Contribuciones al estudio del periodo cuaternario

Resumen

Sea-ice is a very important parameter in the climate and system, which is believed to have experienced large amplitude changes during the recent geologicalpast of the Earth. The most direct proxies of past sea-ice found in marine sediments include sedimentary tracers of particles entrained and dispersed by sea-ice, biogenic remains associated with production associated with sea-ice or with ice-free conditions, in addition to isotopic indication of brine formation or mixing with meltwater. The most common proxies for reconstructing seasonal extent of sea-ice cover are diatoms (opal silica phytoplankton remains), which are principally used in the southern oceans, and dinocysts (organic-walled cysts of protists) principally used in the North Atlantic, Arctic and sub-arctic seas. The isotopic composition (18O) of polar planktonic foraminifera may also provide indication on brine formation associated with the freezing of sea water. In the high latitude of the northern hemisphere, the development of large dinocyst database from the analyses of surface sediment samples permitted the development of transfer functions to reconstruct the duration of sea-ice in terms of months per year from deep-sea sediment studies. During the Holocene, significant fluctuations of sea-ice extent occurred in the Arctic, with different trends in the western and eastern sectors suggesting the involvement of complex mechanisms. At the scale of the last climate cycle, records from the northwest North Atlantic show a coupling between sea-ice extent and large amplitude fluctuations such as the Heinrich events or the Younger Dryas, supporting the hypothesis that sea-ice may act as “amplifier” in the climate system. During the Pleistocene, data from ODP Site 646 in the Labrador Sea, suggest sea-ice occurrence during most of the last million years, with a major sea-ice free interval during isotope stage 11, which corresponds to a particularly warm interval that was possibly the last one characterized by the absence of multi-year perennial sea-ice in the Arctic Ocean.