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

Abstract

The extent to which climate change causes significant societal disruption remains controversial. An important example is the decline of the Akkadian Empire in northern Mesopotamia ∼4.2 ka, for which the existence of a coincident climate event is still uncertain. Here we present an Iranian stalagmite record spanning 5.2 ka to 3.7 ka, dated with 25 U/Th ages that provide an average age uncertainty of 31 y (1σ). We find two periods of increased Mg/Ca, beginning abruptly at 4.51 and 4.26 ka, and lasting 110 and 290 y, respectively. Each of these periods coincides with slower vertical stalagmite growth and a gradual increase in stable oxygen isotope ratios. The periods of high Mg/Ca are explained by periods of increased dust flux sourced from the Mesopotamia region, and the abrupt onset of this dustiness indicates threshold behavior in response to aridity. This interpretation is consistent with existing marine and terrestrial records from the broad region, which also suggest that the later, longer event beginning at 4.26 ka is of greater regional extent and/or amplitude. The chronological precision and high resolution of our record indicates that there is no significant difference, at decadal level, between the start date of the second, larger dust event and the timing of North Mesopotamia settlement abandonment, and furthermore reveals striking similarity between the total duration of the second dust event and settlement abandonment. The Iranian record demonstrates this region’s threshold behavior in dust production, and its ability to maintain this climate state for multiple centuries naturally.

Speleothems from the Middle East: An Example of Water Limited Environments in the SISAL Database

“…from 6300 to 5200 years ago), which suggests local environmental conditions and societal activities, can respond nonlinearly to climate change [132,138,139]. Cultural changes and settlement abandonment are seen from the Near East to northern Mesopotamia as part of the end-phases of the Bronze age [112,140] (Figure 6A).…”

Drying in the Middle East During Northern Hemisphere Cold Events of the Early Glacial Period

“…Our interpretations are supported by models that quantify chemical evolution of karst dripwaters in responses to local environmental changes, as well as global climate model experiments that show the expected moisture transport (column integral of wind multiplied by the specific humidity) and precipitation amount changes in the region that may result from similar-type North Atlantic event forcing. X/Ca ratios and δ 13 C values in stalagmites can be controlled by a number of processes, such as changes in vegetation, biological activity in the soil, karst aquifer water flow rates and flow paths, temperature, and the leaching of aerosols deposited in the soil zone (e.g., Carolin et al, 2019;Day & Henderson, 2013;Dorale et al, 1992;Fairchild et al, 2000;Genty et al, 2003;Tremaine & Froelich, 2013). In general, however, there is a tendency for X/Ca and δ 13 C to increase when there is less water flow in the rocks overlying the cave.…”

“…Interest in investigating past climate change in this region stems from the desire to better constrain our knowledge of the system's precipitation variability and its response to various external forcings (Aubert et al, 2017;Carolin et al, 2019;Flohr et al, 2017;Mehterian et al, 2017;Sharifi et al, 2015;Sharifi et al, 2018). Interest in investigating past climate change in this region stems from the desire to better constrain our knowledge of the system's precipitation variability and its response to various external forcings (Aubert et al, 2017;Carolin et al, 2019;Flohr et al, 2017;Mehterian et al, 2017;Sharifi et al, 2015;Sharifi et al, 2018).…”

“…Society and ecosystems in the center of the Middle East region (Syria, Iraq, and Iran) are highly vulnerable to changes in water availability, with annual precipitation generally low, around 100-200 mm/year, outside of the higher elevation mountainous areas (European Centre for Medium-range Weather Forecast (ECMWF), 2011). Interest in investigating past climate change in this region stems from the desire to better constrain our knowledge of the system's precipitation variability and its response to various external forcings (Aubert et al, 2017;Carolin et al, 2019;Flohr et al, 2017;Mehterian et al, 2017;Sharifi et al, 2015;Sharifi et al, 2018).…”

Quaternary Highlights (December 2018–February 2019)

“…4.2 ky BP, for which the occurrence of a coeval climatic outbreak remains uncertain. Carolin et al [6] carried out high-resolution geochemical analysis of a 5.2 to 3.7 ky old (U/Th dating) stalagmite from an Iranian cave and found two century-scale phases of Mg/Ca increase at 4.51 and 4.26 ky BP, coinciding with gradual increases in stable oxygen isotope ratios (δ 18 O). Mg/Ca peaks were interpreted in terms of increased dust flux from the Mesopotamia region as a result of two significant aridity shifts.…”