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M.Phil. dissertation abstracts 2002 - 2003

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

Petya Blumbach

Dissertation "Millennial-scale palaeoceanographic variability in Marine Isotope Stage (MIS) 6 in a core (MD01-2444) from the Iberian Margin ." , supervised by Professor Sir Nicholas Shackleton (Cambridge).

A multi-proxy analysis of the older section (160 to 141 cal ka), of MarineIsotope Stage 6 (MIS 6) from the high-sedimentation rate core MD01-2444(37°¨33.88°N, 10°¨88.04°W, 2637m water depth) off the Iberian Marginreveals a complex history of millennial and sub-millennial scale variabilityreflecting changes in palaeoclimatology and palaeoceanography.  The Iberian Margin represents a sensitive location with regard to fluctuations in the Polar Front over glacial periods, where this boundary was shifted south from its present interglacial position. High sedimentation rates off the Portuguese coast also allow for the investigation into millennial and sub-millennial scale variability of a number of proxies.

Oxygen isotopes from planktonic foraminifera represent a composite signal of global (ice volume) and local factors (sea surface temperature (SST) and salinity). These provided the general framework for the other multi-proxy analysis. Close alignment of isotopes from core MD01-2444 with a more northerly Iberian Margin core MD95-2040 allowed the construction of an age-depth model to be undertaken.

Three indicative species, G. bulloides, N. pachyderma (sinistral) and Gs. ruber (white) were used as proxies for upwelling, cold and warm conditions respectively. Total benthic foraminiferal concentrations served as an indication of deep ocean nutrient status, whilst total foraminiferal concentrations outlined general productivity changes. Two main intervals within the studied period were identified primarily on the basis of the G. bulloides data, with a shift from cooler to warmer conditions with increased upwelling. A notable transitional phase between these two intervals illustrated some rapid shifts in foraminiferal concentrations.

Alkenone-derived SST data illustrated the changes in surface temperatures over this period. Fluctuations took place on millennial and sub-millennial timescales for all proxy data.

Percentages of lithic particles (larger than 150µm) were used to identify terrigenous influxes, which were determined as mainly being ice-rafted debris (IRD) at this site. One main ice rafting period between 158 and 153 cal ka was identified in the cooler period of the record, and within this a prominent ice-rafting interval 154.7 and 154.2 cal ka constituted a ‘Heinrich-like event’. The period of ice rafting in core MD01-2444 coincided with the latter part and termination of the ice rafting interval defined in core MD95-2040, providing the first independent verification of this data. The combination of IRD peaks aligning with increases in the cold-water indicator N. pachyderma (sinistral), and the presence of grain types (in decreasing importance) such as; quartz (hyaline and pink), haematite-stained grains and volcanic materials (glass and pumice) supports the suggestion that these grains are ice rafted material.

MIS 6 represents a somewhat neglected period of many Quaternary palaeoenvironmental reconstructions, which have largely focused on the last glacial-interglacial cycle (MIS 5e to 1). With an increasing interest in abrupt climatic changes and millennial and sub-millennial scale variability, glacial periods such as MIS 6 during may serve as past models for future climate change, especially with regard to the increasing impact of anthropogenic activity on the Earth system.

Key Words: Marine Isotope Stage 6 (MIS 6), Millennial-scale variability, Iberian Margin, Oxygen isotopes, Planktonic foraminifera, Ice rafted debris (IRD), Alkenone-derived (SST).

Alison Loomis

Dissertation "The role of land carbon 60ky to present: Atlantic Ocean timeslice reconstruction." , supervised by Professor Harry Elderfield (Cambridge).

Atlantic records of ∂13C from Cibicidoides wuellerstorfi and related species, were collected through to the past 60,000 years to present.  Using a time-slice approach, depth profiles of nutrient gradients were reconstructed along a North-South transect.  Inter-comparison of time-slice results in the water-column, show that variations in mean ∂13C match well to Boyle (1988) vertical nutrient fractionation model, however, deviations from the model also suggest that the complexity of circulation does not perfectly explain continental carbon in the oceans.  While transfer between land and ocean are indeed related to nutrient gradients in the ocean throughout the past 60,000 years, the sensitivity to fluctuations in C02 is less evident.  Because of leads and lags in the system, and relationships to specific carbon effects and local variables in the Atlantic Ocean are unclear, this study concludes that other proxies are needed in order to validate these findings.