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Title: High-resolution stable isotope records as indicators of late middle Eocene climate change
Author: Wade, Bridget
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 2001
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High-resolution (3 kyr) stable isotope analyses (d18O, d13C) have been conducted on late middle Eocene planktonic foraminifera from the western North Atlantic (Ocean Drilling Program, Leg 171B, Site 1052). The data indicate significant (>1‰) and abrupt changes in surface water d18O. This variability is greater than that seen in open ocean Pleistocene records and indicates that the middle Eocene climatic system was not consistently warm or stable. There were intervals when annual sea surface temperatures were 4 to 7°C greater than modern mean values. These temperatures are similar to those recorded in the early Eocene, suggesting increased carbon dioxide or other greenhouse gases may have forced warm intervals. Fourier analysis reveals Milankovitch frequencies consistent with the wavelengths of eccentricity, obliquity and precession in the stable isotopic record. The long-period eccentricity signal (400 kyr) governs the large fluctuations in middle Eocene d18O produced significant changes in water column stability and thermal stratification. Large oscillations in sea surface temperatures occurred with surface water temperatures periodically approaching those of deep waters. A possible explanation is that these abrupt shifts in surface water d18O represent orbitally forced variations in upwelling intensity, which greatly reduced sea surface temperatures. It is concluded that the oscillations in the stable isotopic profiles in the western North Atlantic are due to climatic controls on the intensity of upwelling. The prominence of Milankovitch frequencies in middle Eocene climate records indicates that orbital variations in solar isolation were an important parameter of climatic variability during the Eocene transition period.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available