957 resultados para HEMISPHERE WARM POOL
Resumo:
The Sulu Sea is located in the 'warm pool' of the western Pacific Ocean, where mean annual temperatures are the highest of anywhere on Earth. Because this large heat source supplies the atmosphere with a significant portion of its water vapour and latent heat, understanding the climate history of the region is important for reconstructing global palaeoclimate and for predicting future climate change. Changes in the oxygen isotope composition of planktonic foraminifera from Sulu Sea sediments have previously been shown to reflect changes in the planetary ice volume at glacial-interglacial and millenial timeseales, and such records have been obtained for the late Pleistocene epoch and the last deglaciation (Linsley and Thunell, 1990, doi:10.1029/PA005i006p01025; Lindley and Dunbar, 1994, doi:10.1029/93PA03216; Kudrass et al., 1991, doi:10.1038/349406a0). Here I present results that extend the millenial time resolution record back to 150,000 years before present. On timescales of around 10,000 years, the Sulu Sea oxygen-isotope record matches changes in sea level deduced from coral terraces on the Huon peninsula (Chappell and Shackleton, doi:10.1038/324137a0). This is particularly the case during isotope stage 3 (an interglacial period 23,000 to 58,000 years ago) where the Sulu Sea oxygen-isotope record deviates from the SPECMAP deep-ocean oxygen-isotope record (Imbrie et al., 1984). Thus these results support the idea (Chappell and Shackleton, doi:10.1038/324137a0; Shackleton, 1987, doi:10.1016/0277-3791(87)90003-5) that there were higher sea levels and less continental ice during stage 3 than the SPECMAP record implies and that sea level during this interglacial was just 40-50 metres below present levels. The subsequent rate of increase in continental ice volume during the return to full glacial conditions was correspondingly faster than previously thought.
Resumo:
We present sea surface, upper thermocline, and benthic d18O data, as well as temperature and paleoproductivity proxy data, from the International Marine Global Change Study Program (IMAGES) Core MD06-3067 (6°31'N, 126°30'E, 1575 m water depth), located in the western equatorial Pacific Ocean within the flow path of the Mindanao Current. Our records reveal considerable glacial-interglacial and suborbital variability in the Mindanao Dome upwelling over the last 160 kyr. Dome activity generally intensified during glacial intervals resulting in cooler thermocline waters, whereas it substantially declined during interglacials, in particular in the early Holocene and early marine oxygen isotope stage (MIS) 5e, when upwelling waters did not reach the thermocline. During MIS 3 and MIS 2, enhanced surface productivity together with remarkably low SST and low upper ocean thermal contrast provide evidence for episodic glacial upwelling to the surface, whereas transient surface warming marks periodic collapses of the Mindanao Dome upwelling during Heinrich events. We attribute the high variability during MIS 3 and MIS 2 to changes in the El Niño Southern Oscillation state that affected boreal winter monsoonal winds and upper ocean circulation. Glacial upwelling intensified when a strong cyclonic gyre became established, whereas El Niño-like conditions during Heinrich events tended to suppress the cyclonic circulation, reducing Ekman transport. Thus, our findings demonstrate that variations in the Mindanao Dome upwelling are closely linked to the position and intensity of the tropical convection and also reflect far-field influences from the high latitudes.