Reconstructing late-glacial no-analogue climates in northeastern Illinois with expanded pollen-climate relationships: A case study at Crystal Lake, McHenry County, Illinois. Leila M. Gonzales

ISBN: 9781109271454

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253 pages


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Reconstructing late-glacial no-analogue climates in northeastern Illinois with expanded pollen-climate relationships: A case study at Crystal Lake, McHenry County, Illinois.  by  Leila M. Gonzales

Reconstructing late-glacial no-analogue climates in northeastern Illinois with expanded pollen-climate relationships: A case study at Crystal Lake, McHenry County, Illinois. by Leila M. Gonzales
| NOOKstudy eTextbook | PDF, EPUB, FB2, DjVu, audiobook, mp3, RTF | 253 pages | ISBN: 9781109271454 | 4.18 Mb

Late-glacial (17-11 cal ka) Midwestern pollen records have similar vegetation trends, yet poor radiocarbon dating resolution, wide interval counting, and variable sedimentation rates prevent the direct correlation of these patterns with GreenlandMoreLate-glacial (17-11 cal ka) Midwestern pollen records have similar vegetation trends, yet poor radiocarbon dating resolution, wide interval counting, and variable sedimentation rates prevent the direct correlation of these patterns with Greenland ice-core records.

The widespread occurrence of late-glacial vegetation and climates without modern analogues hinders late-glacial climate reconstructions from vegetation proxies. Current statistical methods have been unsuccessful in reconstructing late-glacial paleoclimates from these no-analogue pollen assemblages because they have been unable to fully reconstruct pollen-climate relationships for taxa, such as Fraxinus, that are only partially defined in modern pollen-climate datasets.-In this dissertation, I generated a high resolution pollen record from Crystal Lake, Illinois, a modern pollen-climate dataset designed for modeling late-glacial taxa in eastern North America, and the Expanded Response Surface (ERS) method to reconstruct the late-glacial/early Holocene vegetation and climate conditions at Crystal Lake, in north-eastern Illinois.

I used the Crystal Lake record, a high-resolution pollen record with vegetation changes that are correlated with millennial scale trends in the NGRIP, and the modern calibration dataset to reconstruct the late-glacial climate at Crystal Lake with the ERS method. The central assumption of the ERS method is that pollen abundances are distributed unimodally and symmetrically along climatic gradients. The ERS method expands modern pollen-climate relationships by mirroring pollen abundances around their mode of distribution within a four-dimensional climate space, and recovers the portion of the relationship that is not realized under modern conditions.-The ERS method reconstructed paleoclimates during the height of no-analogue conditions for 37% of the fossil samples where standard techniques only found 13%.

ERS reconstructions indicated cooler-than-present summer and winter temperatures, higher-than-present winter precipitation, and similar-to-present summer precipitation during the no-analogue interval. These results suggest that high moisture availability was strongly influential in the development of Midwestern no-analogue communities that were characterized by high Fraxinus nigra abundances.

ERS reconstructions also indicate similar-to-present high temperature seasonality during the late-glacial interval that does not agree with previous modeling experiments that suggest higher-than-present seasonality caused by higher-than-present insolation. Further work is needed to resolve the temperature seasonality discrepancies between these two lines of paleoclimatic inquiry.



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