Plate tectonics and polar sea straits during geological history
IPY Lead Project No. 77:
PLATES & GATES: Plate Tectonics and Polar Gateways in the Earth system
The topographic relief of the Earth’s surface has constantly changed in Earth’s history through tectonic motions as well as depositional and erosional processes, and so have the geometric conditions for climatic factors such as the distribution of the ocean and atmospheric circulation. Alteration of water mass exchanges between world oceans as a result of continental motion with its opening and closing of ocean gateways have had a significant effect on global climatic changes at long time-scales.
About 100 million years ago, the deep basin of the Arctic Ocean did not exist and corals dominated in a subtropical shallow sea. The opening of the Arctic and the Atlantic Oceans separated Eurasia and North America. Svalbard drifted on the Eurasian side to its present position while Pearya remained at the northern tip of North America. As a result, the Fram Strait opened as an Arctic-Atlantic seaway. Geophysical surveys and geological sampling has been conducted in the central Arctic Ocean basin and its surrounding shelves in order to decipher their tectonic evolution and identify signals of significant climatic changes in the Arctic region. A particular contribution from these investigations is the understanding the role of the Arctic Ocean as an isolated inland sea before the opening of Fram Strait to the Atlantic as well as its function after this deep-water gateway was established 15-18 million years ago. In this context belongs also the study of the opening history of the Baffin Bay for its role as another Arctic-Atlantic gateway between Greenland and Canada.
The tectonic evolutionary history of the southern hemisphere with the growth of the Southern Ocean appeared to have had a significant influence on the global climatic changes on a large time-scale from the Cretaceous hothouse climate to the transition of a coldhouse climate from the early Tertiary to recent times. Enormous volcanic eruption events accompanied the separation of Africa and India from Antarctica and flooded the young ocean floor with gigantic basalt layers during the hothouse period, for instance, during the growth of the Kerguelen Plateau. The separation of Australia, New Zealand and South America from Antarctica are further steps toward a constellation of continents which resulted in a new global ocean circulation pattern. The beginning of the coldhouse climate, at which the global atmospheric temperature decreased by about 5° C and when major Antarctic glaciation began, can be dated to the transition from Eocene to Oligocene times around 35 million years ago. The opening of the Southern Ocean gateways created the tectonic conditions for an Antarctic Circumpolar Current and the thermal isolation of Antarctica. Less heat was transported from lower latitudes towards Antarctica, resulting in a cooling of the continent. Simultaneous to this development, the atmospheric carbon dioxide concentration decreased during the Eocene which reduced the greenhouse effect and contributed to global cooling. However, first drilling results of the ANDRILL project on the ice of the Ross Sea provided indications that Antarctica has experienced repeated phases of less ice coverage since the beginning of glaciation.