The structure of Holocene climate change in mid-latitude North America

Abstract

A sequence of long-term and rapid changes during the Holocene appears in a network of 40 well-resolved paleoclimate datasets from mid-latitude North America, including records of pollen-inferred temperatures, alkenone-derived sea-surface temperatures (SSTs), lake-level changes, dust accumulation, and lake isotopes from Idaho to Maine. Statistical analyses reveal that changes in insolation and the Laurentide Ice Sheet explain 51.7% of the variance in the records, especially multi-millennial trends, but peak rates of change indicate additional rapid changes at ca. 10.8, 9.4, 8.3, 7.0, 5.5–5.2, 4.7, 2.1, and 0.9 ka. Step changes between 9.4 and 8.3 ka relate to ice sheet dynamics that warmed much of the region, and changes at 5.5 ka were the largest since the demise of the ice sheet. The shift at 5.5 ka initiated widespread cooling and increases in effective moisture, which culminated in the coolest, wettest millennia in most areas after 2.1 ka. Replicated evidence from multiple records also shows a spatially-varied set of multi-century fluctuations including 1) low temperatures and high effective moisture at 5.5–4.8 ka in the mid-continent and 2) repeated phases of low SSTs, cool summers, and drought superimposed upon long cooling, moistening trends in eastern North American since 5.5 ka.