28 Nov 2022
28 Nov 2022
Status: this preprint is currently under review for the journal CP.

Patterns of Centennial-to-Millennial Holocene Climate Variation in the North American Mid-Latitudes

Bryan N. Shuman Bryan N. Shuman
  • Department of Geology and Geophysics, University of Wyoming, Laramie, WY, 82071, USA

Abstract. Noise in Holocene paleoclimate reconstructions can hamper detection of centennial-to-millennial climate variations and diagnoses of the dynamics involved. This paper uses multiple ensembles of reconstructions to separate signal and noise and determine what, if any, centennial-to-millennial variations influenced North America during the past 7000 yr. To do so, ensembles of temperature and moisture reconstructions were compared across four different spatial scales: continental, regional, sub-regional, and local scales. At each scale, two independent multi-record ensembles were compared to detect any centennial-to-millennial departures from the long Holocene trends, which correlate more than expected from random patterns. In all cases, the potential centennial-to-millennial variations had small magnitudes. However, at least two patterns of centennial-to-millennial variability appear evident. First, large-scale variations included a prominent Mid-Holocene anomaly from 5600–4500 YBP that increased mean effective moisture and produced temperature anomalies of different signs in different regions. The changes steepened the north-south temperature gradient in mid-latitude North America with a pattern similar to the positive mode of the North Atlantic Oscillation (NAO). Second, correlated multi-century (~500 yr) variations produce a distinct spectral signature in temperature and hydroclimate records along the western Atlantic margin. Both patterns differ from random autocorrelated variations but expressed distinct spatiotemporal characteristics consistent with separate controlling dynamics.

Bryan N. Shuman

Status: open (until 17 Feb 2023)

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Bryan N. Shuman

Bryan N. Shuman


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Short summary
A gap in understanding climate variation exists at centennial-to-millennial scales, particularly for warm climates. Such variations challenge detection. They exceed direct observation but are geologically short. Centennial-to-millennial variations that may have influenced North America were examined over the past 7000 yr. Significant patterns were detected from fossil pollen and sedimentary lake-level changes, indicating ecological, hydrological, and likely human significance.