NOAA/WDS Paleoclimatology - Vestre Oykjamyrtorn Lake Surface Temperature Reconstructions during the last 13 ka

Chironomid subfossil assemblages from six low-alpine and sub-alpine Holocene stratigraphies are presented and compared. They are from five lakes in mid-southern and western Norway and one in central Sweden. When comparing the chironomid-inferred July air temperatures, there are many time segments with a poor among-lake fit in inferred temperatures. Possible environmental variables influencing the fossil chironomid assemblages are discussed using a modern Norwegian calibration data set to indicate taxon–environment relationships. These analyses indicate that local changes in pH, water chemistry, and productivity at times may have overridden the regional temperature signal. In addition, other causes of poor among-site temperature fit are discussed, in particular those related to chronological uncertainties. Holocene temperature inferences from single cores based on chironomids may not always be able to provide a reliable regional temperature signal, but can act as a guide from which hypotheses about past environmental conditions can be tested with the aid of chironomid-inferred temperatures from several sites and from other environmental proxies. We have obtained a regional picture of Holocene summer temperature change by developing a consensus reconstruction based on the overall temperature signal from all six sites. This consensus is developed by fitting a smoother through all 330 site-specific temperature-deviations from the Holocene mean. The consensus temperature deviations vary from −0.8 °C at 8800 cal years BP to +0.8 °C at 6500 cal years BP.

本文呈现并对比了采自6处低阿尔卑斯型与亚阿尔卑斯型全新世（Holocene）地层序列的摇蚊（Chironomid）亚化石组合。这些样本源自挪威中南部与西部的5处湖泊，以及瑞典中部的1处湖泊。在对比摇蚊推断的7月气温时，存在多个时段的湖间重建气温拟合度不佳的情况。本文采用挪威现代校准数据集（calibration data set），探讨了影响化石摇蚊组合的潜在环境变量，以明确类群-环境关系（taxon–environment relationships）。分析结果表明，局部的pH值、水化学特征以及初级生产力变化有时会掩盖区域温度信号。此外，本文还探讨了导致点位间气温拟合度不佳的其他原因，尤其是与年代学不确定性相关的因素。基于摇蚊的单根沉积物岩芯全新世气温推断结果，未必总能提供可靠的区域温度信号，但可作为研究参考框架：借助多点位摇蚊推断气温及其他环境代用指标（environmental proxies），可对过去环境状况的相关假说进行验证。我们通过整合全部6处点位的整体温度信号构建共识重建结果，从而获取了全新世夏季气温变化的区域图景。该共识重建通过对全部330条点位特异性温度距平（相对于全新世均值）进行平滑拟合得到。共识温度距平的变化范围为：距今8800校准年前（cal years BP）的-0.8℃，至距今6500校准年前的+0.8℃。