| Summary: | NER/S/A/2006/14325 A comprehensive theory explaining the relationship between periodic variations in the Earths orbital parameters and the response of the climate system remains elusive. One of the key challenges is that of the Mid-Pleistocene Transition (MPT), during which the dominant mode of glacial/interglacial climatic variability shifted without any corresponding change in the mode of orbital forcing. Subtropical climate on orbital time-scales is sensitive to variability in both the low-latitude ocean/atmosphere circulation regime and the global carbon-cycle (through its effect on atmospheric greenhouse gas levels), both of which may have played a role in the shift in mode of global climate response to orbital forcing during the MPT. This thesis presents a series of multi-proxy (foraminiferal stable isotope and trace-metal) paleoceanographic reconstructions from the subtropical southwest Pacific, as seen in marine sediment core MD06-3018, from 2470m water depth and 23ºS in the New Caledonia Trough, southern Coral Sea. The core age-model, based upon magnetic stratigraphy and orbital tuning, yields a mean sedimentation rate at the site of 20mm/ka and a core-bottom age of 1600ka. The MD06-3018 reconstruction of New Caledonia Trough deep water chemistry, based on benthic 13C measurements, shows that the spatial chemistry gradient within the Southern Ocean between deep waters entering the Tasman Sea and the open Pacific was greater during glacial (relative to interglacial) stages over at least the past 1100ka. This gradient was, however, generally reduced on the >100kyr time-scale across the MPT, consistent with it being a period of reduced deep water ventilation in both hemispheres. The MD06-3018 Mg/Ca-derived reconstruction of subtropical southwest Pacific Sea Surface Temperature (SST) shows glacial/interglacial variability of 2-3ºC but no significant trends on the >100kyr time-scale over the duration of the record. An estimate of the uncertainty associated with the SST reconstruction demonstrates ...
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