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A Millennial-Scale Oscillation in Latitudinal Temperature Gradients along the Western North Atlantic during the Mid-Holocene
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  • Bryan N Shuman,
  • Ioana Cristina Stefanescu,
  • Laurie D Grigg,
  • David R Foster,
  • W.Wyatt Oswald
Bryan N Shuman
University of Wyoming

Corresponding Author:bshuman@uwyo.edu

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Ioana Cristina Stefanescu
University of Wyoming
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Laurie D Grigg
Norwich University
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David R Foster
Harvard Forest
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W.Wyatt Oswald
Emerson College
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Changes in vegetation in North America indicate Holocene shifts in the latitudinal temperature gradient along the western margin of the North Atlantic. The dynamics of tree taxa such as oak (Quercus) and hickory (Carya) showed opposing directions of change across different latitudes, consistent with changes in temperature gradients. Pollen-inferred temperatures from 34 sites quantify the changes and reconstruct a long-term southward shift of the sharpest temperature gradient in winter and a northward shift in summer. During the mid-Holocene, however, an oscillation in tree distributions interrupted the trends indicating that the steepest portion of the seasonal temperature gradients migrated rapidly northward at 5.8-3.2 ka. The shift produced an unusually late summer thermal maxima at 42-43.5°N where oak abundance peaked both in the early and mid-Holocene. The changes appear consistent with orbital and ice sheet forcing as well as millennial variability in the North Atlantic pressure field during the mid-Holocene.