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Impacts of gateways and climate on regional hydrology and carbon cycle processes: A view from the Miocene sediments of Malta.

Zammit, Raymond 2022. Impacts of gateways and climate on regional hydrology and carbon cycle processes: A view from the Miocene sediments of Malta. PhD Thesis, Cardiff University.
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The Miocene represents a key interval in the transition to our modern bipolar icehouse world. The early Miocene climate (23.0 Ma to 19.2 Ma) was typified by a cool-arid climate with large swings in global benthic δ18O records. This climate regime changed to a gradually warming trend (19.2 Ma to 17.0 Ma) until it was replaced by the relative warmth of the Miocene Climatic Optimum from 17.0 Ma to 14.7 Ma. Climate subsequently cooled in a step-wise manner, with a major expansion of the Antarctic ice sheet occurring at 13.8 Ma. In addition to these climatic shifts, a major change in oceanic circulation also occurred during the Miocene. This was due to the restriction of water flow through the Mesopotamian Seaway that connected the Mediterranean with the Indian Ocean. This flow restriction occurred in two steps, one during the early Miocene (19.0 to 20.2 Ma) and the second and complete disconnection between 13.8 Ma and 13.6 Ma. The Miocene deposits of Malta are temporally and spatially ideally situated to investigate local and global paleoenvironmental changes during the Miocene. Lithological and geochemical changes from the Early Miocene il-Blata section outcropping in Malta indicate a regional shift from a cold arid climate to a warm humid climate following the first Miocene restriction of the Mesopotamian Seaway. A marked shift in sedimentation rate at ~19.1 Ma coincident with a change to organic-rich clays and changes in bulk CaCO3, Sr/Ca, K/Al, Ti/Al, Zr/Al and Si/Ti support this interpretation. The closure of the Mesopotamian Seaway and consequent diversion of warm intermediate waters into the Atlantic Ocean is a plausible mechanism for the intensification of the hydrological cycle over North Africa. This transition to a humid regime and associated influence of terrigenous sediment delivery likely helped in the termination of the extensive Early Miocene phosphorites of Malta. Planktic and benthic foraminiferal geochemical records from the Ras il-Pellegrin section (Malta) indicate changes in regional hydroclimate following the Middle Miocene expansion of the Antarctic ice sheet at 13.82 Ma. Foraminiferal Mg/Ca was used to generate temperature records, which enabled the generation of surface and bottom seawater δ18O, and in turn an estimate of sea surface salinity variability. These records show that a significant input of freshwater occurred following the Middle Miocene expansion of the Antarctic icesheet and the closure of the Mesopotamian Seaway. The input of freshwater is precession and obliquity driven and indicates that a strong seasonal, monsoonal type climate was emplaced over North Africa. A new planktic foraminiferal B/Ca record was used with previously published δ13C records from the composite Marsalforn (Gozo Island) and Ras il-Pellegrin sections to investigate carbon cycle dynamics in the Central Mediterranean from 14.4 Ma to 12.8 Ma. The vertical seawater δ13C gradient coupled with B/Ca, Mn/Ca, and calculated [B(OH)4−]/[DIC], indicates a highly active biological pump following the Antarctic icesheet expansion at 13.82 Ma and coinciding with the global CM-6 δ13C excursion. These records also cast doubt on the interpretation of the pCO2 records from Malta published in Badger et al. (2013), and suggests that low latitude shallow water zones are particularly important in carbon cycle dynamics as zones of enhanced carbon burial. Overall, this thesis highlights the importance of the tectonic closure of the Mesopotamian Seaway on regional climate, with possible effects on global climate and cryospheric feedbacks. It confirms the Maltese Islands as a natural laboratory for investigating the Miocene climate. This thesis also underlines the importance of considering the Miocene as a geological time suitable for investigating global environments and climate feedbacks at near-future pCO2 levels.

Item Type: Thesis (PhD)
Date Type: Completion
Status: Unpublished
Schools: Earth and Environmental Sciences
Date of First Compliant Deposit: 26 May 2023
Last Modified: 30 May 2023 08:42

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