Fecal stanols show simultaneous flooding and seasonal precipitation change correlate with Cahokia’s population decline

Abstract

A number of competing hypotheses, including hydroclimatic variations, environmental degradation and disturbance, and sociopolitical disintegration, have emerged to explain the dissolution of Cahokia, the largest prehistoric population center in the United States. Because it is likely that Cahokia’s decline was precipitated by multiple factors, some environmental and some societal, a robust understanding of this phenomenon will require multiple lines of evidence along with a refined chronology. Here, we use fecal stanol data from Horseshoe Lake, Illinois, as a population proxy for Cahokia and the broader Horseshoe Lake watershed. We directly compare the fecal stanol data with oxygen stable-isotope and paleoenvironmental data from the same sediment cores to evaluate the role of flooding, drought, and environmental degradation in Cahokia’s demographic decline and sociopolitical reorganization. We find that Mississippi River flooding and warm season droughts detrimental to agriculture occurred circa (ca.) 1150 CE and possibly generated significant stress for Cahokia’s inhabitants. Our findings implicate climate change during the Medieval Climatic Anomaly to Little Ice Age transition as an important component of population and sociopolitical transformations at Cahokia, and demonstrate how climate transitions can simultaneously influence multiple environmental processes to produce significant challenges to society.

Cahokia: Urbanization, Metabolism, and Collapse

“…Fecol stanols (organic molecules that originate in the human gut, and persist for centuries in soils) closely track reconstructed population trends in the American Bottom (White et al, 2018). The frequency of these molecules, argue White et al (2019), support the idea that massive flooding was related to the late twelfth century changes, including population contraction, catastrophic abandonment of some settlements, a decline in mound construction, and the building of the first palisade.…”

“…Environmental data reveal that centuries before the building of Cahokia, the American Bottom was already an anthropogenic landscape. By around 450 A.D. there was rapid deforestation of both the floodplain and the uplands (Munoz et al, 2014, p. 501;White et al, 2019). Agricultural development seems to have reached a peak just prior to Cahokia's emergence as a political center (Munoz et al, 2014, p. 501).…”

“…Such a flood would cover a large part of the American Bottom. White et al (2019) argue that a major flood and warm season drought occurred at the same time, which would surely have affected cultivation.…”

After Cahokia: Indigenous Repopulation and Depopulation of the Horseshoe Lake Watershed AD 1400–1900

“…The demographic history of Greater Cahokia, from its peak in the eleventh century to its minimum at approximately AD 1350–1400 has received significant academic attention (Benson et al 2009; Bird et al 2017; Emerson 2018; Gregg 1975; Kelly 2009; Milner 2006:120–125; Munoz et al 2015; Pauketat and Lopinot 1997; Reed et al 1968; White et al 2018, 2019), but efforts to understand the repopulation of the region by indigenous peoples prior to the establishment of European colonists at the close of the eighteenth century have been limited (Brown and Kelly 2010; Morgan 2010; Walthall and Benchley 1987; Zitomersky 1994). The primary reasons for which the period after AD 1400 is understudied are (1) limited archaeological evidence for occupation of the watershed between AD 1400 and AD 1700 and (2) widespread acceptance of the Vacant Quarter hypothesis for regional abandonment between AD 1450 and 1550 (Cobb and Butler 2002; Edging 2007; Emerson 1997:54; Fortier et al 2006; Hanenberger 2003; Jackson 1998; Meeks and Anderson 2013; Milner et al 1984, 2001; Williams 1980, 1983, 1990, 2001).…”

“…Investigations of the significant population decline at Greater Cahokia indicate a protracted process and implicate a concatenation of many factors, including drought, flooding, climate change, the overexploitation of resources, political and religious instabilities, sociopolitical factionalism, intergroup conflict, ethnic diversity, and historically contingent circumstances, as well as the loss or departure of prominent individuals, kin groups, leaders, or deities (Benson et al 2009; Emerson 1997, 2018; Emerson and Hedman 2015; Kelly 2009; Lopinot and Woods 1993; Milner 2006; Munoz 2015; Munoz et al 2015; Pauketat 1994, 2018; Pauketat and Lopinot 1997; White et al 2019). In contrast to the considerable attention that has been paid to the dissolution and abandonment of Greater Cahokia, what happened after Cahokia's depopulation is poorly understood.…”