated (after (Sirocko, 1995)). Coretop and latest Holocene analyses from Core M5-422 (closed circles) document the largely Zagros endmember composition of the terrigenous sediments presently accumulating at this site (Fig. 1). Analyses of eolian dusts collected in Bagdad, Iraq and from the Tell Leilan archeological site (northeast Syria) document a largely Mesopotamian eNd and 87/86Sr isotopic signature. The eNd and 87/86Sr values for the abrupt increase in eolian dolomite and calcite near 4025±150 cal. yr BP (Fig. 2) indicate that these samples contain increased (by 30%) proportions terrigenous sediments derived from Mesopotamian sources.  

 
Figure 4. Eolian mineral concentration data for the 6000-2000 cal. yr BP interval in core M5-422. The positions of the AMS radiocarbon age control values are indicated. Note the abrupt increase in eolian dolomite and calcite concentrations commencing near 4025±150 cal. yr BP and ending near 3626 cal. yr BP. The calculated influx of solely eolian dolomite increased from background values of 0.39-043 g/cm2/ka to a weighted average value of 0.97 g/cm2/ka during the dust peak between 4025-3626 cal. yr BP. Calibrated radiocarbon ages of the Imperialization, Collapse, and Resettlement phases of the Akkadian Empire as determined from archeological investigations at Tell Leilan site in NE Syria are shown (dates from Weiss et al., 1993). The mean calibrated ages of these phases, their two-sigma and full age ranges are represented by the filled symbols, boxes, and range bars, respectively. The locations of M5-422 samples containing volcanic ash shards are shown. Extracted shards from these samples were analyzed by electron microprobe and the data are shown and compared to shards analyzed at Tell Leilan in Table 3.

 

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