Paleoecological Environmental Assessment and Research Laboratory (PEARL), Department of Biology, Queen's University, Biosciences Complex, Kingston, ON, K7L 3N6, Canada.
Glob Chang Biol. 2012 Sep;18(9):2869-81. doi: 10.1111/j.1365-2486.2012.02740.x. Epub 2012 Jun 12.
Multi-decadal to centennial-scale shifts in effective moisture over the past two millennia are inferred from sedimentary records from six lakes spanning a ~250 km region in northwest Ontario. This is the first regional application of a technique developed to reconstruct drought from drainage lakes (open lakes with surface outlets). This regional network of proxy drought records is based on individual within-lake calibration models developed using diatom assemblages collected from surface sediments across a water-depth gradient. Analysis of diatom assemblages from sediment cores collected close to the near-shore ecological boundary between benthic and planktonic diatom taxa indicated this boundary shifted over time in all lakes. These shifts are largely dependent on climate-driven influences, and can provide a sensitive record of past drought. Our lake-sediment records indicate two periods of synchronous signals, suggesting a common large-scale climate forcing. The first is a period of prolonged aridity during the Medieval Climate Anomaly (MCA, c. 900-1400 CE). Documentation of aridity across this region expands the known spatial extent of the MCA megadrought into a region that historically has not experienced extreme droughts such as those in central and western north America. The second synchronous period is the recent signal of the past ~100 years, which indicates a change to higher effective moisture that may be related to anthropogenic forcing on climate. This approach has the potential to fill regional gaps, where many previous paleo-lake depth methods (based on deeper centrally located cores) were relatively insensitive. By filling regional gaps, a better understanding of past spatial patterns in drought can be used to assess the sensitivity and realism of climate model projections of future climate change. This type of data is especially important for validating high spatial resolution, regional climate models.
过去两千年中，来自安大略省西北部六个跨越约 250 公里区域的湖泊的沉积记录推断出有效湿度在数十年到百年时间尺度上的变化。这是首次将一种从排水湖（具有表面出口的开阔湖泊）重建干旱的技术应用于区域。该区域代理干旱记录网络基于使用从整个水深梯度的表层沉积物中收集的硅藻组合为每个湖泊开发的单独的湖泊内校准模型。对靠近底栖和浮游硅藻类群之间近海生态边界的核心沉积物中采集的硅藻组合的分析表明，所有湖泊中的这一边界随时间发生了变化。这些变化在很大程度上取决于气候驱动的影响，并且可以提供过去干旱的敏感记录。我们的湖泊沉积物记录表明存在两个同步信号的时期，这表明存在共同的大尺度气候强迫。第一个是中世纪气候异常（MCA，公元 900-1400 年）期间长时间干旱的时期。在该区域记录到干旱，扩展了 MCA 特大干旱的已知空间范围，进入了历史上没有经历过极端干旱（例如北美中南部）的区域。第二个同步时期是过去约 100 年的近期信号，这表明有效湿度增加，这可能与人为对气候的强迫有关。这种方法具有填补区域空白的潜力，而许多先前的古湖深方法（基于较深的中心位置核心）相对不敏感。通过填补区域空白，可以更好地了解过去干旱的空间模式，从而评估气候模型对未来气候变化的预测的敏感性和现实性。这种类型的数据对于验证高空间分辨率的区域气候模型尤其重要。
