南海南部末次冰期以来的孢粉记录及其气候意义

PALYNOLOGICAL RECORDS SINCE LAST GLACIAL MAXIMUM FROM A DEEP SEA CORE IN SOUTHERN SOUTH CHINA SEA

本文通过分析南海南部１７９６４柱状样的孢粉记录，重建了该地区２６０００ａＢ．Ｐ．以来的植被和气候变化历史。南海南部末次盛冰期时高山雨林的范围可能是现在的２～３倍，表明气温明显下降；从末次盛冰期到冰消期，巽他陆架一直为热带低地雨林及红树林占据，表明在此期间湿度没有明显变化，但存在着千年级的准周期波动。这种波动一直持续到全新世中期。本地区在２０００ａＢ．Ｐ．以来芒萁孢子大量增加，一些高山雨林的成分重新出现，可能与人类活动所导致的低地植被的破坏有关。

Our study shows that during Last Glaciation, frequent oscillation marked withalternating predominance of pollen assemblages of upper montane rainforest andtropical lowland rainforest are observed, in which, pollen grains of mangrove and lowmontane rainforest change associated with tropical lowland rainforest while Pinepollen and fern spores fluctuate together in phase with the upper montane rainforest.Such oscillations accelerated during the last deglaciation. Though strong fluctuated,pollen grains of upper montane rainforest increase periodically during the glacial time,reaching its maximum at LGM and keep dominant during the deglaciation. Pollenpercentages of tropical lowland rainforest and mangrove, though variable, keep inmoderately high values in this Pened. The Holocene is characterized by the rapidlyrise of both tropical lowland rainforest and mangrove pollen ratio, and a substantialincrease of Dicranopteris fern spores is observed from 2 300 aB. P. The followingstages in the vegetation development of the South China Sea region were distinguished:(l) From 26 500aB. P. to 18 300aB. P., mangroves and upper montane forestsexpanded gradually, while the habitats of tropical lowland rainforests and lowermontane forests became smaller.(2) From 18 300aB.P. to 9 900aB.P., upper montane forests together with tropicallowland rainforests expanded. while mangroves and lower montane forests decreased.(3) From 9 900aB.P. to 5 200aB.P., both upper and lower montane forests beganto decrease sharply, followed by a quick expansion of mangroves and tropical lowlandrainforests.(4) From 5 200aB.P. to 2 300aB.P., upper and lower montane forests contiuned toretreat, and at the same time mangroves and Tropical lowland rainforests achievedtheir climax. 'The vegetation became stable.Our study suggests that: l) A substantial decrease in temperature occurred duringthe last glacial maximuxn(LGM). The cover of upper montane forests is eshmated tohave been 2 to 3 times larger during the LGM than in the Holocene. 2) During theLGM, large areas of Sunda Shelf were covered by tropical lowland rainforests andmangroves though their distribution fluctuated frequently. So there is no clear evidencefor drier condition in the LGM but from frequent variation of pollen percentage ofmangrove which is largely controlled by precipitation, small oscillations withquasi-millennial cycle in humidity probably existed. 3) The climate optimum isrepresented by the large expansion of mangrove and tropical lowland rainforest, andan evidence of human impact appears from 2 300aB.P.