关键词: 热带亚洲, 山地雨林, 晚第四纪, 孢粉分析, 气候变化

Abstract: Since 70s, most tropical paleoclimate reconstruction for the Last Glacial Maximum used the sea-surface temperatures provided by CLIMAP that suggested the modest changes (<2℃) in tropical oceans of Asia^[1,2]. According to the palynological evidence from the tropics of Asia, the altitudinal belts of vegetation and the snow line of the Last Glacial Maximum (LGM) were much lower than those of present day. In New Guinea, a depression of 1 600 m of the forest limit was repported^[19]. The montane forest zone boundaries in Sumatra region was 500 m~800 m lower than today^[7-9]. In Indochina and southeastern China, the boundary between lowland rain forest and montane rain forest was lowered by the amount ranging from 600 m to 1 000 m^[10,11]. Recently, many studies showed that altitudinal zonation changes of vegetation were partly controlled by multi-factors such as CO₂ concentration^[12] and ultraviolet-B light^[7]. In fact, the reduction of CO₂ in the atmosphere during LGM plays an role as important as temperature particularly to the forest limit depression, but modestly to the boundary between rain forests. This explains the problem that amount of altitudinal zone depression of forest limit was much greater than that between montane forests. Using a number of palynological results from tropical Asia, and considering the influence of CO₂ variation specially to the forest limit during LGM, an average 4℃ cooling over the tropics of Asia was estimated (Fig-5). This result is consistent with the paleoclimate inferred from pollen time sequence in intertropical eastern Africa (4℃±2℃)^[26] and the new paleo-temperature (SSTs) estimates from planktonic foraminiferal assemblages in South China Sea^[3] and from the Sr/Ca ratio in Barbados corals of southweastern Pacific^[4]. The recent climate simulations using an AGCM showed that maintaining ocean heat transport at a value close to present day values, but with otherwise glacial boundary conditions, lead to an enhanced cooling, particularly in the tropics (5-5℃ lower)^[25]. All the above evidences suggested that the glacial climatic changes in tropical Asia were larger than those estimated by CLIMAP^[1,2].

Key words: tropics, Asia, montane rain forest, Late Quaternary, pollen analysis, climatic changes