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Meyer-Lorey, R., Pratt, L. We share the results of Bayesian regression modeling to quantify the relationship between Pacific sea surface temperatures and the water surface elevation of Tulare Lake/Pa’ashi, the largest freshwater lake in California prior to colonial landscape modification. Using tree-ring derived lake levels as our outcome variable, we construct a series of Bayesian linear models with proxy-derived Pacific sea surface temperatures as predictors. The resulting model allows us to produce a ~20,000 year hindcast of Tulare Lake surface elevation with quantified uncertainty. Our results support and refine other paleoclimate reconstructions of Tulare Lake; whereas prior reconstructions provide a series of ’snapshots’ based on physical evidence that is likely biased towards preserving high stands, our model is better able to quantify multi-scalar (e.g., annual, decadal) variability not directly observable in the archaeological record. We find that Pacific sea surface temperatures are a strong predictor of mean lake levels in the long term. Annual and decadal fluctuations are related to rainfall driven by the Pacific Decadal Oscillation and El Niño Southern Oscillation; residual ~35-40-year cyclical deviations in lake level are an emergent property of Tulare Lake’s hydrological system and basin physics. Our results have implications for corroborating ecological and climate models contained within Indigenous oral traditions, understanding the impacts of climate change on California hydrology, and the accessibility of Bayesian methods in archaeology.  Figure 4: (A) Environmental reconstruction data from Negrini et al. (2006) figure 10: their proposed Holocene lake-level reconstruction (dashed) interpolated through individual geological observations (points). (B) Comparison of our hindcast with the Negrini et al. (2006) reconstruction. The interpolated estimate (dashed) overlays our posterior mean (solid blue) and 95% prediction interval (shaded blue). These reconstructions were produced totally independently of one another using local geological deposits and SST proxies respectively, but general trends agree remarkably well across both records. Negrini et al.’s observations fall almost entirely within our prediction envelope: what the geological record preserves as discrete “snapshots” are realizations consistent with our continuous reconstruction. The c. 8,000–10,000 yr BP ‘Rambla highstand’ (~70 masl) lies above our predicted range, likely attributable to early-Holocene Sierra glacial melt not captured by the SST-driven model. Full text available here, or find PDF below.
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Pratt, L., López Aldave, N., Alarcon Ledesma, C., Alaica, A. This article presents the results of survey and excavation in the Chachapoyas region of the Peruvian eastern Andes attesting to human occupation of the mid-altitude cloud forest from at least the Middle Holocene. While the Peruvian eastern Andes have long been identified as an important region in the exchange of domesticated plants and animals between the Pacific coast, Andean highlands, and the Amazon rainforest, little direct evidence dating to before 1000 BP has been reported. In fact, the record of early groups in this tropical montane cloud forest environment is so scarce that some experts have suggested that this landscape was too marginal to support substantial pre- and proto-agricultural populations. Evidence from this study, including radiocarbon dating and faunal and botanical analyses, contradicts such models, showing that foragers were living in this environment from at least 5500 cal BP. Some domesticated species were present by the terminal Preceramic (ca 3600 cal BP), and mixed forager-producer subsistence persists in the Middle Horizon or Late Intermediate Period (1400–500 cal BP).  Maps showing location of A) the Chachapoyas region, and B) sites in the CARECH study. Full text available here, or find PDF below. Garvey, R., Poe, K., Pratt, L. The middle Holocene saw major changes in political and socioeconomic organization in Peru. Still, not all Peruvian groups transitioned to food production or engaged in mound or monument construction, yet we know relatively little about those who maintained a mobile lifestyle centered on foraging. Using GIS and statistical analyses to interrogate a database of radiocarbon dates, we assess the Peruvian record of forager distributions through the middle Holocene. We identify patterns consistent with biases stemming from disproportionate research attention, regional and intrasite sampling methodologies, and taphonomy that may be hampering our study of middle Holocene foragers. Further confounding our understanding of foragers during this period are reports of middle Holocene radiocarbon gaps attributed to population decline across South America in response to climate-induced scarcity of freshwater and other resources. We show, however, that this might also be an artifact of sampling in some cases and argue for both increased archaeological attention to middle Holocene foragers and greater awareness of perceptual biases that might influence research design and, therefore, research attention and outcomes.  Map of Peru indicating sites in our database (black circles), the ten most populous cities in Peru (red triangles; World Population Review, 2023), and the Amazon ecoregion (green shaded area). Purple dashed line represents political boundaries with adjacent countries. Data from ArcGIS online/Esri. Full text available here, or in PDF below Pratt, L., Guengerich, A. In the archaeological tradition of what is today Peru, studies of sedentary agricultural groups have accorded a minor role to the analysis of stone tools relative to other suites of material culture. Here, we illustrate the value of such lithic collections via a case study of settlement sites from the Chachapoyas region of northern Peru (AD 300–1500). This study demonstrates the potential of methods such as use-wear microscopy and raw material analysis to address questions of theoretical interest to archaeologists studying sedentary society, such as subsistence, household behavior, and ceremonial practices. A set of generalized linear models of the spatial distribution of volcanic stone indicates that lithic raw material acquisition at these ceramic period sites was likely embedded in other activities. In addition, we examine an unusual set of limestone and carbonate-patinated artifacts that suggest that lithic procurement and selection were informed and strategic, if not conforming to expected technological priorities. We suggest that, by taking the potential value of lithic artifacts into consideration from project design through field collection and assemblage sampling, researchers can minimize biases that may otherwise limit the value of lithic assemblages.  Prepared limestone tool: (A) dorsal view; (B) ventral view; (C–E) heavily use-worn areas, above and below visible retouch; and (E) intentional retouch. Full text available here, or in PDF below. |
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