NOAA/WDS Paleoclimatology - Elk Lake, Minnesota 12,000 Year Ostracod Abundance and Geochemical Data

Lake response to climate forcing is commonly regarded as being controlled by within-lake processes. We present a case from the northern Great Plains in which Holocene drought response recorded in lake sediments was determined by changes in chemical characteristics of source ground water. Middle Holocene ostracode assemblages were dominated by halophylic Limnocythere staplini, indicating increased lake-water salinity, yet the oxygen isotope values in this period decreased by 2‰ to 3‰, contrary to expectations of evaporative dominance. We infer from these proxy records and ground-water flow-model results that the paleoclimatic record in the lake was mediated by changes in ground-water catchment area and by reduction in evapotranspiration accompanying desiccation of peripheral lake basins.

湖泊对气候强迫（climate forcing）的响应通常被认为受控于湖内过程（within-lake processes）。我们通过北美大平原北部的一则实例研究表明：湖泊沉积物（lake sediments）所记录的全新世（Holocene）干旱响应，实则由源地下水的化学特征变化所调控。中全新世时期的介形类组合（ostracode assemblages）以嗜盐的斯氏湖花介（Limnocythere staplini）为主导，指示湖水盐度（lake-water salinity）升高；但该阶段的氧同位素值（oxygen isotope values）却下降了2‰至3‰，与蒸发主导作用（evaporative dominance）的预期结果相悖。结合上述代用指标记录（proxy records）与地下水流动模型（ground-water flow-model）的模拟结果，我们推断该湖泊的古气候记录（paleoclimatic record）是由地下水集水区（ground-water catchment area）的变化，以及伴随湖滨盆地（peripheral lake basins）干涸所发生的蒸散发（evapotranspiration）降低共同介导的。