Author(s): Thomson, Marcus J; MacDonald, Glen M | Abstract: The rise and decline of many complex, pre-European maize-farming cultures in the American Southwest coincides with the warm, climatically quiescent Medieval Climate Anomaly (MCA, ca. 850-1350 CE) and transition to the cool, hydrologically variable Little Ice Age (LIA, ca. 1350-1850 CE). The effects of drought on early subsistence agriculture in the Southwest is well studied, but the impact of temperature stress and variability on the growth of maize crops and which areas were most resilient to such stress remain open questions. We statistically downscaled outputs from a paleo-climate model experiment (CESM1 LME) to map changes to cumulative growing degree days for maize (GDD, 30/10°C) and precipitation over Utah between 850 and 1449 CE, and downscaled GDD changes to local Fremont Culture archaeological site occupations from radiocarbon-dated contexts mapped as spatially discrete kernel density estimates of summed probability distributions (SPDs). We then analyzed correspondences between Fremont SPDs and GDD/precipitation between 850 and 1449 CE. In general, we found (1) high Fremont occupation intensity coincident with GDD that is less volatile than the long term average, and low occupation intensity coincident with, or following, periods of volatile GDD; (2) intensified occupation of high-elevation sites during the MCA, followed by a retreat to lower elevation sites coincident with a sudden rise in annual temperature volatility and increasing drought conditions; and (3) these occupation changes occurred in spite of the greater temperatures and variability in GDD at low-elevation sites. We found evidence that increased inter-annual variability of growing seasons prior to the onset of the LIA, was likely a determinant of Fremont subsistence strategy decision making, and high-elevation site occupation. The most resilient Fremont occupations in the face of these challenges were sited where growing season lengths were least variable.

中文翻译：

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在中世纪气候异常期间和之后，气候和生长季节的变化影响了弗里蒙特玉米农民的强度和分布

作者（S）：汤姆森，马库斯J；麦克唐纳，格伦 M | 摘要：美国西南部许多复杂的、前欧洲玉米种植文化的兴衰与温暖、气候静止的中世纪气候异常（MCA，约公元 850-1350 年）和向凉爽、水文变化多端的小冰河时代（LIA，约公元 1350-1850 年）。干旱对西南地区早期自给农业的影响已得到充分研究，但温度胁迫和变异对玉米作物生长的影响以及哪些地区对这种胁迫最具有抵抗力仍然是悬而未决的问题。我们从统计上缩小了古气候模型实验 (CESM1 LME) 的输出，以绘制玉米（GDD，30/10°C）和犹他州在公元 850 年至 1449 年间降水的累积生长期日变化图，以及从放射性碳测年背景中缩小 GDD 对当地弗里蒙特文化考古遗址职业的变化，映射为总概率分布 (SPD) 的空间离散核密度估计。然后，我们分析了公元 850 年至 1449 年间弗里蒙特 SPD 与 GDD/降水之间的对应关系。总的来说，我们发现 (1) 高弗里蒙特职业强度与 GDD 相吻合，其波动性低于长期平均水平，而低职业强度与 GDD 波动时期相吻合或紧随其后；(2) 在 MCA 期间，对高海拔地区的占领加剧，随后向低海拔地区撤退，同时年气温波动率突然上升，干旱状况加剧；(3) 尽管低海拔地点 GDD 的温度和变化更大，但这些职业变化还是发生了。我们发现证据表明，在 LIA 开始之前，生长季节的年际变化增加，可能是弗里蒙特生存战略决策和高海拔场地占用的决定因素。面对这些挑战，最具弹性的弗里蒙特职业位于生长季节长度变化最小的地方。