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首页> 外文期刊>Earth and Planetary Science Letters: A Letter Journal Devoted to the Development in Time of the Earth and Planetary System >Holocene precipitation seasonality captured by a dual hydrogen and oxygen isotope approach at Steel Lake, Minnesota
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Holocene precipitation seasonality captured by a dual hydrogen and oxygen isotope approach at Steel Lake, Minnesota

机译：明尼苏达州钢湖通过氢氧同位素双重方法捕获的全新世降水季节

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Middle-Holocene (8 to 4ka BP) warmth and aridity are well recorded in sediment archives from midcontinental North America. However, neither the climatic driver nor the seasonal character of precipitation during this period is well understood because of the limitations of available proxy indicators. For example, an important challenge is to distinguish among the interacting effects of evaporation, temperature, or precipitation seasonality in existing δ~(18)O records from the region. Here we combine hydrogen isotopes of palmitic acid and oxygen isotopes of carbonate to derive lake-water isotopic values during the Holocene at Steel Lake in north-central Minnesota. In combination, these data enable us to separate variations in evaporation from variations in the isotopic composition of input-waters to lake. Variations in evaporation are used as a proxy for aridity and lake-water input isotopic values are used as a proxy for the isotopic values of meteoric precipitation. Our results suggest that lake-water input isotopic values were more negative during the middle Holocene than at present. To test whether these more negative values are related to temperature or precipitation seasonality, we compare pollen-inferred temperatures and the expected isotopic value of precipitation resulting from these temperatures to the reconstructed precipitation isotopic values. Results suggest that middle Holocene warmth and aridity were associated with increased evaporation rates and decreased summer precipitation. These inferences are consistent with climate simulations that highlight the role of seasonal insolation and sea surface temperatures in driving variations in precipitation seasonality during the Holocene. Results also suggest that changes in Holocene precipitation seasonality may have influenced the expansion of the prairie-forest border in Minnesota as well as regional variations in grassland community composition. This study demonstrates the efficacy of the dual hydrogen and oxygen isotope approach for distinguishing changes in evaporation and precipitation seasonality in the paleolimnological record.
机译：在北美洲中部大陆的沉积物中，记录了中全新世（8至4ka BP）的温暖和干旱情况。然而，由于现有替代指标的局限性，人们对这一时期的气候动因和降水的季节特征都不甚了解。例如，一个重要的挑战是在该地区现有的δ〜（18）O记录中区分蒸发，温度或降水季节变化的相互作用。在这里，我们结合棕榈酸的氢同位素和碳酸盐的氧同位素，得出明尼苏达州中北部Steel Lake全新世期间的湖水同位素值。综合起来，这些数据使我们能够将蒸发的变化与湖泊输入水的同位素组成变化区分开。蒸发量的变化被用作干旱的替代物，湖水的输入同位素值被用作替代大气降水的同位素值。我们的结果表明，中全新世期间湖水输入同位素值比现在更负。为了测试这些更负的值是否与温度或降水季节相关，我们将花粉推断的温度和由这些温度产生的降水的预期同位素值与重建的降水同位素值进行比较。结果表明，全新世中期温暖和干旱与蒸发速率增加和夏季降水减少有关。这些推论与气候模拟相一致，后者强调了全新世期间季节性日照和海面温度在驱动降水季节性变化中的作用。结果还表明，全新世降水季节的变化可能影响了明尼苏达州的草原-森林边界的扩张以及草地群落组成的区域差异。这项研究证明了氢氧同位素双重方法在区分古湖泊学记录中蒸发和降水季节变化方面的功效。

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