Plate Tectonics and Polar Gateways in Earth History

Project Description
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The world oceans are a major component of the Earth System and changes in the complex global ocean current system are likely to cause global environmental changes. On geological time-scales, these water mass exchanges are controlled by the deepening and shallowing of areas of ocean floor during the tectonic opening and closing of strategic oceanic gateways and the formation of ocean basins. Establishing the detailed tectonic, geodynamic, sedimentary and paleo-topographic histories of strategic oceanic basins and gateways will provide the essential framework for modelling studies that will relate these events to paleo-climate observations collected across the globe.

PLATES & GATES adopts a multidisciplinary approach by addressing tectono-magmatic, geodynamic, sedimentary and biostratigraphic processes, utilising paleo-biological and geochemical proxies, past and recent oceanographic conditions in the gateways, as well as by using state-of-the-art geophysical techniques, sediment coring, ocean drilling and accompanying land investigations.

The main objectives include:
(1) studies of the crust/lithosphere of the polar ocean basins and polar gateways as well as their continental margins to develop a good understanding of the past and present plate kinematics, mantle processes, margin formations, and crustal subsidence and uplift processes,
(2) understanding the past ocean current systems in the basins and gateways by examining the record of change preserved in deep-ocean sediment deposits and drifts, and by undertaking seismic-stratigraphic investigations and analyses of present and paleo-oceanographic proxies to derive the evolution of deep-water circulation and climate change,
(3) reconstructing detailed ocean basin and gateway opening processes and constraining the timing of shallow and deep water mass exchange between basins,
(4) understanding the long-term paleo-climatic history from Mesozoic-Early Tertiary Greenhouse conditions to upper Tertiary-Quaternary Icehouse conditions, and
(5) identifying and modelling the role of gateway openings/closures in the global carbon cycle, bio-evolution and the development of ice-sheets and climatic changes.

Paleomagnetic, stratigraphic and petrological data from Franz Josef Land, Axel Heiberg I., Ellesmere I., the New Siberian Is. and North Greenland will be collected and analysed. Geoscientific studies including bathymetric mapping, seismic and magnetic surveying, sub-bottom profiling and sediment coring will be carried out in the Amundsen Basin, on transects across the Alpha-Mendeleev Ridge, over the Lomonosov Ridge and from the North Greenland Shelf. Geological and neotectonic studies are planned for North and East Greenland, Svalbard, Bear Island, Mohns Ridge, Knipovich Ridge and the Barents Sea. The gateways between the North Atlantic and the Arctic Ocean will be investigated by a wide spectrum of geophysical and geological approaches to understand the timing and paleo-climatic consequences of water mass exchange. The Bering Strait, as the only freshwater connection between the Arctic and the Pacific, will be investigated by geophysical surveying and geological sampling (drilling). Geophysical and bathymetric surveying as well as geological and biological sampling is planned for critical regions of the Southern Ocean that formed since the break-up of Gondwana. A thorough revision of this break-up will be performed in parallel with new data acquisition giving special emphasis to the compilation and integration of existing data sets. Uncertainties about the early stages of development of the Drake Passage/Scotia Sea gateway will be resolved by studies of the tectonic and sedimentary evolution of the basins and the origin of bathymetric highs, the structure and history of relevant plate boundaries, and deformation of neighbouring land areas. Geophysical data will be collected in the Tasmanian Gateway to constrain the timing of shallow and deep-water opening between the Indian and Pacific Oceans as well as the motion between East and West Antarctica which is critical to the timing of the uplift of the Transantarctic Mountains. Other regions of interest include the passage between the southern Kerguelen Plateau and Antarctic continent as well as major topographically outstanding transform and fracture zone systems in the Pacific.

PLATES & GATES will perform Cenozoic and Mesozoic climate reconstructions using a variety of Earth system models designed to evaluate the effect of ocean gateways and basins on paleo-circulation patterns, the global carbon cycle and nature of polar ice-sheet development. These experiments will include sensitivity runs incorporating new paleo-bathymetric reconstructions arising from the new data acquisition described above. The results from these experiments will be compared with other model simulations, which include different forcing factors such as atmospheric greenhouse gasses and mountain uplift to determine the relative importance of paleo-geography on the evolution of polar and global climates over long geological timescales.