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Title: Paleocene climate and carbon cycle : insights into an unstable greenhouse from a biomarker and compound specific carbon isotope approach
Author: Taylor, Kyle William Robert
Awarding Body: University of Bristol
Current Institution: University of Bristol
Date of Award: 2012
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Abstract:
Climatic conditions throughout the Paleocene (55 - 65.5 Ma) are believed to have remained relatively stable (Shackleton and Hall, 1984a,b; Zachos et al., 1994; Zachos et al., 2001). The Paleocene is generally considered to be time of global warmth and reduced latitudinal temperature gradients compared with the present day (e.g. Zachos et al. 1993, 1994), although generally experienced temperatures relatively lower than those of the late Cretaceous and early-mid Eocene (Zachos et al., 2001; Pagani et al., 2005). It also experienced elevated levels of atmospheric CO2 compared to the present day. Some evidence however suggests that the Paleocene may not have been as stable as is generally accepted; the devastation of marine biota at the Cretaceous/Tertiary boundary (K/Pg) may have disrupted biogeochemical cycles for up to 1 - 3 My (D'Hondt et al., 1996a; 1998), as evidenced by the sustained collapse or suppression of the benthic-planktic carbon isotope gradient (Keller and Lindinger, 1989; Zachos et aI., 1989; Zachos et al, 1992; D'Hondt et al., 1998; Coxall et al., 2006). In the late Paleocene, a decrease in global benthic temperatures (Zachos et al., 2001; Cramer et al., 2009) is recorded, coinciding with a positive carbon isotope excursion in marine carbonates. The Paleocene may therefore represent an epoch with a relatively dynamic carbon cycle and climate, and as such provides an ideal period to study the relationship between carbon cycling and climate change in a high-Co- Earth system. The central aim of this thesis was to determine whether significant climate and carbon cycle instability occurred through the Paleocene using organic biomarker approaches, including the TEX86 palaeothermometer and compound specific carbon isotope analysis of algal and terrestrial biomarkers. Transient climate change and ecological disruption occurred at the K/Pg in the southwest Pacific. Climate instability persisted for c. 1 - 1.2 My, and then proceeded to stabilise, with most climate and ecological parameters returning to pre-K/Pg values; a notable exception is the algal biomarker distributions, which reflect a restructured algal community, in keeping with the suggestion that algal community restructuring, and thus the restructuring of tropic levels, was responsible for the long-term term recovery of the benthic-planktic carbon isotope gradient. Late Paleocene climate reconstructions indicate cooling coeval with l3C-enrichment of terrestrial and marine reservoirs in the Southern Ocean (SO), perhaps associated with enhanced marine productivity and a drawdown of CO2, indicating that this period, referred to as the Paleocene Carbon Isotope Maximum (PCIM) reflects a period of cooling associated with carbon cycle changes. A tentatively dated low-latitude north Atlantic SST III record does not indicate cooling. Assuming a correct age assignment, this could indicate that SST cooling was a more regionally restricted phenomenon, and that the global benthic carbonate ISO-enrichment reflects Southern Ocean (SO) cooling and strengthening of SO sourced bottom waters. Tentatively, drawdown of CO2 and Southern Ocean cooling could have brought about early Antarctic glaciations and an associated drop in sea level. Although such an inference is contentious and evidence presented here is circumstantial, such an event provides a mechanism for the pronounced oceanographic changes, including enhanced cooling and sedimentary anoxia, occurring at the neritic mid- Waipara River site from 58.3 - 58 Ma. Furthermore, these findings suggest that the Paleocene SO climate may have been more sensitive to carbon cycle dynamics than the classic ocean heat transport models suggest; this is in agreement with Paleogene climate models which predict a stronger influence of CO2 on Southern Ocean climate than the thermal isolation brought about by circum-Antarctic circulation (Hub er and Sloan, 2001; DeConto and Pollard, 2003a; 2003b; Huber and Nof, 2004; Huber et al., 2006; DeConto et al., 2008).
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.558094  DOI: Not available
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