Abstract
Drought has long been suspected as playing an important role in the abandonment of pre-Columbian Native American settlements across the midcontinental United States between 1350 and 1450 CE. However, high-resolution paleoclimatic reconstructions reflecting local effective moisture (the ratio of precipitation to evaporation) that are located in proximity to Mississippi period (1050–1450 CE) population centers are lacking. Here, we present a 1600-year-long decadally resolved oxygen isotope (δ18O) record from Horseshoe Lake (Collinsville, IL), an evaporatively influenced oxbow lake that is centrally located within the largest and mostly densely populated series of Mississippian settlements known as Greater Cahokia. A shift to higher δ18O in the Horseshoe Lake sediment record from 1200 to 1400 CE indicates that strongly evaporative conditions (i.e., low effective moisture) were persistent during the leadup to Cahokia’s abandonment. These results support the hypothesis that climate, and drought specifically, strongly impacted agriculturally based pre-Columbian Native American cultures in the midcontinental US and highlights the susceptibility of this region, presently a global food production center, to hydroclimate extremes.
Highlights
Between 1050 and 1450 CE, pre-Columbian Native American agriculturalists, collectively referred to as the Mississippians, developed and occupied an extensive network of settlements with large earthen mounds and plazas across the central Mississippi and lower Ohio River valleys[1]
Horseshoe Lake’s residence time remained effectively unchanged. This fact is illustrated by the minimal impact on the δ18OHSL record, which shows that the isotopic signal was not impacted by watershed modifications and is instead still mainly controlled by changes in precipitation and evaporation (P/E) balance. In light of this evidence, we contend that evaporation would have been a significant influence on the isotopic composition of water at Horseshoe Lake in the past, and δ18OHSL is a reliable indicator of past effective moisture (P/E) changes
The δ18OHSL record indicates that Cahokia emerged as a regional center during the early Mississippi period (i.e., 1050–1200 CE) under relatively wet conditions with high effective moisture
Summary
Between 1050 and 1450 CE, pre-Columbian (pre-1492 CE) Native American agriculturalists, collectively referred to as the Mississippians, developed and occupied an extensive network of settlements with large earthen mounds and plazas across the central Mississippi and lower Ohio River valleys[1]. We test the climate hypothesis using a 1600-year-long authigenic calcite oxygen isotope record from Horseshoe Lake (δ18OHSL), an evaporatively modified oxbow lake situated just north of Cahokia and centrally located within the greater American Bottom region. The Horseshoe Lake record provides a means to assess the timing and nature of P/E balance changes (i.e., pluvial versus drought) that would have directly impacted the agricultural foundations of Cahokia and associated population centers, such as the St. Louis, East St. Louis, and Mitchell p recincts[18,19]. Horseshoe Lake is often flooded, its shallow depth and large surface area results in a hydrology that is sensitive to evaporation This was reflected in field observations between the spring and summer of 2012 CE21, when drought caused lake levels to visibly fall and lake water δ18O values increased (Fig. 1B). Authigenic calcite precipitated from the lake’s alkaline waters constitute an archive of variations in lake water δ18O that respond to changing effective moisture conditions that span the last 1600 years[20]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
