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M.Phil. dissertation abstracts 2004 - 2005

Copies of these dissertations will be held in the University of Cambridge, Department of Geography Library.

Roy Marden 

Palynology from the end of Interstadial 9, Heinrich event 4 and the ensuing Interstadial 8 during the Wisconsinan Stage (Late Pleistocene) (supervisor: Phil Gibbard)

This project presents new pollen data, for the time interval spanning from the end of Interstadial 9, Heinrich event 4 and the ensuing Interstadial 8 climatic improvement, which occur during the Wisconsinan Stage (Late Pleistocene) or Marine Isotope Stage 3 (MIS 3),  from marine core samples of ODP Site 1060 (30º46’N 74º28’W).  These results are compared with existing foraminiferal data (Vautravers et al. 2004) obtained from the same samples giving evidence for Sea Surface Temperature (SST) changes at the core location.  Terrestrial climatic reconstructions from south eastern North America have been controversial, especially during Heinrich events (Grimm et al. 1993, Grimm et al. 2003) so palynological results from BOR are important.  Therefore, Site 1060 can be regarded as a key oceanic coring site providing palaeoclimatic data for south eastern North America as well as information on the Gulf Stream intensity and its function as part of the global thermohaline circulation (THC).  The difficulties with interpretation of the terrestrial record in south eastern North America emphasise the problems of attempting to link terrestrial changes with those in the ocean.  By examining reliable marine vegetational sequences it is possible to compare land and sea records directly via in situ palynological and marine proxy analyses bypassing such correlation problems.  The palynological data confirms the findings of the foraminiferal assemblages pointing to a climatic deterioration during Heinrich event 4 (38,700 years BP) as shown by an increase in pollen of Picea and a decline in Quercus pollen and pollen of other thermophilous taxa.  The climatic improvement of Interstadial 8 (38,500 years BP) is clearly shown by warm foraminiferal indicators, which correlate with the demise in percentage abundance of Picea pollen.  However, pollen of temperate forest taxa is lacking thus pointing to a delay in the recovery of thermophilous taxa.  Heinrich events north of Florida appear to be cold and the possibility of them being wet cannot be excluded.

To validate Site 1060 a second core was examined (ODP 1058, 31°41'N 75°25'W) at a lower resolution during the same time interval to assess the degree of taphonomic bias introduced during transport to the deposition sites.  X-ray Fluorescence (XRF) data allowed each core chronology to be matched by implying synchronous deposition.  Results show good comparison suggesting limited down slope transport and mixing. 

Carolyn Snyder

Palaeoclimatic perspectives on climate sensitivity to Carbon Dioxide  (supervisor: Harry Elderfield)
This research investigates the Earth’s climatic history for insight into the potential values of climate sensitivity to carbon dioxide (CO2).  The goal is to contribute to current debates about anthropogenic climate change and prediction scenarios, and thus a rigorous quantitative and statistical methodology is crucial for the research design.  This research project compares temperature and CO2 records over four time resolutions: Phanerozoic, Cenozoic, late Quaternary, and the rapid change of glacial terminations.  Analytical methods are developed to estimate and incorporate most sources of uncertainty into the final SIMEX regression analysis, and thus represent a great improvement from previous simple linear regressions or point-to-point behaviour, both in the more robust considerations of uncertainty and in the treatment of continuous change rather than just maximum to minimum ranges.  In addition, the research begins with a thorough critique of the available proxy methods to determine the most up-to-date corrections and calibrations, quantify uncertainty, and define limits of time and/or magnitude beyond which the specific proxies are no longer reliable.
The Phanerozoic records are found to not be resolved well-enough to undergo such a quantitative analysis, but new methodological improvements do have implications for previously published estimates and current “decoupling” debates.  The Cenozoic is similarly limited by sparsely available data and high calibration uncertainties, but sensitivities are calculated for bottom water, showing a large range of 0.8-5.2(±3)ºC, whose implications are not clear.  Analyses of the late Quaternary produce many reliable estimates, and a large sample size distributed globally improves the robustness of the analysis.  A summary of the calculated sensitivity values are: 5±1.5ºC for the tropics, 4.5±2ºC for bottom water, 15±3ºC for the poles, and with estimated global sensitivities of, at minimum, 6.5±1.5ºC.  Such means are on the outer edge, if not outside, the sensitivity values currently considered by climate models, and are significantly higher than their mean of 3.5ºC (Houghton et al. 2001).  Thus, this research has strong implications for the climate modelling and policy communities, and suggests that future equilibrium climate change may be on average 2-fold higher than currently discussed.