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High-resolution paleoceanography and modeling of abrupt warming events on greenhouse earth

  • Author(s): Turner, Sandra Kirtland
  • et al.

I begin by investigating patterns of global overturning circulation in the warm Paleocene epoch, a time when previous studies have suggested weak deep-ocean aging gradients and sluggish circulation. Using a new benthic foraminiferal stable isotope dataset from the high- latitude South Pacific, I demonstrate that deep waters formed in the Southern Pacific (probably around the Ross Sea) at least intermittently during the Paleocene. I also suggest a number of distinct reorganizations of overturning during this epoch. I continue by assessing the potential connections between a series of postulated hyperthermal events in the early-middle Eocene with the sequence of hyperthermals in the late Paleocene to early Eocene that bracket the Paleocene-Eocene Thermal Maximum (̃56 Ma). Through a detailed comparison of the structure of all the suggested events in this interval, I demonstrate the similarity of most events, with the PETM and the subsequent Elmo event ̃2 Myr later appearing as outliers. I also use a new method for identifying whether events appear significantly different from background variability. Finally, I adapt a threshold model to suggest that a common mechanism is plausible for all events. I extend my analysis of the multiple hyperthermal events of the Paleocene-Eocene to synthesize records of all possible hyperthermal events from ̃250 to ̃40 Ma. I primarily compare records of bulk carbonate carbon isotopes, but also assess other environmental consequences of each event. This study represents the first such synthesis of postulated hyperthermals. Finally, I use the GENIE model to assess the degree to which an individual deep-sea sedimentary record records the magnitude of environmental perturbation represented by an early-middle Eocene hyperthermal. I develop a method to ̀back' out the true excursion size by utilizing the sedimentary model in GENIE. I use model results to compare the range of and controls on inter-site variability in the size, timing, and overall duration of the event

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