Gateways and climate: The Drake Passage opening

LODOLO E.; GALINDO ZALDIVAR, J.; RUANO, P.; SCHREIDER, A.; BOHOYO, F.; MEDIALDEA, T.; SOMOZA, L.; HERNÁNDEZ MOLINA, J.; MALDONADO, A.; RÓDRIGUEZ FERNÁNDEZ, A.; SURIÑACH, E.; VAZQUEZ, J. T.; CARVALHO DA SILVA, L.; GAREA, M.; TASSONE A.

Rimini , Italia

Congreso; VII Forum Italiano di Scienze della terra; 2009

Societa Geologica Italiana

Present continent-ocean geometry is the result of a long (~200 million years) history of changing spatial configurations. Major changes in plate tectonics which led to the opening (or closure) of oceanic gateways, have had a major influence on oceanic circulation, and determined a profound effect on global paleo-climate. The role of gateways (and barriers) is hence fundamental for recreating the scenario of past climatic histories. Oceans represent one of the most important components of the global climatic system because, with their high thermal capacity (over 1000 times that of the atmosphere), act as a buffer for energy transport from summer to winter hemispheres, and from low to high latitudes. Starting from these premises, it is clear that the key to understanding the Late Cenozoic climate is the knowledge of changes in ocean circulation triggered by tectonic processes such as the opening and closing of oceanic gateways. Moreover, opening and closure of ocean gateways break and create biological land bridges and sea migration routes. The Oligocene opening of Drake Passage between the southern tip of South America and the Antarctic Peninsula, and the subsequent evolution of the Scotia plate, was a crucial Cenozoic tectonic event of the Southern Hemisphere. It has definitively separated Antarctica from the other continental masses, and have created conditions for the development of the Antarctic Circumpolar Current. This annular water flow represents one of the most important ocean currents of our planet, and has had a profound influence on global climate system. This may have, at least in part, contributed to the formation of the Antarctic ice cap, isolating the continent and thus preventing the transfer of heat from low to southern latitudes. Geological and geophysical investigations conducted over the past twenty years at sea and on land in the region of the Scotia Sea and in adjacent areas, have clarified many aspects of the complex geological history of the area, and have revealed significant relationships between tectonic events and climatic changes on a large scale. In the frame of the International Polar Year - IPY, a geophysical and geological survey was carried out onboard the Spanish R/V Hesperides during January-February 2008 in the Drake Passage, to better constrain the age and mechanism of its early development, and analyze the geometries of the conjugate margins of the south-western Scotia Sea. Data acquired include parametric and multibeam mapping, multichannel seismic, gravity, and magnetic profiles. Two profiles were recorded along the spreading corridors of the southern half of western Scotia ridge axis, crossing the oldest oceanic crust, the Terror Rise up to the oceanic Protector Basin. Seismic data show similar features and evidence the continental nature of the Terror Rise. It represents a NNE-SSW elongated ridge which top lies at about 2000 m water depth between abyssal plains of more than 3000 m deep and may be considered the remnant part of the stretched Antarctic passive margin during the Drake Passage opening. In its initial phase of evolution, the Protector Basin was not yet opened and the Terror Rise probably was adjacent to the western flank of the Pirie Bank, which is now located east to the Protector Basin. Similar structural have been described off the Tierra del Fuego continental margin, testifying that the Terror Rise and possibly other continental blocks now dispersed along the south-western Scotia Sea margin, represent the conjugate margin of the southernmost South America.